Sciencemadness Discussion Board - benzyl alcohol oxidation

benzyl alcohol oxidation

Pages: 1 2

sokay - 22-5-2006 at 17:48

any good references for conversion of benzyl alcohol to benzaldehyde using cuo or sulfuric acid or things generally otc

guy - 22-5-2006 at 18:59

Use PCC in with acid catalyst. It can be used for any alcohol --> aldehyde reaction

The_Davster - 22-5-2006 at 19:45

Of course PCC requires anhydrous conditions or you get benzoic acid. And PCC (pyridium chlorochromate) is hardly OTC.

Perhaps sidechain chlorination with TCCA, then hydrolysis, and it will then loose water and go to benzaldehyde. Much more OTC.

praseodym - 23-5-2006 at 01:15

How about using H2O2 for the partial oxidation of benzyl alcohol to benzaldehyde?

Benzyl alcohol, on oxidation with nitric acid, is converted into benzaldehyde as well.

Oxidation of benzyl alcohol to benzaldehyde can also be carried out using tert-butyl hydroperoxide under reflux, in the presence of permanganate(MnO4-)-exchanged Mg-Al-hydrotalcite catalysts.

Benzyl alcohol can also be oxidised to benzaldehyde simply by using O2 with Pd-catalyst. Pd giant cluster catalyses benzyl alcohol oxidation to benzaldehyde and inhibits its further oxidation. Al2O3 can also be added to further increase the rate of reaction.

Polymer-supported IBX esters and amides can also oxidise benzyl alcohol to benzaldehyde. More info here: http://blog.tenderbutton.com/wp-content/polymeribx4.pdf

Ceric ammonium nitrate, ammonium nitrate and sodium nitrite in trifluoroacetic acid are also effective catalysts for the quantitative oxidation of benzyl alcohol to benzaldehyde.

Moreover, there are 2 distinct enzymes which attack benzyl alcohol, namely, xylene oxygenase and benzyl alcohol dehydrogenase; and their catalytic activities were additive in the conversion of benzyl alcohol to benzaldehyde.

Oxidation of benzyl alcohol to benzaldehyde can also be done using a copper bipyridine complex in the presence of 2,2,6,6- tetramethylpiperidinyl-1-oxy and base as cocatalysts.

Furthermore, benzyl alcohol can be oxidised to benzaldehyde in the presence of clayfen using a continuous isothermal reactor under microwave irradiation. More info here: http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleFo...

leu - 23-5-2006 at 04:25

An aqueous solution of sodium hypochlorite commonly known as household bleach is probably the most easily available route, it must be done precisely as stated in US1405261 adjusting the molarity for the difference between calcium and sodium hypochlorite

Such oxidations are published in many different organic expermental laboratory course textbooks, you'll probably need to visit a decent university library after studying the patent :cool:

Organikum - 24-5-2006 at 19:04

Hi Lugh!
Doesnt work though in realwolrd. Gives just a mess and nobody with a brain wants to separate Bz-OH from Bz-dehyde except with bisulfite or so and then you are an idiot for not knowing how to make it better in the first run.

[Edited on 25-5-2006 by Organikum]

leu - 25-5-2006 at 03:46

It works fine in this part of the real world, though apparently not in yours

More details as to how this happens can be found in the WD archives, search and you shall find out how it's done :cool:

[Edited on 25-5-2006 by leu]

[Edited on 26-5-2006 by leu]

solo - 25-5-2006 at 06:03

OXIDATION OF BENZYL ALCOHOL AIMING AT A GREENER REACTION
Hongbing Ji a , Kohki Ebitani b , Tomoo Mizugaki b and Kiyotomi Kaneda b a
React.Kinet.Catal.Lett. Akadémiai Kiadó, Budapest Vol. 78, No. 1, 73-80, 2003

Abstract A highly efficient heterogeneous catalyst Ru-Mn-Fe-Cu-O successfully oxidized benzyl alcohol to benzaldehyde in the presence of oxygen using toluene or water as solvent, and without solvent aiming at greener chemistry. Keywords: Benzyl alcohol, oxidation, green chemistry, heterogeneous catalyst

Attachment: Oxydation of Benzyl alcohols.pdf (41kB)
This file has been downloaded 2482 times

garage chemist - 25-5-2006 at 07:21

I had to test some benzyl alcohol for identity earlier (got some from as supplier who mislabeled two bottles, so I had to test everything).
To do this, I added some of it to a dilute solution of sodium persulfate, and heated. A powerful smell of benzaldehyde was produced quickly, confirming its identity.
However, a precipitate of benzoic acid was also seen shortly afterwards.

evil_lurker - 22-6-2006 at 22:24

How about the oxidation of benzyl alcohol using plain old DMSO?

One mole of benzyl alcohol is mixed with 7 moles of DMSO and heated to reflux for 14 hours. During that time a stream of air was pumped thru the reaction mix. Seperation was achieved by diluting the reaction mix with water and extracting with ether. Yeild is 80%.

JAC vol 86, pg 298-299

unionised - 23-6-2006 at 00:21

Is the by- product of that reaction dimethyl sulphide?
If so please don't do it when I'm anywhere near. (We need a "smiley" holding his nose here).

S.C. Wack - 23-6-2006 at 01:53

No shortage of these in the English-language literature.

Attachment: jacs_86_298_1964.pdf (311kB)
This file has been downloaded 1993 times

kmno4 - 29-6-2006 at 12:04

A long time ago I tried to oxidate BzOH with K2Cr2O7/H2SO4/H2O.
It works, but yield I obtained was 40%-50%. I think it could be higher, by very slowly adding oxidating mixture to stirring suspension BzOH/H2O. I distilled product of reaction and there was signifant amount unreacted alcohol in benzaldehyde (product) and in remainder.
Propably there is an optimum: not oxidated alcohol - overoxidated acid (PhCOOH), so amount of oxidant will be needed higher than stoichiometric.
It is btw, not "good reference"

Ammar - 3-7-2006 at 10:50

you can try Jones reagents in absence of water and in 2:1 ratio to your alcohol. :cool:

oxidation benzyl alcohol

dugstar - 18-7-2006 at 08:31

Can benzyl alcohol oxidise at RT in the presence of air? Does it need a catalyst?

jokull - 18-7-2006 at 09:24

yes dugstar

Benzyl alcohol gets oxidised at RT espontaneously, however the reaction is very slow. If you mean to oxidise BzOH in a short time then you can employ a photocatalytic route, but this kind of synthesis has a lot of limitations although it is very selective.

Ammar - 2-8-2006 at 15:55

Hi.Use of CrO3 with NaHSO4.H2O in 1:1:1 ratio will give you bezaldehyde by 95% yield. ( Im still using it myself,trust it)

cubicon - 16-8-2006 at 00:35

Hi Ammar

95% yield ?
Would you be able to post a workup.Looks like one with potential.

Magpie - 23-4-2008 at 21:02

Synthesis of Benzaldehyde from Benzyl Alcohol
Described below are my experiments in making benzaldehyde from benzyl alcohol.

Introduction and Background
I had been looking for a simple route to benzaldehyde. Fleaker supplied that route by his mention of the oxidation of benzyl alcohol with persulfate. Garage chemist had also recommended the use of benzyl alcohol.

I was at first skeptical of this route as I did not see what would prevent the over-oxidation of benzaldehyde to benzoic acid. I also had no written procedure to follow, just general guidelines from Fleaker and NERV.

Theory
The synthesis of benzaldehyde from benzyl alcohol is an oxidation-reduction reaction. The reaction can be broken into two half-reactions:

C6H5-CH2OH ----> C6H5-CHO + 2H+ +2e-
S2O8-- +2H+ + 2e- ----> 2HSO4- (E=2.1v)

Overall: C6H5-CH2OH + S2O8-- ----> C6H5-CHO + 2HSO4-

This reaction is highly exothermic.

1st Experiment
200mL of water was added to a 500mL RBF set up on a mantle & hot plate-stirrer. 10mL of benzyl alcohol (BnOH) was added and vigorous stirring begun. Even with vigorous stirring not all of the BnOH dissolved.

An equivalent molar mass of Na2S2O8 (23g) was dissolved in 75 mL of water and placed in a pressure equalizing dropping funnel connected to the RBF. Added persulfate solution to the RBF at 1 drop/sec while stirring.

Set up for steam distillation using direct steam method (not live steam). Began heating with the mantle. At one point the reactants suddenly turned from clear to milky. Estimated temperature 60-70C. Eventually an oily yellow colored liquid began floating on the surface. Steam distillation began with condensate coming over in regular spurts. Turned off stirrer as pot was at a regular boil. Stopped steam distillation when condensate almost clear. Total condensate was ~90 mL with about 4-5 mL of separated product on the bottom. Aqueous pH of distillate ~5.

2nd Experiment
Encouraged by the results of experiment 1, a second was performed by doubling the reactants while keeping the water content the same. 150mL of water was added to the RBF followed by 20mL of BnOH and vigorous stirring. Because the solubility of BnOH is only about 5g/100g water there was concern that there would be a poor conversion due to the two-phase nature of the BnOH/water mix.

46g of Na2S2O8 was dissolved in 125mL water and placed in the dropping funnel as before. Oxidant added at 1-2 drops/sec. Turned on mantle heat. Again when the temperature reached 60-70C there was a dramatic reaction and the pot started boiling. This could be called a runaway. Fortunately it was all set up for steam distillation as before. Again a yellow-orangish colored oil formed and began floating on the surface. Continued the steam distillation until the distillate ran almost clear. 135mL distillate collected with 15-20mL of product organic on the bottom of the receiver in a separate phase.

3rd Experiment
Two things became apparent from the results of experiment 2: (1) The amounts of reactants could not be increased using the same methodology and apparatus due to the runaway reaction occurring at 60-70C, and (2) the two phase BnOH/water reactant system had no negative affect on yield.

For the 3rd experiment the reactants were increased to 3X the size of the 1st experiment. Only this time the BnOH/water in the RBF was heated to 65C and kept there during the slow addition of the oxidant.

75mL of water was placed in a 3-neck 500mL RBF followed by 30 mL of BnOH and vigorous stirring. A thermometer was inserted in one of the necks. 69g of Na2S2O8 was added to 188 mL of water and placed in the dropping funnel as before. This worked out OK and the reaction temperature was kept at 65-75C by dropping in oxidant as required. When all oxidant had been added the system was set up for direct steam distillation as before.

Workup
The distillates from all three experiments were combined in a 500mL separatory funnel and the heavy organic was drained off. NaCl was added to the water in the separatory funnel to salt out another mL or two of product. Anhydrous MgSO4 was added to the combined organic for drying.

During all handling of the BnO (crude & final) CO2 was used to backflush all containers and apparatus. Virtually no formation of benzoic acid was noted.

The crude dried BnO was fractionally distilled using a broken glass packed column at reduced pressure (60mmHg). Vapor temperature was 92-93C. The bubbler needed to prevent bumping was supplied with CO2 from a crude reservoir (1000mL beaker). A photo of this setup is shown below:

Results
The combined recovery of BnO was 38mL. Based on the combined 60 mL of charged BnOH, the yield is 64.6%.

Discussion and Conclusions
The product was tested with Fehling's solution, Tollens solution, Bayer permanganate test, and formation of NaHSO3 adduct test. All were positive except for the Fehling’s test. The Fehling’s reagents were verified as good by using fructose as reductant. It seems that the Fehling’s reagent (Cu++) is just not a strong enough oxidant to oxidize BnO. The NaHSO3 adduct test gave a massive formation of white solids.

Of course ether extraction, and formation of the NaHSO3 adduct, could be used instead of steam distillation and fractional distillation at reduced pressure to isolate the BnO. I’m not even sure how necessary it is to use reduced pressure for the distillation of BnO. Vogel seems ambivalent on this.

This would be an interesting method to try on an aliphatic primary alcohol. I believe their aldehydes do give a positive Fehling’s test. Perhaps they oxidize much easier than aromatic aldehydes. This would explain the apparent lack of over-oxidation of BnO to benzoic acid

I am very satisfied with this method of synthesis for BnO. With further work to refine the method, and with use of a larger batch size, the yield could possibly be significantly increased.

[Edited on 23-4-2008 by Magpie]

[Edited on 23-4-2008 by Magpie]

[Edited on 23-4-2008 by Magpie]

[Edited on 23-4-2008 by Magpie]

vacuum distillation.jpg - 89kB

len1 - 23-4-2008 at 22:32

Very nice work Magpie, pleasure to read.

A couple of thoughts:

The persulphate obviously doesnt react below 60C (much the same as it doesnt etch Cu below that temperature) so adding it dropwise to the mixture preheated to that temperature should help avoid run-away, and increase size of yield per batch.

I dont think the two-phase nature need be a concern with stirring- it wasnt in my hydrolysis of BzCl2, which was also two phase. In this case, since the reaction is much more vigorous, I would think its a blessing.

Im not 100% sure there isnt some alcohol in the benzaldehyde - its more soluble in water than the latter - but I believe its solubility in the benzaldehyde is greater still. Their bps at atmospheric are within 25C of each other (though at reduced pressure that increases). A way to check would be to form an adduct and weigh.

Im like yourself curious that the oxidation doesnt go to benzoic acid since BzO would appear to be much easier to oxidize than BzOH judging by the action of O2 on both. Must be peculiarity of persulphate.

Unfortunately BzOH is as hard to get here as BzO - both restricted for sale.

[Edited on 24-4-2008 by len1]

Klute - 23-4-2008 at 23:37

Very nice! I'm impressed about your resuults!
I tried this reaction several times, but using a Cu2+/Fe2+ catalyst system, with mixed results. Trilobite posted a very complete article in the "benzylic oxidation using various oxidants" thread. See patent US 4,146,585. I obtained mixed results, most of the time there was benzoic acid present to some extent.
Did you not use theses salts for a reason, or just didn't know about this variation?

To compensate for the poor solubility of persulfate at RT (i used ammonium persulfate), I added half of it as a conc aq solution, and the other half as a solid. It dissolution is pretty endothermic.
I used bisulfite to seperate the aldehyde from the alcohol, but in retrospect, i think it was that efficient (benzaldehyde losses).

I'm glad to see other people working with what is, IMHO, a pretty versatil compound! And relatively cheap too.

Magpie - 24-4-2008 at 07:53

Thanks Len. From Len:

Quote:

Im not 100% sure there isnt some alcohol in the benzaldehyde - its more soluble in water than the latter - but I believe its solubility in the benzaldehyde is greater still. Their bps at atmospheric are within 25C of each other (though at reduced pressure that increases). A way to check would be to form an adduct and weigh.

I was concerned about this also and for this reason debated whether or not to go with NaHSO3 adduct isolation vs distillation. I plotted the available BnO vapor pressure data (P vs T), and for P=60mmHg T should be 100C instead of my steady 92-93C. I then checked Gmehling's Azeotropic Data for an azeotrope with BnOH. There is none at pressures of 30, 100, 300, and 760 mmHg. So I'm not sure what to think here.

And thank you Klute. Klute says:

Quote:

I tried this reaction several times, but using a Cu2+/Fe2+ catalyst system, with mixed results. Trilobite posted a very complete article in the "benzylic oxidation using various oxidants" thread. See patent US 4,146,585. I obtained mixed results, most of the time there was benzoic acid present to some extent.

I did see this patent. But Fleaker/NERV made no mention of the use of catalysts so I decided to try the simpler approach first.

grind - 24-4-2008 at 12:06

Another very easy way:

1. BnOH + HCl = BnCl

2. BnCl + Hexammin = quat. salt

3. quat. salt you can treat in 2 ways, one way leads to benzaldehyde, the other way gives benzylamine (sommolet and delepine).

Zinc - 24-4-2008 at 12:45

Very interesting. But fortunately I can easily buy benzaldehyde (around 43 $ per liter) and benzyl alcohol (around 75$ per liter).

I know it is a little OT but where could I find out how to make benzyl nitrate and information about its properties?

len1 - 24-4-2008 at 18:28

Its great of course all these people can buy PhCHO and PhCH3O, I cant buy either for love or money. I can get PhCOOH, and PhCH3 - thank heaven for small mercies. Mind you if you have to spend $75/l for benzyl alcohol then making it out of $10/l toluene (the chlorine is essetially free, and the HCl reusable) might still be worthwhile.

Magpie, in your experiment 3 you have already done whatb Ive suggested - sorry I didnt notice that before. What I dont understand is why dont we have

PhCHO + S2O8-- + H2O -> PhCOOH + 2HSO4-

given we have

PhCH3O + S2O8-- -> PhCHO + 2HSO4-

its not like theres a lack of water, and its a well known fact that aldehydes are much more prone to oxidation than the corresponding alcohols. Normal methods for preparation of aldehydes, eg formaldehyde, acetaldehyde, rely on the volatility of the aldehyde to remove it as soon as its formed, so no appreciable concentration builds up on the LHS of the first reaction. But that apparently is not whats happening here.

The only thing I can sugget is that the relative solubility of the alcohol/aldehyde in water is used. The reaction takes place in aqueous medium - thats were the persulphate is. The benzaldehyde separates from this into a separate layer - and so is essentially removed from equilibrium. If one vigorously mixes such a solution instead of letting it separate that should rapidly oxidize the benzaldehyde and send the yield well down. However if one has an excess of the alcohol, so not all of it dissolves stirring is precisely what one has to do to promote the reaction. The result is - this is my hypothesis, that the yield is entirely based on the solubility differential 5gms:0.5gms per 100ml H2O of benzyl alcohol/benzaldehyde. In this case it is indeed impossible to increase the yield as its limited by the amount of water needed to dissolve the small amount of alcohol, i.e. size of vessel is 20 times greater than max yield volume.

Whats protecting the benzaldehyde is its inability to join the aqueous phase - where the alcohol has much less such protection. As the aquesous layer has its alcohol converted more dissolves to make up the difference - however this dissolution must be accompanied by some benzaldehyde dissolving - so theres a limit to the efficiency of this method.

In regards to the bp - my feeling based on my experiences is not too trust thermometers in such arrangements very much, depending on the type and experimental arrangement I have found they can read 10C too low easily. But even if theres no azeotrope, liquid with close boiling points will behave like one, it'll be very hard to separate them. What is needed is an IR or very careful gravimetric analysis. I wish I had access to PhCH3O so I could repeat your experiment and analyse the result.

[Edited on 25-4-2008 by len1]

Magpie - 24-4-2008 at 20:27

Len:

I agree that it is nice to be able to buy BnOH, while hoping that it is not being too heavily watched. However, I don't think anyone should take this for granted, especially in the US. It is good to have other routes, especially those using more OTC reagents.

Quote:

The only thing I can sugget is that the relative solubility of the alcohol/aldehyde in water is used. The reaction takes place in aqueous medium - thats were the persulphate is. The benzaldehyde separates from this into a separate layer - and so is essentially removed from equilibrium. If one vigorously mixes such a solution instead of letting it separate that should rapidly oxidize the benzaldehyde and send the yield well down. However if one has an excess of the alcohol, so not all of it dissolves stirring is precisely what one has to do to promote the reaction. The result is - this is my hypothesis, that the yield is entirely based on the solubility differential 5gms:0.5gms per 100ml H2O of benzyl alcohol/benzaldehyde. In this case it is indeed impossible to increase the yield as its limited by the amount of water needed to dissolve the small amount of alcohol, i.e. size of vessel is 20 times greater than max yield volume.

I think that this is a very good theory. Something I never would have suspected going into my experiments. The proof will be when I try persulfate using n-butanol as reactant. I hope to do this fairly soon.

I trust my thermometer to within a degree or two even though it is a cheap one. What I don't really trust is my vacuum guage. It is a cheap one of the hardware store variety.

[Edited on 24-4-2008 by Magpie]

Nicodem - 25-4-2008 at 05:43

Beautiful experimental work Magpie!
A measurement of the boiling point could give you a very rough estimate on how free of benzyl alcohol is your product. I'm quite sure it must be relatively pure since BnOH steam distill much less efficiently when compared to PhCHO.
Out of interests in seeing how much, if any, benzoic acid forms, you might want to extract it from the reaction mixture rests after the steam distillation (though you probably already discarded it, but just a thought if you would repeat the experiment).

Quote:

Originally posted by len1
Magpie, in your experiment 3 you have already done whatb Ive suggested - sorry I didnt notice that before. What I dont understand is why dont we have

PhCHO + S2O8-- + H2O -> PhCOOH + 2HSO4-

given we have

PhCH3O + S2O8-- -> PhCHO + 2HSO4-

its not like theres a lack of water, and its a well known fact that aldehydes are much more prone to oxidation than the corresponding alcohols. Normal methods for preparation of aldehydes, eg formaldehyde, acetaldehyde, rely on the volatility of the aldehyde to remove it as soon as its formed, so no appreciable concentration builds up on the LHS of the first reaction. But that apparently is not whats happening here.

Fortunately, not all reagents oxidize aldehydes faster than they oxidize alcohols under proper conditions. Those reagents that proceeds trough the oxidation of geminal diols formed by nucleophilic addition of H2O on the carbonyl group will therefore normally not be able to oxidize aldehydes under anhydrous conditions (CrO3 and its complexes are among these). Actually, I think that under anhydrous conditions only radical oxidations can result in the oxidation of aldehydes to carboxylic acids. Other reagents will tend to oxidize alcohols faster than aldehydes even in aqueous conditions (HOCl is one such example; here I once gave a possible explanation on why).

Removing the aldehyde product as it forms is also an effective strategy. The removal of the aldehyde product by extraction might also be efficient to some degree, but the unfortunate problem for such a strategy is in that the partition of compounds in a biphasic system is a function of concentration. For example, let's assume the partition coefficient of the aldehyde would be a magnitude or so lower than for the alcohol. At the beginning of the reaction this difference would work toward the desired end. But toward the end, after the majority of the alcohol would be consumed, the concentration of the aldehyde product in the organic phase would increase so much as to be partitioned in the aqueous phase in greater concentration than the alcohol (resulting in the oxidation of the aldehyde inevitably prevailing over the oxidation of alcohol). Apart the consequential lowering of the yield, such strategy would also be limited to those reagent systems whose ratio of RCHO->RCOOH vs. RCH2OH->RCHO kinetics is at least somewhat less than the ratio of partitioning coefficients of RCH2OH vs. RCHO.

Therefore, I would rather search for the answer to this question in the reaction kinetics of all possible pathways. After all, in organic chemistry, it is the evaluation of all equilibrium species and the comparison of activation energies of all possible transition states that gives an answer as to what the products of a particular reaction under particular conditions are. I would therefore not be too fast in drawing conclusion based on phase transfer only.

PS: A few notes about formulas and abbreviations used in this thread:

"BnO" is a wrong abbreviation since such a molecule can only exist as a radical and it is not identical to benzaldehyde anyway.

PhCH3O is an ambivalent formula for BnOH as it can stand for anisole as well. Using rational formulas is more customary in organic chemistry, while using empirical or partly empirical/partly rational formulas is particularly discouraged exactly to avoid ambivalence.

BzOH stands for benzoic acid.

BzCl2 is not a compound and besides is not benzal chloride as obviously intended

BzO would be the benzoic radical PhCOO*, also not what was intended.

So to reiterate the international organic abbreviation conventions: Ph = phenyl ; Bn = PhCH2- = benzyl ; Bz = PhCO- = benzoyl

Let's take care with these standards or else we well have the forum suffering from an abbreviation induced disorder (nothing new, it happens all the time).

[Edited on 25/4/2008 by Nicodem]

len1 - 25-4-2008 at 06:16

Quote:

BzCl2 is not a compound and besides is not benzal chloride as obviously intended

I know all that - and whats more coudlnt give a hoot and a half. We are not writing the Collins dictionary here - just look around. I havent much time, I understood what Magpie was saying. Thats all that matters. Ill leave the rest to you. Dont know what repels me more, pedantics or obfuscation.

[Edited on 25-4-2008 by len1]

Klute - 25-4-2008 at 07:10

I thought i would give a link of the other benzyl alcohol thread here, in which H2O2 and TCCA/bleach are used in various conditions, to get a more global vision.

Maybe we could just merge this to one big benzyl alcohol thread? it seems to spring up enough interest to be sticky? Just a proposition.

Benzylic and secondary alcohols oxidations using various oxidants

PainKilla - 25-4-2008 at 09:15

I remember wanting to oxidise a benzylic alcohol to a ketone, and found this neat reference, but then I winded up using another route towards my product.

Attachment: Aerobic photocatalytic oxidation of activated benzylic and allylic alcohols to carbonyl compounds catalyzed by molecular (146kB)
This file has been downloaded 1557 times

Magpie - 25-4-2008 at 10:23

Thanks Nicodem. Nicodem says:

Quote:

Out of interests in seeing how much, if any, benzoic acid forms, you might want to extract it from the reaction mixture rests after the steam distillation (though you probably already discarded it, but just a thought if you would repeat the experiment).

When I was distilling the benzaldehyde at reduced pressure I stopped when the temperature dropped off. What was left in the pot was a few mLs of a yellow translucent liquid. After cooling it turned to a milky-yellow slush. I saw no crystals (needles) of benzoic acid. I suppose it could have contained a little MgSO4 from imperfect decanting. And yes, this residual is long gone.

MagicJigPipe - 25-4-2008 at 13:58

I don't see why someone would discard benzoic acid. It's not like it's extremely cheap or common.

An amusing anecdote: When I was trying to acquire benzoic acid from pharmacies about half of them told me it was "prescription only".

Also, why is BnOH watched/unavailable? Because it can be made into phenylacetonitrile in a semi-roundabout way? It wouldn't surprise me. I was just wondering why.

Zinc - 25-4-2008 at 14:17

Is Benzaldehyde and BnOH watched in the US only or in other countries? Where I live fortunately they and a lot of other chemicals are free to buy (if you find someone who will sell them which is very difficult).

And a little OT, but could benzoyl peroxide be made from benzaldehyde? If yes what would be the easiest route?

[Edited on 25-4-2008 by Zinc]

MagicJigPipe - 25-4-2008 at 16:30

No, it's not unavailable in the US (I don't think it is "watched" either). I was speaking of the people in other countries (Austrailia) who said it was watched and/or unavailable.

It's easy to get in the US.

len1 - 25-4-2008 at 17:35

I dont know if we have watched chemicals. We have restricted chemicals - ones you can possess, but cant buy unless youre incorporated. I believe BzOH is restricted because benzyl chloride is, the latter being easily manufactured from the former

BzOH + HCl -> BzCl + H2O

Though I have shown them now how easy it is to make evil BzCl from BzH - which is as abundant as water - and in much better yield. If they want to change that they better refurbish all their refineries - then we'll really see if they are serious.

My advice to LE is learn some chemistry, and start going after the real crooks instead of the periodic table.

[Edited on 26-4-2008 by len1]

Fleaker - 26-4-2008 at 09:45

What do you mean by much better yield? Benzyl alcohol with HCl should give a higher yield than any chlorination of toluene could hope to do.

kmno4 - 26-4-2008 at 11:24

From my old experiments:
1) ØCH2OH can be detected in ØCHO via adduct with NaHSO3 (Na2S2O5 in solid state). Adduct is odorless, alcohol has weak but characteristic smell. ØCHO can be easily recovered from its adduct with the use of Na2CO3 and weithed (as has been said earlier)
2) Detecting ØCOOH can be done just with washing aldehyde with saturated NaHCO3 and precipitating acid with HCl/H2SO4.
Solubility of ØCOOH in ØCHO is high (better than 20g/100g).
3) ØCHO (ØCH2OH too) can be distilled at normal pressure without any complications. The purer ØCHO, the more inert to O2, but the best protection is tight closing bottle.

BTW. In my coutry benzyl alcohol costs ~20$/liter and is OTC, with benzaldehyde are problems, but not so big

[Edited on 26-4-2008 by kmno4]

kmno4 - 26-4-2008 at 14:48

These calculations are OK. but final result is a random number, belonging to chosen values of parameters. Besides I cannot find

PhCO-H <=> Ph-CO* + H* . . . . . . . . . . . . . . . . . BDE2 = 87 kcal/mol <--- this value in RSC paper. On what page shall I search it ?

Nicodem - 26-4-2008 at 15:00

Ups, I wanted to edit my post and I deleted it by mistake. I used the wrong value of BDE1 which is even lower (79 instead of 81 used before "editing"). I got confused with the authors describing a previous estimation was 81 kcal/mol, while their calculated value was ~ 79 kcal/mol. The BDE2 value is on page 179 at the end of the text column (the same value is also referenced in Table 1 of the JOC paper). I agree that the result is a random number, now even 4 times greater due to the corrected BDE1. Thanks for checking out the calculations.

--- the original post that should be above kmno4's reply above, edited with the new BDE1 ---

Being interested in why the oxidation of BnOH is faster than the oxidation of PhCHO with the method Magpie presented, I went to hunt down the information required for a plausible explanation.
The reaction is quite certainly a radical oxidation given the conditions used (aqueous Na2S2O8 at >50°C in close to neutral conditions). Therefore the rate limiting step in the oxidation of either BnOH or PhCHO is the abstraction of the benzylic hydrogen. The bond dissociation energy (BDE; the energy required to abstract the H atom) commonly linearly correlates to the activation energy (Ea

of the two oxidation reactions. The Ea is an important factor in the reaction rate constant equation (the famous Arrhenius equation). Most other parameters in the rate constant and reaction rate equations are either identical (T), average to nearly the same value (concentrations of the two substrates over time), or are assumed to be of a similar order (like the correlation coefficient between BDE and Ea and the A factor in the Arrhenius equation).

In short, the BDE of the two rate limiting processes are:

PhCH(OH)-H <=> Ph-CH(OH)* + H* . . . . . . . . BDE1 = 79 kcal/mol (J. Org. Chem., 70 (2005) 9521-9528)

PhCO-H <=> Ph-CO* + H* . . . . . . . . . . . . . . . . . BDE2 = 87 kcal/mol (J. Chem. Soc., Perkin Trans. 1 (1986) 173-182)

So the corresponding Arrhenius equations can give us a very rough estimate of the rate constants ratio between the two substrate oxidation reactions:

Rate constant of BnOH>PhCHO oxidation: k1 = A1*e^(-Ea1/(RT)) , Ea1 = x*BDE1
Rate constant of PhCHO>BzOH oxidation: k2 = A2*e^(-Ea2/(RT)) , Ea2 = y*BDE2
Approximations: x ≈ y , A1 ≈ A2 (possibly very rough approximations on factors that have a great influence on the outcome!)

Therefore, after solving the above equations we get the ratio of the two rate constants:
ln(k1/k2

= x*(BDE2-BDE1

/(RT)
ln(k1/k2

= x*(33495 J/mol)/( 2769 J/mol) = x*12.1 (taking T = 333 K or 60°C)

Assuming x = 0.5 as a realistic value we get:
k1/k2 ≈ e^(6.05) ≈ 423

Since I'm pretty much dumb in regard to mathematics, I probably made some terrible mistake somewhere in the calculations, but anyway they are not particularly important since the information that BDE2 > BDE1 is already enough to tell us that the oxidation of BnOH is faster than PhCHO in this particular system (even without using a bunch of approximations). Yet, taking those approximations, the calculation indicates the oxidation of BnOH might even be a few hundred times faster than the oxidation of PhCHO (assuming the same order of reaction).

len1 - 26-4-2008 at 16:45

Quote:

Originally posted by Fleaker
What do you mean by much better yield? Benzyl alcohol with HCl should give a higher yield than any chlorination of toluene could hope to do.

Why do you feel so? I have the results for the second reaction - 75% without even trying to optimize for BnCl - if you use a two-step process you can get that to 90%. My experience hydrolizing BnCl shows its an equilibrium two phase process - the yields for such things are not normally very high. Have you gotten a yield?

Rate constant calculations are interesting - I rather tend to trust my suggestion more at this stage because

1) Aldehydes, with BzO no exception, are known to be much easier to oxidize. The rational would have to be that hydrogen abstraction is only relevant to persuphate type oxidation (where its only an approximation - these things depend heavly on reaction conditions) to explain why this type of calculation gives results in accord with a presumed rate difference in persulphate oxidation but not with molecular oxygen. Its too easy to say the latter proceeds by a different mechanism - that would be selectively using facts, such things prove nothing.

2) The solubility difference we know will favour alcohol oxidation without any presumption of things that are hard to prove.

What are the corresponding energies when Ph is replaced by CH3 ? It would add credibility to this theory if they went the other way.

2) can of course be tested directly - stir the contents vigorously for 1hr and see what it does to the yield. The incomete conversion of BzOH in this experiment suggests that is a relevant test.

[Edited on 27-4-2008 by len1]

Fleaker - 26-4-2008 at 17:54

I think we speak of two different reactions. I was talking of reacting benzyl alcohol with HX to give benzyl halide, a smooth reaction which I have done and works exceptionally well, as compared to chlorination of toluene, which works less well and is not as simple.

As for benzyl alcohol and persulfate oxidation to benzaldehyde, I make no claim to its superiority over your method as I've never done either, having had no need as benzaldehyde is purchasable for me. My friend and home chemistry lab ''partner'' has done the reaction and has mentioned its usefulness with the benzylic carbon (I don't recall him mentioning it for other alcohols). His yields were high; I don't recall the exact number, but it was certainly above 80% based on benzyl alcohol. He mentioned that the formed benzaldehyde was free of the alcohol, and that any alcohol that had not been made into the aldehyde was instead oxidised further to benzoic acid. Based on his testimony, we should not assume that this oxidising agent is selective only to the aldehyde, but as you said, depends upon the reaction conditions.

Len, your route is the cheaper of the two (toluene is twice as cheap as benzyl alcohol, about 7 USD/L versus 11/L for the alcohol) but it also comes with the nuisance of benzyl chloride. Not the worst reagent to deal with but for me, it is irritating and bothersome. It is also quite probably a longer synthesis with more material required. I think favourability of which reaction to use for benzaldehyde depends on your locale.

len1 - 26-4-2008 at 20:08

Fleaker, I was talking about the reaction

BnCl + H2O -> BnOH + HCl

the reverse of the reaction you used to make benzyl chloride. I found its equilibrium constant not to be particulalry favourable to either side, and so expected the same to be true for the reverse rection by reciprocity. I dont have any experience with the reverse reaction, because BnOH is restricted here. I have to make it from the chloride rather than vice versa. Even if I could buy it it would be through speciality outlets, where nothing is cheaper than about $40/L. Toluene can be bought from hardware stores and is in a completely different price category. What sort of outlets sell BnOH in the states? I would also be interested in the yield of the above reaction. At best I think it would equal the toluene, it certainly can not be mucg better, which makes a mockery of the restrictions.

I dont of course lay claim to any method of making things, and am always on the look out for interesting reactions. Nonetheless I think the chlorination of toluene is a great way to make BnO even if I had BnOH and even at the cheap price you mention. Thats because persulphate at $10 per 2 mole is I think very expensive, Cl2 in the form of HCl and TCCA is much cheaper here being a mass consumer ingredient.

[Edited on 27-4-2008 by len1]

Fleaker - 26-4-2008 at 20:39

That is a valid point about the molecular weight of the persulfate--one does not get much oxidant on a molar basis.

I don't know what the Keq is for the reaction of PhCH2OH and HCl but I do know that the reaction is practically quantitative in its yield of benzyl chloride. It is a quick and efficient reaction. The acid is the solvent for the alcohol and is in great excess. Everything should be stirred well for several hours (that is probably too long). The dense lower layer is collected and separated with a funnel to remove any of the acid solution. It is then dried with a suitable drying agent and is ready to use for many purposes. Although not necessarily required, a careful distillation of the product could not hurt if one were to plan on making a Grignard reagent. The only reason benzyl chloride should be made in the laboratory is for the simple reason of the cost of shipping as it is considered a hazardous material.

In the U.S. benzyl alcohol is widely available for making bacteriostatic water, and also for use in paint stripping amongst other uses.

JohnWW - 26-4-2008 at 22:03

Quote:

Originally posted by Nicodem
In short, the BDE of the two rate limiting processes are:
PhCH(OH)-H <=> Ph-CH(OH)* + H* . . . . . . . . BDE1 = 79 kcal/mol (J. Org. Chem., 70 (2005) 9521-9528)

PhCO-H <=> Ph-CO* + H* . . . . . . . . . . . . . . . . . BDE2 = 87 kcal/mol (J. Chem. Soc., Perkin Trans. 1 (1986) 173-182)

Please download and post here those two articles, Nicodem.

azo - 27-4-2008 at 02:49

well i live in australia and benzyl alcohol is not restricted here
200 litre drums if you need . benzaldehyde is EUD.
Anyway i don't see why you would want to go to benzyl chloride from toluene when it is a about 100 times easier from benzyl alcohol ! Of course unless you cannot get it.
And if you could get benzyl alcohol it would be much beter to make benzaldehyde by reacting with Mn02 i have done this before and it doesn't get much easier than that.

len1 - 27-4-2008 at 04:41

My statement that its restricted isnt just me saying so - like most things I do I supported it with a quote from a supplier. Can you support your claim?

kmno4 - 27-4-2008 at 04:44

Quote:

Originally posted by Fleaker
I don't know what the Keq is for the reaction of PhCH2OH and HCl but I do know that the reaction is practically quantitative in its yield of benzyl chloride. It is a quick and efficient reaction. The acid is the solvent for the alcohol and is in great excess. Everything should be stirred well for several hours (that is probably too long). The dense lower layer is collected and separated with a funnel to remove any of the acid solution. It is then dried with a suitable drying agent and is ready to use for many purposes. Although not necessarily required, a careful distillation of the product could not hurt if one were to plan on making a Grignard reagent. The only reason benzyl chloride should be made in the laboratory is for the simple reason of the cost of shipping as it is considered a hazardous material.

I see at once that you have never done this. It is the same case as drying ethanol with MgSO4 - virtual experiment with virtual effects.
BTW, crude benzyl chloride must be perfectly dry (istead of wet, heh) and without traces of acid - in another case you will get 40% yield of distillation and flask full of "polybenzyl".
BTW 2 I still cannot find BDE2 = 87 kcal/mol in given paper. I am attaching page 179 - the longest read page in my life

***I have found it, at last. It was classical case of blindness

[Edited on 27-4-2008 by kmno4]

[Edited on 27-4-2008 by kmno4]

azo - 27-4-2008 at 05:20

I can support my claim because i have a 200 litre drum not that i need to make benzyl chloride or benzaldehyde thow.
I have a friend that also has twelve 2 litre bottles of reagent grade benzaldehyde.

isn't that nice

regards azo

len1 - 27-4-2008 at 05:41

As everyone knows chemistry is 90% possession, 10% being able to pour it from a can.

Fleaker - 27-4-2008 at 06:21

Quote:

Originally posted by kmno4

Quote:

I see at once that you have never done this. It is the same case as drying ethanol with MgSO4 - virtual experiment with virtual effects.
BTW, crude benzyl chloride must be perfectly wet and without traces of acid - in another case you will get 40% yield of distillation and flask full of "polybenzyl".

He means perfectly dry and acid-free to prevent the side reaction. If it were perfectly wet it would be acidic :-) wouldn't it? However, he is still correct that I was wrong to suggest a distillation without careful purification. I have never distilled benzyl chloride, or benzyl bromide nor did I claim to have done so. I made it from the alcohol and excess of the concentrated acid and separated and used it without any further purification. That I have done.

My suggestion

Quote:

Originally posted by FleakerAlthough not necessarily required, a careful distillation of the product could not hurt if one were to plan on making a Grignard reagent.

is wrong unless you have done what kmno4 has said to do.

kmno4 - 27-4-2008 at 07:27

"The acid is the solvent for the alcohol and is in great excess. Everything should be stirred well for several hours (that is probably too long). The dense lower layer is collected and separated with a funnel to remove any of the acid solution. It is then dried with a suitable drying agent and is ready to use for many purposes."

At this conditions - dense lower layer is HCl(aq). I do not know what are "many purposes" but making benzyl cyanide from this crude product was very unsuccessful. Besides, I always wanted to do some quantitative measurements of reaction: benzyl alcohol+ HCl(aq)... And now I am going to do that (If I have time

).
Sorry for starting offtopic.

By Nicodem:

Assuming x = 0.5 as a realistic value we get:
k1/k2 ≈ e^(6.05) ≈ 423

(...)Yet, taking those approximations, the calculation indicates the oxidation of BnOH might even be a few hundred times faster than the oxidation of PhCHO (assuming the same order of reaction).

I agree with it. But look at Table 1 in ACS paper:
BDE(C-H) for ØCH2OH is 79 (or ~84) kcal/mol
BDE(C-H) for ØCHO is 86 kcal/mol

and
"Normalized Second-Order Rate Constant of H-Abstraction from H-Donor Substrates by BTNO" in MeCN:
kH for ØCH2OH is 0,94 (1/Ms)
kH for ØCHO is 0,8 (1/Ms)

so k1/k2 &#8776 1
Besides there is large acceleration of rate in protic, H-bonding solvent (AcOH) and order is this time reverted: hydrogen is abstracted from aldehyde faster than from alcohole.

[Edited on 27-4-2008 by kmno4]

Nicodem - 28-4-2008 at 07:48

Indeed I agree. Assuming the Evans-Polanyi relation for the two reactions to be of a similar value (calculated as equal) is the weakest assumption in my calculations. This factor depends highly on the one electron oxidant used and other conditions and I have no idea how the persulfate influences it. Therefore x=y was the only assumption I could take without using too much imagination.
With some transition metal one electron oxidants even the oxidation of toluene to benzaldehyde most commonly completely stops at PhCHO stage (talking about the numerous and well studied Co/Cu/Mn/etc catalyzed oxidations of toluene with oxygen). Often no PhCOOH can be detected. Considering that the BDE of Bn-H is 89 kcal/mol, thus even more than for PhCO-H, I can't think of anything else but that the Ea for radical oxidations of PhCHO is commonly quite higher (but obviously not always as demonstrated by the kinetic measurement you cite).
Anyway, those calculations were plain exercise since they can not give a reliable number given the bold assumptions used. It was more about showing the difference in the BDE values of the two substrates and showing how small absolute differences can give rise to huge differences in the kinetics.
Anyway, if anybody has another explanation for the reaction stopping at the PhCHO stage, I would be glad to hear it. Radical oxidations are not something I'm familiar with.

Quote:

Originally posted by JohnWW
Please download and post here those two articles, Nicodem.

Done.

Attachment: BDE_values_for_BnOH_and_BzH_references.rar (1.2MB)
This file has been downloaded 689 times

Ephoton - 28-4-2008 at 23:16

I found a good source of otc benzyl alcohol the other day I would like to share.
concrete floor stripper. usualy around 20 + %

hehe (I am now a hazard to others look out world)

[Edited on 29-4-2008 by Ephoton]

evil_lurker - 29-4-2008 at 09:12

Take your BzOH, place in diethyl ether with an equivalent of sodium hydroxide and molecular sieves to form sodium benzylate.

React with BnCl ala Williamson ether synthesis to dibenzyl ether (DBE).

Oxidize the DBE with dilute nitric acid catalized with sodium nitrite.

http://www.sciencemadness.org/talk/viewthread.php?action=att...

Reported yields as high as 80% based on DBE with the reaction sucessfully scaled up to 1 mole with similar results.

[Edited on 29-4-2008 by evil_lurker]

kmno4 - 2-5-2008 at 14:24

Offtopically about reaction of benzyl alcohol(=BA) and HCl(aq)(=AC).
On the picture: 5 test-tubes with with mixtures BA and AC, shaken
many times to reach equilibrium or close to it (at least I think so).
Test tube 1: 2g BA/2g AC [ 75 minutes]
Test tube 2: 2g BA/3g AC [ 50 minutes]
Test tube 3: 2g BA/4g AC [ 30 minutes]
Test tube 4: 2g BA/5g AC [ less than 30 minutes]
Test tube 5: 2g BA/6g AC [ less than 30 minutes]
I also made 2g BA/1g AC but this mixture did not split into separate layers ( I waited 8 hours). For the rest of mixtures, time of separating given in [ ].
To estimate degree of conversion BA into benzyl chloride I titrated (twice) remaining water-acid layer.
Results:
Test tube 1: 2g BA/2g AC -------------
Test tube 2: 2g BA/3g AC 44%
Test tube 3: 2g BA/4g AC 52%
Test tube 4: 2g BA/5g AC 67%
Test tube 5: 2g BA/6g AC 73%
Layer from test tube 1 was not investigated, because water+acid was not separated completly from organic layer and it would cause too big errors.
(from 2g BA/1g AC mixture it did not separete at all)
In no case density of organic layer is larger than water layer, as can be seen. To convert alcohol into chloride quantitatively, large excess of acid is needed. Use of CaCl2, ZnCl2 etc..., would be more convenient.

All values given by me are approximations. It would be good if someone could repeat these measurements.
End of offtopic

I have found interesting article about oxidation of benzyl alcohol with persulfate.
Aqueous Media Oxidation of Alcohols with Ammonium Persulfate
Chinese Journal of Chemistry, 2007, 25, 836—838
If someone is interested, link to article: http://mihd.net/egpdyq2

[Edited on 3-5-2008 by kmno4]

alc+bezn.JPG - 42kB

Magpie - 2-5-2008 at 16:14

Thanks, kmno4, for posting that journal article. I will be trying their method for making n-butyraldehyde soon.

evil_lurker - 2-5-2008 at 16:30

Well I think I have me a project for this summer.

1. Partially convert BnOH to BzCl as close to 1:1 ratio within reason. Start by adding the appropriate amount of 37% HCl to the alchol, heat and agitate to 80íC till it reaches equilibrium.

2. Drain water/acd, add in small quantity of NaOH (enough to remove HCl from previous reaction) then add in concentrated NaOH solution with either a tiny bit of triethylamine or tri-n-butylamine to form the ether.

3 Drain NaOH solution, rinse with a little nitric acid to remove alkali, drain again, then add in dilute HN03/NaNO2 catalyst solution and stirr for several hours.

If one used a reaction flask with bottom drain it could damn near be "one pot" with no solvents, use fairly cheap and easy to get reagents, and be completed in 5-6 hours with no need for isolation of intermediate products.

Nicodem - 3-5-2008 at 02:11

Kmno4, that was some nice looking and strict scientific experimentation of which I wish we had posted more and more often.

Thanks also for the paper. It is interesting to see that no overoxidation products are detected. But what is most confusing to me is that butanol reacts efficiently already at 30°C, while for the benzylic, allylic and secondary alcohols they used 75-85°C. Looks like a reversed reactivity order of what is expected for a radical oxidation (and the authors don't even bother giving any hypothesis to account for the differences).

Magpie, you better don't use this method as is on a larger scale since it was developed on a 1 mmol scale. Scaling it up by multiplication could get you in troubles of the type you encountered in your latest butanol oxidation trial. In my experience similar mmol reactions (of which Tetrahedron letter and Synthesis abounds) scaled up usually end up in runaways.

Evil_lurker, you might want to first try out that Bn2O oxidation with HNO3/NaNO2 on BnOH itself before wasting time with its etherification.

[Edited on 3/5/2008 by Nicodem]

evil_lurker - 3-5-2008 at 02:23

Quote:

Originally posted by Nicodem
Evil_lurker, you might want to first try out that Bn2O oxidation with HNO3/NaNO2 on BnOH itself before wasting time with its etherification.

I had considered that... did I miss something in the paper amongst all the tecnical info?

Nicodem - 3-5-2008 at 03:07

You forgot that in 15% HNO3 the media is acidic enough to cleave Bn2O to BnOH. You also forgot the context of the article – the authors were looking for an economical use of Bn2O which is a worthless side product in the industrial preparation of BnOH. Cited from the paper:

Quote:

During the oxidation of DBE, BnOH is formed and oxidised to BzH.[ref 7] Benzoic acid is formed by oxidation of benzaldehyde. Therefore, with the progress of the reaction the yield of BnOH decreases and that of BzOH increases. Presence of BnOH in the final product may not be a serious problem as it can be recovered from the reaction mixture by fractional distillation and is a value-added product.

In short, the treatment of BnOH with refluxing HNO3 gives BzOH just like when starting with toluene (BnH), but at milder conditions (90°C) you can actually get viable yields of BzH with BzOH being the major side product. The presence of nitrite works in your favor, assumingly as a source of NO2 to start the radical chain reaction.

garage chemist - 3-5-2008 at 03:43

KMnO4, the mixtures of benzyl alcohol and conc HCl have to be heated to effect the reaction! Try it again, and this time heat the test tubes in a boiling water bath.

I have very successfully made benzyl chloride many times from conc aqueous HCl and benzyl alcohol. At a certain temperature, the reaction spntaneously takes place and is over in a few minutes, with complete separation of phases. HCl is used in at least threefold excess. No other reagents are added.
Look at Rhodiums methods for benzyl chloride from -alcohol.

detritus - 3-5-2008 at 09:43

Hi,

Really interesting stuff here. But I am not old enough to buy the pure alcohol from any distributors, can anyone help with any info on OTC source of BzOH in the US?

MagicJigPipe - 3-5-2008 at 09:49

There's probably no useful OTC source of BnOH (it's Bn not Bz) in the US. You can get it from pharmacies but when I did that it cost me like $18 for 100mL (I think a couple of other places quoted $40 a quart). Definitely not a practical source unless you work with VERY small amounts like Woelen.

evil_lurker - 3-5-2008 at 09:59

www.lemelange.com $45 gallon USP grade (repacked under non USP conditions so it can't be labelled as such due to FDA regs).

[Edited on 3-5-2008 by evil_lurker]

[Edited on 3-5-2008 by evil_lurker]

MagicJigPipe - 3-5-2008 at 13:39

Hey! They used to be $35 a gallon! Or are you including shipping?

evil_lurker - 3-5-2008 at 14:21

They went up on it I reckon. Need to order a gallon or so.

azo - 3-5-2008 at 20:10

pitty you don't live in australia i could of given you a gallon i use it for work as a addative solvent.

MagicJigPipe - 3-5-2008 at 20:52

Just mail it. Even with shipping it might be cheaper and it's certainly not HAZMAT.

kmno4 - 4-5-2008 at 09:25

Quote:

Originally posted by garage chemist
KMnO4, the mixtures of benzyl alcohol and conc HCl have to be heated to effect the reaction! Try it again, and this time heat the test tubes in a boiling water bath.
(...)

I do not say no. My experiments were conducted at room temperature, concentration of HCl(aq) is 35.4%, only to prove
that Fleaker's post says untruth.
Besides, heating of concentrated HCl somehow scares me....
I do not like gaseous HCl

kmno4 - 7-5-2008 at 02:07

Quote:

Originally posted by Nicodem
In short, the treatment of BnOH with refluxing HNO3 gives BzOH just like when starting with toluene (BnH), but at milder conditions (90°C) you can actually get viable yields of BzH with BzOH being the major side product. The presence of nitrite works in your favor, assumingly as a source of NO2 to start the radical chain reaction.

Original paper (if already posted, delete this post, please):
Kinetics of Oxidation of Benzyl Alcohol with Dilute Nitric Acid
Ind. Eng. Chem. Res. 2005, 44, 325-333

Attachment: ie0303911.pdf (176kB)
This file has been downloaded 2497 times

evil_lurker - 7-5-2008 at 10:37

Dude, the information that paper contains is sweeet.

If it is indeed true, we may now finally have a viable method for the home manufacture of BnH from BnOH.

MagicJigPipe - 7-5-2008 at 12:29

Why would you want to make toluene out of BnOH? What a waste!

evil_lurker - 7-5-2008 at 12:41

Quote:

Originally posted by MagicJigPipe
Why would you want to make toluene out of BnOH? What a waste!

Ummm did you miss something here?

BnH is benzaldehyde, BnOH is benzyl alcohol.

Nicodem - 7-5-2008 at 13:02

I just knew this would happen as it always happens every time abbreviations and acronyms are used on this forum (like the TCCA vs. TCT confusion coming up all the time).

BnH is toluene since Bn stands for benzyl. Benzaldehyde would be BzH since Bz stands for benzoyl. Therefore it would be preferable to simply use PhCHO for benzaldehyde to avoid further confusion among those who are unfamiliar with such organic shorthand conventions as Bz which are rarely used anyway.

MagicJigPipe - 7-5-2008 at 13:12

Yes, evil lurker. Abbv. like that are based on a certain structure/moeity and not just an abbv. of a certain word.

Bn = Ph-CH2 Therefore, like Nicodem pointed out, a benzyl group with a hydrogen is toluene. Another example: Ph is C6H5 so benzene would be PhH (I've also seen benzene represented as "Ph" but that is technically incorrect) and phenol is PhOH. I can understand BzH. If that was used I would have realized he was speaking of benzaldehyde.

I just find BzH easier than typing PhCHO.

[Edited on 5-7-2008 by MagicJigPipe]

Magpie - 7-5-2008 at 15:12

Perhaps a formula for Bz, i.e., "benzoyl," would help as an explanation:

Bz = C6H5-(C=O)-

e.g., benzoyl chloride, C6H5-(C=O)-Cl

BzH then is C6H5-(C=O)-H, or more commonly, C6H5-CHO

[Edited on 7-5-2008 by Magpie]

evil_lurker - 19-5-2008 at 19:22

Well, based upon the extremely strong smell of BnH 2 hours since the start of the reaction, I'd say the reaction kmno4 posted does indeed work.

It also scales up well, self shielding due formed N2O, and if one uses a bubbler it even lets you know when its done.

[Edited on 19-5-2008 by evil_lurker]

Klute - 20-5-2008 at 09:05

Nice setup! I'm jealous

MagicJigPipe - 10-6-2008 at 11:14

I wanted to ask kmno4 a question about his comment of the HCl being the "dense lower layer". When I tried this a while back, that did not seem to be the case.

Wouldn't the BnCl sink to the bottom as long as the HCl (acid) was below ~20% concentration or so?

Quick check of Wikipedia:
38% HCl solution density: 1.18g/mL
BnCl density: 1.1g/mL

This is apparently at room temperature.

I found a list of HCl densities and at 20*C, 20% HCl's density (1.09g/mL) is less than BnCl's.

So, in theory, as long as your HCl was less concentrated than >%20 it should float to the top.

Sources:
http://en.wikipedia.org/wiki/Hydrochloric_acid
http://en.wikipedia.org/wiki/Benzyl_chloride
http://www.solvaychlorinatedinorganics.com/docroot/chlo_inor...

12AX7 - 10-6-2008 at 11:40

Seems to me I recall my professor stating she never believes a synthesis when it suggests which layer is aqueous.

Always test.

Tim

Fleaker - 10-6-2008 at 12:48

MJP, that is what I said long ago from when I tried the reaction of benzyl alcohol to benzyl chloride. kmno4 didn't agree with it since his experience was that the lower layer was the acid. I never saw that. I lost all interest in argument and discussion when he put up his test results from a test in which he did not even reflux the reactants!! That explained it all to my satisfaction! :-) My BzCl sunk to the bottom because I did not use a gross excess of conc. HCl, and also consider well that the conc. of HCl decreased as it reacted with the alcohol. In my case, the benzyl chloride was always at the bottom. As kmno4 found out, that may not always be the case, depending on the amount of HCl you use, and whether you actually heat it like you are supposed to do!

kmno4 - 10-6-2008 at 23:00

Quote:

Where is your refluxing ? Do not play a fool, man.
Besides, I seriously doubt that refluxing HCl(aq) with benzyl alcohol is good solution for making benzyl chloride. This procedure is not recomended by some unavailable reference (it is unavailable because of MagicJigPipe and his banning at solo's wet dreams - info by solo

). Benzyl alc. is sensitive to heating with acids ( info from available online wiley's encyclopiedia): heating same alcohol with acid can be dangerous, because of its spontaneous polycondensation. I think that in case of heating with conc. HCl such a condensation take place, at least partially. And, as I have already written, refluxing conc. HCl does not belong to pleasure things.....

[Edited on 11-6-2008 by kmno4]

Nicodem - 11-6-2008 at 03:12

I have not seen procedures where reflux was used. Generally it is done at room temperature or with just slight warming (it can even be done directly in a separatory funnel). It is counterintuitive to use reflux for reactions that are rapid enough already at room temperature since the increase in temperature often promotes side reactions.
Refluxing conc. HCl results in expelling excess HCl gas untill negative azeotrope forms which is 20% HCl(aq). So it is expected that in such case the lower layer is benzyl chloride.

behemoth - 4-9-2009 at 12:10

The Oxidation of BnOH to BzH can be carried out by the reaction of the alcohol with gaseous NO2 at room temperature in a closed vessel. After some hours, the formed nitric acid and nitrous oxides are evacuated off and pure BzH is left. Procedure in ChemSusChem 2009, 83-88.

Has anyone tried this yet?

ChemPlayer_ - 23-7-2015 at 05:26

Inspired by Magpie's original procedure, we've been working on refining the benzyl alcohol / persulfate oxidation.

It's a tricky one to get right but we can now boast an 85% yield. The trick is controlling the temperature very carefully, not too high so that it is out of control and over-oxidised, but also not going too slowly and therefore risking slow over-oxidation of product. You need to experiment and find the exact temperature (for your set up / solution) which is the 'initiation' point for the radical reaction, and steadily hold the reaction at this point by carefully adding the persulfate with vigorous stirring. Interestingly the occasional transient temperature rise due to too much addition doesn't hurt the yield too much. Above 72-75 degrees C however the yields are lowered due to oxidation to benzoic acid.

We've done a video showing the process and workup:

https://www.youtube.com/watch?v=YQWD4YIKBl4

Magpie - 23-7-2015 at 10:48

Very nice! You folks really took the time to investigate the nuances of this synthesis.

How did you conclude that this is a radical reaction? Can you write the equation for the reaction?

You achieved a significant improvement in yield. But likely you did not get the purity of my procedure. You used the bisulfite adduct. I used a steam distillation followed by vacuum fractional distillation. My product is clear and I obtained a boiling point indication of purity.

I also think that my procedure is somewhat safer than yours. By keeping the product hot enough there is an immediate and complete reaction when the drops of benzyl alcohol are added. There is no risk of a buildup of benzyl alcohol with consequent runaway. I recall very little char, and this is left in the pot during the distillations.

I would not have thought this reaction would be possible thinking instead that the product would be benzoic acid. We have to thank NERV and Fleaker for first mentioning this. I don't know where they got their inspiration. It's too bad they don't post anymore. Fleaker is a highly experienced/knowledgeable professional chemist in the metals area - NERV was a ChE student.

Is Tess married?

[Edited on 23-7-2015 by Magpie]

[Edited on 23-7-2015 by Magpie]

ChemPlayer_ - 23-7-2015 at 18:26

Thanks Magpie - all good points. Yes, we only discovered this variation through curiosity and really playing around, and it took a lot of tries.

For anyone starting out I'd have to recommend starting with your process (and to follow it to the letter exactly), and then if you want to be more adventurous to give this a go.

The first time we tried this we followed your exact process and got a yield of around 50%. This is repeatable if you follow the exact process, but we noticed pretty quickly that even a small increase in temperature and over-oxidation starts to occur, and the most important factor seems to simply be time ; more time in the pot = more product oxidation. It's a delicate balance between a few different variables.

The intent is to vacuum distill the product once our pump is repaired (currently works for filtering but won't hack it for distillation) but you can see from the quantity of adduct that the yield is real. We didn't believe it first time and spent hours re-converting and washing the adduct, and trying to boil off DCM which we thought must be in there...

On the safety front we did do a small worst-case 'Trinity' test which was to saturate a 50:50 methanol-water mixture with persulfate and benzyl alcohol, and then slowly heat the homogenous mixture using a hot water bath. Nothing happens for a while, and then the reaction goes runaway in the space of about 20 seconds (starting at around 60 degrees). It was 'very strong' but not violent, and we concluded from this that so long as you've never got more than about 25ml of persulfate as excess unreacted in the flask you're only risking a slight reflux for a few seconds given the volume of liquid in there before it dies back down. Right at the start is the risky point, and the additional water and the methanol 'temperature buffer' help - the temperature in event of a small runaway reaches about 80C rather than the 110-120C if you don't have it present.

Agree it would be great to find out the exact mechanism of how this works; the way that the reaction goes feels like it's radical based, and persulfate is a known initiator, but of course this isn't evidence. Another clue is the fact that it works at neutral pH (it's acid conditions that favour the persulfate anion acting as the oxidising agent). Unfortunately we have no classical radical initiator compounds lying around we could use to see if this kick-starts the reaction, which would give some evidence.

There is some good research out there on the use of persulfates to degrade organic materials as part of environmental processing, and we're looking at this to give us ideas as to where we take this.

We'll try doing this in slightly alkali conditions (sodium carbonate to help prevent Cannizzaro) as this is known to assist radical formation in persulfate solutions, but typically this is at a pH>10 and our guess is that the pH and possibly the more reactive radicals formed will rapidly destroy the benzaldehyde formed. It might offer evidence of a radical mechanism though if the reaction proceeds spontaneously or at a lower temperature... Chelated iron salts are another unconventional initiator option we could try here.

We think this is worth playing with because it's feasible in theory that a radical oxidation mechanism with the right conditions would be quite powerful and might even open up an aqueous conditions pathway from toluene. Long shot, but worth having a go...

Tess isn't married but her jurisdiction sadly does not afford Silicon based life-forms this opportunity!

CuReUS - 24-7-2015 at 09:33

Quote: Originally posted by Nicodem

You also forgot the context of the article – the authors were looking for an economical use of Bn2O which is a worthless side product in the industrial preparation of BnOH.

I was wondering,if the ether was worthless,it should be quite easily available, cheap as well as less dangerous compared to dimethyl ether.Could it be used to run grignards ?the solubility of other organic compounds in Bn₂O would have to checked first.I will do that tommorrow.

[Edited on 24-7-2015 by CuReUS]

MeshPL - 25-7-2015 at 05:10

I'm supprised nobody mentioned chromyl chloride + toluene --> benzaldehyde. Chromyl chloride oxidises toluene to benzaldehyde but not to benzoic acid.

chloride + chromate + sulphuric acid -distill-> chromyl chloride
chromyl chloride + toluene ---> benzaldehyde

Although the second reaction is quite tricky to do.

CuReUS - 25-7-2015 at 05:54

Quote: Originally posted by MeshPL

I'm supprised nobody mentioned chromyl chloride + toluene --> benzaldehyde.

Quote:

Then 40 g toluene in 2X its volume of CHCl3 was added slowly with stirring to 140 g CrO2Cl2 in 200 ml CHCl3 on a cold water bath. After standing overnight, H2SO3 was added with stirring, the whole was steam distilled, CHCl3 evaporated, and a 44% yield of benzaldehyde was isolated via bisulfite. Their description of this Etard looks different than others that I have seen in the journals.

from http://www.sciencemadness.org/talk/viewthread.php?tid=2223&a...

[Edited on 25-7-2015 by CuReUS]

Chemi Pharma - 13-8-2017 at 05:37

I read all the posts and I'm really surprised with the fact that nobody, except Leu, talked about the OTC Hypochlorite oxidation of benzyl alcohol.

Oxidation of benzyl alcohol with calcium hypoclorite (HTH pool) and alumina (Al2O3) affords 99% benzaldehyde, just stirring the reagents at room temperature for 4 hours, as said in the study i bring to the community as an attachment.

Also, if you are in a hurry to get your benzaldehyde, you can react the same reagents (benzyl alcohol, calcium hypochlorite and moist alumina) in a microwave oven for just 01 (one) minute, to afford 98% benzaldehyde, as said in the another paper i'm attaching.

Sorry guys, mainly Magpie, whose job done with persulfate oxidation of benzyl alcohol is respectable, but I think Hypoclorite oxidation of benzyl alcohol is more OTC and high yielding than all the methods I've seen at this whole thread and prepublication section.

Here's the papers below:

Attachment: alcohol oxidation by CaOCL to aldehydes.pdf (161kB)
This file has been downloaded 582 times

Attachment: Microwave Assisted Selective Oxidation of Benzylic Alcohols with Calcium Hypochlorite under Solvent-Free Conditions.pdf (62kB)
This file has been downloaded 481 times

JJay - 13-8-2017 at 06:06

That's kind of interesting. I have never tried making benzaldehyde, but I suspect the process is rather finicky, especially with an oxidizer as strong as calcium hypochlorite. I'm not sure what the role of alumina is in those procedures....

Melgar - 13-8-2017 at 06:21

Quote: Originally posted by Chemi Pharma

Sorry guys, mainly Magpie, whose job done with persulfate oxidation of benzyl alcohol is respectable, but I think Hypoclorite oxidation of benzyl alcohol is more OTC and high yielding than all the methods I've seen at this whole thread and prepublication section.

Look at the scale of those reactions, then imagine scaling up to... oh, let's say one liter of benzyl alcohol. And to make things interesting, let's try the microwave-assisted variant.

Hopefully you haven't found this out the hard way yet, but the reaction you're proposing is highly prone to thermal runaway at anything approaching useful scales. Truth is, oxidizing benzylic alcohols to benzaldehydes is perhaps the easiest oxidation in organic chemistry, and many a PhD dissertation has been written on new methods for doing it. The hard part is doing it at a useful scale with OTC reagents and an easy workup.

Personally, I've found KMnO4 to work really well, since permanganate will rapidly oxidize a lot of the alcohol to benzaldehyde initially, and MnO2 will selectively oxidize the remaining benzyl alcohol. Even though KMnO4 is able to oxidize benzyl alcohol all the way to the acid, that's only a minor side-reaction if you work out the stoichiometry correctly. By the time there's an appreciable amount of benzaldehyde to react into benzoic acid, the permanganate has mostly decomposed into weaker oxidizers.

Chemi Pharma - 13-8-2017 at 08:13

Quote: Originally posted by JJay

That's kind of interesting. I have never tried making benzaldehyde, but I suspect the process is rather finicky, especially with an oxidizer as strong as calcium hypochlorite. I'm not sure what the role of alumina is in those procedures....

JJay, I don't think that hypochlorite is so strong oxidiser as persulfate, KMNO4 or nitric acid. May be the Alumina role in this reactions is act as a cataliser, avoiding an eventual runaway like Melgar said, giving a milder reaction instead with hypochlorite alone.

Quote: Originally posted by Melgar

Melgar, please, give it a try! I've never read at nowhere, this reaction isn't scalable. Don't blame the authors if they only did a small batch run and ommited about the scalability of the reaction.

I think some of us could run a 500 ml benzyl alcohol batch and tell about the results. I really don't expect a runaway! As i just have written to JJay, I think the Alumina presence makes the reaction milder than with hypochlorite alone.

Of course I agree with you that careful is necessary with microwave assisted reactions, mainly while scaling a reaction involving flamable reagents like benzyl alcohol. It's not commercially feasible, but it may be produce enough to a home made Lab necessities.

Quote: Originally posted by Melgar

Personally, I've found KMnO4 to work really well, since permanganate will rapidly oxidize a lot of the alcohol to benzaldehyde initially, and MnO2 will selectively oxidize the remaining benzyl alcohol...

Ok, and what about the yields of benzaldehyde in this KMNO4 oxidation? I have my doubts if it not results in a mixture with near equal quantities of benzaldehyde and benzoic acid due the powerfull oxidating properties of permanganate.

JJay - 13-8-2017 at 09:23

Hmm... I had thought hypochlorite was a stronger oxidizer than almost anything except hydrogen peroxide... this table doesn't really say: http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch19/ox...

Chemi Pharma - 13-8-2017 at 09:58

Take a look here JJay:

http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/electpot.h...

As you can see, hypochlorite anion has an eletrochemical potencial of + 0,90V, while HNO3 has + 0,96V, Chlorine + 1,36V, KmnO4 + 1,49V, H2O2 + 1,78V and persulfate + 2,01V.

So, hypochlorite has the minor oxidant power between all this reagents above.

[Edited on 13-8-2017 by Chemi Pharma]

JJay - 13-8-2017 at 10:14

Isn't there more to oxidizer strength than electrode potential, though? Dichromate has lower electronegativity than hypochlorite, but chromium +3 is oxidized to chromium +6 by hypochlorite....

Chemi Pharma - 13-8-2017 at 10:36

It's cause the oxidant agent able to oxidate Cr+3 to Cr+6 is the free chlorine produced by the dissociation of the hypochlorite anion at low PH (below 7), nor the hypochlorite ion.

As you can see at the table, free Chlorine has a redox potencial of + 1,36V, while Cr+6 has 1,33V. This little difference may explain why chromium salts are only slowly oxidated to Cr+6 during chlorination of drinking water.

I found a theme at PubMed telling about the fact. Take a look:

Oxidation of Cr(III) to Cr(VI) during chlorination of drinking water

https://www.ncbi.nlm.nih.gov/pubmed/22487808

No way the oxi-redox table were wrong JJay, otherwise it would be a breakdown of all the expected phisicochemical rules.

JJay - 13-8-2017 at 11:18

I've oxidized Cr+3 to Cr+6 at high pH, so I'm not really sure what you're getting at. I don't think anyone said the table is wrong.

Chemi Pharma - 13-8-2017 at 12:04

Quote: Originally posted by JJay

I've oxidized Cr+3 to Cr+6 at high pH, so I'm not really sure what you're getting at. I don't think anyone said the table is wrong.

Ok JJay, I apologize for the misunderstanding. Let me try to explain in the right way:

1- It's not possible a reaction with eletrochemical potencial lower than other displace the equilibrium in favor of the first. To do this we need to force some variables like pression, temperature, eletrochemical charge input, like electrolisys, etc.

It's the same principle behind the reaction of metals more eletropositive than hydrogen reacting with acids to give hydrogen gas (displacement), while metals like silver and copper doesn't.

The eletrochemical potencial of a reaction can tell us about the strenght of the oxidazing or reducting power of a reagent, cause the two things it's intimally related.

What's facilitate an oxi-redox reaction? the hability of the reactant to receive electrons and the reagent to give them. Then, to know if some reaction will be spontaneous or not, just look at the electrochemical potencial of the equation, based on the table.

2 - Therefore, when we oxidate Cr+3 to Cr+6 with hypochlorite, at really, the residual molecular free chlorine in solution is who do the job, not the hypochlorite anion, cause ClO- to Cl is more eletropositive than Cr+3 to Cr+6. That is impossible.

Off course free molecular chlorine exists dissolved in a hypochlorite solution, even with PH 14. I just said that if you diminish the PH, it favours the formation of hypochlorous acid (HCLO), releasing more free chlorine in solution, increasing the oxidating power to transform Cr+3 in Cr+6.

Forgive me if you feel offended by the way I expressed my ideas. It was not my intention.

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