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Picric-A
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Benzyl chloride from Benzyl acetate
I have recently bought 2l of Benzyl acetete off ebay for 99p (yep 99p  ) and i
plan to do something with this.
I want to make some benzyl chloride and am considering the different methods of doing this.
1) Boil 10ml of Benzyl acetate in a sodium hydroxide solution then seperate the benzyl alcohol from the reaction mix by distillation.
React the benzyl alcohol produced with hydrochloric acid. These react easily producing the product, no long reflux or H2SO4 needed. (according to http://www.erowid.org/archive/rhodium/chemistry/benzylchlori...)
Seperate Benzyl chloride by a seperating funnel.
2) Reflux 10ml of Benzyl acetate in an exess of conc HCl.
Seperate the Benzyl chloride.
Obviously the second method is a lot simpler but will this work? I see no reason why not- i would be left with a solution of acetic acid and
hdyrochloric acid and a seperate layer of my product.
Any imput would be helpfull.
[Edited on 22-12-2009 by Picric-A]
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ScienceSquirrel
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I would make a large amount of benzyl alcohol, nice harmless chemical and easy to store.
I would make a few grams of benzyl chloride and see how you go. I made dozens of substituted benzyl halides at one time but I have never touched
benzyl chloride itself. Some of them were potent lacrymators and some were pretty mild.
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sonogashira
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Maybe acetate can be used as a leaving group to save need for conversion to chloride?
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mr.crow
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I was also thinking of the possibility of turning esters into alkyl halides.
The general procedure in Vogel for alcohols is to use conc HCl and a catalyst like ZnCl2. The HCl will also hydrolize the ester at the same time so it
can be done in one pot.
But now there are two equilibriums, the ester and alcohol, and alcohol and chloride.
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Picric-A
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That is true for aliphatic primary + secondary alcohols but according to the site aromatic alcohols (specifically benzyl) will react with an excess of
conc HCl at room temp without the need for a catalyst.
Will the acetate be a good enough leaving group with CN- as the neucleophile?
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Nicodem
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Yes, of course you can use benzyl acetate directly in that benzyl chloride preparation. I could find no examples of this specific transformation in
the literature, but there are several examples of various arylmethyl acetates being transformed to the corresponding arylmethyl chlorides by using HCl
at temperatures from rt to 50°C and the use of a cosolvent where needed (solid substrates etc.). Just heat to 40-60°C if you want to make sure the
reaction goes to completion.
The acetate group is a lousy leaving group and in practice it is near to useless in the SN2 substitutions (it does work good when protonated and for
SN1 substitutions though, which however is not applicable to the cyanide as nucleophile).
I could find no examples of phenylacetonitriles preparation from benzyl acetates, except for the one described in Org. Synth., which however is a reaction on a lactone (beta- and gamma-lactones alkylate nucleophiles much faster than the corresponding
open chain analogues). As you can see even for phthalide the reaction requires some harsh conditions (180-190°C), so for benzyl acetate it would
either require a temperature beyond its boiling point or the use of a solvent promoting the reaction at lower temperatures. In any case the conditions
might even be too harsh to avoid side reactions. But you can always try to heat KCN in benzyl acetate reflux and follow by TLC. The addition of a
small amount of a crown ether or polyethyleneglycol should catalyse the reaction by separating the K(+)CN(-) ion pair. Certainly a nice amateur
research project in my opinion. It should be quite rewarding for an amateur to go beyond what professional chemists published.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Picric-A
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Hmm... well i guess the acetate leaving group is out of the question...
Back to hydrolysis to the alcohol. I tried this today, 20ml of 10M NaOH (not all dissolved at once- required heating) was added to 5ml of benzl
acetate in a 50ml RBF.
The mix was refluxed for one hour. After an hour the contents were allowed to cool and were checked and it seemed like none had undergone hydrolysis
(i.e. the layer was the same thickness)
I also must stress, i didnt use bumping granules in this as they seemed to cause more bumping than without, they would get to the heavy benzyl layer
then bounce back down causing lots of foaming- thus without the granules there was fairly bad bumping, this was sorted with a air condensor between
the liebig and flask.
Tommorow i will try hydrolysis with a solution of 80% EtOH 20% H2O with NaOH dissolved in. Hope this helps merge the layers for an easier hydrolysis.
If not it wil; have to be a 24 hour relfux for just ~ 10ml of product by the looks of it
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entropy51
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For esters not appreciably soluble in water, I find KOH in EtOH to be a good base for hydrolyzing the ester. This should go faster than aqueous NaOH.
Rapid magnetic stirring is usually preferable to anti-bumping granules.
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Nicodem
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Why? Haven't you read my post above?
| Quote: | | Back to hydrolysis to the alcohol. I tried this today, 20ml of 10M NaOH (not all dissolved at once- required heating) was added to 5ml of benzl
acetate in a 50ml RBF. |
What is the point in using such a huge NaOH concentration and sixfold excess? You don't heat 10M NaOH in a flask unless you want to ruin it.
| Quote: | | The mix was refluxed for one hour. After an hour the contents were allowed to cool and were checked and it seemed like none had undergone hydrolysis
(i.e. the layer was the same thickness) |
What is this "same thickness" supposed to mean? Have you analysed the reaction mixture in any way or not? If you have not, then how do you now that
the hydrolysis did not occur.
Besides, if unsure, why don't you just stick to a literature example?
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Picric-A
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Quote: Originally posted by Nicodem  |
Why? Haven't you read my post above?
| Quote: | | Back to hydrolysis to the alcohol. I tried this today, 20ml of 10M NaOH (not all dissolved at once- required heating) was added to 5ml of benzl
acetate in a 50ml RBF. |
What is the point in using such a huge NaOH concentration and sixfold excess? You don't heat 10M NaOH in a flask unless you want to ruin it.
| Quote: | | The mix was refluxed for one hour. After an hour the contents were allowed to cool and were checked and it seemed like none had undergone hydrolysis
(i.e. the layer was the same thickness) |
What is this "same thickness" supposed to mean? Have you analysed the reaction mixture in any way or not? If you have not, then how do you now that
the hydrolysis did not occur.
Besides, if unsure, why don't you just stick to a literature example?
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Sorry i did read your post however i figured i would leve the expermentatioin to anothertime (when i am not using CN- as the nucleophile!!!! i dont
fancy gassing myself with the stuff as i am trying high temps!
I used too much i know, i just wanted to provide a very alkaline eviroment to speed up the hydrolysis, my flask was unaffected though, which did seem
odd to me. I used an old, heavily scratched flask so i didnt care if any ethching took place.
The same thickness meant the layer of Benzyl acetate containted the same volume of liquid. Benzyl alcohol is micible with water so when it formed it
would go to the aqeous layer, and so the end point of the reaction would be the merging of the layers, no analysis needed.
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not_important
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But could you have salted out the benzyl alcohol? There's going to be a pretty high concentration of NaOH remaining and a bunch of sodium acetate.
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Nicodem
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| Quote: Originally posted by Picric-A |
The same thickness meant the layer of Benzyl acetate containted the same volume of liquid. Benzyl alcohol is micible with water so when it formed it
would go to the aqeous layer, and so the end point of the reaction would be the merging of the layers, no analysis needed. |
Benzyl alcohol is not miscible with water! Just look at it structure. It should immediately be obvious it can not be. Its solubility in water is small
(few grams per 100 mL), and you can safely assume it is negligibly soluble in an concentrated aqueous solution of salts like sodium hydroxide and
acetate.
You said you don't want to do research, so why do you try to improvise where it is not needed? For something as trivial as benzyl acetate hydrolysis
rather follow a literature example.
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Picric-A
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I never said i didnt want to try research, i said i didnt want to try something new with cyanides.
Sorry, thats is where i have been wrong all along, i assumed benzyl alcohol is micible with water, lesson learnt.
Thanks Nicodem.
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smuv
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@ picric, for hydrolysis (at least of a solid amide) I have found that it is absolutely imperative that all of the compound is dissolved, or else the
reaction rate becomes incredibly slow. Also I think an hour reflux is a little skimpy, I would honestly just let it go overnight.
I have also wondered... what would happen if an ester or amid was fused with 1eq or more of NaOH, would that not be a very quick way of decomposing an
ester?
"Titanium tetrachloride…You sly temptress." --Walter Bishop
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Picric-A
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@ smuv- we are not trying to 'decompose' the ester, we are trying to hydrolyse (saponify) it, ie, we are doing this:
Ester + Water <--> Acid + Alcohol
By using sodium hydroxide we are pushing the equation to the right by removing the acid, according to Le Chatteliers Principal. In short no, fusing
would not work with esters.
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DJF90
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Smuv: It could work if the ester/amide to be reacted melts at a sufficiently high temperature, much like the hydrolysis of PET (as shown in prepub?
Perhaps even work carried out by yourself, I do not recall); after all its not called a polyESTER for nothing.
Picric A: See above note. Using Le Chatelier in this context is basic (probably taught for your age group); you need a mechanistic reasoning to be
able to rationalise most things in organic chemistry though... Of course physical explanations also need to be taken into consideration also
(enthalpy/entropy etc.)
And Smuv is right in calling it a decomposition; its not an ester when you've finished (unless you cock something up) and hence the ester has
decomposed to an acid/carboxylate salt. Of course hydrolysis is the appropriate term (as is saaponification, although this is more used among
biochemists/biodieselists/soap makers IMHO). But in chemistry you have to learn to be flexible with terminology (acetic/ethanoic, 2-propanone/acetone,
2-butanone/methyl ethyl keton etc... You don't need further examples).
[Edited on 25-12-2009 by DJF90]
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smuv
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...I was careful not to use the word hydrolysis because there would be no water involved in a fusion with sodium hydroxide. I don't want to get into
a war of terminology, but I question whether a saponification is a hydrolysis (though it is widely labeled as such) as no water is involved.
R'OOR NaOH --> R'OONa + ROH
Also picric, I would appreciate if in the future you don't simply dismiss a post you don't understand. There are a lot of intelligent people on this
forum and simply jumping to a conclusion that they don't understand what they are talking about will only hold you back. After all if you took
nicodem's, entropy51's or my own advice, that ester would already be saponifed. I as well don't understand after nicodem's thorough posts why you are
even saponifying the ester and not directly making benzyl chloride from the acetate.
[Edited on 12-25-2009 by smuv]
"Titanium tetrachloride…You sly temptress." --Walter Bishop
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DJF90
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yes that is correct, some people are obviously beyond help, even when they have such great minds on their case.
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Picric-A
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Wrong, sorry. I have taken everything you say into account and have 200ml of very poure Benzyl alcohol.
I performed a hydrolysis in a methanol/water/KOH mix, then seperated by distillation. Yield 93% based on the acetate. took 2 hours.
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DJF90
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Very pure by what means? How have you determined the purity? What % purity did you get by analysis?
I thought the whole aim of this thread was to get benzyl chloride from the acetate. If you just wanted the alcohol why didnt you just follow a
standard hydrolysis procedure as outlined in an experimental text like Vogel?
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Picric-A
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I did a B.P test to identify it then fractionated it with a 60cm fractionating column, finally measured its refractive index and got a reading of
1.540, ie, its very pure.
This stuff is very interesting, i immersed a quartz tube inside it and it seemed to dissappear, just a fun little experiment 
I did want the chloride however i took the adivce given to me to prepare the alcohol first and from then esterify with HCl to form the chloride, this
is what i will be doing tommorow.
[Edited on 26-12-2009 by Picric-A]
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entropy51
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Gee, who would ever have thought this would work? | Quote: | | I performed a hydrolysis in a methanol/water/KOH mix |
You're welcome.
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JohnWW
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I thought that benzaldehyde, rather than benzyl alcohol, was the starting-point for several drug and other important syntheses. However, it can be
oxidized to benzaldehyde, although careful choice of reagent and conditions is necessary to avoid oxidation to benzoic acid.
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DJF90
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JohnWW: What are you going on about? Who suggested drug synthesis? Or any other synthesis for that matter??! Of course benzyl alcohol can be oxidised
to benzaldehyde, and overoxidation isnt so bad if you know what you're doing and use a selective reagent (i.e. one that wont oxidise and aldehyde to
an acid).
I'm utterly confused by your post.
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Picric-A
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| Quote: Originally posted by entropy51 | Gee, who would ever have thought this would work? | Quote: | | I performed a hydrolysis in a methanol/water/KOH mix |
You're welcome. |
You indeed did give me the idea of using KOH instead of NaOH however i knew using a water/alcohol mix would speed up hydrolysis by meerging the
layers.
DJF90 - I think he could be implying i am trying to make drugs?
....not sure however that is all the sense i could make out of that most.
If i wanted benzaldehyde i would to the toluene oxidation using MnSO4 and H2SO4 route, not mess though benzyl alcohol.My target is benzyl chloride.
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