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Author: Subject: toluene --> benzaldehyde
S.C. Wack
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[*] posted on 16-1-2005 at 23:19


Went to the library to follow up on some research on oxidations to aldehydes, not looking for toluenes->benzaldehydes at all. So of course I found nothing useful in the area that I was looking for, but with this thread fresh in my mind noticed some references. Looked some up.

JOC 16, 604 (1951) went the MnO2/H2SO4 route to make 3-t-butyl-4-methoxybenzaldehyde from the corresponding toluene. 400 g. of the methylanisole, 221 g. MnO2, and 2000 g. 30% H2SO4 were agitated vigorously for 28 hrs at 62-65C. 226 g. of unreacted precursor and 187 g. of the aldehyde were found in the oil layer. Given cheap or unreacted, recyclable precursor and cheap H2SO4, the low yield may not be so bad.

A reference to NiO2 also caught my eye. Useful stuff considering how easy is is to make, use, and regenerate. Doesn't get much easier, so I am suspicious of
DE127388

But if that doesn't work out, there is another way to use it to get benzaldehyde. If one goes from benzyl chloride to the alcohol such as in
US2221882
a nearly quantitative yield can supposedly be had, because those are the kinds of yields of aldehydes that aqueous alkaline NiO2 gives in minutes. Alcohol->aldehyde reagents are a dime a dozen, there are many other options.

EDIT: wow, that is what happens when you stay up too late. Of course I am and was well aware that NiO2 makes acids, not aldehydes, from alcohols. Except when I got to that last paragraph. Which is why I said that I am suspicious of that patent producing much benzaldehyde. How then I came up with that last bit, I don't know. Going from the alcohol to the aldehyde is still a good idea, just not with NiO2.

[Edited on 18-1-2005 by S.C. Wack]
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[*] posted on 17-1-2005 at 02:37


Quote:

JOC 16, 604 (1951) went the MnO2/H2SO4 route to make 3-t-butyl-4-methoxybenzaldehyde from the corresponding toluene. 400 g. of the methylanisole, 221 g. MnO2, and 2000 g. 30% H2SO4 were agitated vigorously for 28 hrs at 62-65C. 226 g. of unreacted precursor and 187 g. of the aldehyde were found in the oil layer. Given cheap or unreacted, recyclable precursor and cheap H2SO4, the low yield may not be so bad.

Quite similar to the german patent I posted. Toluene seems to stand an higher acid concentration, all references talk about 50-60% H2SO4.

I will post some practical results lateron, the advantage of MnO2 is its availability.
The electrolytic re-oxidation of the spent sulfate sounds nice but is tedious, if one doesnt have an electrolytic cell around its not worth the effort IMHO.
Reoxidation by 30% H2O2 will be explored for the simple reason that its OTC for me.

/ORG




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[*] posted on 17-1-2005 at 09:57


Found an article:

K. Ohkubo, K.Suga, K. Morikawa, S. Fukuzumi; J. Am. Chem. Soc., 2003, 125, 12850-12859

where they oxidise toluene to benzaldehyde photochemically (>300 nm) by oxygene in acetonitrile in presence of a photocatalyst tetrafluoro-p-dicyanobenzene, getting 3% conversion with 100% selectivity after 10 h. (we have lots of time). One could most probably change the solvent. Some articles referred to using acetic acid..

In article there are given 12 different photocatalysts, all are benzene rings with some chlorine and/or fluorine and/or cyano substituents.
As I understand, photochem oxidation begins with exitation of the photocatalyst, and all photocatalysts presented in article seems to be some electron poor benzene rings...
Any idea if this electron poorness is an criteria to select a good photocatalyst? Or am I totally wrong?
Otherwise one could choose 1,3,5-trinitrobenzene as the photocatalyst :o

Btw, in another interesting article on photocatalysis they used TiO2 as catalyst:

G. Marta, V. Augugliaro, S. Coluccia, Studies in Surface Science and Catalysis, 2000, 130A, 665-670.
(havn't printed it yet.. gonna check it out soon..)
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[*] posted on 17-1-2005 at 12:00
Toluene to benzaldehyde


A quick search for toluene to benzaldehyde gave me - unsurprisingly - a lot of hits. The extract from the article below is a solvent-free oxidation with potassium permanganate supported on montmorillonite, but does not suffer from the particularly large amounts of oxidant often required for such transformations. Still, it isn't a procedure you'd use on a large scale. The following is exemplified for indane -> indanone, with the same procedure giving benzaldehyde in 60% yield in 18h when applied to toluene. Taken from Tetrahedron Letters, 43, 5165-5167 (2002):


2.1. Oxidation of indan under classical conditions
Potassium permanganate (3.16 g, 20 mmol) and montmorillonite K10 (6 g) were ground together in a mortar until a fine homogeneous powder was obtained. Indan (0.24 g, 2 mmol) was added to this KMnO4/K10 mixture (4.5 g, 9.9 mmol) in a 25 mL round bottomed flask and mixed magnetically at room temperature until TLC (eluent: hexane–ethyl acetate) analysis indicated a completed reaction (20 h). The residue was then washed with CH2Cl2 (2×20 mL). After filtration and removal of the solvent, the crude product was chromatographed on silica gel (eluent: hexane–ethyl acetate) to give purified product (0.22 g, 1.7 mmol, 85%)


Using microwave irradiation, as below, gave benzaldehyde in 54% yield in 12 minutes:

2.3. Oxidation of tetralin under microwave irradiation
In a 25 mL Teflon beaker, tetralin (0.26 g, 2 mmol) was added to KMnO4/K10 (4.5 g, 9.9 mmol). After 3 min of mechanical stirring, the mixture was irradiated at medium power for 25 min. At the end of exposure to microwave irradiation, the mixture was cooled to room temperature and eluted with CH2Cl2 (2×20 mL). After filtration and solvent removal the crude product was chromatographed on silica gel (eluent: hexane–ethyl acetate) to give purified product (0.24 g, 1.7 mmol, 82%).


Some other references for the oxidation of toluene to benzaldehyde are:

Synthetic Communications, 29(7), 1177-1182 (1999), using sodium bromate and cerium dioxide;

Tetrahedron Letters, 28(10), 1067-1068 (1987), using ceric methanesulfonate (91% yield);

DE168291, in which 'air and water' is used;

DE127388, using nickel oxide (edit: duh, of course this is the same as posted by S. C. Wack above);

DE101221 (which appears to be the one cited by Orgy as DE102221), DE107722 and Journal of the Chemical Society, 91, 263 (1907), using manganese dioxide and sulfuric acid;

DE158609, using cerium dioxide and sulfuric acid;

and DE175295, using 'manganese dioxide sulfate'.

That's pretty much it for the easy to get reagents. I haven't read any of the papers (partly as I don't speak German) so I'll keep my fingers crossed that they are of use.

[Edited on 17-1-2005 by Kinetic]
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[*] posted on 17-1-2005 at 20:54


Quote:

JOC 16, 604 (1951) went the MnO2/H2SO4 route to make 3-t-butyl-4-methoxybenzaldehyde from the corresponding toluene. 400 g. of the methylanisole, 221 g. MnO2, and 2000 g. 30% H2SO4 were agitated vigorously for 28 hrs at 62-65C. 226 g. of unreacted precursor and 187 g. of the aldehyde were found in the oil layer. Given cheap or unreacted, recyclable precursor and cheap H2SO4, the low yield may not be so bad.


This is actually a pretty good yield. Similar could probably be attained with toluene. Is it difficult to separate a mix of toluene/benzaldehyde that contains 226 g toluene and 187 g aldehyde as above?




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[*] posted on 17-1-2005 at 21:06


Bisulfite.
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[*] posted on 18-1-2005 at 03:15


120°C.
cheaper and more OTC.




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thumbdown.gif posted on 19-1-2005 at 10:32
first try


350ml 38% H2SO4
110ml toluene
100g MnO2
8g CuSO4 pentahydrate

This was refluxed for 3 hours, and steamdistilled, toluene stripped and yielded a small residue of benzoic acid.

Nada benzaldehyde.

/ORG




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thumbdown.gif posted on 19-1-2005 at 13:58
second try


150ml 38% H2SO4
110ml toluene
100g MnO2
8g CuSO4 pentahydrate

This was refluxed for 3 hours, and steamdistilled, toluene stripped and yielded some benzoic acid and a neglectible amount of benzaldehyde.


I would like to say that - at least with somehow bigger amounts - high temperature/refluxing will end in benzoic acid and no stirring will give lousy results anyways.

More the next days.
/ORG :mad:




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[*] posted on 20-1-2005 at 00:15



Looked up Kinetic's JCS ref. There were other oxidants in that article as well. Looked in CA and found some things. Found Beilstein (all versions except online, stingy Uni), the sometimes helpful Richter's Organic Chemistry, and the Fiesers' Reagents... of no use. Looked strictly for toluene->benzaldehyde without high temps and in English.

First in the JCS was PbO2. 280 g of it and 300 ml of H2SO4 (sp. gr. 1.52) were mixed in a lead vessel with ice bath cooling. CO2 was blown in to the reactor. With stirring, 50 g toluene was added. This was steam distilled after 3 hrs and a 24% yield of benzaldehyde was isolated with bisulfite. They got an 18% yield without the ice bath and with slow addition of the toluene. The temp got up to 40C either way.

Also in lead, 100 g MnO2, 300 ml of the 1.52 H2SO4, and 50 g toluene were stirred for 5 hrs. Less than 1% yield. Repeating with "freshly precipitated" MnO2 and 6.5 hrs, a 5% yield.

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. BTW, when I mentioned the Etard earlier, I was only asking for a ref specifically for DCM/toluene. DCM and other chlorinated solvents often work, usually not as well, on various substrates. The Etard will give phenylacetaldehyde with ethylbenzene, and phenylacetone with propylbenzene. Styrene also gives benzaldehyde.

And last, they mixed 200 g ammonium persulfate, 500 ml 4N H2SO4, 2 g Ag2SO4, and 40 g toluene with stirring. Steam distillation and bisulfite gave a 78% yield of the aldehyde.

CA 23(4), 3217 (1929) abstracts an obscure (outside of Japan, maybe inside it as well) journal. Unfortunately not the experimental details. The abstractor or author was kind enough to tell of the huge amount of experimentation, with the ideal conditions for benzaldehyde production determined, all experimental variables being explored, without actually giving any clue as to what the magic combination is. What it does say is that MnO2 from heating of Mn(NO2)2, or from KClO3, were both tried. Also from MnSO4 and Cl2 or KMnO4. Mn2O3 and Mn3O4 were also tried. It speaks of "oxidizing power", not yield of aldehyde. Mn2O3 was best with 70%, and the MnO2 from simple heating the worst. Other forms, 40%. I'll look up the author later, he promised to give more details.

Later in that volume (p. 3680), the first of a series of Soviet J. Chem. Ind. abstracts. The author claims almost 100 experiments to tell us the most favorable: temp, 18-19C; H2SO4 conc., 65%; ratio of toluene:MnO2, 4:1; yield based on MnO2, 55%. Catalytic amounts of HNO3 had a slight accelerating effect. CuSO4 and KI were found without effect. Different types of MnO2 gave different activity, pyrolusite is to be avoided, except perhaps to make MnSO4 and precipitate MnO2 from that.

In the next one, 150 g toluene, and 300 g of H2SO4 (sp. gr. 1.57) were stirred up, and CuSO4 catalyst and a mix of 45 g MnO2 and 50 g H2SO4 (1.57) was added gradually. After no more than 2 hrs (when the color lightens the reaction is done, it says) steam distillation was done, the organic layer decanted and washed with Na2CO3, and an amazing 15 g of benzaldehyde was isolated from the bisulfite intermediate.

Last, a comrade mixed up 60% H2SO4 with toluene, and added pyrolusite gradually with rapid stirring and some heating. He said that conc. of the acid should not vary far from 60%, temp should not go much above 35C, excess MnO2 hurts, and long reaction time favors production of the acid. Again, if there are details, little things like isolated yield, they aren't in the abstract.

High yields can be had by applying some electrons to the situation, if you're into that kind of thing - it's been done in a few articles with the Mn sulfates, but I thought this of not much interest even here.

[Edited on 20-1-2005 by S.C. Wack]
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[*] posted on 20-1-2005 at 05:48


Yay, S.C.Wack, the persulfate route seems very interesting specially because ammonium persulfate seems easy to prepare. Can you please give the reference to this?

As for ammonium persulfate preparation, heres what my nonorg book told:

It is prepared electrolytically:
2(NH4)2SO4 - 2e- --> (NH4)2S2O8 + 2NH4+

A glass jar is filled with cold 50% H2SO4. Into the solution, a clay pot is placed, filled with saturated soln of ammonium sulfate.
As anode, a platinum wire is used (dipped into ammonium sulfate soln). As cathode, theyre using a lead pipe which is coiled several times around the clay pot. Through the pipe, cold water is led to make efficient cooling.
Electrolysis is done at 2,5-3 A/cm2 (does not say if it's on cathode or anode). Voltage depends on the resistance of cell, usually 10-20V is enough.
On the anode there will evolve some oxygene and ozone.
Because of low solubility of persulfate, it will precipitate. After 4-6 hours electrolysis is ceased. Colorless solid is filtered through porous glass filter, washed once with cold water and dried at 50-60*C. Salt is stable in air.

So, this seems doable. If only we could change anode to graphite and cathode to copper tubing... In my experience copper is quite ok as cathode in sulfuric acid solutions.. though I'm not sure if the oxidaton of sulfate requires Pt anode..

[Edited on 20-1-2005 by frogfot]
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[*] posted on 20-1-2005 at 07:06


I posted two methods for manganese persulfate preparation before here - nonelectrolytically ones.

Electrolytically ways for (subst.)toluene to benzaldehyde are abundant in the patent literature:
US780404
US4582942
US808095
US4387007
US4814510
US4411746
DE163813
.....

Subst. Toluenes are far easier oxdized to benzaldehydes than plain toluene, this should not be forgotten.

I personally would favor a non-electrolytically way, manganese persulfate seems advantageous over MnO2 anyways.
An interesting question is if Mn(II)sulfate can be oxidized to Mn(III)sulfate by means of H2O2, what would be nice. I remember having read that vanadium-sulfate catalysts can be treated this way - maybe manganese behaves similar?

I also prefer a 30% yield method successfully done by me in my kitchen over any 95% yielding method in literature or somebodies else´s kitchen.


/ORG




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[*] posted on 20-1-2005 at 09:27


Manganese persulfate route is good if one has lots of conc H2SO4. When massproducing benzaldehyde (which I planned to do..) I'd prefer using electrolytical route since there are needed only dilute H2SO4 both in prep of ammonium persulfate and oxidation itself.
(I can "safely" evap battery acid to max 70%).

I've just bought a proper clay pot to test this out :P

Btw, was that second oxidiser you've posted (manganese(III)sulfate) actually tested in oxidation of toluene? Sorry if I overlooked something.
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[*] posted on 20-1-2005 at 10:17


The concentrated H2SO4 is actually only needed for turning the MnO2 into Mn(II)sulfate.
The further oxidation to Mn(III)sulfate can be done with strong oxidizers like MnO2, KMnO4 (dangerous), hopefully with H2O2 (has to be tried) or for sure electrolytically (more tedious as it sounds).

neogravitron does it just one step, turning MnO2 into the sulfate and this into the persulfate, its all in this post with the-hive quotes of mine.

My experiences with electrolytic methods are not so very promising, not with this special synthesis but overall. For this reason I will avoid this so any possible.
But feel free to do otherwise if you like to, no problem.

/ORG

PS: For the steamdistillation you need a setup which should allow you to concentrate the battery-acid to 98%.




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[*] posted on 20-1-2005 at 22:46


A Soviet abstract stated that they got Mn sulfate to work best with 1.500 sp gr. H2SO4, 50C, and a Pb anode current density of 2A, per what they don't say. They got 1 part benzaldehyde from less than 2 parts toluene.

That is close to an earlier Japanese abstract that said that the perfect conditions were 800 ml MnSO4 in H2SO4 (from 100 g in 1 L 55% H2SO4) mixed with 250 ml (217 g) toluene, separated with a diaphragm, a catholyte of 55% H2SO4, 400 cm2 porous Pb plate electrodes, a current of 2A (1A/ 300-400 ml anolyte) 2.75 - 2.8 V, vigorous stirring for 5 hrs, and a temp of 53-55.

An abstracted Formosan journal reported that anodic oxidation with Mn2(SO4)3 gave a 77% yield of bisulfite-isolated benzaldehyde, or a 70% yield based on the Mn, which was prepared in 97% yield from electrolytic oxidation of MnSO4.4H2O.The yield was 86% with Mn2(SO4)3.H2SO4.H2O (separated from the anode in H2SO4) in 55% H2SO4, or a 55% yield based on the Mn.

Also see DE189178

In JCS 1336 (1960), 69 g of toluene was vigorously stirred for 2 hrs at 60C with 360 g of Na persulfate in 600 ml of a .01M AgNO3 soln. It was mostly done at 30 minutes, it seemed. After extraction with benzene, base and acid washes, and distillation, 40 g of benzaldehyde and 2 g of toluene were isolated.

With 13.5 g benzyl alcohol, 60 g of Na persulfate, 0.17 g AgNO3, 100 ml H2O, and stirring for 2 hrs at 30C, a 75% yield of benzaldehyde was isolated by distillation.

[Edited on 21-1-2005 by S.C. Wack]
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[*] posted on 20-1-2005 at 22:52
persulfate


Just breezing through so excuse me if this has been posted already.(likely)

Patent GB190317982

17,982. Johnson, J. Y., [Badische Anilin & Soda Fabrik]. Aug. 19. Aldehydes; carboxylic acids.-The methyl groups of aromatic hydrocarbons or of substituted aro- matic hydrocarbons are oxidized to aldehydes or acids by the use of so-called " manganese super- " oxide sulphate." The acids are obtained by using either an excess of the sulphate or a higher temperature, or both. The sulphate is prepared by electrolytically treating a mixture of manganous sulphate and sulphuric acid, until the red solution, or the precipitate, of manganic sulphate is con- verted into a brown solution. The process may be such as is described in Specification No. 17,981, A.D. 1903, [Abridgment Class Electrolysis]. The acid solution thus obtained, when run slowly into o-nitrotoluene at a temperature of from 50 to 60 C., which is subsequently raised to 100 -110 C. during stirring, forms o-nitrobenzaldehyde, which is distilled off by steam and separated from the excess of o-nitrotoluene which distils over with it. The acid residue may be electrolytically recon- verted into the " manganese superoxide sulphate," as above. If the acid solution is slowly added to toluene while stirring at 40 to 50 C., and the product distilled in a current of steam, benzalde- hyde and toluene pass over. These can be sepa- rated. To obtain benzoic acid, either benzaldehyde or toluene must be added slowly to a sufficiency of the "manganese superoxide sulphate." The reac- tion is slow, but is quantitative. A sulphuric-acid emulsion of benzyl alcohol is similarly oxidized at a temperature of from 40 to 50 C. to benzalde- hyde, which is driven off along with the excess of alcohol by means of steam. To separate the benzaldehyde from the alcohol, the former is con- verted into its bisulphite compound. Or an emul- sion of benzyl chloride and sulphuric acid may be oxidized by adding gradually the " manganese " superoxide sulphate," and heating on the boiling water-bath. Benzoic acid forms.

Worth a read perhaps.

Electrolytic (su)persulfate:
GB190317981

For those who speak Chinese
Patent CN1415592

A process for preparing benzaldehyde compounds includes such steps as reaction between manganese sulfate and ammonium carbonate to obtain manganese carbonate, calcining at 200-800 deg.c to obtain Mn2O3, and liquid-liquid-solid three phase reactino on sulfuric acid and teluene to oxidize the toluene into benzaldehyde compounds. Its advantages are simple process, high utilization rate of raw materials and low cost.


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[*] posted on 21-1-2005 at 04:45


Some corrections:
MnSO4 aka Mn(II)sulfate aka manganosulfate
Mn2(SO4)3 aka Mn(III)sulfate aka manganisulfate
Mn(SO4)2 aka Mn(IV)sulfate aka manganperoxidisulfate aka manganese persulfate

I hope I got this right now.

btw. ammonium persulfate is made by electrolysis of ammoniumhydrogensulfate says the Kirk-Othmer, if it can be made from plain ammoniumsulfate I dont know.


MnO2 + 2H2SO4 = Mn(SO4)2 + 2H2O
But neogravitron says H2SO4 and MnO2 are to be used in equimolar ratio?
Hmmmm......

Experiment will show.
/ORG




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[*] posted on 21-1-2005 at 12:50


I think it is unlikely that Mn(SO4)2 could exist, especially in solution. The Mn++++ ion has too high a charge density to exist without hydrolysis. I think that a basic Mn(IV) sulfate, MnOSO4, would be more likely
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[*] posted on 21-1-2005 at 13:15


I took the information from the german patent DE163813 which says that Mn(SO4)2 is only stable in H2SO4 of 40°Be to 55°Be what should be 60% to 70% when I remember this right. The color of the solution is deep-brown to black.
Solubility is 15% with 40°Be and 5-6% with 55°Be, its stable up to 60°-80°C.
Under boiling of the solution oxygen escapes and Mn2(SO4)3 is formed what can be recognized by its reddish color.
When the acidic solution is poured into water a brownish solution results which discolors and manganese superoxydhydrate precipitates:
Mn(SO4)2 + H2O = MnO3H2 + 2H2SO4

With conc. H2SO4 "Manganoxydsulfat" (whats this now? Manganisulfat again?) is formed and oxygen escapes.

Yes, thats it, or that was it in 1903 :D
It correspondends well with the preparation of Mn2(SO4)3 in the "Brauer".
/ORG

PS: Does anybody know what "Eisenoxydulsalz" is?
I also found no °Be to % H2SO4 table, is my estimation of 40°Be ~ 60% and 55°Be ~ 70% H2SO4 ok?

[Edited on 21-1-2005 by Organikum]




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[*] posted on 21-1-2005 at 15:12


Quote:
With conc. H2SO4 "Manganoxydsulfat" (whats this now? Manganisulfat again?) is formed and oxygen escapes.
It's the common Mn(II)-sulfate (MnO3H2 ≡ MnO2 • H2O):
MnO2 + H2SO4 '+ Δ' → MnSO4 + ½ O2 + H2O

And "Eisenoxydulsalz" is simply a Fe(II)-salt; the sulfate in this context.




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[*] posted on 21-1-2005 at 16:23


Ancient CRC H2SO4 tables, in whole Be, or whole %.

Attachment: h2so4_tables.pdf (163kB)
This file has been downloaded 1279 times

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[*] posted on 25-1-2005 at 18:08


There is another oxidant worth trying: persulphates are used in electronics etching and easy available. I read a patent that used persulphates and compounds of copper, silver, or iron as catalysts for the toluene->benzaldehyde. I tried without succes before using ammonium persulphate like patent.

Problem was that I did not follow the given methods closely enough. Now I can make a better try but I have lost the patent. It was from the hive before. Does anyone recall this patent and give advices? I need to know patent number. It looked good for OTC and simple equipment.




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[*] posted on 25-1-2005 at 22:59


There is another oxidant worth trying: persulphates are used in electronics etching and easy available. I read a patent that used persulphates and compounds of copper, silver, or iron as catalysts for the toluene->benzaldehyde. I tried without succes before using ammonium persulphate like patent.

Tetramer, I am not quite sure of your answer.

Are you stating that this reaction was successful?
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[*] posted on 26-1-2005 at 04:56
Benzaldehyde via Cl2/toluene


Hi folks,
what follows is some discouragement for the Cl2/toluene method and then a procedure for making benzaldehyde using electricity.

I would just like to add that anyone attempting to make benzaldehyde using the toluene chlorination route to think again, unless you know EXACTLY what you are doing. It is a bitch and a half.
I've done it, twice. It will take months to get rid of the benzyl chloride smell off the glassware & general lab area.
First time I did this experiment, my method for checking the progress of the chlorination was to intermittently weigh it out (and measure the volume), to measure the density. It works, but the stuff is tear gas'n a half. Within seconds of opening the reaction vessel, my eyes were involuntarily fused shut, with tears running down my face...Ahh the joys of chemistry. I would say working with benzyl chloride is about 5 times worse than working with chlorine, at least.
By the end of the first experiment, I'd been chlorinating for days and I had fairly pure benzyl chloride (at least 70%, pre distillation) which is only half way there - "To hell with this!" I thought. I dumped my benzyl chloride, only to learn a month later that I could have reacted it with my Kg of hexamine to make benzaldehyde!!!!! (Instead of the benzal chloride route I was aiming for.)

During the second experiment, I used a hydrometer actually inside the 3L 3neck RBF to measure the density without actually having to open the RBF. This is a genuinely good idea. It was held in place by allowing the top couple inches of the hydrometer to fit inside a large tube that was fixed to the cork of the middle neck. The idea is that as the hydrometer bobs around (up and down) inside the refluxing flask it can't go anywhere but up and down (so it can't smash against the side of the flask during reflux).
But, in the end I got fed up and decided to go electrochemical instead.
At first the chlorination thing seemed quite tempting, but halfway through I thought the electrochemical route (which I'd done before) was like a dream come true! And it is by comparison, unless you live in a desert like Mendeleev said.

A good way of doing this reaction is by using US patent 808095. Its the electrochemical route, but runs 24 hours a day, and with my 2amp DC power supply, takes around 60 hours to fully regenerate. It produces around 100ml benzaldehyde per run (based on 1Kg of regenerable oxidizer).
I've done this many times, and it works like a charm. Basically, I do it in a giant 3L pyrex beaker, with 2 lead electrodes (the positive anode is larger with a much larger surface area than the cathode). This requires no membrane!
It is absolutely fool proof! If anyone wants to see pictures, I will take them and post them here - just say.

I use approximately 1Kg of manganese ammonium alum, made by adding manganese sulfate to sulfuric acid (60%+) which already has an excess of ammonium sulfate dissolved in it. The molar ratio for MAA is 2 moles manganese sulfate to 1 mole ammonium sulfate. It is a orangy-yellow precipitate. When you pass a current through it - it oxidizes and turns dark red. Its really cool to watch, you see the dark red pouring off the anode, gradully turning the yellow mix dark red. It lasts a long time, I've never worn it out - getting used over and over and over again!
The ratios (from the patent, scale down accordingly) are: 47.5 Kg mangano-ammonium sulfate, 45 Kg water, 79Kg of 98% sulfuric acid.
The reaction mix is heated to 50 C, and with stirring 4Kg toluene are added. When the dark red solution has turned yellow again - reaction is finished!!! The solution REAKS of cherries!
The patent says steam distil, but don't. Use solvent extraction, the steam will leach out your acid from the mixture. The product (from 4kg toluene) is 3.7Kg benzaldehyde, 0.6 Kg toluene, of course if you are using 1Kg of oxidant instead of 47.5 then you will get about 100ml or so.
My experience is that this is a little on the high side, but that may be due to the impurity of the MAA I'm using (i didn't isolate the yellow precipitate before making up my electrochemical solution, I just added molar ammount of manganese sulfate to excess of ammounium sulfate in sulfuric acid)

Now, what is brilliant about this electrochemical cell is that is can be used for all kinds of oxidations! It can turn alcohols into aldehydes, ie formaldehyde, acetaldehyde, eugenal into vanillin (haven't tried that yet), etc. It can also be used for producing organic acids by adjust the reaction temperature and acid concentration.
The only things this cell consumes is reactant (ie. toluene, methyl alcohol, ethyl alcohol, etc) and electricity...My point exactly.

I see that people are looking for non-electrochemical methods for making benzaldehyde, but I suggest taking a closer look at this procedure, I've used it many, many times and it is quite versatile. It is the real mckoy.
I made my manganese sulfate from dismantled D size alkaline batteries, by reacting the MnO2 (100g per battery) with HCl to make the chloride (vent chlorine outside!), and then reacting the chloride with sulfuric acid to make the sulfate.
BTW, I then used most of that sulfate to make the carbonate (by reacting it with sodium bicarbonate) and then with acetic acid to form the acetate, but that is for another experiment that I won't go into detail here....Maybe down at the hive when it's up and running again. Hey hive guys, I'm wondering if this oxidizer (MAA) can be used to react benzene+acetone in the same way manganese(III)acetate can. That is my next project.

Anyway, the sulfate isn't hard to make from scratch, and ammonium sulfate from the garden centre was first purified by doing the following:
The crude brown ammounium sulfate was dissolved in water (almost saturated), then vacuum filtered (any filter will do, really) a couple of times to remove most of the gunk. Then I boiled it down to a mushy mix with constant stirring, then let it cool a bit. Then I added methylated spirits (or denatured alcohol if you are in the US) and all that brown crap just floats to the top, carefully remove it with a baster/syringe/dropper. I used a dropper, which took a while!
When your crystals are reasonably white, just boil off all the alcohol, done!! You can use your purified ammonium sulfate (as is)for the electrochemical cell. That wasn't hard, was it?
I made my electrodes by making a form out of Al foil, and then melting lead in a crucible made from a STEEL deodorant can cut in half, with a handle made from a C-clamp stuck on the top. I used a blow lamp to melt the lead (I put the lead fishing weights in the can and heated), then just poured the lead into the Al foil mold on a disused wooden breadboard, mmm - I love the smell of burnt wood.
Or you could just buy lead sheet, but I couldn't be bothered.

[Edited on 2-13-2005 by Polverone]




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[*] posted on 26-1-2005 at 05:27


The electrolytic method described is the one presented by Uncle Fester, patent US808095.
It has the same drawback like many electrolytic pathways and like the ammonium-persulfate method:
The amounts of oxidant etc. used are a little large - scaling up to interesting amounts of benzaldehyde - 500ml or more - calls for quite bulky setups, lots of H2SO4 etc.
Ok when you have a spare garage to dedicate for benzaldehyde production though.

You can do the math yourself to find this out.

When going technical/continous, the toluene oxidation by air in the gasphase as posted by Polverone are probably much better, when doing batches - we will see.

I agree that BzCl is a bitch. Therefor I by now experiment to find and later to present a WORKING OTC kitchen method with MnO2 (pigment quality - pyrolusite) in the 100ml product range.

/ORG

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