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Author: Subject: Benzene synthesis
Nick F
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[*] posted on 14-3-2004 at 08:46


Has anyone mentioned organometallic methods? Electrolysis of LiCl in acetone (or pyridine, if you can find it!) to get lithium, dissolve p-DCB in hexane, add Li, add water...
Or you could use a similar method involving grignard formation in ether.

Oooh, but separation may be tricky depending on your solvent choice...

(Sorry if this has been mentioned, I looked through the topic quickly and couldn't find it...)




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[*] posted on 14-3-2004 at 12:31
Reduction


Won't Li reduce acetone to 2,3-dimethyl-2,3-dihydroxybutane? I know Na and K both do this.

Also, forming lithiorganics are not easy with p-DCB. It is very inert to both lithiation and grignard formation. Lithiation is easier, but from what I have seen, requires the use of a combination of butyllithium and lithium metal in an inert solvent under argon.
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[*] posted on 15-3-2004 at 15:04


There is a patent which discusses electrolytic production of lithium using solvated lithium compounds, I'm pretty sure it said that acetone could be used (although the lithium is formed as a spongy mess which isn't very convenient).

I had a feeling p-DCB may not be very eager to get metallated, but if it needs BuLi then it's really not worth the effort...




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[*] posted on 3-8-2004 at 01:25
Re: Synthesis of benzene


Most (technical-grade, at least) benzene is from fractionation in petroleum refining, possibly with some dehydrogenation, although it is very difficult to obtain free of thiophene, which has similar physical and chemical properties. In fact, thiophene was originally discovered as a contaminant in petroleum-derived benzene some decades ago, when a reaction of benzene (with thiophene impurity) from petroleum was found not to occur in benzene made synthetically.

It is, however, probably still cheaper to obtain it this way than from some synthetic method, of which the best for large-scale industrial production is undoubtedly the trimerization of acetylene under suitable temperature and pressure and catalytic conditions. Acetylene is obtained from heating crushed lime with a surplus of carbon (e.g. as coke from coal) which produces calcium carbide, CaC2, in which the carbon is present as the acetylide anion, and this is hydrolysed by water to produce acetylene.

As a means of producing benzene for large-scale use as an industrial solvent, or for synthesis of aromatic compounds e.g. as reagents or plastic polymers, it is still more expensive than that derived from petroleum, but this will eventually change.

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[*] posted on 3-8-2004 at 01:52
Disproportionation


Disproportionation of toluene or xylene using the Radzivanovskii* in-situ AlCl3 catalyst works and yields about 30% benzene from toluene.

*This catalyst is usually prepared by venting dry HCl gas into benzene/Al. Here the Al can be added to the toluene directly, foil works. HCl is vented in for several hours then the benzene is distilled off continously.




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[*] posted on 4-8-2004 at 10:39


I gave a try to the NaC6H5COO + NaOH reaction and it was a success :)

From 50g NaC6H5COO and 14g NaOH I got ~24ml of orange liquid with a sharp smell and a boiling point of ~82C. It probably contains impurities so I will redistill it tomorrow. Theoretical yeild would have been 26ml.

It seems that this method is quite productive, and the best, very simple :)
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[*] posted on 4-8-2004 at 12:51


Sharp smell? In my experience benzene has a rather pleasant smell, very similar to toluene.



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[*] posted on 5-8-2004 at 03:01


Benzene is definitively a colorless liquid with a pleasant aromatic smell - being the mother of all aromatics the smell of benzene is THE aromatic smell per definition.

I thought the sodium benzoate to benzene synthesis would require CaO and a copper-salt catalyst, but I may be wrong here.




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[*] posted on 5-8-2004 at 03:52


on a side note; my recent oxidation of toluene with persulfate yielded a yellow/orange layer too. Maybe this is another oxidation/polymerisation product?



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[*] posted on 5-8-2004 at 09:27


Puh..
...dunno, vulture. No recent experiences with persulfate oxidations and memory...

The Radzivankovskii catalyst is somehow tricky it seems. It takes a long time until the reaction HCl/Al kicks in. The addition of AlCl3 or SnCl4 so avail should help. Other salts will be tried soon.
Amalgamation of a small amount of the Al works well (no poisonous Hg-salts required, just add some Hg to a piece Al-foil...).

Alternativly some AlCl3 may be prepared with Al in DCM or perchlorethylene and chlorine. This can be used to kickstart the HCl/Al reaction....

No problem, I prefer Cl2 over HCl-gas anytime :D




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[*] posted on 5-8-2004 at 12:41


Mixtures of Al and chlorinated solvents can decompose violently. I bet you can get a detonation if you add Cl2 and are unlucky.

The deffinitive aromatics are from the resins benzoin, tolu, and styrax.
Benzene stinks, but it's not "sharp". my guess is an impurity the colour hints at that too.

[Edited on 5-8-2004 by unionised]
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[*] posted on 7-8-2004 at 05:52


Well there certainly are some impurities as I evaporated a small sample of the distillate and it left small amount of orange highly staining precipitate. I would have redistilled the benzene today but I forgot make some ice. :(

I also noted that the bottom of my 250ml rb flask was severely dissolved, probably because of the NaOH :(
Next time I test this I will use that CaO and copper-salt catalyst as Organikum said.

[Edited on 7.8.2004 by IPN]
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[*] posted on 7-8-2004 at 07:14


Maybe certain chlorinated solvents form explosive mixtures with Al under certain conditions. But I guess if chlorine is present in excess decomposition is unlikely to happen.
I had never problems using DCM or perchlorethylene and the method is not mine but from some russian article.

But of course - and thats truely my fault that I didnt mention this - chlorination of Al in chlorinated solvents has to be done IN THE COLD - cooling is to be applied. Also here: adding a small piece of amalgamated Al, a piece of foil 2x2cm dipped into mercury for five minutes suffices, will get the reaction going smoothly and no elevated temperatures are needed anyways.

Sorry its easy to forget things which got understood for oneself.




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[*] posted on 7-8-2004 at 07:20


Another point:
Toluene and chlorinated solvents have to be dried before use - mostly.
I have one manufacturer I know the solvents are dry but another - the products even higher priced but coming in nice brown chem-glass-bottles - has water in all products as I found out. To late I want to add.

CaCl2 for two days and shaking from time to time does the trick nicely. Coffee-filter filtration is sufficient, some small amounts of CaCl2 dont have negative influence here, perhaps it even helps, NaCl2 (dry) is told to do so.




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[*] posted on 8-8-2004 at 04:27


At last I got it redistilled and as a result I have 22,6ml of water clear benzene (or so I think :P) which boils at ~81C and smells much nicer than the unpurified stuff :)

Finally I can make some aniline. :D

Btw. when I made benzene in the first place I noticed that the temperature control is quite critical, too hot and you get very dark orange oil, too cold and you get nothing.
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[*] posted on 15-8-2004 at 11:25


After reading this thread I decided to try the distillation of a benzoate to benzene.
In a rb flask, in a heating mantle, I placed 15 gms of sodium benzoate.
After about 20 minutes or so of heating, through the condenser, began to arrive a slightly viscous, yellow-orange liquid with no appreciable smell. It was about the thickness of motor oil and I don’t really know what it was but it certainly didn’t remind me of benzene. Yield was about 4ml until the residue in the flask was fully carbonized.
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[*] posted on 15-8-2004 at 11:59


Maybe from not understanding the method.

C6H5COONa -> C6H6 + whatever,
Whats wrong with this picture? Missing hydrogen.

It would be very interesting to know what you have made. Maybe biphenyl, maybe benzophenone.

The idea of the pyrolysis with Ca(OH)2 or excess NaOH is that the H provides the missing hydrogen as the CO2 is removed.

Basic calcium benzoate decomposes,
Ca.C6H5COO.OH => C6H6 + CaCO3.

The reaction with sodium hydroxide doubtless proceeds in a very similar manner.
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[*] posted on 15-8-2004 at 12:55


I have an idea that, if there was any water present, the oily yellow-orange liquid, instead of the expected benzene, obtained from pyrolysis and distillation of sodium benzoate, may be a (possibly impure) solution of benzoin in benzene or other organic liquid, with NaOH being left behind:

2 C6H5COONa + 2H2O -> C6H5-CO-CHOH-C6H5 + 2NaOH

Its usual method of pure synthesis is by the self-condensation of benzaldehyde in the presence of KCN, however.

To produce C6H6 from C6H5COONa, in any case, requires a source of additional H in a reducing environment, with other possible left-behind products being Na2CO3 and HCOONa if there is cleavage from the C6 ring. In the absence of a source of additional H, probable products would instead be substances like biphenyl, C6H5-C6H5, or diphenyl ether, C6H5-O-C6H5, or benzophenone, (C6H5)2C=O, or diketobenzoin, C6H5-CO-CO-C6H5, or benzoic anhydride, C6H5-CO-O-CO-C6H5, depending on the temperature conditions and any other substances present. The last two do not involve any cleavage of the C6H5-C bond. In any case, pyrolysis of compounds like benzoates seldom results in any one pure product.

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[*] posted on 15-8-2004 at 21:55


Seems to be a few extra oxygens on the left of that equation John. I'm not convinced you could sell me a pyrolysis reaction that leaves sodium hydroxide behind anyway.

After furthur consideration, and dispite the lack of calcium or any other divalent cation in the system, I'd put my money on benzophenone as the primary distillate.
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[*] posted on 15-8-2004 at 22:30
Many Methods


There are several methods used to decarboxylate and decarbonylate aryl compounds.

Heating aromatic aldehydes with H2SO4 yields the arene + carbon monoxide.

Benzoic acid heated with copper and quinoline yields benzene. You can even heat benzoic acid with concentrated H2SO4 and end up with decent yields of benzene.

Other noncatalytic methods involve redox disproportionation of calcium formate benzoate half salts.

I can post mechanisms for most of these style of reactions if the desire arises.

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[*] posted on 16-8-2004 at 01:06


The mixed calcium salt of benzoic acid and formic acid is the classic (allthough not very high yeilding) method for benzaldehyde.

It would be nice to see some yeilds for these processes, but I havn't seen any.
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[*] posted on 16-8-2004 at 10:20


Quote:
The reaction pathways for the decomposition of salts of aromatic carboxylic acids was investigated by TG-MS. The calcium, potassium, and sodium benzoates undergo major weight losses at 509 ± 2 °C. Calcium benzoate undergo a free radical decomposition reaction to form benzophenone, benzene, and calcium carbonate as the major products. Sodium and potassium benzoate undergoes an uncatalyzed Henkel Reaction to form dicarboxylic acids and aromatic hydrocarbons and a free radical reaction to form coupled aromatic products and char.


The entire article makes interesting reading.




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[*] posted on 21-8-2004 at 12:04


I read,that benzene can be made by distillation of phenol and Zn-powder.Has someone more information about it?
Phenol can be made by heating salicylic acid and I think it is a good starting material.
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[*] posted on 21-8-2004 at 13:13


Quote:
Originally posted by Marvin
Seems to be a few extra oxygens on the left of that equation John. I'm not convinced you could sell me a pyrolysis reaction that leaves sodium hydroxide behind anyway.

After furthur consideration, and dispite the lack of calcium or any other divalent cation in the system, I'd put my money on benzophenone as the primary distillate.


I have checked the equation I gave for balance, and it seems to be correct.

John W.
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[*] posted on 21-8-2004 at 13:15


Quote:
Originally posted by thefips
I read,that benzene can be made by distillation of phenol and Zn-powder.Has someone more information about it?
Phenol can be made by heating salicylic acid and I think it is a good starting material.


That method would be thermodynamically favored; any electropositive metal would probably do it

John W..
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