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Author: Subject: Benzene synthesis
leu
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[*] posted on 27-4-2007 at 04:05


There's little doubt that the route through the distillation of benzoate salts with a base is the most practical method to produce benzene for most members of this forum :P The disproportionation of toluene is also facile :D Reppe's methods are available to those who can acquire or produce the carbonyl catalysts :) If one has industrial type facilities one could probably distill coal and fractionate the distillate if one wanted to :o As far as from dichlorobenzene, this article describes a means:

Photoreductive dechlorination of chlorinated benzene derivatives catalyzed by ZnS nanocrystallites.
Chem. Commun. (Cambridge) (1998), (24), 2683-2684.
Abstract
ZnS nanocrystallites effectively enhanced photoredn. of chlorinated benzene derivs. in the presence of triethylamine as a sacrificial electron donor under UV irradn. (l > 300 nm), leading to selective and stepwise dechlorination to give benzene at the final stage.


:cool:

[Edited on 27-4-2007 by leu]




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[*] posted on 27-4-2007 at 15:17


Does anyone here have a reference they may share for the disproportionation of toluene , via HCl plus Al ect. ,
which extensively describes that process ?

BTW , I have about a gallon and a half of reagent benzene rebottled and saved from the last five gallon can I bought . So think of my interest as academic .
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[*] posted on 27-4-2007 at 17:49


I had success with the toluene disproportionation and with the benzoate route. Trust me, the benzoate route is superior and as shown again by AXT lately it gives a whopping +80% yield. What do you want more.

If not pure lust on experimentation is on your mind but if you just want some benzene of excellent quality - do the dry distillation. If you dont want to powder NaOH, whats the only nasty part is then accept some lower yields and use Calcium Hydroxide which comes already conveniantly powdered. Regarding the low prices of the starting materials (if the benzoate is bought in bulk, some 10kg up) this doesnt really matter.

And its a beautiful reaction for the absolute beginner: One needs not a single piece of glassware to do it! Some standard coppertubing and the condensor must not even be soldered, it can be glued with some epoxy - no problem. Other connections can be accomplished by just sticking the coppertubing together, sealed by some teflon tape.
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[*] posted on 27-4-2007 at 17:53


Quote:
Originally posted by Rosco Bodine
Does anyone here have a reference they may share for the disproportionation of toluene , via HCl plus Al ect. ,
which extensively describes that process ?
.....
No I have not seen such a thing, but Polverone once posted some russian articles/abstracts where these catalysts were described, tested and compared to AlCl3 and FeCl3. The most active catalysts were stronger and therefor they should accomplish the disproportionation of toluene easily.



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Rosco Bodine
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[*] posted on 27-4-2007 at 19:34


Quote:
Originally posted by Organikum
I had success with the toluene disproportionation and with the benzoate route. Trust me, the benzoate route is superior and as shown again by AXT lately it gives a whopping +80% yield. What do you want more.


Yes I see that the benzoate route is more efficient . But also
one must already have or obtain the sodium benzoate . So I wished to consider any alternatives which may be useful ,
and toluene is very common as a paint solvent .

At 100% yield with the toluene route , only half the toluene is converted to benzene while half becomes xylene
byproduct . I was simply trying to find some way of
expediting that disproportionation of toluene method .

When you said that 30% yield of benzene was produced ,
please clarify , did you mean only 30% of the theoretical ?
Much better of course would be conversion of 30% of the total toluene to benzene . Also , does the mixture have to reflux for a very long time , or is the disproportionation completed in a reasonable time ? Must the benzene be
distilled off as it forms ? Or will the dispropotionation
occur simply in the standing mixture if it sits for a long time ?

The description mentioned aluminum amalgam to expedite
formation of ACl3 , when using HCl .
I thought that perhaps some strategy for formation of ACl3
insitu could be better than using dry HCl . Perhaps even
using FeCl3 along with the aluminum amalgam , or DCM
added to the toluene ....would be less awkward than
dry HCl . IIRC aluminum is attacked by some chlorinated solvents , and I was thinking perhaps DCM was one of these .

It would be nice to have a jug of toluene from which you
can obtain benzene in a substantial quantity , if it was as easy as dropping in some short cut pieces of aluminum electrical wire which have been dipped in mercuric chloride ,
add some DCM , and a pressure releasing coneseal screw cap .....come back a week later and distill your half jug
of benzene from the xylene byproduct . :D

[Edited on 27-4-2007 by Rosco Bodine]
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[*] posted on 27-4-2007 at 23:38


Quote:
Originally posted by Rosco Bodine
At 100% yield with the toluene route , only half the toluene is converted to benzene while half becomes xylene
byproduct . I was simply trying to find some way of
expediting that disproportionation of toluene method .

Actually, the very end thermodynamic product is mesitylene (1,3,5-trimethylbenzene). However, that would require a very long reflux time and a truly efficient long distillation column to continuously separate out the benzene. I never saw a reference for the experimental even though this is described in many books and almost every review about FC alkylations. When I'll have the time and opportunity, I'll see what I can get about it.

PS: If using HCl to prepare AlCl3 in situ from Al foil, you absolutely need to dry the HCl gas (bubbling it trough conc. H2SO4, for example) as it tends to carry quite some H2O with it (which is very bad to AlCl3).
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[*] posted on 24-9-2007 at 23:40


The benoate route does work and you can buy sodium benzoate from www.unitednuclear.com at a fairly decent price (8oz for $12). Or if you're weird about buying stuff online:

The first time I obtained sodium benzoate I got a phone book and started calling all pharmacies in the area (starting with the ones that specifically mention "compounding") and asking them for sodium benzoate. The first one that had it asked me what I would be using it for and I said, "to preserve baked goods" and he said, "ok". Unfortunatley, the Sodium Benzoate USP for compounding is prohibitivley expensive (~$15 for 100g).

But those are some options worth considering, let me know if you find something better. Like a company that will sell benzene to individuals!

Just remember, you can obtain a lot of good shit if you are good at bullshitting.
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[*] posted on 2-10-2007 at 14:49


I once tried the disproportionation with toluene and AlCl<sub>3</sub>, just for kicks, and took no proper notes. Refluxed the mixture for a while and then distilled slowly through a Vigreux column. The temperature on top of the column quickly rose over 80 degrees, no matter how careful I tried to distill. I took a sample of the first portions of the distillate, 1H NMR gave indeed the peak for benzene, but majority of the small portion of distillate was still toluene. Obviously benzene was formed only in very small amounts in those conditions, so I never repeated the experiment.

In this reaction, there is one mechanistic issue that seems to be overlooked all the time. The superacid HAlCl<sub>4</sub>, from HCl and AlCl<sub>3</sub>, protonates toluene to give an ion pair of ring-protonated toluene and AlCl<sub>4</sub><sup>- </sup>. This ion pair separates from the organic phase with ca. 8 molecules of toluene per each ion pair (IIRC), giving what is known as "red oil" in older Friedel-Crafts lingo. This is one of the first know ionic liquids, a polar phase with catalytic activity in Friedel-Crafts alkylations.

The disproportionation reaction begins when a molecule of toluene is protonated at the same aromatic carbon where the methyl group is attached to. This molecule then electrophilically alkylates another molecule of toluene with its methyl group, giving rise to a protonated xylene molecule having AlCl<sub>4</sub><sup>- </sup> as its counterion. The first molecule of toluene in question now has a hydrogen where it had a methyl, and has thus become benzene.

Point being, for all this to happen you not only need to have reasonable amount of AlCl<sub>3</sub> in the reaction, but also a reasonable amount of HCl, otherwise there is not enough HAlCl<sub>4</sub> to catalyze the disproportionation well. Of course some HCl is always formed as the conditions aren't completely anhydrous, but is it enough? Distilling doesn't help either with keeping gases in the reaction mixture, so one should either bubble HCl gas or perform the reaction under pressure and then distill the thermodynamic mixture.

It is my understanding that the colour Radzivanowskii catalyst assumes when activated with HCl gas is a result of formation of a catalytically active "red oil" layer on the surface of aluminium metal. Also the fact that reacting aluminium metal with HCl gas in aromatic solvents proceeds readily when some AlCl<sub>3</sub> has been added is easily understood, considering the need to have a polar phase for reactions like this to proceed well.

[Edited on 10/2/2007 by trilobite]
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[*] posted on 20-4-2008 at 11:26


Bringing up an old thread here... Regarding the benzene synthesis using acetylene and a nickel catalyst at approx 70 C (as described previously). If the acetylene gas was bubbled through a suspension of nickel in water (?) whilst heated under reflux then would benzene form? The acetylene could be had from a welding supplier or made in the lab via the reaction of calcium carbide with water. The benzene could then be distilled off from the water and nickel, and then the reaction could be repeated. Magnetic stirring would probably be required for the continuous suspension of a nickel powder but it would also aid the absorbsion of the acetylene gas? Just speculating at the moment, still trying to gather a collection of glassware together :P
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[*] posted on 20-4-2008 at 12:36


Seems to me water molecules would get in the way, perhaps causing assorted hydration products? More importantly, it would probably spoil the catalytic surface, oxygen (as H2O or OH-) lone pairs binding to the nickel ions I would suppose?

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[*] posted on 20-4-2008 at 13:29


I haven't looked into the chemistry of it, but what about Sodium benzoate and ascorbic acid? i know at least in drinks that contain both, small amounts of benzene are produced. I'd imagine if you made the conditions favorable to produce benzene with those compounds perhaps it could be a good method?
Just an idea i had, but like i said i haven't looked at the reaction so it could be a total waist
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[*] posted on 20-4-2008 at 13:33


Yeh I was reading up on the ascorbic acid/benzoate dilemma earlier. It could be a viable route, and it seems to be a light and heat affected reaction (i believe i read this somewhere). It depends on the availability and cost of the ascorbic acid, of which I don't know off the top of my head.
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[*] posted on 20-4-2008 at 23:31


Sodium benzoate is already expensive as far as cheap chemicals go. Then you go and add another expensive "cheap" chemical to it and you just upped the price.

If NaOH/CaO works then why not use it? They are both much cheaper than ascorbic acid.




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[*] posted on 21-4-2008 at 00:00


Quote:
Originally posted by DJF90
If the acetylene gas was bubbled through a suspension of nickel in water (?) whilst heated under reflux then would benzene form?

The metallic nickel catalyzed acetylene cyclotrimerization is in my limited knowledge a vapor phase reaction and requires specially treated nickel, usually on solid support. If you know any articles where anything (using unliganded nickel) even remotely similar to what you are proposing is described, then please give us the reference so we can discuss it.
Quote:
Originally posted by kclo4
I haven't looked into the chemistry of it, but what about Sodium benzoate and ascorbic acid?

Please do not spread unintentional misinformation like that about "the ascorbic acid/benzoate dilemma" since for some reason such things catch fast among the beginners who are too lazy to check the original references. That is NOT a preparative reaction and as such it has actually nothing to do with the thread's topic.




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[*] posted on 21-4-2008 at 05:54


Sorry, I don't have a reference for it, I was just daydreaming :P... but if I come across one I will gladly post it on here :) Although I think you may be right about the cyclotrimerisation occuring in the vapor phase.
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[*] posted on 21-4-2008 at 13:54


Quote:
Originally posted by Nicodem
Quote:
Originally posted by kclo4
I haven't looked into the chemistry of it, but what about Sodium benzoate and ascorbic acid?

Please do not spread unintentional misinformation like that about "the ascorbic acid/benzoate dilemma" since for some reason such things catch fast among the beginners who are too lazy to check the original references. That is NOT a preparative reaction and as such it has actually nothing to do with the thread's topic.


I was just asking about it, i don't see how i was spreading "unintentional misinformation" but i'll try to check out ideas first, i just didn't have time.

However, that is a good point about the prices Magic! i wasn't even considering that, i was just thinking about reactions that produced benzene.
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[*] posted on 2-6-2008 at 03:41


How much did concentration of AlCl3 and HCl use for toluene disproportionation?
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[*] posted on 17-12-2008 at 08:11


Finally I found a study about toluene to benzene/xylene Friedel-Crafts disproportionation. All this time I had it on my computer but never noticed till yesterday.

CCVI.-The Friedel-Crafts’ Reaction. Part III. Migration of Alkyl Groups in the Benzene Nucleus.
M. Copisarow
J. Chem. Soc., Trans., 119 (1921) 1806-1810. DOI: 10.1039/CT9211901806

Attachment: The Friedel-Crafts reaction Part III.pdf (287kB)
This file has been downloaded 1051 times





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[*] posted on 19-12-2008 at 01:51


Quote:
Originally posted by DJF90
Bringing up an old thread here... Regarding the benzene synthesis using acetylene and a nickel catalyst at approx 70 C (as described previously).


Sorry, but it isn't that easy. It's possible for the really talented garage chemist, after all, we have guys here making their own CS2 :cool:

You also probably can't use acetylene from a welding tank since it's contaminated with acetone. Anyway, attaching a paper describing how it's done.

All things considered, you're better off with the benzoate method.

Attachment: benzene.pdf (354kB)
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[*] posted on 27-3-2009 at 10:08


Hi guys,

I'm having a bit of trouble synthesizing benzene, i was just wondering if some of you more experienced chaps could help me out here a bit. I've mixed the sodium hydroxide/sodium benzoate to the appropriate proportions, but since i do not own any fancy distillation equipment i cannot distill it as usual.

So what i have done is placed a hollow metal tube through a milo can lid, and sealed it with teflon tape, i've placed a rubber stopper through that tube and placed it on the open end of an erlenmeyer flask. Pretty shitty i know, which is probably why it does not work when i heat it? All that happens is i get the smell of a burning rubber tire. :-/
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[*] posted on 27-3-2009 at 10:51


Teflon is only usable to about 220C IIRC, which may, or may not, be above the temperature required for distillation. Not sure if rubber is resistant to benzene or not. You may not be heating it enough to cause decarboxylation, especially if you are heating a sizeable amount.

A complete metal setup can be made using a can and some copper tubing (used for plumbing) to make the "stillhead" and condensor. This is generally what moonshine distillers use and theres quite a lot of instructions on the internet. In prepublication there is a thread on benzene manufacture, I suggest you read it.
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[*] posted on 29-5-2009 at 08:40


Benzene synthesis is giving me the shits. I've now used copper tubing etc... It all seems to be so fucking annoying, i'll keep trying though, i wish i could just buy a 200l drum full of benzene, would be so much easier.
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[*] posted on 29-6-2009 at 11:40


Benzene rich oil by the decarboxylation of PET
http://staff.aist.go.jp/tohru-kamo/FSRJ/output/7_nenkai/09/P...
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[*] posted on 2-7-2009 at 04:48


Ive searched my ass off but i cant find any schematics on this breakdown.
I somewhat understand how decarboxylation should look like, still i cant project this on how the PET(e) should break down into benzene.
What happens to the CH2-CH2.
Could another hydroxide be used and would using an overhand be interesting

Can someone be so kind to give an idea about this.
I really have to do something about my organics.
I know, a lot of question :(

[Edited on 2-7-2009 by User]




What a fine day for chemistry this is.
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[*] posted on 2-7-2009 at 07:32


You mean in the paper S.C. Wack posted? The PET gets hydrolysed to ethylene glycol and terephthalic acid, the latter then undergoes conventional aromatic decarboxylation as when done using NaOH and the acid. The fate of the glycol is not stated, and likely is complex.

Ca(OH)2 is likely the cheapest effective hydroxide. The system is based on solids in a column, with several zones for the different reactions. Doing the same with liquids, such as molten alkali hydroxides, could be tricky. Some of the higher valency oxides such as ThO2 seem to promote the formation of ketones by the reaction 2 RCO2H => RCOR + H2O + CO2 , while calcium generally is less effective at this plus the use of an atmosphere of steam helps suppress that reaction. The steam also dilutes the reactants, which could reduce the formation of biphenyl and higher analogues from phenyl radicals formed during decarboxylation.

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