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leu
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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  The disproportionation of toluene is also facile  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  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.
[Edited on 27-4-2007 by leu]
Chemistry is our Covalent Bond
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Rosco Bodine
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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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Organikum
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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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Organikum
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| 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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| 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 .
[Edited on 27-4-2007 by Rosco Bodine]
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Nicodem
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| 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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MagicJigPipe
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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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trilobite
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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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DJF90
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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
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12AX7
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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?
Tim
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kclo4
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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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DJF90
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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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MagicJigPipe
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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.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Nicodem
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| 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.
…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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DJF90
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Sorry, I don't have a reference for it, I was just daydreaming ... 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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kclo4
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| 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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Filemon
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How much did concentration of AlCl3 and HCl use for toluene disproportionation?
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Nicodem
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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 1463 times
…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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Foss_Jeane
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| 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).
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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
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)
This file has been downloaded 1153 times
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Defibrilator
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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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DJF90
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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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-TheMadMen-
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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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S.C. Wack
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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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User
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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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not_important
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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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