Sciencemadness Discussion Board

Benzene synthesis

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Organikum - 5-9-2004 at 22:12

Whats going on ?
ordenblitz, I used the 4-fold amount of benzoate and the 8-fold amount of sodium hydroxide thtas it.
Marvin will have known why he asked for scaled up results.

The problems are not only one:
- clinging of the fused mass to the glass threatening to destroy it.
- not all benzoate reacts. The fused mass is an nice insulator and makes it hard if not impossible to get all to react after a certain amount has fused.

I am talking about 100g+ benzoate here, please realize that this is hardly comparable to 25g or less.

Yes. Scaling up is the interesting part and I believe I have an easy and cheap solution.
Later more.

Marvin - 6-9-2004 at 15:51

Actually the reason I was hoping for scaled up experiments has nothing to do with chemistry. I just get a kick out of the idea something so fundamentally important/useful can be made on a large scale from what is available.

I had an idea about protecting the glassware but Hermes beat me to it. Rather than use nickel though which I'm unsure if its easy to plate, use silver. Silver metal is cheep in small amounts, reduce the salt with formalin say and precipitate onto the inside of a well washed with dilute NaOH flask and that should produce a good layer of silver. Silver mirror test basically.

With some luck that will prevent destruction of the flasks.

When you are talking about 80 or 85C are you talking about the temperature of the vapour or the temp of the mass being heated. You arnt using a reflux column are you?

Temps for the decomposition of sodium benzoate alone were in the 500C+ so I'm a little confused why the numbers given are so low, even if its the vapour, why is it cooling down so quickly?

I will search around locally for some sodium benzoate but I wont be trying it for a while, I'm unhappy with my ventillation for anything carcinogenic and as yet, I dont have any use for the benzene.

[Edited on 6-9-2004 by Marvin]

Organikum - 6-9-2004 at 22:35

- The temperature named, 80-85°C is of course the temperature on the Claisen and measures the vapors coming over.
The temperatur in the flask is MUCH higher.
- Using a column would be not so good an idea. Liquid dropping back would rather probably crack the flask already during the reaction. (see the second reference from S.C. Wack whoc was btw right that smoke indicates to high a temperature here and gives no more benzene).
- using a metal vessel or coating the glass with metal will solve perhaps the problem of the cracking, but wont solve the problem with the heatdistribution when bigger amounts are processed.

I am optimistic to have found a solution for both problems now:
- cracking is no problem as disposable winebottles are used.
- heatdistribution is equalized by stuffing the bottle with steelwool, the cheapo kind used on wooden floors. (defat before use)

Looks VERY good! uiii!

Results and pictures will get posted after redistillation.

Results of the glassware-murder runs:
- first produced 25ml benzene from 100g benzoate and 60g NaOH. (flat bottom flask)
- second produced almost 35ml benzene. (Erlenmeyer)
So more NaOH gives better results. The Erlenmeyer gave better results what I blame on the more surface area.

Organikum - 7-9-2004 at 12:30

Some images:

Here the bottle and the steelwool. I stuffed later more steelwool into the bottle, but one gets the idea I guess.

This is how I made the conection to the condensor (condensor still missing).
A cork, a 14 to 29 adapter and Teflon-tape. The adapter isnt essential, two corks and a metal tube (copper/steel...) and tape would do the trick to, its not hard.

Results after workup. Looks good up to now.

ordenblitz - 7-9-2004 at 18:53

Organikum said:
not all benzoate reacts. The fused mass is an nice insulator and makes it hard if not impossible to get all to react after a certain amount has fused.
I am talking about 100g+ benzoate here, please realize that this is hardly
comparable to 25g or less.

Excellent point!
I was using a 500ml flask with 32 gm of reactants. That certainly would create enough surface area to get the job done more efficiently. Typically I would add the mix, then spin the flask to make the powder ride up the sides before putting it in the mantle. And now that you mention it, I do remember seeing the fused mass somewhat pulling away from the sides of the flask later in the process.

One think I didn't mention was that I heated fairly slowly. Usually it took 30 to 40 minutes before any condensate began to form. It is possible that a gradual temperature rise allows for better heat transfer before the reaction progresses to fast in the outer layers thus insulating the mass further inward.

Question for Marvin:

Organikum - 9-9-2004 at 10:36

You wrote befor, that benzoic acid and conc. H2SO4 gives "decent" yields of benzene.
- What are "decent yields"?
- Wont this end with a sulfonation of the ring? Similar to toluene to toluenesulfonic acid?
- Or is this some equilibrium building up, say parts sulfonation, parts decarboxylation with benzene removed and the equilibrium shifts? As sulfonation is reversibel as I know......

But would conc. H2SO4 be the right thing to use, wouldnt 70-80% be preferable?

A mechanism would be the hit.


BromicAcid - 9-9-2004 at 11:40

Possibly similar to the dehydration of formic acid to carbon monoxide with concentrated sulfuric.

HCOOH ----> H2O + CO

I could see many different compounds forming from the dehydration of benzoic acid, benzene might be among them.

Organikum - 9-9-2004 at 12:49

And now: Whats that?

Thats what happens when you add NaOH (preferable aqueous, aka lye) to sodium benzoate dissolved in water.

This precipitate is what the author talks about in the second article posted by F.C.Whack.

Sorry for the delays my coffee-grinder died the death of true heros - and I now can tell from own experience that finely divided sodium benzoate is dangerous, ok, it was a "puff" and no "bumm" but it shows what can happen.
Ignited by the grinder, which seems to have died from shock. Or electrocution after the smell.....

Soon more, this precipitate looks even better to me...

Tomorrow to the second hand store for a new old grinder......

Marvin - 10-9-2004 at 03:58

Hmm. That sounds like something I'd say but I'm damned if I can find my post either here or on roguesci and Ive searched for an hour.

Which post did I say that in?

I dont think Ive ever been under the impression it would be a good method compaired to pyrolysis but I've heard other people mention it. I dont have a description, but frogfot posted a general mechanism on roguesci in the phenole thread,

Thats from March, but I think its a generic mechanism for decarboylation of an aryl carboxylate with sulphuric acid rather than a specific one for benzoic acid.

Organikum - 10-9-2004 at 10:54


Which post did I say that in?

Earlier in this thread. If you use "printable version" on top - left side, you get the whole thread in one piece and ctrl-f "Marvin" will help you to find it then. ;)

Polverone - 10-9-2004 at 13:57

Actually, it was Turel who said that benzene can be produced from benzoic acid and H2SO4. It's a long and confusing thread by now, I know!

But he offered to explain things. So, Turel, how about the explanation for transformation of benzoic acid to benzene via H2SO4?


Organikum - 10-9-2004 at 23:52

Yes it was Turel, I overread the name whilst skimming through the thread.

I apologize.


thefips - 12-9-2004 at 19:49

I often think about the synthesis of benzene from phenol and Zn-dust.Has someone an idea how to make it?I want to make some experiments.I thought:
1.: heating an mixture of phenol and Zn-dust and looking,if tere is a distillate and the smell of benzene.

2.: heating phenol and passing the smoke over heated Zn-dust,I remembered that ethene could be made by passing EtOH-steam over heated Zn (or was it Mg?I think it was Zn)

Which one could be possible or could be possible?I want to try it the next days.

Basic sodium benzoate ?

Organikum - 13-9-2004 at 01:06

Marvin wrote:

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

Am I right when I guess that the precipitate formed on addition of lye to a solution of sodium benzoate is basic sodium benzoate? But what formula has this?

calcium benzoate:
= 2 Ca.C6H5COO.OH

sodium benzoate:
+ NaOH
= Na2.C6H5COO.OH

This basic salt decomposes similar to the calcium salt:
Na2.C6H5COO.OH = Na2CO3 + C6H6

Thus right or wrong ?

Marvin - 13-9-2004 at 01:37

I have to say Organikum, you had me worried there for a while. 'conc. H2SO4' and 'decent yeilds' are terms I use all the time, but using them together would have meant me giving an opinion on something I had no information about :D

I wasn't very clear with my use of basic salts. I'll try to clarify this at the risk of overexplaining. Calcium is a 2+ ion, so it can form basic salts, eg...

Calcium hydroxide is [Ca]2+ [OH]- [OH]-

So basic calcium benzoate would be,

[Ca]2+ [C6H5COO]- [OH]-

And should form in preference to a mixture of calcium hydroxide and neutral calcium benzoate because the mixture would have a higher pH. This is a hunch because if neutral calcium benzoate is less soluable, this might form instead.

In the same sort of way sulphuric acid forms acid salts like [Na]+ [H]+ [SO4]2-

Sodium only has one positive charge, so it cant form basic salts. What is trying to form here is a good mechanical mixture of sodium benzoate and sodium hydroxide to get the hydroxide and benzoate as close as possible. It will never be as good as a basic calcium benzoate (assuming my hunch is right) but sodium hydroxide is a much stronger decarboxylating agent than calcium hydroxide so the reaction with sodium hydroxide could give better yeilds and should start at a lower temperature.

So it would be more accurate to write,
NaC6H5COO + NaOH => Na2CO3 + C6H6

If its possible to make a solid solution of sodium benzoate and sodium hydroxide the line between a basic salt, and a mechanical mixture becomes very blurry.

Organikum - 13-9-2004 at 02:22

New setup:

Glass is jsut not the right material with caustic alkali - lets try metal. :D


The first picture is more for showing how the connection was made between the can and the condensor. Gladly a 1" thread fits nicely into the can and my 29/32 grounded glass joints fit nicely into the adaptors made for coppertubing.
"Nicely" says, "with reasonable but not excessive amounts of thick Teflon-tape".


[Edited on 13-9-2004 by Organikum]

Organikum - 15-9-2004 at 13:19

The solvent-can setup yielded after the can was put onto the flame directly (flamesieve was used though) about 200ml of a morning-piss yellow liquid with a pungent odor. After redistilliation 170ml benzene was received.

(the yellow color and the smell was already described by IPN in this thread)

300g sodium benzoate
180g coffee-grinder grinded NaOH

Sorry no quantitative results for the NaOH/benzoate precipitate, this got a little outa control and I have now masses of this stuff, but dont know how much benzoate per gram is in it.... ;)
As soon I have used this up I will make a more controlled run of this.

I would striktly discourage the use of glassware for making the precipitate and for drying it. This strips emaille from pots like nothing and it also stripped the Teflon from a pizza-pan like nothing.
Use an old iron pot, or an emailled old iron pot - afterwards it will be a iron pot without emaille anyways.... :o

Organikum - 16-9-2004 at 02:55

I hope thus gets not to boring......

This is the received liquid before redistillation. The lower part is water, what else.

It looks like, yes, like - eh - something else, but its discolored benzene. ;)

I spare you all a picture of the redistilled benzene, as waterclear liquids are not so very impressive..... :D

Organikum - 18-9-2004 at 08:11

I made several runs now and always got at least 120ml benzene from 300g sodium benzoate.

(the before posted 175ml referred to a run with 450g+ benzoate, sorry, I messed this up)

120ml is about 105g benzene, is about 1,35 mole.
300g sodium benzoate are about 2 mole.

This gives a molar yield of 68% thats ok for me.
Hope I didnt mess this up again, but I the pictures tell that this is not made up.


A run with calcium hydroxide instead of grinded sodium hydroxide gave less product which was much more decolorized, thats a pity as Ca(OH)2 comes already as a fine powder and would make the grinding unnecessary.
So I stay with my (new-old) coffeegrinder and NaOH.... :)

[Edited on 18-9-2004 by Organikum]

ordenblitz - 18-9-2004 at 16:14

Not having anything else particularly interesting to do today.. I decided to fire up the FTIR and see what it thought about the products obtained from the decomposition of NaC6H5COO + NaOH in my tests.

benzene.JPG - 16kB

ordenblitz - 18-9-2004 at 16:19

And the solid residue after the redistillation.

diphenyl.JPG - 32kB

Organikum - 19-9-2004 at 02:33

Thanks ordenblitz, but I have no experience at all in interpreting such data, can you add some words of explanaition perhaps? Would be helpful for me at least?

(I would guess it says the benzene is VERY good though... )

New run, better yields:

300g sodium benzoate
200g sodium hydroxide (grinded)


After IPNs and my own experiences this will give about 160ml/140g benzene after redistillation (95%), what are ~1,8 mole.
The benzoate used was ~2,1 mole.
Says ~85% molar yield, yes? :D

All credits go to IPN and ordenblitz who actually DID it first and to F.C.Whack who posted the articles.
Mine is just some tinkering with the setup and the use of the industrial way of thinking.

This dry distillation business is promising, and this process is very similar to the dry distillation/condensation of the Ca or Na salts of acetic acid and phenylacetic acid, which iyields 1-phenyl-2-propanone.
Also the making of benzaldehyde this way as mentioned by Marvin before is for sure worth a try and to invest some work into the optimization of ratios and setup.
I propose though that the solvent-can/steelwool setup beats a flask all time here.

More professional would be to use a more robust vessel made from steel/iron and to fill it with iron or coppertubing pieces (length = 1,25xdiameter) similar to Raschig rings.
Thats at least how I will go on.... :cool:

[Edited on 19-9-2004 by Organikum]

ordenblitz - 19-9-2004 at 12:06

Thanks ordenblitz, but I have no experience at all in interpreting such data, can you
add some words of explanaition perhaps? Would be helpful for me at least?

Bear with me as I have no actual formal training on a FTIR, what I know comes only from reading the books and playing with it for a few years. I got this one used at an asset sale where no one except me, really knew what it was and more importantly, what it was worth. The best part was that it came with very extensive spectral libraries. Without good libraries, the machine is only useful for comparing things you yourself have scanned. Therefore there is no "known good" standard by which to compare unless you trust your sampling technique, conditions and materials to be as good as the commercially available libraries.

My benzene sample for instance, was scanned and appears in the photo as the upper red spectra. I then asked the machine to search the libraries for any matches. Luckily there were quite a few stored spectra of benzene in my libraries to compare too. What the software search function did was find the ones that were the closest to the tested sample. The best match according to Omnic was "benzene 99+ ACS". This of course does not mean that my sample was equivalent in quality, it simply meant that it was the best match from the available spectra in my libraries. The Aldrich library contained three benzene, Toronto forensic had two and the commercial materials library had several industrial quality examples of C6H6, about 8 in all to compare too. Omnic seemed to think that my sample was closer to the reagent then the industrial grade materials, but that is by no means a certification of its quality. One other interesting feature is the "subtract option" where I can take my sample spectra and have the machine subtract from it, the value of the ' known good ' library spectra, leaving the remainder, which in theory should be any impurities. I could then take that impurity spectra and search the libraries to see if it finds any matches. Kind of a clever idea, but to date I really haven't found it to work that well.

You will notice that the upper spectra contained several peaks that were obviously not in the lower library spectra. These are typically water vapor and other gasses that are normally in the beam path of the machine. There is a distinct double peak around 2360nm on both the benzene and biphenyl spectra I posted. It is carbon dioxide.
Usually FTIR are equipped with a N2 purge system to solve that problem, but I couldn't be bothered to hook one up. The Omnic software has several corrections, which can be applied to account for this, and that is what I asked the machine to do when searching the libraries. There are many things that the software search function uses to decide what weight to place on any peaks in the frequency range when comparing spectra. Unfortunately having no idea what they are, I don't try to visually interpret the spectra, I just let the machine take it's best guess.

I hope that helps to explain what you're looking at in the above-posted pictures. I am by no means well schooled in the use of a FTIR and if there is any one else that cares to weigh in about this interesting subject… please do!

P.S. here is a picture of the actual machine.

ftir360.JPG - 20kB

ordenblitz - 19-9-2004 at 12:15


I really like your can…
a solvent can you called it?
I haven't seen anything like it and it looks pretty handy…
where did you get it?

Marvin - 19-9-2004 at 12:57


Nice work with the spectra. Heres you being envious of the can Organikum is using when there is a thousand of us being envious about not having access to an IR spectrometer, let alone a FTIR. Out of interest, does it need a compressed air supply?

Organikum, some nice results, but where is the water coming from? It worries me. I thought these were just runs with the materials being ground together?

ordenblitz - 19-9-2004 at 14:25

Thanks Marvin.

It's all easy if you have the tools. Fortunately for me, I don't have a wife to dictate where the money will be spent therefore I am free to explore the limits of my chemical dependency as it were.

There is a purge port on the ftir and you are supposed to flush with N2 or dry air. Nitrogen is preferable since this will eliminate both the CO2 and H2O peaks. I don't use the thing often enough to justify the effort and expense, so I have to apply the appropriate software correction and deal with some loss of accuracy.

Organikum - 19-9-2004 at 15:09

Marvin, the water is coming from my faucet, just a quick wash with bicarb/brine and I put always some water into my receiving jar for its easier to see when it starts coming over, dropping.

In the distillation some minimal amounts of water come over, probably from the NaOH sucking water from the air whilst grinding.

Benzoate and grinded NaOH are not ground together, they are merely mixed well, barmixer style.....
Grinding NaOH does not harm my coffee-grinder, benzoate does. Puff and out. Deflagration is the right word I believe, grinding benzoate and NaOH with mortar and pestle is for masochists and plain not necessary. Gladly I want to add.

ordenblitz, I get the cans when I buy solvents over the street in the paints store, looks like this:
And I have more than one, one makes about three to four runs and then its finished.

stygian - 19-9-2004 at 20:04

Originally posted by notagod
If I remeber right, it does'nt have to be benzoic acid, the sodium salt will do. Mix it with waterfree sodium carbonate and heat it gently. Benzene will distill over. You can also have some sand mixed in to have a more "smooth" reaction.

Does this mean sodium salicylate + sodium carbonate == phenol? :)

Marvin - 20-9-2004 at 08:45

I'm not convinced by sodium carbonate but salicylic acid decarboxlyates a lot easier than benzene. Its also more, for want of a better word, fragile. Heating salicylic acid with lime will work, or with plain sand will also work. I dont know what the yeilds are like but yes this will make phenol.

Organikum, I was wondering if it was washing water, and I couldnt figure out how else such a large molar amount of water would come from, but since it was just described as the distillate I did wonder.

ordenblitz, I have the main unit of a much older nicolet insument and it has an air bearing! Needs compressed air supply and I dont know what pressure. No interface card so I cant try it, not sure if it would work or not. I know complete working units (even secondhand) are out of my price band though. I also bought a dual beam instument on ebay but I was unlucky and everything of value inside had been stripped.

thefips - 24-9-2004 at 13:00

I had an idea,but I don´t know,if it would work.If phthalic anhydride is dissolved in a solvent,phthalic acid can be precipitated by adding HCl(aq).The structure of phthalic acid is C6H4(COOH)2.If phthalic acid is heated,I think CO2 is released and benzene distills over.But I am not sure,if it is right.

Simplified Setup

Organikum - 24-9-2004 at 14:28

For not having to use my glassware anymore for the benzene from benzoate synthesis a made this simplified setup from pieces I had around, mostly coppertube and Teflon-tape.

Works fine. :D

S.C. Wack - 24-9-2004 at 14:34

True, but not mentioned before because for most it isn't as cheap, or as easy to buy or make (toluene/KMnO4/Na2CO3).

Interesting observation with benzoate to benzene

Organikum - 9-10-2004 at 03:46

When the product of the sodium-benzoate destructive distillation is NOT washed with water before distillation a clear distillate with a sharp pungent smell comes over at about 70°C. This is obviously an azeotrope of benzene with an unknown compound.

This compound is water sensible. I say so because of the fizzling sounds which are to notice when the distillate of the benzoate-pyrolysis is collected in a jar filled with water.

Whats this?
Some anhydride and maybe useful?

Any ideas?
Its not the diphenyl, thats the yellow contamination.

IPN - 15-10-2004 at 11:13

Nice job with the improvements Organikum. :)
This way to benzene seems so easy that someone should document it into a pdf so it will never be lost. :P

As a side note I'm really happy with my ~1l of benzene at the moment. :D
Azo dyes, here I come!

[Edited on 15.10.2004 by IPN]

Organikum - 16-10-2004 at 08:34

I will compile this pdf document for having the pictures its probably up to me I guess.

no hurry please.

Blackout - 26-11-2004 at 19:46

I want to know if there is a way to extract benzene from polystyrene?


UpNatom - 27-11-2004 at 13:00

'Extraction' wouldn't be possible. Pyrolysis to styrene, oxidation to benzoic acid and finally decarboxylation to benzene is a viable synthesis however.

[Edited on 27-11-2004 by UpNatom]

Magpie - 10-3-2005 at 19:43

I recently decided I needed some benzene so have read this thread with great interest. I have a procedure for decarboxylation of benzoic acid in my old college lab manual, i.e., "Unitized Experiments in Organic Chemistry," by Brewster et al (1961). It is an abbreviated version of that in Norris posted by S. C. Wack. The procedure intrigues me as I had never seen a "dry distillation" procedure before. I wondered how it could work.

I started with Na benzoate (small prills) and Red Devil lye (very small prills).

My first 2 attempts resulted in failure. That is I did the same thing twice and got the same results twice ;). Then I decided I wasn't giving it enough heat so bought a new, full propane cylinder and tried it again. This time I got a few drops of benzene - still a failure. The 4th time I dried the paste mixture of Na benzoate/NaOH/H2O for 2 hours at 100C in an oven and then ground it to a powder in a mortar & pestle. I then placed half of it in the 25x200mm test tube, keeping it dry with a rubber stopper until ready for use. Then I really put the heat to it until I could see the NaOH melting and reacting with the Na benzoate. This was effective and all benzoate reacted leaving just the NaOH, (Na2CO3?), and patches of carbon black. The benzene looked to be in good yield but has an orange color.

The other half of the batch I placed in the 25x200mm test tube with a copper scrub pad. This gave the same result but was harder to observe and control during heating. I found it notable that the copper pad seemed unaffected by the molten NaOH.

I agree with previous observations that the main issue here is with good heat transfer. When I was just using the paste my heat transfer was terrible. With the dry powder it lay nicely in the bottom of the horizontal test tube. In a few days I will try a full batch in the test tube.

The waste products in the test tube wash out easily. However, the molten NaOH does permanently etch the test tube somewhat clouding it. But it is completely reuseable, at least for the this same procedure.

I agree with Marvin and vulture that much satisfaction comes from making useful reagents from OTC ingredients, especialy when it is a challenge. :D

When I get access to a scanner I will post my 1961 lab manual to the forum library. It is remarkably different in scope from my current lab manual (Pavia, Kriz, et al).

[Edited on 11-3-2005 by Magpie]

[Edited on 11-3-2005 by Magpie]

[Edited on 11-3-2005 by Magpie]

[Edited on 11-3-2005 by Magpie]

BromicAcid - 10-3-2005 at 21:01

I also ran across some interesting information that could lead to benzene lately. DMSO decarboxylates a number of compounds at very low temps (~30 - 50C), benzoic acid could be heated with DMSO and benzene would (in theory) continuously distill off, just add more benzoic acid when the distillation started to slack. You could really get away cheap by oxidizing the toluene yourself with an aquarium pump bubbling air through toluene under water in the presence of some transition metal catalyst (or so I've been lead to believe).

Organikum - 11-3-2005 at 04:59

Shit, most of my pictures are missing, I will upload them again later.

historical reference

Magpie - 11-3-2005 at 21:31

I thought it would be interesting to read the original journal article on this method by E. Mitscherlich as published in "Annalen der Chemie" (1834). I will post it in the original German and hope someone will translate it to English. Sorry I can't post the whole article but I was getting writer's cramp as it is. My apologies for lack of proper notation on some of the "e's". I hope it is still translatable. Here is what appears to be the most meaningful excerpt:

Ueber das Benzol und die Sauren der Oel- und Talgarten

Das Benzol (Benzin)

Mengt man Benzoesäure mit einer starken Base, woyon man mehr nimmt als hinreichend ist um die doppelte Menge. Benzoesäure zu sättigen, mengt man z. B. 1 Th. Benzoesäure mit 3 Th. gelöschter Kalkerde, und unterwirit das Gemenge der Destillation, so geht zuerst Wasser und zuletzt eine dünnflüssige ölartige Flüssigkeit über, welche auf dem Wasser schwimmt. Wenn man das Gemenge sehr langsam erwarmt, so ist der Rückstand in der Retorte vollkommen farblos, und läfst beim Auflösen in Säure, wobei sich Kohlensäure entwickelt, keine Spur eines Rückstandes zuruck; die Auflösung in der Säure ist farblos, und es wird keine Gasart bei der destillation entwickelt. Die Benzoesäure zerlegt sich also in Kohlensäure und in die ölartige Flüssigkeit. Die ölartige Flüssigkeit kann man vom Wasser vollständig trennen, wenn man sie mit der Pipette abnimmt, dann mit etwas Kali schüttelt und destilliert. Läftst man Kalium lange Zeit mit dieser Flüssigkeit in Berührung, oder destillirt man sie damit, so bleibt die Oberfläche des Kaliums metallisch glänzend, so dafs sie also keinen Sauerstoff enthalt. Da diese Flüssigkeit aus der Benzoesäure gewonnen wird, und wahrscheinlich mit den Benzoylverbindungen im Zusammenhang steht, so gibt man ihr am besten den Namen Benzol, da der Name Benzoyn shon für die dem Bittermandelöl isomerische Verbinung von Liebig und Wöhler gewählt worden ist.

Organikum - 12-3-2005 at 04:02

Mixing benzoic acid and calcium hydroxide 1/3 w/w followed by distillation yields an oily layer on water which is redistilled and the resulting liquid is christened "benzene" as the name benzoyl was already taken for something else.


Magpie - 12-3-2005 at 06:52

Thanks for the translation abstract organikum. Is the rest of the text irrelevant? If you would have the time I would appreciate a full translation out of curiosity and historical interest. ;)

Organikum - 12-3-2005 at 07:14

The rest says, that the residue in the retort is colorless, dissolves in acid and CO2 is evolved, the resulting solution is also colorless. The distillation (of the benzoic acid and calcium hydroxide) produces no gases, ergo the reaction splits CO2 from the benzoic acid.
Potassium added to the benzene keeps its metallic surface, so this "benzene" contains no oxygen.

Thats really all whats written.

ordenblitz - 17-7-2005 at 16:26

Taking a big jump up in size to see if economy of scale applies in this case, I constructed the following monster distillation setup.

You can see the lead in end of the water jacketed condenser I whipped up for the occasion. Here is the other end in a 2000ml. bottle waiting to receive its load.

In the can was put 4 or 5 shredded stainless steel scrubber pads, for a conduction aid and a specially wet granulated, densified and beaded mix of 2500 gm sodium benzoate + 1250 gm calcium hydroxide. I prefer to use Ca(OH)2 since I have to use less personal protection when mixing and granulating. Clean up is easier and of course the stuff is cheaper.

I cranked up this monster and after waiting 3 hours for about 250ml I got frustrated and broke out the Big burner and commenced to roasting that bastard! You can see I just disconnected the other burner and slipped in the big guns. I had that can pretty red!

After another hour or two, when things started to slow down I shut it down and this is what I got.

650 stinking milliliters for all that hard work and waiting, pathetic! I expected about 1500ml. After opening the can I noticed that most of the center of the mass was un-reacted and the top looked all but untouched. I had the lower 1/3 of the can cherry red after the 3rd hour. Organikum was right on the money about the poor heat conductivity of the reacted mass. I really thought that if I just upped the heat input, I could convince the thing to happen. Hmm maybe someone should look at this material for heat shielding because it's conductive properties are crap. I think I blew through a full cylinder of propane doing it.

My conclusion is that scaling this reaction up without a lot of fairly technical hardware, is probably just not worth the effort.

Washed and ready to distill!

sep.JPG - 23kB

12AX7 - 17-7-2005 at 19:43

Sounds like you need a refractory lined furnace. :D

If conductivity is the problem you say it is, it might be worth say pressing into cakes and/or only using smaller retorts- anything with more surface area and thinner cross section.

It could well appear to be low in conductivity due to heat consumption as well as insulation; I imagine the reaction is mostly endothermic, especially with the evaporation. Calcium carbonate powder isn't exactly known for its conductivity, at least as a porous lump.

BTW, can PETE be pyrolyzed/decarboxylated to ethylene/ethane and benzene (or other aromatics)? Plenty of it around. It's a polyester of pthalic acid and ethylene glycol, plus whatever modifiers they used.


Magpie - 18-7-2005 at 12:37

A valiant effort Ordenblitz! Indeed you have confirmed the poor heat transfer inherent in dry powder. What you need is a minature lime kiln with tilted, rotating cylinder and hanging chains to keep the powder mixed. ;)

I'm impressed with your equipment framework, stainless steel drain, etc. Is all that your own personal equipment?

ordenblitz - 18-7-2005 at 15:40

What you need is a miniature limekiln with tilted, rotating
Cylinder and hanging chains to keep the powder mixed.

That’s a good idea. I could put some ceramic milling media with the feed stock in the cylinder, rotate it for a while to grind everything up nicely and then turn on the heat. Now all I have to do is figure out some sort of high temp banjo fitting for the out port and I am in the benzene business.

I'm impressed with your equipment framework, stainless
steel drain, etc. Is all that your own personal equipment?

Thanks. Yes it's mine. I picked up this hood in a refinery auction for $100 All I had to do was build a pedestal for it and run some duct work to a restaurant style exhaust fan and viola' The frame is a Fisher monkey bar kit that I installed and even anodized a few of the pieces black. I am going to do a post about do it yourself anodizing when I get around to it.

I've had quite a few years to put my lab together. Some people have expensive boats or 4 wheelers etc. I have a chemical dependency.

[Edited on 18-7-2005 by ordenblitz]

hood.JPG - 34kB

jimwig - 18-7-2005 at 15:59

Stir it up - but like you say more technical equipment required.

Keep it stirred with a huge mechanical stirrer. Ok stop laughing.

You gotta use stainless as the reaction vessel then put a old speaker magnet on a motor shaft. Plug it into a variac. Use teflon tape coated steel bar for the stir bar. Maybe an epoxy stir bar would last a short time in the hot alkali.

[Edited on 18-7-2005 by jimwig]

Magpie - 18-7-2005 at 18:22

$100 for a fume hood! Together with your FTIR spectrometer you have really picked up some bargains. :P

I just happened to be in the middle of building a fume hood system in my garage using parts purchased from local non-scientific sources like Home Depot. I'm using a 475 cfm (@ 0.75" H2O) open one-side blower, SS316 discharge duct, and 8" PVC suction ducting. The hood will be epoxy coated wood 48" wide x 46" high x 28" deep. It will be a constant volume bypass type using a tempered glass sash with PVC frame. I had the SS316 discharge piece fabricated by a sheet metal shop. The blower will sit in my rafters. My total cost will be over $1000 just for materials. :o

The_Davster - 18-7-2005 at 19:41

Wow, coincidently I am in the process of making a fume hood as well, it is rather small just 7" square by 13" tall, but it is big enough to fit over a simple setup emitting bad fumes. Powered by an old computer fan(30W) that takes 115 volts...rather monster for a computer fan. It is just something that can be placed over whatever is emiting fumes to draw them outside. I am aware that this fan will die soon from corossive vapours, but they are free(seems everyone in my family has a couple...), so it is not too difficult to replace one. Due to the layout of my backyard my neighbours can see everything unless I am under a tree, so work outside in the past has been risky durning the day, or done late at night.

The 'glass' of the hood is lucite...does not really matter but it sounds impressive.:P

Impressive ordenblitz...and that hood is in your house? Nice.

[Edited on 19-7-2005 by rogue chemist]

Lets try this again.

ordenblitz - 27-7-2005 at 18:21

rogue chemist.. No it's not in my house.

Taking a second look at the monster distillation can for benzene, I decided to scale the quantity back and shorten the time. I put 1100g of my 2/1 sodium benzoate/calcium hydroxide mix (about 30% of the original load) into the can. This filled it roughly 1.3 inches. I wanted a thin layer this time. I then connected the condenser and fired up the burner. In 30 minutes the distillate stopped coming over and I had 210ml of product.

Not bad for 40 minutes of work. Next I decided to try sodalime to see if the lower melting point would hasten the reaction or increase the yield. So to 1100g of the mix I added 200ml 40% NaOH solution, mixed thoroughly and added to my can. I turned on the flames and in less then 20 minutes it was all over. This time I had 200ml of liquid goodies. So, faster yes but slightly poorer yield.

While the can is still hot I open it up and hit it with the hose and the thermal shock breaks the clinker into a thousand pieces and I simply dump out the chunks, load her up and off we go again. A day of this and quite a bit of benzene could be had. Geez.. I don't even know what I am going to do with this benzene and here I am making liters of it.

I have run this now about 4 times and I think the can should last quite a while. The only thing I need to replace is the cap seals, which I cut out of high temp silicone.

It is interesting to note that the faster you push this reaction the redder the product gets. Compared to my first batch it looks a deep red. The only difference between the first run and the second was load in the can and how fast I heated it up. The final test will be when it's distilled and the tally taken. I assume that I made a bit more biphenyl by pressing it hard. I will sort out the final count and post.

[Edited on 28-7-2005 by ordenblitz]

colors.JPG - 11kB

Steam dealkation of toluene...

Eclectic - 27-7-2005 at 19:46

Hot tube, some kind of catalyst, maybe vanadium or molybdenum...

[Edited on 28-7-2005 by Eclectic]

ordenblitz - 31-7-2005 at 19:53

All the batches are now finished and from 2500gm/1250gm, sodium benzoate/calcium hydroxide and some time I have about 1.4 liters of benzene. Not too bad at all. I managed to save the unreacted material from my first run and add it to subsequent runs. As long as I keep the load in the can at about 1000 grams, I get very good yields.

I distilled the darker batches and the lighter yellow ones separately. While the distillate from the faster hotter runs is more toward the red/orange, it results in less solid matter (biphenyl etc) remaining after the finish distillation. So I say, hotter and faster is better.

I got a picture of the clinker that I broke out of the can. It is very light and porous looking a lot like lava rock or pumice. One other interesting thing is that it is very hard after coming out of the can but upon exposure to the air for a day it completely disintegrates into dust. So to make cleanup easy after a run, just let your vessel sit open for a while and dump out the powder.

moonrock.JPG - 38kB

Magpie - 26-1-2006 at 19:32

This is an old thread but I have some recent contributions, and questions. I need about 50 mL of benzene so am making it by decarboxylation of Na benzoate using NaOH according to a procedure in my 1960 lab manual. Since I'm using a 25mm x 200mm test tube I find that to optimize heat transfer to maximize yield (60-70%) it's best to use 1/2 batches. This only gives me about 5mL per heat. So it is a labor of love to get my 50 mL. ;)

C6H5CO-ONa + NaOH + heat --> C6H6 + Na2CO3

Here's a picture of the business end. This is an early picture and shows a full batch in the tube - it's too much. From the rubber stopper a 5mm glass tube leads to my gg thermometer adapter fitted to a condenser. I pour the heat to this using my propane fired bunsen burner until the dry powder fuses. This causes generation of benzene plus an orange chemical dissolved in the benzene. There has been previous speculation that this is biphenyl; but is that orange? Also there is this curious looking "smoke" that is generated and goes down the condenser before the benzene comes over. Now what the hell is that? :o Before I'm done the residue left in the tube is black. So I'm carbonizing some of the benzene and/or the generated Na2CO3? Today for the first time I saw a green tint to the powder as it was heated. I think this is most likely a Ni or Cu compound coming in as an artifact from the kitchen spoon I use in making up the powder matrix. So it is very interesting and I thought some members would also find it so. I'll post a 2nd picture showing the receiving pot with the orange colored benzene.

Oops: I need to crop these photos first so will send them next post (sorry).

[Edited on 27-1-2006 by Magpie]

Magpie - 26-1-2006 at 19:49

Benzene making, 1st picture:

<img src="" width="800" />

<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: reduced image size(s); hosted image(s) at]

[Edited on 12.12.13 by bfesser]

Magpie - 26-1-2006 at 20:01

Benzene making, 2nd picture:

<img src="" width="800" />

<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: reduced image size(s); hosted image(s) at]

[Edited on 12.12.13 by bfesser]

ordenblitz - 26-1-2006 at 20:28

Magpie said:
There has been previous speculation that this is biphenyl; but is that orange?

The FTIR thinks it is.
Would you call that speculation?

Magpie - 26-1-2006 at 20:31

Nope. That's good enough for me. :P It's just when I looked in my CRC no color was given for biphenyl. Thanks for the confirmation. ;)

mantis - 27-1-2006 at 10:52

What about phenol?

garage chemist - 27-1-2006 at 11:25

The yellow color is from polymerized gunk (tar- like substances), as biphenyl is actually colorless.
The reaction is not clean at all and produces a small amount of random organic stuff. But simple distillation gets rid of this and pure benzene can be isolated.

Another approach to benzene manufacture:

I hope to get some anhydrous AlCl3 soon (I placed an order) and want to try the "disproportionative dealkylation" (I made up that word) of toluene.

2 C6H5-CH3 ----(AlCl3)----> C6H6 + C6H4(CH3)2

Toluene is converted into Benzene and Xylene. The equilibrium is shifted to the right side by constantly removing the formed benzene by slow distillation of the reaction mix through a column.
I'l report my findngs, and I'll also try what influence the amount of AlCl3 has on the benzene yield.

[Edited on 27-1-2006 by garage chemist]

mantis - 27-1-2006 at 12:13

I heard about the dehydrogenation of cyclohexan or cyclohexen, with metallic palladium as catalyst. Has anyone ever tried this?

BromicAcid - 28-2-2006 at 18:09

One day while reading through "Technical Bulletin Reaction Solvent Dimethyl Sulfoxide" I ran across some entries on pages 51-52 regarding the use of DMSO as a reaction solvent for decarboxylation reactions giving high yields of product and thought, "Hey... I can get sodium benzoate... add a little HCl and get some benzoic acid, add to DMSO, and distill off the benzene.." Today I got to the last step of that series of events.

For completeness here is a general outline of the conversion of sodium benzoate to benzoic acid.

  1. Dissolve 230 grams sodium benzoate in 375 ml H2O to give a clear solution
  2. Filtered it because there was some insoluble particulate
  3. Added 50 ml concentrated HCl more was necessary but the solution at this point was too thick to stir
  4. Filter and wash the precipitate with copious amounts of water
  5. An additional 150 ml of the HCl was added
  6. Precipitate filtered, sodium chloride noticed as a contaminate in this batch so additional washing was preformed
  7. Combined filter cakes were allowed to air dry for three days and crushed
  8. Total yield was roughly 92% (176 grams)

Ta dah! Benzoic acid, be wary of the dust from it, it's terrible on the lungs.

So, 100 grams of benzoic acid was placed into a 1L 2-neck FB flask and 70 ml of DMSO was also added. The benzoic acid proved to be fairly soluble in the DMSO and a nice mostly liquid solution was obtained on stirring. A stopper was placed in the second neck of the flask and the main neck was connected to a still head, Liebig condenser, vacuum adaptor, and finally to a 250 ml Erlenmeyer.

The solution was heated and subjected to magnetic stirring. Initially a whiteness appeared on the inside of the flask leading me to believe some substantial sublimation was due to occur but this did not appear to be the case. The mixture continued to heat and small droplets started to condense in the upper walls of the flask. Finally the liquid hit the still head and the temperature was anything but steady, going between 50 C and 85 C up and down, up and down. Strange.... Some distillate started to come over after some time and a smell was noted.

The smell was like the lingering taste that becomes apparent after getting DMSO on the skin. It was fairly pungent and sulfurous, unlike H<sub>2</sub>S though so I felt a little safer. Still, it was annoying and troublesome. At any given time I could put my finger over the vacuum adaptor at the end of the distillation apparatus and pressure would build up fast, indicating at least to me that a gas was being generated (CO<sub>2</sub> assuming things were going right) Because of this smell and the slow rate of distillation though (by this time the still head had leveled out near 80C) I opted to add some water to the mixture.

Hold it! Water? Why water you ask? Well, the information in the DMSO technical bulletin lead me to believe water could be helpful in this reaction, some of the decarboxylations occurring in 70% DMSO with 30% water (it is also noted the NaCl is beneficial to some decarboxylations but I didn't pursue this path). A second reason was that water and benzene form an azeotrope, and I was hoping to take advantage of that to help strip the benzene out of the solution. So I decided to add 40 ml of water to the mixture. I opened the second neck of the flask and added 10 ml. A strong gas evolution was noted, very strong that blew out gasses almost, I assumed this is because the mixture was much hotter then the boiling point of the water. The gasses were very sulfurous and they burned my eyes badly despite the goggles. I felt like an idiot.

Remaining water was added in a second aliquot. This did not generate the intense gas evolution as previously noted. Immediately after the stopper was replaced water began to very quickly distill over. The rate of distillation was very rapid. I continued heating and distilling for nearly an hour and according to the side of my receiving flask all the water had distilled over. The still head had remained just below 100C the whole time so I don't think much benzene came over with the water, the water was a milky color. An organic layer was floating on top of the water though. I am not sure if this was carried over by the water, but I think the bulk of it came from the initial distillation without the water.

I have yet to analyze this organic component but I believe it to be benzene based on its boiling point (from before I added the water) coupled with the fact that it is insoluble in water whereas if it were DMSO that had steam distilled it would have dissolved in the water. I would like to repeat this process with a short path distillation and more time using no water as I did appear to be getting results, however slowly. In complete contrast to my short path idea, I additionally think a reflux condenser would be most useful in this case to prevent DMSO from making its way over to the receiving flask.

The whole reason behind this little excursion (considering that I have plenty of benzene) was just to see if this process could give better yields of benzene as opposed to the dry distillation process. Additionally this process can use simple glassware as opposed to steel works (however I do prefer steel tubes, they're cheaper and more abundant). I will attempt this process again in the future, if it works then it would be a continuous use for DMSO as it would merely act as a reaction solvent, more benzoic acid added continuously, the only chemical consumed being the ever cheap HCl.

If anyone has any thoughts on this burning acrid gas coming out of the solution when I added water of the gas that failed to condense that managed to sneak its scent out I would be glad to hear them.

[Edited on 3/1/2006 by BromicAcid]

budullewraagh - 1-3-2006 at 12:38

the gas was probably DMSO, considering the fact that it penetrated your goggles and burned your eyes and smelled sulfurous.

BromicAcid - 7-5-2006 at 16:18

I doubt the gas was DMSO as it was for all intents completely different in terms of smell and burning sensation. From the DMSO Technical Bulletin I found the following entry that might explain what the smell was I noted in my decarboxylation of benzoic acid with DMSO experiment:
Chemically, DMSO is stable above 100 C in alkaline, acidic or neutral conditions. Prolonged refluxing at atmospheric pressure will cause slow decomposition of DMSO. If this occurs, it can be readily detected by the odor of trace amounts of methyl mercaptan and bis(methylthio)methane.

Although it didn't smell like the stuff that they add to propane to make it smell. It burned more then that. A possibility though.

bio2 - 7-5-2006 at 18:24

.... I additionally think a reflux condenser would be most useful in this case to prevent DMSO from making its way over to the receiving flask.........

You could put the still head on a short reflux condensor kept
a little above the boiling point of benzene to condense the DMSO that tries to carry over or heat tape a claisen.

This would also help prevent the benzene from refluxing.

hinz - 19-11-2006 at 16:33

I've tried to decarboxyate sodium terephthalate, with miserable yield. The sodium terephthalate was made by dissolving PET-bottles in a hot/boiling saturated aqueous NaOH solution, it went quite fast if the solution was hot enough.
I went on with heating of the solution for a few hours, then I added more NaOH and poured the viscous mass in a retort, about 300g.

This retort was heated by a wooden fire in the chimney outside the house. Note the clear liquid in the glass bottle isn't benzene, it's water mixed with ethylene glycol, the solvent and product of PET hydrolysis.

The yield was extremly bad, the only product I've got is this 1-2ml floating on top of the aqueous layer in this test-tube. It's red like the benzene obtained by others here, it burns with a grimy oxygen deficent flame and it smells like an aromatic compound. Close to this is the porous material, mostly Na2CO3 I broke ourt of the steel tube.

The strange thing I observed when heating the tube beyoint the point the water/EG came over, was a white smoke or mist in a flammable gas. This stuff can be seen above the water in the glass bottle. It's strange because I don't understant to which flammable gas sodium terephthalate could be decompose without loosing a carbon atom or (nearly impossible) forming acetylene. But the porous material doesn't contain any free carbon.

Any possible reactions as explanation for this phenomenon?

BTW, Where/ as what does the remaining sodium benzoate end up in this reaction: 7 gm. NaOH + 25 gm. C7H5NaO2 = 7ml C6H6? Maybe by destilling as free acid, but this in improbable due the alkaline conditions, maybe oxidised... .

chromium - 20-11-2006 at 12:15

I do not know how much ethylene glycol was in water layer but mix of water and EG can probably dissolve some benzene. This might explain low yield.

I did some fast calculation with sodium terephthalate and benzene formulas and it seems that 100% yield would be aproximately 1/3 of mass of dry sodium terephthalate.

If i had suitable retort i would like to try just heating pieces of PET with NaOH and no water at all. This could give mix of benzene and ethylene glycol.

roamingnome - 21-4-2007 at 08:18

this has been a interesting thread to catch up on and

it seems that ORGANIKUM is defintaly the benzoate master here. Ill certainly save benzoate if i run into a sack of it, but

acetylene condensation needs to be figured out now...

i wonder if cyrogenic josseling of the gas might click them together with the right magic wand waving on the side

Russian Chemical Bulletin
Issue Volume 5, Number 12 / December, 1956
C14-labeled benzene was synthesized by the condensation of acetylene-C14 diluted with steam at 740°, the time of contact being 3.5 seconds. The yield of benzene-C14 was 30% on the amount of active carbon taken.

the yield of just benzene without regard for labels might be higher.... any acetlyene condensators out there?

The Nobel Laureate Gustaf Dalén was blinded by an acetylene explosion. bummer

Rosco Bodine - 25-4-2007 at 22:40

Originally posted by Organikum
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.

And further ....

Originally posted by Organikum
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

What about using aluminum amalgam in isopropanol to produce benzene from paradichlorobenzene moth crystals ?

This might even work concurrently with the toluene disproportionation , if the paradichorobenzene were dissolved in toluene ,
as the reaction mixture would be
anhydrous from the formation of aluminum isopropoxide ,
and AlCl3 would also be formed in situ .

PS: If a 500 pixel image width limitation is enforced ,
the text formatting will not be trashed by the pictures
which members post here .

[Edited on 28-4-2007 by Rosco Bodine]

Nicodem - 26-4-2007 at 11:27

Isopropanol is an alcohol and as such it quenches AlCl3.

Where did you hear that aluminium amalgam in isopropanol reduces p-dichlorobenzene to benzene?

Rosco Bodine - 26-4-2007 at 11:35

Actually I never heard of it , and never tried it ,
it just seemed like a plausible result to me .

I know paradichlorobenzene may be almost
paraffinic in its unreactivity , but it isn't teflon .

Suppose you (partially) neutralize aluminum isopropoxide
with (anhydrous , nascent ) HCl , if not AlCl3 is what will be in solution as the result .....then what will be ?

Under anhydrous condition , I just don't see the chlorohydrate being likely , but I am not certain .

There would definitely be a tug of war for any
potential water or hydroxyl fragment :D


I found an old post where aluminum amalgam has already been tried and didn't react it is pretty certain
that it would take some really extreme conditions of
temperature and pressure to get any reaction to proceed
involving the chlorines of paradichlorobenzene .
See bottom post page 3 by Polverone .

[Edited on 26-4-2007 by Rosco Bodine]

not_important - 26-4-2007 at 17:17

p-dichlorobenzene + AlCl3 gives mostly a mix of the dichlorobenzene isomers, the chlorines seem happy to hop about on the ring but don't like to jump rings. Careful fractionation of the mix might be able to remove benzene, I've not tried that as several reports stated no ring jumping for Cl although Br has been stated to ring jump.

If the mixed dichlorobenzene isomers are cooled so the much of the para isomer freezes out, the ramaing mix is a useful not-too-reactive solvent.

BromicAcid - 26-4-2007 at 18:08

I'm pretty sure this has been mentioned before but your attempts remind me of using magnesium and isopropanol to give benzene from chlorobenzene, as shown in:

Organic Syntheses, Coll. Vol. 5, p.998 (1973); Vol. 47, p.103 (1967).

Nicodem - 26-4-2007 at 21:49

Direct link would be: Reduction of organic halides. Chlorobenzene to benzene.

But I don't think aluminium amalgam would do that. I know it can't do that in the presence of water, but I doubt anhydrous conditions would make much difference. Mg can insert in the Ar-Cl bond but I never saw an equivalent electron transfer from Al to aromatic halides. Even zinc would have more chances of working.

Rosco, AlCl3 is a very strong acid and as such will complex even with such weak bases as water or alcohols. It coordinates with the oxygen's lone electron pair just like other acids do (just like H<sup>+</sup>, for example). Like any acid/base reaction this complex is also equilibrium:
R-OH + AlCl<sub>3</sub> <=> [R-O-AlCl<sub>3</sub>]<sup>-</sup> + H<sup>+</sup> <=> R-O-AlCl<sub>2</sub> + HCl

When you want AlCl3 to efficiently catalyze FC reactions, then the solvent must never be more nucleophilic or basic than substrate is.

[Edited on by Nicodem]

leu - 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.
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]

Rosco Bodine - 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 .

Organikum - 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.

Organikum - 27-4-2007 at 17:53

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.

Rosco Bodine - 27-4-2007 at 19:34

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]

Nicodem - 27-4-2007 at 23:38

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).

MagicJigPipe - 24-9-2007 at 23:40

The benoate route does work and you can buy sodium benzoate from 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.

trilobite - 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]

DJF90 - 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

12AX7 - 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?


kclo4 - 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

DJF90 - 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.

MagicJigPipe - 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.

Nicodem - 21-4-2008 at 00:00

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.
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.

DJF90 - 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.

kclo4 - 21-4-2008 at 13:54

Originally posted by Nicodem
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.

Filemon - 2-6-2008 at 03:41

How much did concentration of AlCl3 and HCl use for toluene disproportionation?

Nicodem - 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 994 times

Foss_Jeane - 19-12-2008 at 01:51

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)
This file has been downloaded 676 times

Defibrilator - 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. :-/

DJF90 - 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.

-TheMadMen- - 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.

S.C. Wack - 29-6-2009 at 11:40

Benzene rich oil by the decarboxylation of PET

User - 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]

not_important - 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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