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Author: Subject: Benzene synthesis
S.C. Wack
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[*] posted on 25-7-2009 at 10:33


Looked up reference 2 in the paper that I linked to - in Chem. Lett. 33, 282 (2004), the most ideal conditions for benzene in that system were: PET powder was heated with Ca(OH)2 at 700C at a 10:1 Ca(OH)2 : PET ratio, giving a distillate that was 45.5% of the weight of the PET, and benzene accounted for 36% of the weight of the PET.

They analyzed the products closely and quantitatively under the various parameters used, and quite a number of things were present. Under the ideal conditions, the highest % contaminants of the distillate were, again in wt.% of PET: 3.5% biphenyl, 2.3% toluene, 1.36% styrene, and 0.6% acetophenone. Using any less, and especially much less Ca(OH)2, dramatically decreased the selectivity for benzene.

[Edited on 25-7-2009 by S.C. Wack]
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JohnWW
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[*] posted on 25-7-2009 at 20:38


But, on an industrial scale, how would such a process for obtaining benzene, based on hydrolysis of PET (probably from recycled plastic drink bottles, most of which BTW are shipped to China) and decomposition of the monomeric products thereof, compare for unit co$t and efficiency with either fractionation of benzene from petroleum, or direct synthesis of benzene by polymerization of acetylene under heat and pressure? (The acetylene, C2H2, having been generated by hydrolysis of calcium carbide, CaC2, obtained by pyrolysis of lime with coke or anthracite in a retort). As a chemical engineer, I am aware of such considerations.
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[*] posted on 14-9-2009 at 07:14


Sorry if this is a little off topic, but is there any way toluene could be obtained by some pyrolysis procedure like benzene can?



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[*] posted on 14-9-2009 at 09:02


Yes, heating 2-methyl-benzoic acid with NaOH will produce toluene
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Eclectic
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[*] posted on 8-11-2009 at 08:55


Does anyone know if benzenesulfonic acid would distill (190 C) from benzoic acid in hot sulfuric acid as a decarboxylation solvent? Perhaps with a little copper as catalyst?
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manimal
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[*] posted on 6-4-2010 at 15:12


Apparently, Org recently passed away from cancer. One wonders if his fondness for chemicals such as this played a part.
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[*] posted on 6-4-2010 at 16:13


Org? Organikum? What kind of cancer?

Whoever it was, rest in peace!
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[*] posted on 6-4-2010 at 17:48


Quote: Originally posted by Jor  
Whoever it was, rest in peace!


Seconded.

Organikum, yes; I'm not sure of the details, that's just what I read on another forum (WD).
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hissingnoise
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[*] posted on 7-4-2010 at 03:41


It's saddening to note that our clandustrial priest won't be posting again.
I hope he enjoyed his life.
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S.C. Wack
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[*] posted on 7-4-2010 at 11:31


IIRC he mentioned a terminal lung cancer diagnosis (he was a smoker) in passing in his deliberately last post there in a threat --- about 5 months before his last post here. Note how the last login here is much later. IDK if he said anything in whimsy here that no one noticed, if he hated the RIP Halfapint thread at the-hive, or what the deal is. Anyone that knows for sure isn't saying.



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unionised
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[*] posted on 25-4-2010 at 12:38


I just looked through this thread and didn't see a reference but has anyone considered the pyrolysis of polyvinyl acetate (or alcohol) as a synthetic pathway to benzene?

Pyrolysis of PVC works too, but I'd not be happy about the potential for making chlorinated aromatics.

Not sure how well this link will work, but it indicates that benzene is a major product (based on gc peak area which isn't a brilliant way to quantify stuff)
http://books.google.co.uk/books?id=AY__YWnIE_4C&pg=PA312...

There's a table of products on p326.

[Edited on 25-4-10 by unionised]
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[*] posted on 25-4-2010 at 13:21


Sort-of-on-topic: I heard about a company in Houston which is using large plasma reactors to reprocess waste such as PET, other plastic scraps, and about anything else which can be vaporized in their chambers, the output being fractionated with (I am guessing) MHD or other very large scale electric-magnetic-mass-??? separators.

I'm trying to track this down... google didn't have anything suggestive last time I looked. Any rumors anywhere?
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[*] posted on 25-4-2010 at 20:57



http://en.wikipedia.org/wiki/Plasma_arc_waste_disposal

http://www.popsci.com/scitech/article/2007-03/prophet-garbag...


While aromatics are formed in high temperature mixes rich in carbon and hydrogen in roughly unity ratio, SFAIK the yield generally aren't great and you tend to get mixtures.





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[*] posted on 26-4-2010 at 03:09


Quote: Originally posted by S.C. Wack  
IIRC he mentioned a terminal lung cancer diagnosis (he was a smoker) in passing in his deliberately last post there in a threat --- about 5 months before his last post here. Note how the last login here is much later. IDK if he said anything in whimsy here that no one noticed, if he hated the RIP Halfapint thread at the-hive, or what the deal is. Anyone that knows for sure isn't saying.


Is it true that he is dead? If it is true then it is a great loss to internet chemistry forums. I truly miss his posts and his sense of humour, to hear that he is no longer here is very saddening.




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[*] posted on 8-5-2010 at 08:26


Quote: Originally posted by BASF  
Do you have more information on the decarboxylation of benzoic acid?
Decomposition temp. and similar things?

I think the decarboxylation of benzoic acid would be very attractive for the home chemist due to the widespread use of benzoic acid in the food industry, and therefor it should be easy to get and not that expensive.
I still have some 100-200g of benzoic acid from a drug store.

HLR


Wikipedia has an interesting article on benzene in soda, not very much mind you but it is still benzene. It was apparently caused by decarboxylation of benzoic acid.

http://en.wikipedia.org/wiki/Benzene_in_soft_drinks

I have heard of thermal decarboxylations on amino acids, I have heard that ketones act as catalysts and increase yields, It used Tryptophan or Lysine in xylene with a dash of MEK (2-butanone) I am not sure what yields are or if the ketone does anything at all. Although the wiki article says citric acid and some other things in citrus soda's catalyze the reaction of benzoic acid.

[Edited on 8-5-2010 by majortom]

[Edited on 8-5-2010 by majortom]
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[*] posted on 8-5-2010 at 08:57


that has been brought up before, the amounts formed are microscopic.

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[*] posted on 8-5-2010 at 10:47


Diffidently, only a few micrograms but if the reaction can take place, albeit slowly, in soda in a very cool temp(even if it is 100 F) than what would happen if we heated it up to 150 C in some high boiling point solvent?

[Edited on 9-5-2010 by majortom]
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[*] posted on 20-10-2013 at 04:45


I am unfortunate to not to be able to find data which could indicate how xylene or benzene could be transferred to toluene. Does anyone have any data or sources for this process?

I found one possible route:

p-Toluic acid is first made from xylene with KMnO4, and then it is decarboxylated with 2 moles of NaOH, leaving toluene and sodium carbonate residues.

[Edited on 20-10-2013 by testimento]
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[*] posted on 20-10-2013 at 07:29


It might be possible to form benzene via decarboxylation of benzoic acid. The main article cited in wikipedia, from the Journal of Agricultural and Food Chemistry, does not make a thorough effort to find the best conditions for benzene synthesis, as it's goal is to find out whether decarboxylation occurs in realistic beverage storage and consumption conditions. And indeed it does, albeit in microscopic amounts, as has already been pointed out. I'm curious if yield could be improved by heating/refluxing, by finding a better decarboxylating agent (ascorbic acid is used, citric acid is also mentioned but this produces even lower yields), or by finding a better transition metal catalyst (mainly iron and copper compounds are used). I've had this in mind for months now, but unfortunately, I can't afford the equipment or reagents to test this, or find a suitable place to carry out these experiments.



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[*] posted on 20-10-2013 at 10:14


Quote: Originally posted by amazingchemistry  
It might be possible to form benzene via decarboxylation of benzoic acid.


Have you not bothered reading this thread?? Benzene was fairly easily obtained by this route. A friend of mine did this to make over 3 L of benzene.
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[*] posted on 20-10-2013 at 20:54


By "fairly easily" do you mean by the high-temperature solid-solid distillation of benzoic acid and sodium hydroxide? The same distillation where you have to be very careful temperature-wise or your glassware melts on you (molten hot NaOH being death to glass)? Do you mean the same distillation that because of this, more often than not, requires all-metal setups (many of which are pictured in this and other threads)? Do you mean the same distillation that yields an unsightly red product that you have to redistill to get anything close to pure benzene? Or have we made progress in the couple of months I've been away from this forum? If you bothered to read the paper in question you'd know that this particular decarboxylation was achieved in an aqueous solution of sodium benzoate, maintained at pH 2 with a buffer, using ascorbic acid as a hydroxyl radical donor and a transition metal catalyst. There was some decarboxylation going on even at room temperature. No need for homemade metal setups, crazy temperatures, etc. Although the reported yield is very small at typical beverage storage and consumption conditions, the paper did make me think about whether efficient benzene synthesis can be achieved by this route, given optimized reaction conditions. This is a valid research question, but unfortunately I have neither the equipment nor the place to pursue it. Maybe others can?

[Edited on 21-10-2013 by amazingchemistry]




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[*] posted on 20-10-2013 at 21:00


Decarboxylations can be done at lower temperatures with other reagents. Here is an example. Although I see no reason to abandon the current established route, as NaOH is dirt cheap and readily available and the procedure itself is piss easy for anyone who has a spare paint can.



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[*] posted on 21-10-2013 at 09:51


I don't see a reason to abandon the current route either (after all, we know it works). However, as far as I know, no experiments have been done to explore whether the above route or other routes would be feasible, or perhaps even better than the current one. I'm interested in the route described above because both ascorbic acid and sodium benzoate are cheap and readily available, and because the procedure described in the paper amounts to little more than 'mix and heat.' If that doesn't work, maybe we can learn something from it. We're chemists after all, and most of the stuff we do doesn't work :D



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[*] posted on 21-10-2013 at 12:44


Quote: Originally posted by amazingchemistry  
...procedure described in the paper amounts to little more than 'mix and heat.'


In such simple terms, thats exactly what the current method is.
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[*] posted on 6-2-2014 at 15:25


What might be the easiest way to oxidize styrene, toluene or xylene into benzoic acid?
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