Sciencemadness Discussion Board

Making Benzene/KMnO4 Tolulene method

Mirage - 1-2-2012 at 22:53

I would like to be able to produce some benzene for multiple organic experiments. It seems the only place to find this compound is on Alfa or Sigma etc! As I was trawling through my subscriptions on YouTube, I came across a synthesis of benzene from Tolulene and KMnO4. Both of these reagents, I have readily available, but the purity of my Tolulene may be lacking. Has anyone done this process with hardware brand Tolulene, or is it necessary to distill it first.

The rest of the synth, was X grams KMnO4 and X grams Tolulene, refluxed for a couple hours, the benzene seperated from the other by products, and then purified.

In conclusion,
1. Is the hardware store Tolulene pure enough?
2. If so, then has anyone had any experience with this process
3. If anyone knows any sources of benzene, then a reply would be greatly appreciated.

Chemically yours,
Mirage

UnintentionalChaos - 2-2-2012 at 08:52

That'll make benzoic acid, not benzene. The KMnO4 has to be in solution so only small amounts of toluene can be reacted at a time...we have an excellent thread on making benzene here. Many members, myself included, have had success with the high temperature decarboxylation of sodium benzoate in the presence of sodium hydroxide. I only made 180ml, but there are some who've made liters this way.

Hell, it's even on youtube.

[Edited on 2-2-12 by UnintentionalChaos]

Mirage - 2-2-2012 at 10:37

Thanks for the reply! Yes I'd seen the other method on YouTube as well, for me, I would not be able to get that much sodium benzoate to make any reasonable amount of benzene. On the YouTube video with the kmno4/Tolulene method, he explains that this should make benzoic acid, however, If you reflux long enough, it should somehow convert to benzene... (shrug smiley) Oh well, I guess I should find a source of sodium benzoate

Mirage
Quote:
That'll make benzoic acid, not benzene. The KMnO4 has to be in solution so only small amounts of toluene can be reacted at a time...we have an excellent thread on making benzene here. Many members, myself included, have had success with the high temperature decarboxylation of sodium benzoate in the presence of sodium hydroxide. I only made 180ml, but there are some who've made liters this way.

Hell, it's even on youtube.

UnintentionalChaos - 2-2-2012 at 11:00

Quote: Originally posted by Mirage  
Thanks for the reply! Yes I'd seen the other method on YouTube as well, for me, I would not be able to get that much sodium benzoate to make any reasonable amount of benzene. On the YouTube video with the kmno4/Tolulene method, he explains that this should make benzoic acid, however, If you reflux long enough, it should somehow convert to benzene... (shrug smiley) Oh well, I guess I should find a source of sodium benzoate

Mirage


I bought 2.25kg off ebay for $30USD after shipping as bait preservative. It's still available and the seller ships to canada.

The decarboxylation of benzoic acid without catalyst needs very high temperatures to provide the activation energy. Copper seems to be the catalyst of choice, but it won't work in aqueous solution. You're much better off mixing it with NaOH and pointing a flame at it.

There's a nice writeup here if you don't want to wade through the thread. http://www.sciencemadness.org/member_publications/benzene_pr...

Mirage - 2-2-2012 at 12:32

Wow! That's an awesome deal! Guess I do have a method now. Probably should have searched the threads before I posted. Thanks for all your help!
Quote:
I bought 2.25kg off ebay for $30USD after shipping as bait preservative. It's still available and the seller ships to canada.