Benzene synthesis - decarboxylation with NaOH

loki · guinea pig

"This reaction can be done with certain carboxylic acids themselves, but the acid would have to be solid. For example, benzene can be made by heating soda lime with solid benzoic acid (benzenecarboxylic acid), C6H5COOH.

C6H5COOH + NaOH --> C6H6 + Na2CO3 + H2O

You can think of this as first a reaction between the acid and the soda lime to make sodium benzoate, and then a decarboxylation as in the first example."
http://www.chemguide.co.uk/organicprops/acids/decarbox.html

It occurs to me that this may be a more achievable reagent than benzaldehyde, and opens up the possibility of exploring the acetone enolate synthesis and the manganese (III) acetate synthesis, and the friedel-crafts chloroacetone alkylation. Oxidise toluene all the way to benzoic acid and then decarboxylate to benzene. I am wondering whether this same decarboxylation method may allow the removal of carboxylic acid groups from interesting amino acids, but i have my doubts that this will be effective due to either interference from amine groups or from oxidation. Of course, common commercial tradesman grade toluene contains thio-toluenes which is a problem. Sodium benzoate is probably easy to aquire and looks to me as tho it's just heat and distill (no wonder there are questions about the safety of sodium benzoate). Cinnamic acid would not be difficult to reduce back to benzene either...

i just thought i'd post this because i've always wondered about where one would acquire benzene, and while searching for info on decarboxylation i found that one so i thought i'd pop it in here to see if this info is of interest to anyone. The other thing was the decarboxylation aspect as well, of course, i'd not previously bumped into the use of sodium hydroxide for decarboxylation before.

boredbastard · Thu May 05, 2005 2:35 am

There is a great thread on this at sciencemadness.

http://www.sciencemadness.org/talk/viewthread.php?tid=325

bio · Working Bee

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..........just thought i'd post this because i've always wondered about where one would acquire benzene,..............

Well, you could just go BUY some, seems much easier. True the price went waaay up in the last few years due to the cancer scare/hype but it's not listed and is about as common as dirt. It's still used for residue analysis and myriad solvent uses. Synthesis is actually a smaller use for smaller scale users.

Not too far back there was a gocart racing fuel called Kartane that was straight benzene and PhMe w/ tetraethyl lead is still OTC. Hell if you are too lazy to start a little company just ask your servicestation attendant friend to get the place to order for you but in HI there are at least 3 places that stock it. Try the one on K street by the freeway.

While you are working on your sob story how the old Kart just don't run like it used too might as well get some ACS nitromethane. It's not listed either but acetone, MEK, toluene and ether are!

While I really do admire DIYness there comes a time you have to get off of dead center and owning solvents is not a crime except in Bolivia where an individual owning over 50L of ANY solvent (includes kerosene etc.) is committing a crime. Even if you buy over the threshold it's just a simple damn form to sign and the supplier usuallly handles that. Trust me they aren't yet investigating every fiberglass shop that uses more than 50gals Me2CO a month.

Contrary to what you may have heard (I've seen it on some off the forums) it is NOT illegal to buy or own a listed chemical in the USAl. There is no liscence required and the so called permit isn't even a permit just a f........g disclosure form. We are talking Listed Essential Chemicals here NOT controlled substances. When anybody can go down to Kilgo's Hardware and buy as much acetone as they want does anybody really think that they will be investigated buying a liter or two of the CP grade at V....R.

Look we've all heard horror stories but unless Big Brother recently changed all the damn laws buying listed chems is easy, very easy. Just if you are stupid enough (not meaning you Loki) to buy ephedrine then the knock on the door will come sooner or later.

bio · Working Bee

Hey Loki; I just remembered a benzene synthesis that requires only one ingredient, acetylene, available everywhere at reasonable cost and pretty damn pure if you don't get the "oil pumped" grade.

I'll post the article/reference as soon as found in my archive. It does require a little engineering effort but not more than a simple furnace tube rig at 700deg IIRC.

Java probably has a few of these. It's a very old and sucessful method but superceeded, I think, in this day and age.

Hmmm, with a furnace tube some benzene a little formaldehyde, maybe a pinch of your favorite catalyst and LOTS of gumption you should be able to make damn near any phenyl compound. Given enough time no doubt.

bio · Working Bee

Here she be!

Acetylene, propylene and even methane can be converted into benzene. (E.P., 374,422 ; 369,351 ;
366,394.)