electrolosis of organic salts

[zeocrash]

ok its 3 weeks before my chemistry As level and we were doing some revision, and covering organic salts e.g. sodium ethanoate, sodium benzoate etc.
these compounds are ionic, which got me wondering, what do you get if you electrolyse these. my chemistry teacher didn't know, i was wondering if there was a general rule,
e.g. sodium benzoate ==> Na+ and C6H5O-
which then goes to phenol and sodium hydroxide.
any ideas

[John Ashcroft]

Electrolysis of carboxylic acid salts induces decarboxylation. For example, electrolysis of sodium benzoate solution should yield biphenyl and some phenol.

[kingspaz]

thanks john, thats pretty interesting.

[jfk]

yes but then youn have to seperate the biphenyl and the phenol, right?

any ideas?

[zeocrash]

isn't there any way to either break down biphenyl to phenol or to turn phenols into biphenyl.

[John Ashcroft]

Nothing realistic.

[zeocrash]

looking at the merck index it looks like it should be easy to separate the 2. biphenyl is insoluable in water, whereas phenol is not.

[Marvin]

Its called Kolbe electrolysis. You form radicals at the electrode which decarboxylate, and then typically dimerise as John has said. Acetic acid would form CH3COO*, losing CO2 to produce methyl radicals, CH3*, which would become ethane gas. Benzoates should form phenyl radicals C6H5* which should mostly react with themselves to form biphenyl basically 2 benzene rings linked together. Butanoic acid would produce CH3CH2CH2* radicals reacting to hexane. Its been used a lot to make long chain alkanes.

Phenol is a weak acid, it will dissolve in aq sodium hydroxide, and be ppt by HCl. Sodium carbonate wont work.

Edited for apalling grammer and content.

[inFinie]

I think that's wrong.
If you electrolyse C6H5ONa solution you will get H2 and O2 because electronegativity(positivity for positive valences) of them are greater than C6H5O- and Na+ .

Kolbe electrolytic reaction(it says like that):
a process for preparing alkanes by electrolysis of Na salts of carboxylic acids. The carboxylic group must be at the end of a carbon chain. A cold concentrated solution of a salt is electrolyzed using Pt electrodes.

[Marvin]

Good point.

We arnt electrolysing sodium phenate however as sodium benzoate. Both these compounds have highly stabilised anions, its possible they might object rather more to being oxidised than alkyl carboxylic acids. Its also possible the ring structure resonance might stabilise the radical and provide a lower yeild of decarboylated products. Lowest redox potential reactions arnt the only reactions that happen in a normal electrolysis, it only means there is a cell voltage below which they are the only ones happening. In order to get a decent current, the cell voltage is usually lot higher and the lowest potential reaction doesnt even have to be the dominant reaction. If you electrolyse a solution of sodium chloride you dont just get oxygen or chlorine, you get both. Cell voltage, concentrations, and electrode overpotentials for each reaction make big differences.

Its quite possible these effects would vastly reduce the amount of biphenyl and phenol produced in the reaction current wise, it might also introduce a lot of unwanted side products. Biphenyl is usually thought of as the wurtz side product in phenyl grignard reactions, and got rid of as it has no real value. I cant see this as being a useful method for phenol production either, even if production was quantative as there are easier ways.

[inFinie]

In the first post it says C6H5O- and i tricked :mad:

[yt2095]

Has anyone tried to electrolyse Hexamine?
I`m about to start sometime today, and wondered if anyone else had tried this and maybe we could compare results?
also, does any have any predictions as to what may or maynot be produced as a result?
my Organic chemistry isn`t particularly brilliant, but my GUESS would be the liberation of Ammonia gas probably leaving Formalin.
any input?

Additional: it`s been running now for about an hour, I started at 4.5v, hardly a fizz, I`ve now stepped it up to max of 36V, a little more fizz but nothing noteworthy, Cathode is Stainless steel, Anode a Carbon rod.
here`s a rough pic as it is at the moment;
http://www.yt2095.net/tests/hmtaelec.jpg
the PSU is homemade from an old CB powerpack, hence the voltage control in the middle, you may also be able to make out the Hexamine box.