Random
International Hazard
Posts: 1018
Registered: 7-5-2010
Location: In ur closet
Member Is Offline
Mood: Energetic
|
|
Electrolysis of aqueous acetate salts
What is formed by electrolysis of aqueous acetate salts?
I read on wikipedia:
In the laboratory, ethane may be conveniently prepared by Kolbe electrolysis. In this technique, an aqueous solution of an acetate salt is
electrolysed. At the anode, acetate is oxidized to produce carbon dioxide and methyl radicals, and the highly reactive methyl radicals combine to
produce ethane.
But what is formed at another electrode?
If I perform electrolysis on sodium acetate, will naoh, ethane and hydrogen be formed?
Maybe this question is easy to answer, but please answer.
|
|
|
Paddywhacker
Hazard to Others
Posts: 478
Registered: 28-2-2009
Member Is Offline
Mood: No Mood
|
|
yes
|
|
|
woelen
Super Administrator
Posts: 7977
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
I did quite some experimenting on this kind of electrolysis and have written a web page about it. It might be an interesting read for you:
http://woelen.homescience.net/science/chem/exps/precision_el...
|
|
|
bbartlog
International Hazard
Posts: 1139
Registered: 27-8-2009
Location: Unmoored in time
Member Is Offline
Mood: No Mood
|
|
Thanks for the link, woelen. Thought I'd read through all your experiments but clearly I missed at least one.
As to the topic at hand, according to one of the books in the sciencemadness library you can also get methanol at the anode. This would be consistent
with a CH3 radical combining with an OH- ion (which woelen avoided by making sure his solutions were acidic).
|
|
|
not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
Member Is Offline
Mood: No Mood
|
|
The production of the corresponding one less carbon alcohol is often referred to as a non-Kolbe or Hofer-Moest reaction.
The Kolbe reaction is favored by high current densities and low temperatures, the non-Kolbe products are increased by addition of indifferent
electrolytes such as KHCO3 (0.2 M) and Na2SO4 (1+ M).
Smooth electrodes of platinum, iridium, or rhodium give the best results, graphite electrodes give little to no Kolbe product. Most other common
electrode materials, with the exception of vitreous carbon, also give poor yields.
|
|
|
chimico
Harmless
Posts: 1
Registered: 22-7-2010
Location: Italy, Palermo (sicily)
Member Is Offline
Mood: No Mood
|
|
if you use carbon as electrod the methyl radical react with water to form methanol....
(sorry for my english...i'm italian...)
|
|
|
Hoveland
Harmless
Posts: 20
Registered: 20-7-2010
Member Is Offline
Mood: No Mood
|
|
I am absolutely certain that I read in a book that the methyl radical does indeed form.
The reaction stated (if I remember correctly) was
CH2C(=O)-O-O-C(=O)CH3 --> 2CO2 + 2CH3.
Peroxy acetic acid is stable, however; I have worked with it (11% solution).
I do not know whether the 'peroxy acetic anhydride' has the ability or time enough to hydrolyze with water (forming peroxy acetic and acetic acids)
before its decomposition to any extent.
Somewhat relevant to this, I have found that a 30% solution of hydrogen peroxide becomes unstable when enough acetic anhydride is added (although
there was actually just a little concentrated HCl solution in the mixture also). On slow, gradual periodic addition of acetic anhydride, the mixture
first did nothing, then I started seeing minute bubbles rising from an insignificant scratch in the bottom of the glass beaker, then adding just a
little more Ac2O, more bubbles appeared. No more Ac2O was added, but after only two minutes the bubbling became more violent and the beaker became hot
to the touch; eventually "steam" started coming out and a little bit of solution spilled over, even though the beaker was not initially filled even
half way. Methyl radicals may have been transiently produced in this reaction.
|
|
|
DJF90
International Hazard
Posts: 2266
Registered: 15-12-2007
Location: At the bench
Member Is Offline
Mood: No Mood
|
|
Diacetyl peroxide does indeed fragment to give methyl radicals. The process occurs in two steps:
CH3C(O)-O-O-(O)CCH3 => 2CH3C(O)-O* => 2CH3* + 2CO2
What does this have to do with Kolbe electrolysis of acetate though?
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
