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Dave Angel
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Re: Sodium acetate in methanol
Today I have been electrolysing a saturated solution of sodium acetate in methanol. I used a computer PSU's 5.5 V line which managed to get a
current of between 300 and 400 mA flowing, the current increasing as the electrolysis proceeded. I didn't use a salt bridge for this - it was
done in a single pyrex bowl with the cathode (copper) and the anode (graphite) as close together as possible. The 'apparatus' was lightly
covered in clingfilm to limit evaporative losses of the alcohol although ingress of moisture wasn't prevented with this set up. The current was
passed and plenty of bubbling was observed on the cathode, much less so at the anode as it's quite a hunk of graphite (a crucible) with large
surface area.
After ca. 4 hours I came back to the set up and found that there was a good deal of white precipitate in the bowl, with no appreciable difference in
level of methanol. This could of course be due to displacement of the remaining methanol by the precipitate as it forms... or something else. So, I
added some straight methanol to the bowl and dissolved up most of the precipitate, allowing the solution to remain saturated. Checking the pH of the
initial solution against this with universal indicator solution showed that the solution which had undergone electrolysis had a higher pH than it
started off with.
Another 5 hours or so and yet more precipitate! The solution was filtered and pH of both filtrate and a saturated solution of the precipitate in
methanol were checked, although the precipitate was still quite wet and the tests both gave a similar result to the previous one - both solutions had
higher pHs than saturated sodium acetate solution, so some more accurate work is needed.
I hope that Tacho is right and that NaOMe is being produced! 
What's next? I'm building a new set of electrodes which will be separated by 2-3 mm. The set up will likely a 2L 3-neck rb flask fitted with
a condenser and drying tube, the electrodes and a stopper in the final neck. Stirring is probably a good idea to prevent build up of precipitate in
any one place, especially around the electrodes and one could even heat the flask if desired.
With any luck, fractional crystallisation could be used to separate the product(s) from the acetate.
I also should note that initial tests using a copper anode produced less than satisfactory results. Whilst there is a build up of blackness on the
cathode over time which does not affect operation, a copper anode quickly becomes covered in a green layer which prevents any current flowing.
Graphite seems to be doing a good job for now.
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a123x
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Sodium amalgam to make sodium methoxide. I recently read that sodium amalgam can be produced by electrolyzing a solution of sodium chloride, sodium
hydroxide, and I would assume sodium acetate with a mercury cathode. Rather than release hydrogen, it forms the amalgam. I figure that this might
allow for rather convenient production of sodium alkoxides by simply electrolyzing a solution of sodium acetate in an anhydrous alcohol using a
mercury cathode. This will form the amalgam which, when the current is stopped, will react with the alcohol to form the alkoxide. Thus, with a small
amount of mercury, one could make very large amounts of sodium methoxide since the mercury is recycleable in the process. Too bad mercury is
toxic(although I imagine it shouldn't contaminate the methoxide much). I know molten gallium and liquid gallium/indium/tin alloys can dissolve
aluminum to make a substance similar to aluminum amalgam and should be able to dissolve sodium but the thing I wonder is whether gallium can be used
as a cathode to form such an alloy starting with a solution of sodium salt. I realize that gallium is fairly pricy but only a small amount is needed
and I tend to prefer pricy to toxic, even if the toxicity is generally exagerated.
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BromicAcid
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A decent idea that has been discussed before, the major hurdle being that the solid amalgam formed only contains a few precent of sodium and therefore
this process would have to be repeated many times before any major results were obtained, not to mention drying the amalgam before reacting with
methanol otherwise adhering water would decompose the methoxide and additionally it takes some time for these alloys to react entirely with methanol.
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a123x
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I was actually thinking along the lines of making the sodium amalgam in a methanol solution and then just stopping the current to allow it to react.
Also, one of the main uses for methoxides is in nucleophillic substitutions with halogen groups on aromatic rings. So, I had a thought. Rather than
make a duel chamber electrolytic cell with a salt bridge to use in making methoxide directly by an electric current(as opposed to the indirect method
of making the amalgam and reacting with methanol), why not have a single chamber which results in the methoxide being reacted before it can reach the
anode and be oxidized. For example, have a cell containing sodium acetate in methanol and also bromovanillin/bromoanisaldehyde/some other
bromoaromatic dissolved in the methanol. Include a bit of copper powder as the catalyst. It'll need to be heated to fairly high temperatures as
well and have a reflux condensor. The methoxide is formed at the cathode and reacts with the bromoaromatic rather than being oxidized at the anode. I
assume that some will reach the anode and some will react with the bromoaromatic to form NaBr(which I'm guessing is insoluble in methanol, if it
is soluble than there are issues with Br2 forming). If NaBr is soluble then a duel chamber cell might be used with one containing a bromoaromatic and
the other containing the initial aromatic which will react with bromine formed to give the bromoaromatic. I figure if built properly it would
ultimately give a low maintanence cell which would need little more than a fresh supply of methanol, aromatic, and electricity to produce methoxylated
aromatics.
Now, I'm sure there's something wrong with this idea so feel free to let me know what it is.
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jarynth
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After reading the thread about Na production by Castner cell, I succeeded in electrolyzing NaOH with a Ni welding electrode as the anode. The main
obstacle that remains is the removal of liquid Na above the cathode during the process. Instead, the Na/NaOH solution was simply allowed to solidify.
The presence of sodium metal was confirmed by the observation of small yellow burning and fuming beads on contact with water.
Now, the analogous reaction with anhydrous MeOH (or EtOH, etc) would yield NaOEt (which dissolves) contaminated with NaOH (less soluble in the
anhydous alcohol).
This procedure involves one simple electrolysis step, anhydrous alcohol and a means to separate NaOH and the alkoxide from the alcohol, thus should
prove no harder than the alternatives presented above. The question remains, how to separate the sodium compounds and store the purified alkoxide.
@a123x: what happens at the cathode is always nice and smooth, but to skip an accurate analysis of the anodic processes would be unforgivable. With
halogenated benzenes you'd get biphenyls and whatnot at the cathode: polymeric mess. Plus, methoxylations are more successfully carried out in weakly
ionizing solvents, so you'd get only a tiny current flowing. Most importantly, the NaOAc is a weak base and will probably cleave the halogen before
you even reach reflux (but we'll need an expert opinion on this). The number of electrolysis products increases exponentially with the number of
species in your flask. The reaction won't be as clean as you purport.
[Edited on 4-9-2008 by jarynth]
[Edited on 4-9-2008 by jarynth]
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