Sciencemadness Discussion Board - Alkoxide salts

Alkoxide salts

cnidocyte - 3-1-2011 at 14:25

I have a bit of an obsession with alkoxide salts. So little is written about them, they're pretty mysterious to me. All I know is they're very strong bases. Anyone here have experience with making alkali metal alkoxide salts by reacting pure a pure alkali metal with the alcohol? I have some pure Li and some 2-propanol so I want to make some lithium 2-propoxide. I can't really find any information on this class of reactions, I assume reacting Li with an alcohol is gonna be highly exothermic and more violent than Li + H2O reaction. Are there any other dangers I should know about before attempting this?

DJF90 - 3-1-2011 at 14:47

Alkali metals react less violently with alcohols than they do with water. Ethanol dissolves sodium fairly slowly in my experience and if I recall correctly reflux is even advised when doing the reaction on a preparative scale. longer chain alcohols react even more slowly (2-propanol is advised for primary quenching potassium residues, as is t-butanol). The reaction of lithium metal with 2-propanol is a relatively safe reaction I'd expect. Just be careful with open flames as the alcohol is flammable (compared to the reaction of Li with water) and you should have no issues.

turd - 3-1-2011 at 14:54

Quote: Originally posted by cnidocyte

I have a bit of an obsession with alkoxide salts. So little is written about them, they're pretty mysterious to me.

You must be kidding!? Whole books have been devoted to the subject:
http://www.google.com/search?q=alkoxides&btnG=Search+Boo...
Alkoxide chemsitry (mostly the hydrolysis thereof) is THE thing in materials chemistry which in turn is super-hyped. There is NO shortage of info on the subject.

ScienceSquirrel - 3-1-2011 at 16:04

Alkali metal alkoxides eg sodium methoxide, potassium t-butoxide, etc are widely used as bases or reagents in organic chemistry.
They are available off the shelf and are also often prepared in situ from the alcohol and the alkali metal.
The metal reacts a lot slower with the alcohol than with water. The solutions are strongly corrosive but compared with most things in the lab pretty harmless.

Sedit - 3-1-2011 at 16:10

Lithium in my experiance reacts rather slowly with IpOH and EtOH. It will slowly bubble as its consumed and the surface of the lithium will take on a bluish color simular to the color of the background on this forum. Atlest that is my experience with the Lithium obtained from batteries.

mnick12 - 3-1-2011 at 17:35

I prepared some lithium methoxide a while ago from lithium foil (the stuff from batteries) and pretty dry methanol, the reaction was quite exothermic and lithium dissolved rather quickly. But it is quite easy to keep under control as long as you dont add to much at one time.

dann2 - 3-1-2011 at 17:39

Attached is some info. from Kirk Othmer on Alkoxides.

Anyone know how to make a Bismuth containing Alkoxide?

Cheers,
Dann2

Attachment: alkoxides.pdf (174kB)
This file has been downloaded 1168 times

turd - 4-1-2011 at 00:32

http://www.lmgtfy.com/?q=bismuth+alkoxides

vulture - 4-1-2011 at 14:07

Sodium metal takes quite a few days to dissolve complete in MeOH and Na/K alloy reacts only very slowly with t-butanol. Reaction with isopropanol is faster, but still nothing compared to the reaction with water.

Fleaker - 4-1-2011 at 16:56

Seriously vulture? I suppose this is true if you throw a large brick of sodium into a small volume of methanol, but my personal experience is vastly different.

I had a research project long ago that required me to make a lot sodium methoxide for transesterification. We were using BF3 but it wasn't working too well. Sodium dissolves very rapidly with methanol in my experience. In a liter of MeOH reaction, the first 20 or so grams goes quick--and it is vigorous, enough to boil the alcohol so a reflux condenser is needed. As the solution gets cloudier and cloudier the sodium won't dissolve as well. No heat is needed, even towards the end and because there was so much methoxide in the methanol, the bp was elevated and the flask far too hot to touch!

ScienceSquirrel - 4-1-2011 at 17:11

I made a few benzyl ethers by the Williamson synthesis at one stage and I found that sodium would react quite quickly and smoothly with methanol and ethanol if plenty of the alcohol was present.
Reaction with the benzyl halide was also very fast and yields of the ether were near quantitative.

cnidocyte - 6-1-2011 at 10:38

Quote: Originally posted by DJF90

Alkali metals react less violently with alcohols than they do with water. Ethanol dissolves sodium fairly slowly in my experience and if I recall correctly reflux is even advised when doing the reaction on a preparative scale. longer chain alcohols react even more slowly (2-propanol is advised for primary quenching potassium residues, as is t-butanol). The reaction of lithium metal with 2-propanol is a relatively safe reaction I'd expect. Just be careful with open flames as the alcohol is flammable (compared to the reaction of Li with water) and you should have no issues.

Thanks. All my lithium has been tarnished by oxygen, would I need to remove the Li2O layer first?

Quote: Originally posted by turd

I stand corrected.

Sciocrat - 6-1-2011 at 10:56

I am also interested in alkoxides - mainly in lithium ethoxide, which I will probably synthesize soon. However, I have been looking for info regarding the solubility of the mentioned compound, and found only a value of 12.5 grams per 100 ml of ethanol. Does the solubility rise considerably upon heating?