Sciencemadness Discussion Board

Tetramethylorthosilicate synthesis

Hexavalent - 2-4-2012 at 14:23

Can anybody suggest a viable synthesis route for tetramethyl orthosilicate? I was thinking something along the lines of some kind of esterification perhaps between an isomer of silic acid or maybe even a silicate salt and methanol. . .although I'm probably wrong.

Structure of the compound, for reference;






I need it for trying out some organic synthesis, as Si(OCH3)4 can been used to convert ketones and aldehydes to the corresponding ketals and acetals, respectively. It is also a nice precursor to silica aerogel, another geeky curiosity:)

[Edited on 2-4-2012 by Hexavalent]

DJF90 - 2-4-2012 at 22:22

You'll probably need to go via silicon tetrachloride, not something I suggest you be handling. Acetal formation can be had many other ways, much simpler ways, without the need for such a reagent. Carbon based orthoesters are more "usual" in this respect, and are easier to form, but oftentimes you can get away with just reacting the carbonyl with the respective alcohol in the presence of an acid catalyst (TsOH works nicely). This is particularly the case for dioxolane formation (where alcohol is ethylene glycol) using toluene as solvent in a dean stark apparatus. Bear in mind that acetal formation is an equilibrium process, and water must be removed by some mechanism (azeotropic distillation as with toluene, will work with methanol also; chemical removal, eg using orthoesters of carbon like trimethyl orthoacetate; removal with a dessicant e.g. magnesium sulfate) for the acetal formation to go forward.

[Edited on 3-4-2012 by DJF90]

chemx01 - 3-4-2012 at 22:47

I think that the best option would be using SiCl4 and corresponding alcohol. The problem in this reaction is that the formed HCl attacks the alcohols forming water and alkylchloride and the water yields SiO2 mess which will lower the yield and also make the cleaning of the reaction flask very tedious process.

I think that the best option and the highest yeilding one would be using sodium alkoxide and SiCl4, but I haven't found references of anyone making it this way, but I found references of using alcohol and SiCl4 but the yields were around 70-80%.

DJF90 - 5-4-2012 at 11:33

The reaction using SiCl4 and alcohol will likely employ triethylamine or similar to neutralise the HCl as its formed. Again, I suggest the preparation of triethylformate as per OrgSyn (take care with sodium and chlorinated hydrocarbons) as this reagent will form ethyl acetals easily with acid catalysis, but there are almost always more than one way to skin a cat.

Hexavalent - 7-4-2012 at 07:50

Thanks for your suggestions everyone. Unfortunately, I have no access to SiCl4 ATM, so I may have to look at purchasing some of it or indeed the full the target compound.

kristofvagyok - 8-4-2012 at 04:31

Long ago I had a friend who wanted to make tetraethyl-ortosilicate as a precusor for aerogel. The project was unsuccesful, because he couldn't make inert atmosphere for silicon tetrachloride and the project failed.

A few month ago I needed some of the title compound (Si(OEt)4) and I planned to make it and looked for some recipes. The first was the usual SiCl4 and alcohol, but in the end I would have needed 1liters of it, so I have chosen to order it from Sigma-Aldrich, it wasn't so expensive that I thought... And didn't had to mess with SiCl4 what is not a really friendly substance.

But when I planned to make it, I have found some recipes what looked much more friendly like the SiCl4 and alcohol, here are them:

The fist and the most "OTC" from FR961808
Quote:

Exemple 1. -- On ajoute lentement, et pendant une période de 2 heures. 130 grammes de siliciure de magnésium à 1500 cm de méthanol anhydre, dans un ballon de 3 litres comportant un condenseur à reflux. Les gaz qui s'échappent passent à travers un condenseur refroidi par de l'air liquide et sont mesurés par un compteur à gaz humide. Une grande quantité de chaleur apparaît et il est nécessaire de refroidir le ballon avec de la glace. On obtient 4 molécules d'hydrogène par molécule de siliciure de Mg. En fin de réaction, on obtient par distillation 110 grammes de silicate de méthyle.


My fast translation looks like this:
130g of magnesium silicide (Mg2Si, made easily from SiO2 and Mg reaction). mixed with 1500cm3 abs. methanol in a 2500cm3 round bottomed flask, equipped with a magnetic stirrer, a reflux condenser and a drying tube. It should be stirred there for 3 hours with strong cooling (ice-salt bath), because the reaction is really exothermic.
A lot of hydrogen will come out (4moles).

The resulting mixture should be distilled to get back the excess methanol and the next fraction the Si(OMe)4. The Mg(OMe) will be lest at the bottom of the flask.

Yield: 110g.

-This method also works with ethanol and other types of alcohols.

Another method could be done with SiS2 and methanol. Here the H2S will evolve and come out from the mix, it will be really-really smelly, so this method is not preferred :D

[Edited on 8-4-2012 by kristofvagyok]