Organic chemists: Why ethanol instead of methanol?

Question

Hi. I'm going to do some experiments to synthesize some silica particles and I'm using tetra-ethyl-ortho-silicate (TEOS), ammonia solution and ethanol as a catalyst. I've been asked why I would use ethanol instead of methanol. Being an inorganic chemist myself, I've no idea. Any suggestions?

Answer 1

There are several possibilities.

The TEOS solubility in water is negligible. It is not much better in methanol, but it does adhere to the ethyl group of ethanol to some degree.

The boil point of ethanol is 78.4 degrees C, which is higher than the boiling point of methanol (at 64.7 degrees). This might be a factor.

The last has to do with the physical size and role of the alcohol as a catalyst. Methanol is smaller and may not have the correct geometry.

I totally agree with the suggestion to experiment, using the same molar quantities for methanol and ethanol. You might also want to try n-propyl alcohol to give additional data.

By the way, chemistry being what it is, you might try searching for additional answers using an alternate name for the TEOS. It is also called Tetraethoxysilane.

Answer 2

If you used methanol as a solvent the TEOS would rapidly undergo solvent exchange with the methanol and you would be working with Tetra Methyl Ortho Silicate instead.

In general the shorter alcohols bound to the silicon lead to increased reactivity as they are more rapidly exchanged or removed to allow hydrolisation reactions and condensation reactions to silica. If you want to form ordered silica particles these reactions need to be controled with reaction conditions. Exclusion of water and addition of acid are effective methods.

I strongly recommend the book "Sol-Gel Science - The Physics and Chemistry of Sol-Gel Processing" by C.J. Brinker and G.W. Scherer for more information on the reactions occurring (Academic Press; ISBN 0-12-134970-5)

Answer 3

TEOS hydrolyzes readily in water to give silica and ethanol...
Si(OCH2CH3)4 + 4H2O ---> 4CH3CH2OH + [Si(OH)4] ---> SiO2 + 2H2O

So ethanol offers a neater, non-competitive reaction than methanol...and TEOS is more soluble in ethanol.

Moreover, methanol is toxic...why expose yourself to it?

Answer 4

i would say that ethanol has 2 carbons which inturn would make it easier to absorb the compound but it would need to be treated to be used as a cataylst as it is very stable.

Answer 5

More non-polar than methanol

Answer 6

Try both and see which gives a better yield.

Answer 7

b'coz....ethanol is ethyl alcohol...methanol is methyl alcohol not mentos...all the carbon compounds 2gether created car-boon
da who would even answer your question???