[Elench]

Hello chemist-buddies!

I read an article about hydrolysis and condensation of silicon alkoxides and have found many reaction mechanisms which are based on acid or base catalysts. However,  the mechanisms are still not very clear for me. I would appreciate if someone could share their knowledge with me (I am not very good in organic chemistry, always been a big challenge for me!)

.
Figure 1

In figure 1 we can see that the hydrolysis of alkoxide group will occur to produce silanols, these silanols can react with another silanol group, resulting in a silanol network which is shown in figure 2.


Figure 2

So I've found that by using an acid or base catalyst we can speed up the hydrolysis and condensation of silicone alkoxides (figure 1+2). However, I would like to know if the hydrolysis and condensation can occur without the present of catalyst, if yes: what would be the first one to make the attack? In figure 1 we see that the H2O group attacks the -OCH3 group, is this viable? And is it possible that the -OH groups of silanol  react with each other without hesitation (without catalyst also)?

I hope someone could make me more 'wiser'!

Regards,

A chemist student

[pgk]

1). Hydrolysis of silyl ethers can occur without a catalyst, if the rest of the molecule is hydrophilic, e.g. poly(ethyleneoxy)-trimethoxylsilane. But even so, their hydrolysis demands high temperatures and long reaction times.
2) A silanol can react with a silyl ether without a catalyst. But the reaction time is more than a year, at room temperature.
3). Theoretically, a silanol can react with another silanol without a catalyst. But in practice, hydrolysis doesn’t occur due to the extremely drastic conditions that are needed.
4). The mechanism's representation is wrong. This happens sometimes in polymer chemistry textbooks and more rarely, in polymer chemistry articles.
Anyway, water attacks on the silicon and methoxide is the leaving group, which further forms methanol by picking the hydrogen from the so formed, protonated silanol.
5). In a similar way, the silanol hydroxyl group attacks on the silicon atom of another silanol, forming a siloxane.

[Elench]

Hi Pgk,

It is been a while ago (better late than never they say haha), but thank you for your reply.

In the mean while, I ve found that it would be possible with transition metals as catalyst.

[pgk]

You are welcome.
Salts and organometallic compounds of transition metals, are Lewis acids and thus, they behave as acidic catalysts.