The synthesis of trichloroacetaldehyde with water has a low yield.?

Question

Explain why the synthesis proposed would have a low yield and suggest how the synthesis should be SLIGHTLY altered to increase the yield.

Trichloroacetaldehyde + Water Yields Chloral Hydrate

I want to synthesize chloral hydrate and I proposed to react the trichloroacetaldehyde with water.

Answer 1

I assume you are making chloral hydrate:

Cl3CHO + H2O --> Cl3CH(OH)2

This reaction should proceed quickly with aldehydes and ketones with electron withdrawing groups in the alpha position to the carbonyl.

Again, the exact reaction conditions should be given to be able to asess what went wrong.

1) You didn't get enough of the chloral into solution - solvent change?
2) The solvent was too polar or too acidic to allow the chloral hydrate to separate? - Solvent/acid base adjusment.

Answer 2

The three Cl groups and the O are very electronegative causing the carbonyl to become slightly positive. If you add water, which is a weak nucleophile, it will attach to the carbonyl but the reaction wont go as fast as something that is a stronger nucleophile i.e. OH-. So if you increase the pH above 7 using a base to add OH- to solution, you can make the reaction go faster.

Answer 3

You haven't given enough information, but I suspect that the answer is that water is not nucleophilic enough, and the reaction requirs the addition of a bit of alkali (eg NaOH).