[bioe419]

I am having trouble being able to predict whether benzoin condensation would work with reactants other than benzaldehyde, namely 4-tolualdehyde, 4-trifluoromethylbenzaldehyde, and 4-N-ethylaminobenzaldehyde.  I know that the benzoin condensation is a coupling reaction between two aldehydes to form α-hydroxyketones, and the mechanism makes sense with benzaldehyde is the reactant.  Must the α-hydroxyketone be benzoin?  If not, I would predict that benzoin condensation would occur with 4-tolualdehyde, but I am unsure about 4-trifluoromethylbenzaldehyde, and 4-N-ethylaminobenzaldehyde.

Thank you for any assistance.

[sjb]

As far as I know, the benzoin condensation does not just make benzoin - the ArCHO does not have to be benzaldehyde if you see what I mean. However, other reactions may also be going on the pot as well. So in my opinion 4-tolualdehyde, 4-trifluoromethylbenzaldehyde would probably also react in a similar fashion, but I'm not sure about 4-N-ethylaminobenzaldehyde - assuming I've converted name to structure correctly there may be issues with enamine formation as a side reaction..?

[agrobert]

If your benzoin condensations are not working with NaCN, try thiamine hydrochloride activated by NaOH.