The crossed aldol condensation of acetaldehyde with benzaldehyde is aided by the fact that benzaldehyde bears no alpha-proton.

The crossed aldol condensation of acetaldehyde with benzaldehyde is aided by the fact that benzaldehyde bears no alpha-proton. However, a possible competitive reaction is the “self-condensation” of two molecules of acetaldehyde. Slow addition of the acetaldehyde to a benzaldehyde solution containing an NaOH/ethanol/water mixture will often result in less self-condensation. Explain.