The crossed aldol condensation of acetalaldehyde with benzaledye isaided by the fact that bezaldehyde bears no alpha protons. However,a possible comeptitive reaction is the "self condesnation" of two molecules of acetaldehyde. Slow addition of the acetaldehgyde to abenzaladehyde solution contain an NaOH/ethanol/water mixture will often result in less self condesnation. Explain.