First of all, the semi-acetal (ketone) reaction takes aldehyde (ketone) and alcohol as raw materials. Aldehyde condensation reaction takes one molecule of aldehyde (ketone) containing α-hydrogen and one molecule of aldehyde (ketone) without α-hydrogen as substrates. It is necessary to distinguish between these two reactions.

The first reaction mechanism is aldol condensation, and the product is (hoch2) 3-c-CHO;

In the second step, the reaction mechanism is that (HOCH2)3-C-CHO is rearranged in alkaline environment to generate carboanion (HOCH2)2-C*-CO-CH2OH, which is condensed with formaldehyde aldehyde to obtain (HOCH2)3-C-CO-CH2OH.