The second decarboxylation of malonic acid in aldol condensation

4-Hydroxybenzaldehyde and 4-hydroxy-3-methoxybenzaldehyde will be turned into 4-hydroxybenzene and 4-hydroxy-3-methyoxybenzene when they react with malonic acid througth decarboxylation of two times.This is a novel method to form 4-hydroxybenzene.However,3-hydroxybenzaldehyde and other similar compounds can't decarboxylate in their second step.The electric effection in this reaction is discussed.