Knoevenagel condensation

A modified Aldol condensation in which carbanion is formed on active methylene compound. The loss of water molecule gives α, β - unsaturated dicarbonyl compound which is subjected to hydrolysis so as to form α, β - unsaturated-1,3-dicarboxylic acid. The later upon heating loses a molecule of carbon dioxide to form α, β - unsaturated carboxylic acid.