Krapcho decarboxylation
# Krapcho decarboxylation

The Krapcho decarboxylation is the chemical reaction of esters with halide anions. The ester must contain an electron-withdrawing group in the beta position, such as β-ketoesters, malonic esters, α-cyanoesters, or α-sulfonylesters. It works best with methyl esters, since methyl groups are more susceptible to $S_N2-reaction$ than are larger alkyl ester substituents, such as ethyl or propyl groups. The byproducts of this decarbomethoxylation are chloromethane and $CO_2.$ They are lost as gases, which helps drive the reaction.

The Krapcho decarboxylation is a useful way to manipulate malonic esters because it cleaves only one of the two ester groups. The apparent alternative, base hydrolysis followed by decarboxylation, requires a subsequent step to regenerate the ester.

