Stereochemistry of electroreductions III. Dichloromaleic, chloromaleic, dichlorofumaric and chlorofumaric acids

Abstract

The polarographic behavior of dichloromaleic acid, chloromaleic acid, dichlorofumaric acid and chlorofumaric acid has been investigated over a wide range of pH. In strong acid, chloromaleic and chlorofumaric acids are reduced in a 2-electron process to give chlorosuccinic acid as the product. The dichloromaleic and dichlorofumaric acids are reduced in two 2-electron steps to give a mixture of chloromaleic and chlorofumaric acids as intermediates which are then reduced to chlorosuccinic acid. As the pH is increased, the chloromaleic acid and chlorofumaric acid are reduced further to succinic acid; the extent of this reaction increases as the pH is increased. A mechanism is proposed to explain the experimental results which involves a potential-determining step for the reduction of the double bond, and competing processes for the addition of a proton or the elimination of a group are then suggested. In the case of the chloro-derivatives, chloride is eliminated to give chloromaleic and chlorofumaric acids. As the pH is raised, a second elimination reaction successfully competes with the protonation to give maleic or fumaric acids as intermediates and then succinic acid as the final product of reduction.