A polarographic study of the reduction of unsymmetrical benzils.

[摘要] This investigation applied the techniques of polarography and controlledpotential electrolytic reduction to the study of a series of unsymmetrical benzils.Eleven unsymmetrical benzils were synthesized and studied in 50% ethanol-water(by volume) solvent systems buffered at pH 1, 5, and 13. The results showed that,with unsymmetrical benzils substituted with electron-withdrawing or electrondonatinggroups, the carbonyl closest to the ring with the least electron-donatingpower was the preferred reaction site. However, the dicarbonyl system was neverthelessreduced as a unit, and Hammett sigma values of disubstituted symmetricalbenzils were approximately additive. This was ascertained by comparing the easeof reduction of eight unsymmetrical benzils to the ease of reduction of the correspondingdisubstituted symmetrical benzils. It was proposed that the electronswere added to the oxygen of one carbonyl, and that the second carbonyl was involvedin the reduction chiefly through complete polarization of the dicarbonyl systemat the electrode.In general, the reduction of unsymmetrical benzils appeared to follow thesame path previously reported for symmetrical benzils.

[发布机构] University:Georgia Institute of Technology;Department:Institute of Paper Science and Technology

[效力级别] Benzils

[关键词] Polarography;Benzils;Benzoin;Isomers;Electrolytic reduction;Carbonyls