MECHANISTIC STUDY OF THE ALDOL CONDENSATION OCCURING IN THE ALKALINE SOLUTION OF 3-HYDROXY 2-OXO PROPRANOATE (Β HYDROXYPYRUVATE)

Article abstract of DOI:10.1016/S0040-4020(01)92421-4

With 3-bromo-2-oxopropanoate (β bromopyruvate) and its ethyl ester, the ionisation of the gemdiol of the hydrated form BrCH2-C(OH)2-COOR 1 initiates the elimination of the bromide anion yielding 3-hydroxy-2-oxopropanoate 2 (β-hydroxypyruvate).The mechanism of the reaction was investigated essentially by polarography in aqueous solution.In neutral ( and acid) media, the polarographic behaviour of 2 resembled that of other α-ketoacids: reduction at the mercury electrode yielded glycerate.In alkaline media, there was evidence of the carbanion enolate .3'.The overall rate constant was determined according to a kinetic law of the type: : found k = 1.56 min^-1 in NaOH 0.5N at 25 deg.In the pH range 10.5 to 11.5, 3' existed in minor amounts and initiated a slow aldol codensation with the tautomer 3-oxo-2-hydroxypropanoate 4 (tartrone semialdehyde) according to a kinetic low of the type found at 25 deg., at pH 11.0.The aldol product was isolated as a sodium salt and its structure established by 13CNMR.