PHOTOFRAGMENTATION OF α‐OXOCARBOXYLIC ACIDS IN AQUEOUS SOLUTION. AN EPR STUDY. FORMATION OF SEMIDIONE RADICALS BY DECARBOXYLATIVE SUBSTITUTION OF α‐OXOCARBOXYLIC ACIDS BY ACYL RADICALS–II. OXALOACETIC ACID (OXOSUCCINIC ACID)*

Abstract— –On in situ photolysis (Λ= 250–400 nm) of aqueous oxaloacetic acid solutions, between pH 5 and 10, the radicals ‐O2CCH2C(O‐>=C(O+)CH2CO2‐ and ‐O2CCH2C(OH)CO2 are identified. With acetone present, CH2CO2, CH3C(OH)CO‐2, CH3C(O‐)=C(O)CH2CO2 and ‐O2CCHCOCO2 are also observed. CO2 and CO are identified as reaction products. The experimental results are explained in terms of α‐cleavage of the electronically excited keto‐isomer dianion of oxaloacetic acid to yield O2CCH2CO and CO2‐. ‐O2CCH2CO adds to the keto‐isomer of oxaloacetic acid and to pyruvic acid, which is formed from oxaloacetic acid by thermal decarboxylation, to yield ‐O2CCH2C(O‐)= C(O‐)CH2C0‐ and CH3C(O‐)=C(O)CH2CO‐2, respectively, via a decarboxylase substitution reaction. CH2CO2 is derived from ‐O2CCH2CO by decarbonylation. CO2‐ is scavenged by oxaloacetic acid and pyruvic acid to yield O2CCH2C(OH)CO2 and CH3C(OH)CO2‐, respectively.