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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‐I: GLYOXYLIC, PYRUVIC, α‐OXOBUTYRIC, α‐OXOGLUTARIC AND α‐OXOISOCAPROlC ACIDS
Author(s) -
Steenken S.,
Sprague E. D.,
SchulteFrohlinde D.
Publication year - 1975
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1975.tb06715.x
Subject(s) - chemistry , radical , decarboxylation , electron paramagnetic resonance , aqueous solution , medicinal chemistry , adduct , photodissociation , photochemistry , yield (engineering) , organic chemistry , catalysis , physics , materials science , nuclear magnetic resonance , metallurgy
— By means of in situ photolysis EPR of aqueous solutions of α‐oxocarboxylic acids (RCO‐CO 2 H) at pH values above 5, semidione radical anions [RC(O ‐ )=C(O‘)R] and α‐hydroxy‐α‐carboxy alkyl radicals [RC(OH)CO 2 ‐] were detected. C0 2 was identified as a reaction product. On photolysis of mixtures of α‐oxocarboxylic acids (RCOCO 2 H and R'COCC 2 H), “mixed” semidione radical anions [RC(O ‐ >=C(O)R’] were observed in addition to RC(O ‐ )=C(O‘)R, R'C(O ‐ )=C(O’)R‘, RC(OH)CO 2 ‐ and R'C(OH)CO 2 ‐ . The experimental results are explained in terms of photodecarboxylation (α‐clea‐vage) of electronically excited RCOCOJ to yield RCO and CO 2 . The radicals RC(OH)CO 2 ‐ are formed by reduction of RCOCO 2 ‐ by CO 2 ‐ . The semidione radicals are produced by addition of RCO to RCOCO 2 ‐ followed by decarboxylation of the intermediate adduct. This mechanism was confirmed by generating acyl radicals independently and reacting them with α‐oxocarboxylic acids. Selected product studies support the mechanism suggested.