Oxidation of a-hydroxy acids

The oxidation of a-hydroxy acids is slow41 it has been comprehensively studied, using glycolic acid as a model.42 Three reactions have been proposed as occurring. 

Steric effects dominate in the oxidation of dialkyl, alkyl phenyl and benzal methyl phenyl sulfides to their sulfoxides by quinolinium fluorochromate (QFC) in aqueous acetic acid. QFC oxidation of phenoxyacetic acids has been smdied. Imidazolium dichromate oxidations of a-hydroxy acids have been smdied. ... 

The oxidation of a-hydroxy acids by benzyltrimethylammonium tribromide (BTMAB) to the corresponding carbonyl compounds shows a substantial solvent isotope effect, A (H20)/A (D20) = 3.57, but no KIE for a-deuteromandelic acid.133 The oxidation of glucose by hypobromous acid is first order in glucose and the acid.134 [l,l-2H2]Ethanol shows a substantial kinetic isotope effect when oxidized by hexamethylenetetramine-bromine (HABR) in acetic acid to aldehyde.135 Kinetics of the oxidation of aliphatic aldehydes by hexamethylenetetramine-bromine have been studied by the same group.136 Dioxoane dibromide oxidizes y-tocopherol to 5-bromomethyl-y-tocopherylquinone, which spontaneously cyclizes to 5-formyl-y-tocopherol.137... 

The oxidation of a-hydroxy acids by hexamethylenetetramine-bromine (HABR) is first order with respect to each of the hydroxy acids and HABR. The oxidation of o -deuteriomandelic acid exhibited a kinetic isotope effect of kn/ko = 5.91 at 298 K. The rates of oxidation of the substituted mandelic acids show excellent correlation with Brown s er+ values with negative reaction constants. A mechanism involving transfer of a hydride ion from the acid to the oxidant has been postulated.128... 

Fi>2 is a member of a family of homologous flavoproteins that catalyze the oxidation of a-hydroxy acids. It is located in the intermembrane space of yeast mitochondria and provides pyruvate for the Krebs cycle as well as participates in a short electron-transfer chain involving cytochrome c and cytochrome oxidase, making it an important respiratory enzyme. Unlike many other flavoproteins that oxidize a-hydroxy acids, F 2 has very poor reactivity toward oxygen. Fi>2 is a homotetramer with each monomer containing both an FMN and a heme The catalytic cycle has five redox steps (Scheme 7). In the first step, lactate is oxidized to... 

Clagett et oi. (1949) in a study of the oxidation of a-hydroxy acid by enzymes obtained from the leaves of soybean, tomato, and potato plants found the presence of an enzyme capable of oxidizing both lactic and glycolic acids. This enzyme was not activated by ascorbic acid in fact, with glycolic acid the oxidation was somewhat inhibited. 

Oxidation of a-hydroxy acids with hydrogen peroxide and ferrous salts (Fenton s reagent) to a-keto acids or of 1,2-glycols to hydro aldehydes ... 

Waters 25S) suggests that the neutral hydroxyl radicals are the catalysts in ferrous ion - catalyzed oxidations of a-hydroxy acids to 2-keto acids ... 

The MCC oxidation of substituted anilines in ACOH-H2O to corresponding azobenzenes is fractional order in substrates and H+ ions. The rates are retarded by electron-withdrawing substituents and enhanced by electron-releasing substituents. The PPCC oxidation of a-hydroxy acids in the same solvent is fractional order in H" " ion and the rates increase with decrease in dielectric constant. The order of the reactivity is mandelic > lactic > glycolic acid. ... 

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