Kinetics and mechanisms of 1,5-dihydroflavin reduction of carbonyl compounds and flavin oxidation of alcohols. III. Oxidation of benzoin by flavin and reduction of benzil by 1,5-dihydroflavin

Journal Article · Tue Nov 23 23:00:00 EST 1976 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00440a051· OSTI ID:7317564

Bruice, T C; Taulane, J P

The oxidation of benzoin by lumiflavin-3-acetic acid (Fl/sub ox/) to provide benzil and 1,5-dihydrolumiflavin-3-acetic acid (FlH/sub 2/) is a readily reversible reaction. It has been established that the mechanism involves general base ionization of benzoin carbon acid (..cap alpha..-ketol) to yield endiolate anion, followed by partitioning of the endiolate anion back to benzoin through general acid proton donation and to benzil by reaction with Fl/sub ox/. The reaction of endiolate anion with Fl/sub ox/ is not subject to acid or base catalysis. Evidence that ionization of benzoin precedes its oxidation by Fl/sub ox/ stems from the observation that the rate attributed to the latter process possesses a constant equal to that for racemization of (+)-benzoin and O/sub 2/ oxidation of benzoin and that this rate constant is characterized by a primary deuterium kinetic isotope effect (k/sup benzoin//k/sup ..cap alpha..-/sup 2/H-benzoin/) of 7.24 +- 1.5. Reduction of benzil to benzoin by FlH/sub 2/ is pH and buffer insensitive below the pK/sub a/ of FlH/sub 2/. These results are consistent with either general acid catalyzed attack of benzoin carbanion at the 4a-position of Fl/sub ox/, followed by a specific base catalyzed collapse of adduct to diketone and dihydroflavin (Scheme III), or to the uncatalyzed reaction of carbanion (endiolate anion) with flavin to provide a semidione-flavin radical pair which then goes on to diketone and dihydroflavin in a non-acid-base catalyzed reaction (Scheme V). These mechanisms are discussed in terms of the kinetics of reaction of other carbanion species with flavin.

• Research Organization: Univ. of California, Santa Barbara
• OSTI ID: 7317564
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 98:24; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
ALCOHOLS
ANIONS
AROMATICS
CARBON COMPOUNDS
CHARGED PARTICLES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DEUTERIUM
HETEROCYCLIC COMPOUNDS
HYDROGEN ISOTOPES
HYDROXY COMPOUNDS
IONS
ISOALLOXAZINES
ISOTOPE EFFECTS
ISOTOPES
KETONES
KINETICS
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OXIDATION
RACEMIZATION
REACTION KINETICS
REDUCTION
STABLE ISOTOPES