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 · Wed Nov 24 00:00:00 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), Vol. 98:24
• Country of Publication: United States
• Language: English

Related Subjects

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