Hydride transfer reactions. A kinetic study of oxidation of 10-methyl-9-phenylacridan by some π acceptors and a one-electron oxidant

The kinetics of oxidation of 10-methyl-9-phenylacridan (1(H)) and 9-deuterio-10-methyl-9-phenylacridan (1(D)) to 10-methyl-9-phenylacridinium ion (3) by eight oxidants have been investigated. The oxidants included the π-acceptors 1,4-benzoquinone (BQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), p-bromanil (BA), p-chloranil (CA), tetracyanoethylene (TCNE), 2,3-dicyano-1,4-benzoquinone (DCBQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in acetonitrile (AN), BQ in 50:50 (v/v) AN-water, and the one-electron oxidant tris(2,2′-bipyridyl)cobalt(III), [Formula: see text] in AN. The seven π acceptors cover a 109-fold range of reactivity from BQ to DDQ and the deuterium kinetic isotope effect varies from 11.9 (BQ in AN) to 5.8 (DDQ). For π acceptors (BQ, TCNQ, CA, TCNE, and DCBQ) previously investigated with 10-methylacridan (NMA), 1(H) is less reactive than NMA by factors ranging from 9.1 (BQ) to 1.7 × 102 (TCNE). The isotope effects and relative reactivities for the π acceptor oxidations are most simply explained by a one-step hydride transfer mechanism.

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Kinetics of the reduction of 1-methylquinolinium cations by 1-benzyl-1,4-dihydronicotinamide

Canadian Journal of Chemistry ◽

10.1139/v85-107 ◽

1985 ◽

Vol 63 (3) ◽

pp. 655-662 ◽

Cited By ~ 14

Author(s):

John W. Bunting ◽

Norman P. Fitzgerald

Keyword(s):

Rate Constants ◽

Isotope Effects ◽

Hydride Transfer ◽

Second Order ◽

Hydroxide Ion ◽

Order Rate ◽

Kinetic Isotope ◽

One Step ◽

High Concentrations ◽

Kinetics Of

The reduction of a series of 3-W-1-methylquinolinium cations (1: W = H, Br, CONH2, CO2CH3, CN, NO2) by 1-benzyl-1,4-dihydronicotinamide has been investigated. In all cases the kinetically controlled product from these reactions is the appropriate 3-W-1,4-dihydro-1-methylquinoline. Only for W = Br is any significant amount of the 1,2-dihydro isomer obtained (15% in this case). This kinetic preference for C-4 attack over C-2 attack in dihydronicotinamide reductions contrasts with the kinetically preferred attack at C-2 by hydroxide ion and in borohydride reductions. Rates of reduction were measured for each 1 and also 1,2-dimethyl- and 1,4-dimethylquinolinium cations in 20% CH3CN – 80% H2O, ionic strength 1.0 at 25 °C, under pseudo-first-order conditions. Kinetic saturation due to nonproductive 1:1 complex formation was observed for several cations at high concentrations (> 0.1 M). Second-order rate constants [Formula: see text] were evaluated for each W, and also kinetic isotope effects from second-order rate constants [Formula: see text] for reduction by 1-benzyl-4,4-dideuterio-1,4-dihydronicotinamide. Second-order rate constants are correlated with σp− for W with ρ = 4.5, and are also closely correlated with [Formula: see text] for pseudobase formation at C-4 of these quinolinium cations by: [Formula: see text]. Values of [Formula: see text] vs. [Formula: see text] describe a Westheimer curve reaching a maximum of 5.8 for W = Br and falling to 1.5 for W = NO2 and 4.2 for W = H. These data are consistent with an intrinsic barrier of 2.9 ± 0.5 kcal/mol for hydride transfer between this 1,4-dihydronicotinamide and quinolinium cations. However, quinolinium cations display a dramatically enhanced rate of dihydronicotinamide reduction relative to hydroxide ion attack when compared with isoquinolinium cations. This observation, and the predominance of C-4 rather than C-2 reduction, suggests that these reactions may not be simple one-step hydride transfer processes.

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