Hydride transfer reactions. Oxidation of N-methylacridan by π acceptors
| Autor: | Gunzi Saito, Frances J. Sharom, Allan K. Colter |
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| Rok vydání: | 1977 |
| Předmět: | |
| Zdroj: | Canadian Journal of Chemistry. 55:2741-2751 |
| ISSN: | 1480-3291 0008-4042 |
| DOI: | 10.1139/v77-382 |
| Popis: | The oxidation of N-methylacridan (1) to N-methylacridinium ion (2) by the π acceptors p-benzoquinone (BQ), 7,7,8,8-tetracyanoquinodimethane (TCNQ), p-chloranil (CA), tetracyanoethylene (TCNE), and 2,3-dicyano-1,4-benzoquinone (DCBQ) has been investigated. Second-order rate constants in acetonitrile (AN) vary by a factor of more than 107 for this series. The rate of reaction of 1 with BQ increases 45-fold as the solvent composition is varied from AN to 50% (v/v) AN–water, but is insensitive to changes in buffer ratio or concentration in 75% AN. Spectroscopic evidence for charge-transfer complexing between the reactants was obtained with BQ and CA, and kinetic evidence for complexing was obtained with BQ in 75% AN. The primary isotope effect, p, calculated from the rates of oxidation of 1, 1-9-d, and 1-9,9-d2 (1(HH), 1(HD), and 1(DD)) in AN varied from 4.5 (TCNE) to 13 (BQ), while the secondary isotope effect, s, was approximately constant (∼1.1). Values of the isotope partitioning ratio, ipr (the ratio of 2(D) to 2(H) formed in reaction of 1(HD)) were determined for BQ in three AN-water mixtures and for CA, TCNE, and DCBQ in AN. For all systems studied, except BQ in 90% AN, where determination of the ipr is complicated by isotopic exchange between unreacted 1 and product (2), the ipr agrees with p/s from the kinetic measurements. These results are discussed in terms of mechanism and compared with those of other hydride transfer reactions involving dihydronicotinamide donors. |
| Databáze: | OpenAIRE |
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