Mechanism of hydride transfer reaction from 4-(dimethylamino)phenyl methane derivatives to 2,3-dichloro-5,6-dicyano-p-benzoquinone

The kinetics of the hydride-transfer reactions from bis[4-(dimethylamino)ph enyl] methane (MH2), bis[4(dimethylamino)phenyl] methoxy methane (MHOMe), L euco Malachite Green (MGH) and Leuco Crystal Violet (CVH) to 2,3-dichloro-5 ,6-dicyano-p-benzoquinone (DDQ) have been investigated spectrophotometrical ly by means of the stopped-flow technique. The negative activation enthalpi es were obtained for the hydride-transfer reactions from MH2, MHOMe and MGH to DDQ in dichloromethane. These negative activation enthalpies suggest th at the charge-transfer (CT) complexes are true intermediates in the hydride -transfer reactions from these donors to DDQ, as previously pointed out for MH2-DDQ system in trichloroethane. The formation of charge-transfer comple xes between MH2, MHOMe, MGH and CVH and p-chloranil (CA) were observed in E PA (ethylether-pentane-ethanol) at low temperatures. The oxidation potentia l (E-ox(o) of MHOMe, MGH and CVH were estimated using the linear correlatio n between the CT transition energy and the E-ox(o) value for the known CT c omplexes between CA and N,N-dimethylaniline derivatives. The rates were fou nd to be correlated to the E-ox(o) values of the donors.