Mechanism of hydride transfer reaction from 4-(dimethylamino)phenyl methane derivatives to 2,3-dichloro-5,6-dicyano-p-benzoquinone
作者:Shunzo Yamamoto、Tetsuo Sakurai、Liu Yingjin、Yoshimi Sueishi
DOI:10.1039/a809358j
日期:——
The kinetics of the hydride-transfer reactions from bis[4-(dimethylamino)phenyl] methane (MH2), bis[4-(dimethylamino)phenyl] methoxy methane (MHOMe), Leuco Malachite Green (MGH) and Leuco Crystal Violet (CVH) to 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) have been investigated spectrophotometrically by means of the stopped-flow technique. The negative activation enthalpies were obtained for the hydride-transfer reactions from MH2, MHOMe and MGH to DDQ in dichloromethane. These negative activation enthalpies suggest that 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 complexes between MH2, MHOMe, MGH and CVH and p-chloranil (CA) were observed in EPA (ethylether–pentane–ethanol) at low temperatures. The oxidation potential (Eox°) of MHOMe, MGH and CVH were estimated using the linear correlation between the CT transition energy and the Eox° value for the known CT complexes between CA and N,N-dimethylaniline derivatives. The rates were found to be correlated to the Eox° values of the donors.
从双[4-(二甲氨基)苯]甲烷 (MH2)、双[4-(二甲氨基)苯]甲氧基甲烷 (MHOMe)、靛青绿 (MGH) 和晶体紫 (CVH) 到 2,3-二氯-5,6-二氰基对苯二酮 (DDQ) 的氢化物转移反应动力学已通过停止流动技术进行光谱测定。 在二氯甲烷中,来自 MH2、MHOMe 和 MGH 到 DDQ 的氢化物转移反应获得了负的活化焓。 这些负的活化焓表明,电荷转移 (CT) 复合物是真正的中间体,在从这些供体到 DDQ 的氢化物转移反应中,正如之前在三氯乙烷中的 MH2–DDQ 系统所指出的那样。 在低温下,观察到 MH2、MHOMe、MGH 和 CVH 与对氯苯醌 (CA) 之间的电荷转移复合物的形成。 通过已知的 CA 和 N,N-二甲基苯胺衍生物之间的 CT 复合物的 CT 跃迁能量与 Eox° 值之间的线性关系,估算了 MHOMe、MGH 和 CVH 的氧化电位 (Eox°)。 发现反应速率与供体的 Eox° 值相关。