Cai Yang, Koshino Nobuyoshi, Saha Basudeb, Espenson James H
Ames Laboratory and Department of Chemistry, Iowa State University of Science and Technology, Ames, Iowa 50011, USA.
J Org Chem. 2005 Jan 7;70(1):238-43. doi: 10.1021/jo048418t.
Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.) which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in the presence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer from NHPI to PINO(.), e.g., PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.). The substantial KIE, k(H)/k(D) = 11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather than stepwise electron-proton transfer. These data were correlated with the Marcus cross relation for hydrogen-atom transfer, and good agreement between the experimental and the calculated rate constants was obtained. The third reaction studied is hydrogen abstraction by PINO(.) from p-xylene and toluene. The reaction becomes regularly slower as the ring substituent on PINO(.) is more electron donating. Analysis by the Hammett equation gave rho = 1.1 and 1.8 for the reactions of PINO(.) with p-xylene and toluene, respectively.
已获得邻苯二甲酰亚胺氮氧自由基（PINO(.)）和N-羟基邻苯二甲酰亚胺（NHPI）衍生物三种不同类型反应的动力学数据。第一种是PINO(.)的自分解，发现其遵循二级动力学。在4-甲基-N-羟基邻苯二甲酰亚胺（4-Me-NHPI）的自分解中，在过量4-Me-NHPI存在下，氢原子夺取与自分解相互竞争。研究的第二组反应是氢原子从NHPI转移到PINO(.)，例如，PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.)。正向和逆向反应的显著动力学同位素效应（KIE），k(H)/k(D) = 11，支持了氢原子转移的归属，而不是逐步电子-质子转移。这些数据与氢原子转移的Marcus交叉关系相关，实验速率常数与计算速率常数之间取得了良好的一致性。研究的第三个反应是PINO(.)从对二甲苯和甲苯中夺取氢原子。随着PINO(.)上的环取代基供电子性增强，反应规律地变慢。通过Hammett方程分析，PINO(.)与对二甲苯和甲苯反应的ρ值分别为1.1和1.8。
