氮氧自由基研究:XXI,水溶液中哌啶氮氧自由基单电子还原反应机理的极谱研究

本文采用取样直流极谱, 常规脉冲极谱, 微分脉冲极谱和交流极谱考察了,2,2,6,6-四甲基-4-羟基哌啶 -1-氧和2,2,6,6-四甲基-4-氧哌啶 -1-氧由基及2,2,6,6-四甲基哌啶 -1-氧自由基在水溶液中的还原反应, 并研究了它们的还原经历电化学过程 。

Stueies on nitroxides:XXI. The mechanism for the one-electron reduction electrode reaction of piperidine nitroxides in aqueous solution studied by polarography

The experimental results obtained from sampled d.c. polarog. (SDCP), normal pulse polarog. (NPP), differential pulse polarog. (DPP), and a.c. polarog. (ACP) with 2,2,6,6-tetramethyl-4-hydroxypiperidinyl-1-oxy; 2,2,6,6-tetramethyl-4-oxopiperidinyl-1-oxy; and 2,2,6,6-tetramethyl-piperidinyl-1-oxy in aqueous solution showed that these nitroxides can be reduced on the electrode with the formation of the corresponding hydroxylamines as their products. The half-wave potentials and the peak potentials increased with a decrease in the pH of the medium. A linear relation between the peak potentials of ACP of the nitroxides and the pH of the medium was found with a slope of -0.03 V/pH unit. The ratio between the total limiting current of NPP and that of SDCP is independent of the pH and the nitroxides studied. A heterogeneous electron transfer followed by protonation in a homogeneous medium (EC) is proposed for the reductive process.