Nucleophilic activation of hydrogen peroxide. On the formation and the reactivity of 1H-1,2,4-triazoleperoxycarboxylic acid and O-p-nitrophenylmonoperoxycarbonic acid †
作者:Carsten Bender、Hans-Dieter Brauer
DOI:10.1039/a903852c
日期:——
Measurements of the infrared phosphorescence of singlet molecular oxygen (1O2) at 1270 nm have been employed to demonstrate the formation of 1O2 in the system N,Nâ²-carbonyldi-1,2,4-triazole (CDT)âhydrogen peroxide and in the system 1H-1,2,4-triazolecarboxylic acid p-nitrophenyl ester (TCNP)âhydrogen peroxide in tetrahydrofuran. At hydrogen peroxide concentrations of [H2O2] â¥Â 2 [CDT] or â¥Â 2 [TCNP] one molecule of 1O2 is generated per molecule of CDT and TCNP, respectively. In both systems a very reactive peroxy-intermediate is formed. In the system CDTâH2O2 the 1H-1,2,4-triazoleperoxycarboxylic acid (1) is generated, in TCNPâH2O2 the p-nitrophenylmonoperoxycarbonic acid (4). For the epoxidation of cyclohexene in THF by 1 a rate constant k15 â3 Ã 100 dm3 molâ1 sâ1 can be estimated. For 4 the corresponding rate constant was found to be k20 â 6 Ã 10â2 dm3 molâ1 sâ1. The Arrhenius parameters of the formation of 1 and 4, respectively, and in addition of their consecutive reactions with hydrogen peroxide were determined. The results are consistent with the assumption that the nucleophilic displacements by hydrogen peroxide at the carbonyl carbon atom are additionâelimination processes, which take the form of a BAC2-mechanism.
在四氢呋喃中,通过测量单线态分子氧(1O2)在1270 nm处的红外磷光,证明了在N,N'-羰基二-1,2,4-三唑(CDT)–过氧化氢体系和1H-1,2,4-三唑羧酸对硝基苯酯(TCNP)–过氧化氢体系中1O2的生成。当过氧化氢浓度[H2O2]≥2[CDT]或≥2[TCNP]时,CDT和TCNP分子各自生成一个1O2分子。在这两个体系中,都形成了一个高度活性的过氧中间体。在CDT–H2O2体系中生成1H-1,2,4-三唑过氧羧酸(1),在TCNP–H2O2体系中生成对硝基苯单过氧碳酸(4)。对于1在THF中环己烯环氧化反应的速率常数k15≈3×100 dm3 mol−1 s−1可以估算出来。对于4,相应的速率常数被发现为k20≈6×10−2 dm3 mol−1 s−1。分别确定了1和4的形成以及它们与过氧化氢的连续反应的阿伦尼乌斯参数。结果与假设一致,即过氧化氢在羰基碳原子上的亲核取代是加成-消除过程,表现为BAC2机制。