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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Mechanisms of Oxidation of 1,2,5-Trimethylpyrrole: Kinetic, Spectroscopic, and Electrochemical Studies
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Mechanisms of Oxidation of 1,2,5-Trimethylpyrrole: Kinetic, Spectroscopic, and Electrochemical Studies

机译：1,2,5-三甲基吡咯的氧化机理：动力学，光谱学和电化学研究

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The oxidation of 1,2,5-trimethylpyrrole (TMP) in aqueous and organic solvents is studied by various techniques. Heating oxygenated chlorobenzene solutions of TMP results in autoxidation that is initiated via reaction of TMP with O_2 and partly propagated via oxidation of TMP by a TMP-derived peroxyl radical. In radiolytic experiments, TMP is oxidized rapidly by Br_2·~- (k = 2.3 * 10~9 L mol~(-1) s~(-1)), I_2·~- (k = 5.1 * 10~8 L mol~(-1) s~(-1)), CCl_3O_2· (k = 5 * 10~8 L mol~(-1) s~(-1)), and N_3· radicals in aqueous solutions and by peroxyl radicals in organic solvents. One-electron oxidation forms the radical cation, which exhibits significant absorption in the UV (λ_(max) ～ 270 nm, ∈ ～ 1300 L mol~(-1) cm~(-1)) and weaker absorptions in the visible range. This species undergoes rapid dimerization (2k ～ 5 * 10~8 L mol~(-1) s~(-1)), and the dimer is very easily oxidized to a stable product absorbing around 460 nm. NMR analysis of the product formed in irradiated CH_2Cl_2 solutions is in accord with a dication of dimeric TMP. Other products are also formed under different conditions, probably resulting from addition of peroxyl radicals to the pyrrole ring. In cyclic voltammetry experiments at low scan rates, an irreversible peak at a potential of 0.72 V vs SCE is found for oxidation of TMP in acetonitrile solutions, and a stable product absorbing at 460 nm is formed. The formation of this product involves the transfer of more than one electron per TMP monomer. At very high scan rates, a reversible oxidation step is observed, from which a redox potential of 0.87 V vs SCE is derived for the couple TMP/TMP~(·+). Several mechanisms are suggested for the consumption of O_2 by TMP in organic solvents, including electron transfer and σ-bonding via peroxyl radical addition.
机译：通过各种技术研究了1,2,5-三甲基吡咯（TMP）在水性和有机溶剂中的氧化。加热TMP的氧化氯苯溶液会导致自氧化，这是通过TMP与O_2的反应引发的，并通过TMP衍生的过氧自由基通过TMP的氧化而部分传播。在放射性实验中，TMP被Br_2·〜-（k = 2.3 * 10〜9 L mol〜（-1）s〜（-1）），I_2·〜-（k = 5.1 * 10〜8 L mol）快速氧化。 〜（-1）s〜（-1）），CCl_3O_2·（k = 5 * 10〜8 L mol〜（-1）s〜（-1））和N_3·自由基在水溶液中和过氧自由基有机溶剂。单电子氧化形成自由基阳离子，它在紫外线下表现出明显的吸收（λ_（max）〜270 nm，ε〜1300 L mol〜（-1）cm〜（-1）），在可见光范围内吸收较弱。该物种经历快速二聚化（2k〜5 * 10〜8 L mol〜（-1）s〜（-1）），二聚体很容易被氧化成稳定的产物，吸收约4​​60 nm。在辐照的CH_2Cl_2溶液中形成的产物的NMR分析与二聚TMP的指示一致。在不同条件下也可能形成其他产物，这可能是由于过氧自由基加到吡咯环上所致。在低扫描速率下的循环伏安法实验中，发现乙腈溶液中TMP的氧化存在0.72 V vs SCE的不可逆峰，形成了稳定的产物，在460 nm处吸收。该产物的形成涉及每个TMP单体转移一个以上的电子。在非常高的扫描速率下，观察到了可逆的氧化步骤，从中可得出TMP / TMP〜（·+）对的氧化还原电势为SCE 0.87V。对于有机溶剂中TMP消耗O_2的机理，提出了几种机理，包括电子转移和过氧自由基加成的σ键。

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