2,2,6,6-Tetramethylpiperidine-1-Oxyl-Promoted Hydroxylation of Benzene to Phenol over a Vanadium-Based Catalyst Using Molecular Oxygen

Rapid benzene hydroxylation was achieved using a reaction system that consisted of a vanadium-based catalyst, ascorbic acid, and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) with molecular oxygen as the oxidant. The hydroxyl radicals that form by a Fenton-type process attack the benzene ring to produce a hydroxycyclohexadienyl radical. The hydroxyl hydrogen is then abstracted quickly in the presence of TEMPO and phenol forms by the transfer of a hydrogen atom from the benzene ring to oxygen. Over the [(CH3)4N]4-PMo11VO40 catalyst the phenol yield reached 8.3% with a selectivity of 95% in 1 h while trace amounts of phenol were obtained in the normal system without TEMPO.

摘要以钒基化合物为催化剂, 在 TEMPO (2,2,6,6-四甲基哌啶-1-氧自由基) 存在下, 能形成快速催化分子氧氧化苯制苯酚的催化体系. 在反应过程中, 由类似芬顿试剂反应过程生成的羟基自由基亲核进攻苯环, 形成羟基环己二烯自由基; 该羟基氢可在 TEMPO 存在的催化体系中消除, 同时苯环氢可立即转移至氧原子而生成苯酚. 在以 [(CH3)4N]4-PMo11VO40 为催化剂的体系中, 反应 1 h 苯酚收率可从不加 TEMPO 时的 1.2% 提高到 8.4%; 而以 V-AlPO5 为催化剂时, 苯酚收率可从不加 TEMPO 时的 5.0% 提高到 9.5%, 且选择性均较高.

A rapid catalytic system for the hydroxylation of benzene to phenol was achieved using molecular oxygen over a vanadium-based catalyst, ascorbic acid and 2,2,6,6-tetramethylpiperidine-1-oxylFigure optionsDownload as PowerPoint slide