One Step Hydroxylation Of Benzene To Phenol By Molecular Oxygen

Phenol is an important chemical in industry, as an intermediate for biphenol A, phenol-aldehyde resins, nylon-6, etc. It's mainly produced by cumene peroxidation process, which requires three steps of reactions and is limited by the market requirement of equimolar byproduct acetone. Because it needs many kinds of acid and organic reagents, cumene peroxidation process brings the problems of wasting materials and environment pollution. For economical and ecological environment reasons, the one-step direct hydroxylation of benzene with cleaner and cheaper oxidants becomes one of the most exciting challenges of catalytic chemistry.In this dissertation, we studied the catalysts, reaction conditions and mechanism of one-step hydroxylation of benzene to phenol oxidized by molecular oxygen, which is the cleanest and the most economical process. Benzene and oxygen or air are the only materials of this process, which greatly simplifies the synthesis process and can save a great deal of raw materials so that the cost of phenol production decreases a lot. Molecular oxygen is one of green oxidants, by which the benzene oxidation gets nearly 100% phenol selectivity, thus this reaction route will not damage the environment.The synthesized mesoporous materials of CuSBA-15 VOx/CuSBA-15 catalysts have hexagonal structure and large BET surface. And the VOx/CuSBA-15 catalysts and the mixture of NH4V03 and CuSBA-15 effectively catalyze the benzene hydroxylation by molecular oxygen at high pressure and atmosphere pressure respectively.The benzene hydroxylation catalyzed by NH4VO3 and CuSBA-15 mixture at atmosphere pressure gets the benzene conversion of 9.3% and the phenol selectivity of 100% by using oxygen as oxidant, ascorbic acid as reducing reagent and high concentration of aqueous acetic acid as solvent. And the VOx/CuSBA-15catalysts have very high catalytic activity towards benzene hydroxylation at high pressure, which obtains the high benzene conversion of 37% and the phenol' selectivity of 98.6% by oxygen at 4MPa and the benzene conversion of 18.9% and the phenol selectivity of 99.7% by air at 8.4MPa. All the results above are much higher than current reports.Solvent and reducing reagent play very important roles in the benzene hydroxylation oxidized by molecular oxygen. It can just react in aqueous acetic acid and only when the concentration is as high as 50vol.%-80vol.% does the solvent effectively accelerate this reaction. Oxalic acid and ascorbic acid are the very reducing reagents by which the high yield of phenol can obtain, and ascorbic acid is better than oxalic acid.According to our experiment results and the former researches by other scientists, we suppose the 4-step mechanism. Firstly, copper and vanadium react with reducing reagent to Cu( I) and V(III) species. Secondly, oxygen molecules captured by Cu( I) with the assistance of H+ generate H2O2 which transferred to V(III) active sites immediately form vanadium peroxo species. Thirdly, the vanadium peroxo species go on to form the active vanadium(V) oxidants with two OH radicals and activate benzene molecules as the same time. Finally, -OH radicals attack benzene molecules, which has been activated already to produce phenol.