Cyclohexanol Formation via Partial Hydrogenation of Benzene

In the two-step process for manufacturing cyclohexanol via cyclohexene from benzene, the procedure for effectively hydrating cyclohexene only in a reaction mixture obtained by partial hydrogenation of benzene is very important. This is because separating cyclohexene from the reaction mixture obtained in the first step is much more difficult than recovering benzene and cyclohexane after converting cyclohexene to cyclohexanol in the second step. Therefore, we investigated the optimum hydration conditions to obtaind cyclohexanol from a mixture using sulfuric acid and an additive. At a reaction temperature below 30°C, both the hydration rate and cyclohexanol yield decreased with lowering of the temperature. At a temperature over 30°C, the sulfonation of benzene and polymerization of cyclohexene easily occurred. Essentially the same was observed at the concentration and amount of sulfuric acid. Thus, the optimum temperature, sulfuric acid concentration and the used hydration were 30°C, 75%, and 2.7 mole to 1 mole of cyclohexene, respectively. As additives all metal salts were effective, but no alcohol used at this stage promoted cyclohexanol formation. The best additive was nickel sulfate. When a mixture of benzene (0.05mol), cyclohexene (0.15mol) and cyclohexane (0.3mol) was treated with 75% sulfuric acid (0.4mol) in the presence of nickel sulfate (0.01mol) at 30°C for 35h, the cyclohexanol yield was about 80%.