The synthesis of o-cyclohexylphenol in supercritical carbon dioxide:: towards a continuous two-step reaction

The use of supercritical carbon dioxide, scCO(2), as an environmentally friendly reaction medium for the continuous synthesis of the fine chemical omicron-cyclohexylphenol has been investigated. The alkylation of phenol was carried out using a solid acid catalyst, gamma-Al2O3, using both cyclohexene and cyclohexanol as alkylating agents. Though cheaper, cyclohexanol gave poorer results because of the water formed in the reaction inhibiting the catalyst performance. The possibility of performing the reaction as a two-step process was then investigated. The dehydration of cyclohexanol over the same catalyst was found to be quantitative. Clearly, the water by-product must be eliminated before the alkylation step and, although this was found to be difficult to achieve on a small scale, the process looks promising as a two-step reaction.