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

Use of supercritical carbon dioxide, scCO sub(2), as an environmentally friendly reaction medium for the continuous synthesis of the fine chemical o-cyclohexylphenol was investigated. The alkylation of phenol was carried out using a solid acid catalyst, gamma -Al sub(2)O sub(3), using both cyclohexene and cyclohexanol as alkylating agents. When the alkylation was carried out using cyclohexanol, the selectivity dropped due to water formed as a by-product in the reaction, deactivating the catalyst towards the alkylation step. The results showed that the reactions carried out in the presence of sub(sc)CO sub(2) gave significantly better yields and selectivities than the reaction without CO sub(2), which suggested that scCO sub(2) played a positive role in the reaction.