Additive-assisted Rupe rearrangement of 1-ethynylcyclohexan-1-ol in near-critical water

We performed the Rupe rearrangement of 1-ethynylcyclohexan-1-ol in near-critical water to study the reaction under high temperature conditions. The final product thus obtained was primarily 1-cyclohexen-1-ylethanone which was identified by GC-MS. The influences of reaction time, temperature, and initial reactant-to-water ratio on the yield of 1-cyclohexen-1-ylethanone were examined. The yield of 1-cyclohexen-1-ylethanone was 49 % in pure water at 260°C for a reaction time of 60 min. However, when additives such as ZnSO₄, FeCl₃, and NaHSO₄, respectively, were introduced to the water to investigate the effect of salts on the Rupe rearrangement reaction, the yield increased markedly to as much as 88 % in 5 mole % NaHSO₄ aqueous solution under the same conditions. The catalytic ability of the additives decreased in order: NaHSO₄, FeCl₃, ZnSO₄. On the basis of these results, a possible reaction mechanism of the Rupe rearrangement of 1-ethynylcyclohexan-1-ol in near-critical water was proposed.