Reactions of supercritical alcohols with unsaturated hydrocarbons

The reactions of some supercritical alcohols were investigated using 1,1-diphenylethylene, styrene, allylbenzene, and diphenylacetylene as the reaction partners. 1,1-Diphenylethylene in supercritical methanol was hydroxymethylated to afford 3,3-diphenyl-1-propanol as the major product. The alkenes containing a single and no conjugate phenyl group were also hydroxymethylated in supercritical methanol, but the reaction rates were significantly reduced when compared with that for 1,1-diphenylethylene. Styrene was converted to the hydroxyalkylated products in supercritical ethanol and 2-propanol as well as in supercritical methanol. The rates of the hydroxyalkylation of styrene were strongly dependent on the structures of the supercritical alcohols; the order of reactivity was 2-propanol>ethanol>methanol. The relation between the structures of the alcohols and the rates of hydroxyalkylation suggests that the reaction begins with an attack on the electrophile (+CR2OH or δ+CR2OH) by the pi electrons of the styrene double bond. All the examined alkenes afforded their hydrogenated derivatives other than the hydroxyalkylated ones. In addition, supercritical alcohols acted as hydroxyalkylating or hydrogenating reagents for the triple bond in the reaction with diphenylacetylene.