A study has been made of the kinetic relationships and composition of products of the alkaline breakdown of cumyl hydroperoxide in chlorobenzene (CB), dimethylformamide (DMF) and mixed solvents: DMF-hexamethylphosphorotriamide (HMPA), CB-HMPA, and also in chlorobenzene with additions of phenylacetylene. It was established that the mechanism of alkaline breakdown of hydroperoxide and the rate of ionic decomposition are related to the basicity of the solvent.