Solvents as phase-transfer catalysts in reactions initiated by solid bases

For reactions initiated by solid bases (e.g. potassium hydroxide, sodium hydroxide, potassium carbonate), solvents (e.g. water, ButOH, polyethylene glycol, MeCN, Me2SO) may act as solid-liquid phase transfer catalysts (e.g. for C–H, N–H or O–H alkylation by alkyl halides, or epoxidation by sulfonium or sulfoxonium salts).