N-Substituted thioureas were synthesized efficiently by two-step reaction: (1) acyl chlorides and primary amides reacted together in functional [emim]SCN rapidly at room temperature to form N-benzoyl-N′-alkylthioureas in high yields. [emim]SCN acted both as an initial material and reaction solvent. (2) N-benzoyl-N′-alkylthioureas were hydrolyzed in NaOH/H₂O/EtOH to yield N-substituted thioureas with almost 100% yield. A new efficient and green synthesis of N-substituted thioureas showing good practicality was provided.

Key words: acyl chloride, amine, functional ionic liquid, N-substituted thiourea