The reaction of N-(2-chloro-4-methyl-3-thienyl)thiourea (I) with methyl iodide in methanol gives S-methyl-N-(2-chloro-4-methyl-3-thienyl)isothiouronium iodide (II), m.p. 113-5 C, which is then condensed with ethylenediamine (A) in methanol at 100 C.