Abstract N-Benzoyl-N'-(2-carboxy-and 2-methoxycarbonylphenyl) thioureas have been obtained by the reaction of N-benzoyl isothiocyanate with anthranilic acid and methyl anthranilate, respectively. Kinetics of cyclization of these compounds into 2-mercapto-3, 4- dihydro-4-quinazolone have been studied in water and in methanol. In the base-catalyzed cyclization of N-benzoyl-N'-(2-carboxyphenyl) thiourea the proper cyclization is preceded ...