The synthesis of ethyl [3-(cyanomethyl)-5-alkyl-4H-1,2,4-triazol-4-yl] carbamates (2a-d) was performed starting from ethyl 2-[ethoxy(4-(aryl) methylene] hydrazinecarboxylates (1a, 1b). The treatment of 2a with thiosemicarbazide afforded ethyl [3-[(5-amino-1,3,4-thiadiazol-2-yl) methyl]-5-(4-nitrophenyl)-4H-1,2,4-triazol- 4-yl] carbamates (3a), whereas compound 2b produced 5-{[4-amino-5-(4-methylphenyl)-4H -1,2,4-triazol-3-yl] methyl}-1,3,4-thiadiazol-2-amine (3b) in the same reaction conditions. The treatment of tert butyl 2-[2-(4-chlorophenyl)-1-ethoxyethylidene] hydrazinecarboxylate (5) with malonohydrazide or cyanoacethydrazide gave the corresponding 1,2,4-triazol-ylcarbamate derivatives (6 or 9); then the hydrolysis of these compounds resulted in the formation of 3-{[4-amino-5-(4-chlorobenzyl)-4H -1,2,4-triazol-3-yl] methyl}5-(4-chlorobenzyl)-4H -1,2,4-triazol-4-amine (7) and [4-amino-5-(4-chlorobenzyl)-4H -1,2,4-triazole-3-yl] acetonitrile (10), respectively. The synthesis of the Schiff base derivatives 3-(4-chlorobenzyl)-5-{[5-(4-chlorobenzyl)-4-[(2-hydroxyphenyl-methylene) amino]-4H -1,2,4-triazol-3-yl] methyl}-N-(2-hydroxyphenylmethylene)4H-1,2,4-triazol-4-amine (8), and (5-(4-chlorobenzyl)-4-{[(2,6-dichlorophenyl) methylene] amino}-4H -1,2,4-triazol-3-yl) acetonitrile (12) was performed from the reaction of compounds 7 and 10 with salicyl aldehyde (for 8) or 2,6-dichlorobenzaldehyde (for 12), respectively. The treatment of compounds 5 or 10 with thiosemicarbazide gave 5-{[4-amino-5-(4-chlorobenzyl)-4H -1,2,4-triazol-3-yl] methyl}-1,3,4-thiadiazol-2-amine (11). 
All the newly synthesized compounds were screened for their antimicrobial activities and were found to possess good or moderate antimicrobial activity.