Acetylation of 5-Amino-1H-[1,2,4]triazole Revisited

Abstract

The products of the acetylation reactions of the common herbicide 5-amino-1H-[1,2,4]triazole were investigated using HPLC, GC-MS, 1H NMR, and FTIR spectroscopy. The conventional annular monoacetylation procedures with acetyl chloride are not regioselective and furnish a mixture of isomers. Traditional diacetylation in neat acetic anhydride under reflux produces a mixture of di-, mono-, and triacetylated derivatives. By using equivalent amounts of acetic anhydride in a dimethylformamide solution, a rapid and selective annular monoacetylation of 5-amino-1H-[1,2,4]triazole was achieved. The monoacetylation proceeds via the formation of the intermediate, 1-acetyl-3-amino-1H-[1,2,4]triazole, which had not been observed previously and which undergoes transformation into the known 1-acetyl-5-amino-1H-[1,2,4]triazole. Neat acetic anhydride at room temperature affords the diacetylated derivative, 1-acetyl-3-(acetylamino)-1H-[1,2,4]triazole both from 5-amino-1H-[1,2,4]triazole itself and from either 1-acetyl-5-amino-1H-[1,2,4]triazole or 5-(acetylamino)-1H-[1,2,4]triazole. The atypical product of the second acetylation, 1-acetyl-5-(acetylamino)-1H-[1,2,4]triazole, has been identified. These results may be useful in the development of effective and selective preparative procedures for the acetylation of 5-amino-1H-[1,2,4]triazole.

Synthesis, Structure and Properties of N-Acetylated Derivatives of Methyl 5-Amino-1H-[1,2,4]triazole-3-carboxylate

“…The multinuclear NMR, the 1 H- 15 N gradient heteronuclear single quantum coherence (g-HSQC), the gradient heteronuclear multiple bond connectivity (g-HMBC) in DMF-d 7 and the CPMAS experiment (Tables 2, 3; Chart 1) reveal that in both solutions and the solid state, 2 has the structure of methyl 5-amino-1H- [1,2,4]triazole-3-carboxylate and its hydrochloride 1 has an 1H,4H ϩ -triazolium cation. The cations of this tautomeric type are commonly found in the crystals of 5-amino-1H- [1,2,4]triazolium salts.…”

“…It is interesting to note, that no difference in the susceptibility to hydrolysis of both isomeric diacetylated amino-[1,2,4]triazoles has been found. 15) The study brings the following suggestions for preparing 4 and 5. Because isomer 4 is the kinetic product of the acetylation of 6 (Chart 2), its highest yield can be reached through the reaction of 6 with Ac 2 O under mild conditions.…”

“…Methyl 1-Acetyl-5-amino-1H-[1,2,4]triazole-3-carboxylate (3) We have previously found 15) the acetylation of AT in DMF or DMSO solutions with 1 eq Ac 2 O at 20°C to be almost instantaneous. Firstly the kinetic product 1-acetyl-3-amino-1H-[1,2,4]triazole was formed (Fig.…”

“…2B). AT in boiling anhydride also forms in addition to the diacetylated compound a triacetylated species, 1-acetyl-3(5)-(diacetylamino)-1H-[1,2,4]triazole 15) (Fig. 2C).…”

Analytical mass spectrometry of herbicides

“…Amitrole ( 30 ) (Scheme ) is 5‐amino‐1H‐[1,2,4]triazole, and it is an ingredient in several active herbicide products. The proton of the ring N is liable, and 30 can exist in several tautomeric forms; however, the structure shown is reported to be the commercial product and the dominate form (Dżygiel, Masiukiewicz, & Rzeszotarska, 2002). Several related compounds that are ingredients in active herbicide products are carfentrazone‐ethyl ( 31 ) (Scheme ) and sulfentrazone ( 32 ) (Scheme ), which have oxidized and substituted 1,2,4‐triazole structures.…”