No abstract

A modified synthesis of methyl 3-chloro-5-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-1-methylpyrazole-4-carboxylate (halosulphuron) is described. The merits of the synthesis are (i) one pot chlorination of methyl 1-methyl-1H-pyrazole-4-carboxylate (1) in presence of sulphuryl chloride resulting in methyl 3,5-dichloro-1-methyl-1H-pyrazole-4-carboxylate (2) (ii) conversion of 3-chloro-5-mercapto-1-methyl-1H-pyrazole-4-carboxylate (3) to 3-chloro-1-methyl-5-sulfamoyl pyrazole-4-carboxylate (4) under mild reaction conditions utilizing tetrabutyl ammonium chloride, N-chlorosuccinimide and ammonium carbonate (iii) condensation of sulphonamide (4) with carbamate (6) by microwave irradiation. Efforts were made to calculate, atom economy, reaction mass efficiency and E-factor for all the reaction steps involved in the synthesis of halosulfuron. The E-factor values in step 2 and step 4 reaction is lower, indicating that these reactions are greener (generation of less waste) when compared to the remaining steps in the synthesis.