Humic acid: a rarely explored, robust, green catalyst for solvent-free synthesis of 4H-benzo[4,5]thiazolo[3,2-a]pyrimidine-3-carboxylate and benzo[d]thiazole

Humic acid, a rarely used non virulent, easily accessible, inexpensive, environmentally benign, high molecular weight polymer, because of its extraordinary catalytic activity has been explored for the synthesis of functionalised 4H-benzo[4,5]thiazolo[3,2-a]pyrimidine-3-carboxylate and its derivatives along with functionalised benzo[d]thiazole. Environmental friendliness, low catalyst loading, outstanding yield, magnificent functional group forbearance and renewability up to fifth run without any noteworthy loss of its activity at the finishing point of reaction, are the cue significances of these methods.