the invention to a stirred solution of methyl alpha 2 thienylethylamino n 2 chlorophenyl acetate as hcl salt of formula ii 1 0 kg in water 5 0 l was added para formaldehyde 130 24 gm and 1 0 ml hcl at room temperature the reaction mixture was stirred and heated to 78 80 u00b0 c for 2 hrs the aqueous layer was first separated out from the sticky mass and extracted with petroleum ether 5 0 l at ph 2 2 2 6 the aqueous layer was re extracted with petroleum ether 3 0 l the combined organic layer was concentrated at 40 45 u00b0 c under 400 600 mm vacuum to furnish the product as colorless sticky liquid the yield of the end product was found to be 780 gm 83 57 the chemical purity was checked by gas chromatography and found to be 99 90 preparation of methyl s alpha 2 chlorophenyl 6 7 dihydrothieno 3 2 c pyridine 5 4h acetic acid methyl ester clopidogrel formula i as hydrogen sulfate salt a solution of 100 gm of methyl s alpha 2 chlorophenyl 6 7 dihydrothieno 3 2 c pyridine 5 4h acetic acid methyl ester clopidogrel formula i in a mixture of acetone 260 ml 2 60 v amp toluene 40 ml 0 4 v was cooled to 9 10 u00b0 c the first portion of conc sulfuric acid 98 was added at 9 10 u00b0 c under stirring after complete addition of sulfuric acid the reaction mixture was heated to.