Industrial process for preparation of Clopidogrel hydrogen sulphate

An improved process for the manufacture of Clopidogrel starting from 2-(2-thienyl) ethylamine, which eliminates the isolation of an unstable intermediate like 2-(2-thienyl) ethyl formimine by subjecting it to a one pot cyclization to get 4, 5, 6, 7-tetrahydrothieno (3,2-c) pyridine of Formula II and further reacting with halo-compound of Formula III (where X is Cl or Br) at 20 to 90° C. temperature characterized in a solvent like water and/or dichloroethane in presence of organic or inorganic bases is disclosed herein. This invention further discloses a process for resolution of racemic Clopidogrel into its optical antipodes and converting the dextroclopidogrel base into its known polymorphs namely 'Form I' or 'Form II' in solvents selected from methyl propyl ketone, methyl isopropyl ketone, diethyl ketone or their mixture thereof, mixture of ethyl acetate and methyl propyl ketone, mixture of ethyl acetate and methyl isopropyl ketone, or mixture of ethyl acetate and diethyl ketone or ethyl acetate.