In glass-lined reactor placed 21.1 Kg (96.34 mole) of 3-piperazinylbenzo[d]isothiazole; 31 kg (134.7 moles) of 6-chloro-5-(2-chloroethyl)indolin-2-one; 1.1 kg of potassium iodide; 20.0 kg (111.92 mole) of potassium carbonate and 63.2 lit of sulfolane. The contents of the flask were initially heated to 75° C. to 80° C. for 2 hrs. Then temperature was raised to 95° C. to 100° C. and stirred till completion of the reaction. After completion of the reaction 210 lit of DM water was added to the reaction mixture and stirred. The product was filtered off and washed with water and dried to obtain 29.75 kg of 5-(2-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)ethyl)-6-chloro-1,3-dihydro-2H-indol-2-one (Ziprasidone).
