ethyl 6 chloro 1 3 dihydro 2h indol 2 one and the hydrated hydrochloride salt are prepared according to the following synthetic reaction scheme is reacted with a molar excess of 2 chloroethyl 6 chloro oxoindole formula iii in a solvent and in the presence of a mild base to form 5 2 4 1 2 benzisothiazol 3 yl piperazinyl ethyl 6 chloro 1 3 dihydro 2h indol 2 one formula iv the molar excess of 2 chloroethyl 6 chloro oxoindole used in this reaction stage is typically between about 1 to about 3 fold and preferably about 2 fold suitable solvents for this synthetic stage include water 1 benzisothiazole 3 piprazinyl hydrochloride is added to the aqueous sodium carbonate solution at ambient temperature the sodium carbonate is dissolved in water to form a 2 6 solution by weight the mixture is stirred for one hour to obtain a suspension 2 chloroethyl 6 chloro oxindole followed by sodium iodide is added to the suspension and the combined mixture is heated at a temperature of from about 50 to 100 u00b0 c for 20 to 30 hours after completion of the reaction the mixture was cooled to ambient temperature and filtered the crude ziprasidone obtained is again heated with water cooled to room temperature filtered and dried to obtain in the purified product in greater than 95 hplc purity in the present invention the coupling reaction is conducted in water this in situ aqueous based coupling process is more efficient and has a lower environmental burden because the handling and disposal of organic solvents are.