The present invention provides a process for the preparation of crude 1-[3-(dimethylamino)propyl]-1-(4-fluorophenyl)-1,3-dihydro-5-isobenzofura- n carbonitrile base with substantially low levels of impurities by arresting the formation of substantial amount of carboxamide impurity, high molecular weight impurities and suppressing the formation of desmethylcitalopram besides taking the cyanide exchange reaction to near completion and thus avoiding an extensive and expensive purification process.