x by reaction with an alcohol r 3 u2014 oh wherein r 3 is as defined herein for formula iii preferably said acid chloride is prepared by treatment of 5 carboxyphthalide with pocl 3 pcl 5 or socl 2 neat or in a suitable solvent such as toluene or toluene comprising a catalytic amount of n n dimethylformamide it is understood that the term u201c intermediate u201d as used in the context of u201c method for preparing an intermediate suitable for the synthesis of citalopram or escitalopram u201d includes 5 cyanophthalide and also the alkoxycarbonylphtalide as such thus the alkoxycarbonylphtalide may be subjected to further process steps e g as disclosed herein for the synthesis of 5 cyanophthalide and finally to citalopram and escitalopram it is understood that the above mentioned method for preparing an intermediate suitable for the synthesis of citalopram or escitalopram may be subjected to any of the corresponding process condition as indicated above for the method of the invention for preparing a alkoxycarbonylphtalide in particular with respect to further purification procedures such as by washing recrystallisation additional filtration and drying of the alkoxycarbonylphtalide product additionally the above mentioned preferred properties for the alkoxycarbonylphtalide likewise applies to the alkoxycarbonylphtalide produced in the present context by the process of the.