Process for the preparation of the polymorph f of sodium neridronate

Abstract

The present invention relates to a new process for the preparation of the crystalline polymorph of sodium neridronate in form hemihydrate F, comprising the following steps: a) reacting the 6-aminohexanoic acid with a mixture of phosphorous acid and methanesulfonic acid at a temperature in the range from 60 to 80° C., under stirring, until a clear solution is obtained; b) adding phosphorus trichloride to said solution of step (a) under stirring at a temperature in the range of 60 to 80° C.; c) diluting with water the reaction mixture obtained from the previous step (b) and heating said water diluted mixture at a temperature in the range from 80 to 120° C.; d) cooling the heated mixture obtained in step (c) up to room temperature, diluting it with water, then slowly adding an aqueous sodium hydroxide solution up to a pH in the range from 4.2 to 4.6, to obtain a neutralized solution; e) bringing the neutralized solution of step (d) up to a temperature of about 70° C., then subjecting it to a temperature increase in the range from 70 to 140° C., until evaporation of at least 70% of the initial volume of the neutralized solution of step (d), thus obtaining a suspension to be kept under stirring for at least 1 hour; f) cooling the suspension of step (e) up to a temperature in the range from around 5 to 25° C.; and g) recovering the crystalline sodium neridronate in hemihydrate form F by filtering the suspension of the previous step (f). The process is particularly simple, scalable and environmentally sustainable.