Process for the preparation of a stable modification of torasemide

Abstract

The present invention provides a process for the preparation of crystalline torasemide in the pure modification I (monoclinic, space group P2 1 /c, .[.melting point 162° C.).]. .Iadd.in prism form) .Iaddend.from torasemide of modification II (monoclinic, space group P2/n, .[.melting point 169°.),.]. .Iadd.in leaflet form), .Iaddend.wherein a suspension of torasemide of modification II is stirred in water with the addition of a catalytic amount of modification I until the rearrangement is complete. The present invention also provides a pharmaceutical compositions containing .Iadd.stable .Iaddend.torasemide of modification I.

What is claimed is: 
     
       1. A process for the preparation of torasemide in the pure modification I (monoclinic, space group P2/c, .[.metling point 162° C.).]. .Iadd.in prism form) .Iaddend.from torasemide of modification II (monoclinic, space group P2/n, .[.melting point 169° C.).]. .Iadd.in leaflet form) .Iaddend.comprising stirring a suspension of torasemide of modification II in water with at least a catalytic amount of modification I, to rearrange the torasemide in modification II into .Iadd.stable .Iaddend.torasemide of modification I. 
     
     
       2. The process of claim 1, wherein the rearrangement is carried out at a temperature of from ambient temperature to 90° C. and the rearrangement is carried out for a time of from 3 hours to 14 days. 
     
     
       3. The process of claim 2, wherein the torasemide of modification II is used in the form of a salt-containing, approximately neutral solution, obtained by the precipitation of torasemide from alkaline solution. 
     
     
       4. The process of claim 2, wherein crystalline torasemide of modification I is recovered from the rearrangement reaction mixture. 
     
     
       5. The process of claim 1, wherein crystalline torasemide of modification I is recovered from the rearrangement reaction mixture. 
     
     
       6. The process of claim 1, wherein the torasemide of modification II is used in the form of a salt-containing, approximately neutral solution, obtained by the precipitation of torasemide from alkaline solution.