PROCESS FOR THE PREPARATION OF THE MODIFICATION OF A CIMETIDINE

摘要

Prepn. of the A modification of cimetidine (I-A; N-cyano-N' methyl-N'-(2-((5-methylimidazol- 4-yl)methylthio)ethyl) guanidine) from the H-modification (I-H; also called cimetidine M-1) comprises thermal dehdyration with a flow of gas preheated to 40-110 deg.C. The gas (which may be air, inert gas or N2) is at 60-100 deg.C and dehydration is carried out while maintaining the crystalline state at all times.