Process for the preparation of cimetidine A

摘要

The A form of cimetidine is prepared from so-called crude cimetidine. The crude cimetidine is a mixture of polymorphic forms. Crude cimetidine is dissolved in an aprotic solvent having a dielectric constant of between 30 and 200 and a dipole moment in the range from 3.00 to 5.00 debye and is precipitated by means of another aprotic solvent having a dielectric constant of between 0 and 29.9 and a dipole moment in the range from 0.00 to 2.99 debye.