Polymorphism of (+)N-tosyl-L-glutamic acid

It has been shown that polymorphism is the reason for the occurrence of (+)N-tosyl-L-glutamic acid 1 with various melting points. 1 occurs in two crystalline forms: α and β. Form α-1 (prisms) having a melting point of 145–147°C is chemically pure and stable. Form β-1, however, is unstable and is formed as a result of the stabilizing effect of an organic solvent not introduced into the structure of the crystal. At about 125°C the β forms is transformed to the α form. The melting point of the β form depends on the amount and type of solvent contained in the crystal, which, during measurement cannot leave the system.