Concerning the identity test for caffeine in the pharmacopoeia - Part 2: Constitution of the dye from the modified reaction

Under modified conditions the products of alkaline hydrolysis of caffeine a nd theophylline give blue dyes with imidazo[1,5-a-]pyrimidium salts as inte rmediates. From caffeidine results as final product-in contrary to the prev ious assumption-the 2,4-bis-[2-[4-dimethylaminophenyl]-ethenyl]-1,7-dimethy l-8-(N-methylcarbamoyl)-imidazo[1,5-a]pyrimidinium diperchlorate. Theophyll idine gives rise to a mixture of two condensation products with one mole p- dimethylaminobenzaldehyde in each case. The UV/VIS spectroscopic comparison of the dye resulting from the modified method shows the non identity with that of the pharmacopoeia test, caused by the changed stoichiometry of the reactants. The pharmacopoeia test is not specific for caffeine, because all 7-substituted xanthines, which can give an analogous product to caffeidine by alkaline hydrolysis generate a positive reaction.