METAMORPHOSIS OF CAFFEINE HYDRATE AND ANHYDROUS CAFFEINE

The phase stability, interconversion and physicochemical characterisat ion of caffeine (1,3,7-trimethyl-purine-2,6-dione) hydrate and anhydro us caffeine relate to the strength of the available hydrogen-bonds. A hydrogen-bonded T-branched spine of hydrate molecules establishes a we ak lattice bond for the caffeine hydrate which, under ambient conditio ns, transforms to a beta-anhydrous phase which in turn, at 155 degrees C and with an enthalpy of 3.6 kJ mol(-1), converts to a trigonal phas e alpha-anhydrous caffeine. The anhydrous phases are stabilised by wea k CH3 to CO hydrogen bonds.