FORMATION OF A TOPOCHEMICALLY PHOTOREACTIVE MIXED-CRYSTAL BY GRINDINGAND ITS MECHANISTIC INTERPRETATION

A mixed crystal of ethyl and propyl alpha-cyano-4-2-(4-pyridyl)ethenyl ]cinnamate was formed in the solid state by simple grinding. The mixed crystal formation was ascertained by the change in the X-ray diffract ion pattern upon grinding and by H-1 NMR and HPLC analyses of the phot oproducts. According to several attempts, it was concluded that a mech anical treatment was necessary for the formation of the mixed crystal phase. The kinetic data concerning the analysis of the topochemical ph otoproducts revealed that the following growth of the mixed crystal ph ase was triggered by each of the mixed crystal nuclei and that the gro wth of the mixed crystal phase was accelerated by either thermal annea ling or exposure in humidity. During the early stage of mixed crystal growth, the growth rate was nearly proportional to the surface area of the nuclei of the mixed crystal.