First investigations of the kinetics of the topochemical reaction of p-formyl-trans-cinnamic acid by time-resolved X-ray diffraction

Abstract

Under UV irradiation p-formyl-trans-cinnamic acid (p-FCA) crystals in the beta-phase dimerise irreversibly to solid 4,4'- diformyl-beta-truxinic acid. The experimental conditions were chosen in such a way (non-aqueous environment and room temperature) that the product formed is amorphous. The kinetics of this bimolecular reaction, which has not yet been characterised, was investigated by picosecond time-resolved X- ray diffraction. From the experimental results a mechanism for this topochemical reaction is proposed including two observed time constants, one less than 100 ps and another of several seconds. The feasibility of investigating this class of substances by time-resolved X-ray diffraction from third generation synchrotron sources and future free-electron lasers is discussed