X-ray studies of a single crystal chemical reaction: photo-oxide of anthracene to (anthraquinone, anthrone)

Abstract

The chemical reaction proceeds via intermediate stages of disorder, decomposition and re-crystallization which can be followed in detail by means of X-ray diffraction at room temperatures, since the reaction is then slow, taking upwards of 200 h for completion or near completion. As the temperature is raised the rate of reaction increases and X-irradiation becomes unnecessary except for the diffraction studies. At 80 °C the reaction takes 7 to 20 h but a ‘single’ crystal still results. The geometrical mechanism of the reaction seems to be the same whether it is caused by X-irradiation or by heat. Above 110 °G the original crystal is liable to fall to a powder in a few minutes, and at or near to the m.p. 166 °C, it explodes. The ‘single crystal’ reaction generates some 5% ‘free space’ in the original crystal, thus allowing room for the gaseous products of the reaction to remain within the structure. The natures of the final product and of some probable breakdown and intermediate molecules or radicals were determined by mass spectrometry. Some related reactions are discussed.