Experimental and theoretical studies of pyrolysis of chrysophanol and its derivatives

Rhubarb has been used as a tobacco additive recently. In order to understand the smoke emissions of herbal cigarettes with rhubarb additive, the pyrolysis of major components of rhubarb: chrysophanol and its derivatives (emodin, rhein and aloe-emodin) have been studied by synchrotron VUV photoionization mass spectrometry (SVUV-PIMS) combined with molecular-beam sampling technique. Various pyrolysis products are observed due to the different substituent groups. The main pyrolysis products of chrysophanol come from the CO and H2O elimination reactions. The CO, CO2 and HCOOH elimination reactions are the primary pyrolysis processes for rhein. Besides, elimination of H2 from aloe-emodin and loss of OH radical from both emodin and rhein also occur in the pyrolysis process. Furthermore, theoretical calculations are used to deduce the decomposition pathways and determine the geometries of pyrolysis products. Our work shows that the combination of SVUV-PIMS measurements and theoretical calculations is powerful to study pyrolysis behavior of complex organic compounds.