Thermal cracking of indan in deuterium at 8 MPa pressure

Abstract

The thermal cracking of indan, at 500 and 515 °C in an atmosphere of pressurized deuterium of 8 MPa, produces several cracking products, each of which consists of a mixture of isotopically-substituted molecules with various numbers of deuterium atoms. The yield of the deuterated components increases with the reaction time; the products formed at reaction times close to zero contain no or only low levels of deuterium. The deuterium in the reaction products results from a stepwise hydrogen-deuterium exchange, which occurs preferentially at naphthenic carbon atoms. In the cracking reactions of indan, which proceed by α- and β-ring opening mechanisms, indan itself functions as a hydrogen donor substance which splits off the hydrogen atoms required in the initiation of the α-ring opening and which quenches radical intermediates by intermolecular hydrogen transfer. Radical quenching with deuterium gas is a much slower reaction and accounts for <25% of the primary products formed. Taken with conclusions from previous work, the present findings indicate that the thermal hydrocracking of indan might shift from the α- or β-ring opening mechanism with direct radical -H 2 interactions towards a H-donor mechanism where radical intermediates are quenched by H-transfer from indan. This shift would be caused by increasing the concentration of indan in the system.