STUDIES OF THE MECHANISM OF THIOPHENE HYDRODESULFURIZATION - H-2 NMR AND MASS-SPECTRAL ANALYSIS OF 1,3-BUTADIENE PRODUCED IN THE DEUTERODESULFURIZATION (DDS) OF THIOPHENE OVER PBMO6S8 CATALYST

The deuterodesulfurization (DDS) of thiophene was investigated over PbMo6S8 at 400 degrees C using a flow-microreactor, Evidence indicates that 1,3-butadiene (BDE) is the first desulfurized product; its deuterium content was established by H-2 NMR and mass spectrometries. At different levels of thiophene conversion (0.86-10.2%), the amount of deuterium incorporated into BDE remains constant at 3.47 D atoms per BDE molecule. Unconverted thiophene incorporates 0.42 D atoms at 10.2% thiophene conversion but only 0.05 D atoms at 0.86% conversion. Reaction of 2,5-dihydrothiophene (2,5-DHT) with D-2 at 400 degrees C over PbMo6S8 liberates BDE as the only hydrocarbon product. This BDE incorporates no deuterium. Thiophene and H2S effectively inhibit both BDE hydrogenation and deuterium exchange. The results indicate that during the DDS process, a total of 3.2 deuterium atoms are incorporated into the BDE; 0.83 D are in the D-A-position while 1.2 D are in each of the D-B-and D-C-positions. Several HDS mechanisms proposed in the literature are consistent with these results; two are not. Details of all of these mechanisms are discussed.