Sulfur Compounds as Catalyst Modifiers in the Selective Hydrogenation of 1,5 Cyclooctadiene to Cyclooctene

Selective hydrogenation of cyclic-diolefins to cyclo-monoenes is a basic route to reactive olefin intermediates for the synthesis of c8 or C12 lactams, dicarboxylic acids, and their derivatives. Frequently the yield to the desired olefin can be improved by the addition of a small amount of material that modifies the system. Sulfur compounds in small amounts have been suggested for this purpose but the type of sulfur compound and the concentration required to enhance the selectivity has not been reported for a palladium catalyst. Experiments were conducted in a 300 ml autoclave at room temperature, about 25�C, under the hydrogen pressure of 413.7 kPa (60 psig). The results show that the detailed reaction sequence fits the experimental data well when the individual reaction steps are considered first order. With the sulfur containing compounds used in this study, thiophene, c4H4S, and mercaptan, c10H21sH, thiophene was the best reagent to enhance the selectivity and increase the yield of desired product, cyclooctene. However, the concentration of thiophene should be controlled in a range between 10 to 40 ppm. If excessive amounts of thiophene are employed the reaction remains very selective, but the rate of conversion of 1,5 cyclooctadiene is dramatically reduced; consequently, a low net yield of cyclooctene is obtained. The results also indicate that, at the same sulfur content, the mercaptan, c10H21sH, immediately poisoned the catalyst and sharply retarded the hydrogenation rate, resulting in significant low net yields to cyclooctene.Chemical Engineerin