Catalytic dechlorination of 1-chlorooctadecane in supercritical carbon dioxide

Palladium catalyzed hydrodechlorination of 1-chlorooctadecane in supercritical carbon dioxide (SC-CO2) was performed and compared to dechlorination in isopropanol at atmospheric pressure (liquid isopropanol). The reaction utilized isopropanol as a hydrogen donor and its rate in SC-CO2 was significantly faster than in isopropanol at atmospheric pressure. The dechlorination yield in liquid isopropanol was increased by addition of NaOH, while the presence of either NaOH or triethylamine in SC-CO2 lowered the dechlorination yield significantly. Experimental parameters such as pressure, temperature, and the concentrations of reagents (isopropanol and palladium) in the absence of base were optimized in SC-CO2 to obtain complete dechlorination. Kinetic studies of the reaction were then performed to deduce the reaction mechanism. The apparent activation energies of the reaction were 43 ± 5 kJ mol-1 in SC-CO2 and 35 ± 3 kJ mol-1 in liquid isopropanol. The rate determining step of the reaction was deduced to be adsorption of 1-chlorooctadecane on the palladium surface

Catalytic hydrodechlorination of 1-chlorooctadecane, 9,10-dichlorostearic acid, and 12,14-dichlorodehydroabietic acid in supercritical carbon dioxide

Kinetic and thermodynamic analyses of catalytic hydrodechlorinations in supercritical carbon dioxide (SC-CO2) were performed using 5% Pd supported on γ-Al2O3. The selected standard compounds used for the study represented chlorinated wood resins commonly found in pitch deposits; 1-chlorooctadecane (C18-Cl), 9,10-dichlorostearic acid (Stearic-Cl2), and 12,14-dichlorodehydroabietic acid (DHA-Cl2). The reaction utilized isopropanol as a hydrogen donor. Pressure, temperature, and the concentrations of isopropanol and palladium were varied to study the effect of each parameter and to optimize the dechlorination yield. The reaction in SC-CO2 was compared to the one in liquid solvents at atmospheric pressure. By applying a Langmuir-Hinshelwood kinetic model, the rate-determining step of the reaction was deduced to be adsorption of the chlorinated molecules on the palladium surface. The apparent activation energies of the reactions for C18-Cl, Stearic-Cl2, DHA-Cl2 were 43 ± 5, 40 ± 7, and 135 ± 7 kJ mol-1, respectively, in SC-CO2. The relatively high activation energy for DHA-Cl2 was apparently due to structural differences from the other two compounds. The apparent activation energy of dechlorination of C18-Cl in liquid isopropanol at atmospheric pressure was determined to be 35 ± 3 kJ mol-1, leading to the conclusion that the rate-determining step is the same for this compound in both fluid systems. The enthalpies of desorption of stearic acid and dehydroabietic acid were determined to be 18 ± 2 and 12 ± 2 kJ mol-1, respectively. These values being less than half of the apparent activation energies of dechlorination of their corresponding chlorinated compounds indicates that desorption of the dechlorinated products is not the rate-determining step of the reaction. This was consistent with the conclusion that the rate-determining step is adsorption, on the understanding that the reaction mechanism is same in both fluid systems