Eun Joo Jang

Hydrodechlorination of CCl4 over Pt/Al2O3: effects of platinum particle size on product distribution

Abstract The impregnated platinum catalysts showed various platinum particle sizes depending on the nature of the platinum precursors (Pt(NH 3 ) 2 (NO 2 ) 2 versus H 2 PtCl 6 ) and on the pH of the Al 2 O 3 suspension. The average platinum particle size increased with decrease in pH of the suspension in case of Pt(NH 3 ) 2 (NO 2 ) 2 , but this trend was vice versa for H 2 PtCl 6 . The product distribution in hydrodechlorination (HDC) of CCl 4 varied greatly with the platinum particle size; the larger the platinum particle size was, the higher was the selectivity to CHCl 3 . To elucidate the origin of this platinum particle size effect on product distribution, CO chemisorption, NH 3 and CO 2 temperature-programmed desorption (TPD), high resolution transmission electron microscopy (HRTEM), temperature-programmed surface reaction (TPSR), Fourier-transformed-infrared spectra (FT-IR) and X-ray absorption fine structure (XAFS) experiments were carried out. The formation of completely dechlorinated CH 4 was favorable owing to the strong chemisorption of CCl 4 on the small platinum particles characterized by low surface coordination numbers and by an electron-deficient property. The nature of carbonaceous species formed on platinum surface at the beginning of reaction also varied greatly with platinum particle sizes and changes of electronic state of platinum particles affected catalytic activity and products’ distribution.

Regioselective synthesis of ibuprofen via the palladium complex catalyzed hydrocarboxylation of 1-(4-isobutylphenyl) ethanol

Abstract The synthesis of 2-(4-isobutylphenyl) propionic acid (ibuprofen) by the hydrocarboxylation of 1-(4-isobutylphenyl) ethanol with carbon monoxide and water has been studied in the presence of PdCl 2 –PPh 3 –HCl catalyst system. An almost regiospecific synthesis has been achieved under moderate reaction temperatures and pressures. In this reaction system, the liquid phases comprised of an acid-stable organic solvent and an acidic aqueous phase, and the miscibility between two phases were important for efficient hydrocarboxylation. The rate of reaction and the selectivity to the desired branched acid depended strongly upon the pressure of carbon monoxide, the ratio of phosphine ligand to palladium, the concentration of hydrochloric acid, and the nature of halide ion used.

A palladium complex catalyst for the regioselective hydrocarboxylation of 4-methylstyrene

Abstract With a homogeneous catalyst system of PdCl 2 CuCl 2 PPh 3 dissolved in a polar solvent, highly regioselective hydrocarboxylation of 4-methylstyrene to the branched α-(4-methylphenyl) propionic acid has been achieved. Effects of additives (mineral acids and O 2 ) and reaction conditions (amounts of catalyst components, reaction temperature, pressure and solvents) have been studied. Compared with the previous results of hydrocarboalkoxylation of 4-methyl-styrene to the ester by the same catalyst, the hydrocarboxylation required severer reaction conditions and the presence of a polar solvent that could solubilize water. Efficient hydrocarboxylation was achieved only after fine adjustments of the reaction conditions and addition of a halogen compound. And the addition of HCl improved the reaction rate significantly. This improvement was due to the effect of chlorine, not the effect of the proton. The addition of oxygen reduced reaction rates by oxidizing carbon monoxide and PPh 3 .

Liquid-phase hydrodechlorination of CCl4 in a medium of ethanol with co-production of acetal and diethyl carbonate

During the liquid-phase hydrodechlorination (HDC) of CCl4 over supported Pd or Pt catalysts in the presence of C2H5OH and molecular oxygen, the selective catalytic synthesis of CHCl3 as well as the conversion of C2H5OH to diethyl carbonate (DEC) and 1,1-diethoxyethane (DEE) was observed. The protic solvent, C2H5OH, could easily donate proton that reacts with the adsorbed chlorine on the catalyst surface to form HCl. This facile removal of chlorine from the catalyst surface could be the main reason for the enhancement of the catalytic stability and conversion of C2H5OH. The rate of DEC formation was accelerated with the increase in the partial pressure of molecular oxygen, and the selectivity to DEE was enhanced by the increased surface acidity of catalysts. Compared to the reactions of the hydrodechlorination of CCl4 without C2H5OH, the conversion of CCl4 and the selectivity to CHCl3 was greatly enhanced in the presence of C2H5OH.

Hydrocarboxylation of 1-(4-isobutylphenyl) ethanol catalyzed by heterogeneous palladium catalysts

Heterogeneous palladium catalysts were employed for the synthesis of 2-(4-isobutylphenyl) propionic acid (ibuprofen) by carbonylating 1-(4-isobutylphenyl) ethanol (IBPE) with carbon monoxide and water. Among the supported palladium catalysts tested, palladium anchored on montmorillonite showed good activity for the carbonylation and good selectivity to ibuprofen. For the palladium/montmorillonite catalyst, the presence of triphenylphosphine and hydrogen chloride in the reaction solution was essential for its catalytic activity even if triphenylphosphine and chloride ion had already been coordinated to the palladium precursor. The effects of reaction variables on the heterogeneous carbonylation have been investigated for the regiospecific synthesis of ibuprofen, and it was revealed that the palladium/montmorillonite showed better selectivity to ibuprofen than the homogeneous counterpart. This heterogeneous catalyst recovered by filtration after a batch of the reaction showed activity similar to that of the fresh catalyst for a new batch of reaction. Furthermore, the filtrate without the solid catalyst did not show any carbonylation activity. These implied that dissolution of palladium component from the solid catalyst had not been serious.