Meenakshi Goyal

Direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol using Pd–Cu based redox catalyst system

A catalyst system was designed for direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol. Besides Pd carbonylation catalyst, inorganic and organic redox cocatalysts were included in the catalyst system for in situ regeneration of active Pd species. Copper(II) acetate was used as inorganic redox cocatalyst and hydroquinone was found to give good results as organic redox cocatalyst. Efficiency of various bases, effect of a drying agent, and optimum reaction conditions for achieving high catalytic activity were also investigated in detail. Using suitable components of catalyst system and under optimum reaction conditions, a Pd turnover number of 250 could be obtained.

Solid‐phase thermal polymerization of macrocyclic ethylene terephthalate dimer using various transesterification catalysts

Thermal ring-opening polymerization of a uniform macrocyclic ethylene terephthalate dimer with and without catalyst was investigated for the first time. Although polymerization progressed without a catalyst, the reaction was extremely slow and all the products were colored. Various transesterification catalysts were tested for their activity toward this ring-opening polymerization. Among the various catalysts, 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane exhibited the highest catalytic activity, and a colorless polymer with a weight-average molecular weight of 36,100 was obtained in 100% yield by heating for 3 min at 200 °C. It is noteworthy that our method does not need a vacuum because no side products are formed during the process.

Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd dinuclear complex bridged with pyridylphosphine ligand

Abstract Pd dinuclear complexes bridged with pyridylphosphine ligand such as Pd 2 (Ph 2 PPy) 2 X 2 (Ph 2 PPy: diphenyl-2-pyridylphosphine, X: Cl, Br, I, OCN, SCN, NO 2 , N 3 ) were investigated as catalysts for direct synthesis of diphenyl carbonate (DPC) by oxidative carbonylation of phenol using carbon monoxide (CO) and air. Pd 2 (Ph 2 PPy) 2 X 2 /redox catalyst/ammonium halide system were found to be more effective than not only conventional PdBr 2 /Ce(Trop) 4 (Trop: tropolonate)/(Ph 3 P=) 2 NBr (bis(triphenylphosphoranylidene)ammonium bromide) system but Pd 2 (dpm) 2 X 2 (dpm: bis(diphenylphosphino)methane)/Mn(TMHD) 3 (TMHD: 2,2,6,6-tetramethyl-3,5-hepentanedionate)/(Ph 3 P=) 2 NBr system too. The best efficiency was obtained by using Pd 2 (Ph 2 PPy) 2 (NO 2 ) 2 /Ce(TMHD) 4 /(Ph 3 P=) 2 NBr system where TOF reached 19.21 (mol-DPC/mol-Pd h).

Effect of inorganic redox cocatalyst on Pd‐catalyzed oxidative carbonylation of phenol for direct synthesis of diphenyl carbonate

A catalyst system for direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol was investigated with special emphasis on the inorganic redox cocatalyst component. Besides the inorganic redox cocatalyst, the catalyst system was composed of a Pd carbonylation catalyst, an organic redox cocatalyst, a base and a drying agent. Ce(OAc)3·H2O was found to be the most efficient inorganic redox cocatalyst giving DPC in 76% yield with a Pd turnover number of 250 and without producing any major side products.

Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd complex with diimine ligands

Pd complexes with diimine ligands were investigated as novel Pd catalysts for direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol using carbon monoxide and air. Best efficiency was obtained by using a PdCl2(ArN=CH–)2 or PdCl2(ArN=CMe–)2/Mn(TMHD)3/(Ph3P=)2NBr system where TOF reached 8.08 and 8.00 mol-DPC/mol-Pd h, respectively. The efficiency was increased with increases in the CO pressure.

Direct synthesis of aromatic polycarbonate from polymerization of bisphenol A with CO using a Pd-Cu catalyst system

Abstract Direct polymerization of bisphenol A with CO was carried out using a Pd–Cu-based redox catalyst system. A base for activating the hydroxy group of bisphenol A and a dehydrating agent for removing the water produced during the reaction were other important components of the catalyst system. Synthesized polycarbonate was characterized using IR, NMR, and GPC. MALDI-TOF mass spectroscopy was used for understanding the structure of polymer chain end groups.

Pd catalyzed polycarbonate synthesis from bisphenol A and CO: control of polymer chain—end structure

Abstract Direct polymerization of bisphenol A with CO was carried out using a catalyst system constituted of a Pd carbonylation catalyst, an inorganic redox catalyst, an organic redox cocatalyst, a base and a dehydrating agent. Usage of Cu(OAc)2 as inorganic redox cocatalyst led to the synthesis of polycarbonate of Mw 3600 but the formation of o-phenylene carbonate (o-PC) and salicylic acid type groups at the chain ends was observed. In an attempt to eliminate end group formation and explore the possibility of higher molecular weight polymer synthesis, various modifications were made in the catalyst system. On replacing Cu with Ce, o-PC formation could be eliminated completely. In addition, the usage of bis(triphenylphosphoranylidene) ammonium bromide (PPNBr) instead of tetrabutylammonium bromide [n(Bu)4NBr] resulted in elimination of acid group formation leading to the synthesis of polymer of Mw 3.8×10 3 (determined by GPC), with hydroxy group at both chain terminii. Polymer structure was investigated in detail by IR, NMR, and MALDI-TOF-MS studies.

Novel usage of palladium complexes with P-N-P ligands as catalysts for diphenyl carbonate synthesis

Two palladium complexes with P-N-P ligands [Pd{(sPPh(2))(2)N}(2)]{Pd(S,S)} and [Pd{(SePPh)(2)N}(2)] {PPd(Se,Se)} were prepared and investigated as novel polladium catalysts for oxidative carbonylation of phenol using carbon monoxide and oxygen along with a redox catalyst (for in situ regeneration of palladium) and ammonium halide, The efficiency of these new catalysts was compared with that of a PdCl2-based catalyst system. In order to obtain the maximum efficiency, the effects of various parameters such as concentration of redox catalyst and ammonium halide, the effect of solvent, the influence of a quinone-type redox catalyst in addition to inorganic redox catalyst, and the effect of temperature were studied, Under the reaction conditions employed, the Pd(S,S) catalyst was found to perform better than PdCl2-based catalyst system, whereas the Pd(Se,Se) catalyst had extremely low efficiency.

Thermal polymerization of uniform macrocyclic ethylene terephthalate dimer

Abstract Thermal ring-opening polymerization of uniform macrocyclic ethylene terephthalate dimer was examined at various temperatures above its melting point. From SEC study, it can be indicated that the polymerization proceeded through chain reaction, not through a typical polycombination reaction. Maximum molecular weight of the polymer obtained under optimum reaction conditions reached to a sufficiently high level of more than 20,000 (Mw). It is noteworthy that this new reaction for synthesizing poly(ethylene terephthalate) progresses without any catalyst under atmospheric pressure.

Palladium catalyzed synthesis of aromatic carbonates

Abstract A catalyst system was designed for direct synthesis of aromatic polycarbonates by oxidative carbonylation of various diphenols. The catalyst system is constituted of a Pd based carbonylation catalyst, a combination of inorganic and organic redox cocatalyst for in situ regeneration of active Pd species, a base and a dehydrating agent. Resulting polymers were characterized by IR, NMR, MALDI-TOF mass, and GPC analysis. GPC results showed that polymers of Mw up to 7.9 x 10 3 could be synthesized successfully.