Solid Phase Transfer Catalyst Research Articles

Kinetic model, recycling, regeneration, and reusing of tri-phase catalytic nucleophilic substitution esterification

This research aims to develop a liquid–solid–liquid phase-transfer catalyst (PTC) catalytic kinetic model of carboxylate esterification unpublished previously. The bimolecular nucleophilic substitution reaction of sodium benzoate with benzyl bromide has been experimented with the immobilized solid PTC to propose the kinetic model and calculate the apparent reaction rate constant and activation energy. We proposed the proper kinetic model of the esterification successfully. In addition, the experimental results comprehensively matched the pseudo-first-order reaction formula. Under the multiple steps of recovery, reuse, and regeneration, the structure of tri-phase PTC support remains well, nor will it destroy the activated site immobilized on the support. Comparing the reactivity of the fresh PTC with PTCs recovered four times, the reactivity does not decrease with the continued recovery, indicating excellent catalytic reactivity. Besides, the esterification, etherification, and benzylation reactions catalyzed by regenerated PTCs and their yields are not much different from those of the original fresh PTCs. It shows that the catalytic activity of regenerated PTC is quite excellent. In our opinion, exploring the regeneration and reduction of PTC can reduce cost, save resources, possesses the potential to apply to other reaction systems, and improve conventional production.

Palladium-phosphinous acid complexes catalyzed Suzuki cross-coupling reaction of heteroaryl bromides with phenylboronic acid in water/alcoholic solvents

Highly active, air-stable and water-soluble palladium-phosphinous acid complexes have been applied to Suzuki cross-coupling reaction of heteroaryl bromides under mild conditions in water/alcoholic solvents. Suzuki cross-coupling reaction of heteroaryl bromides with phenylboronic acid occurred efficiently using palladium phosphinous acid complexes (POPd) and phase transfer catalyst (tetrabutylammonium bromide and polyethylene glycol) in water/ethanol mixture, water/propanol mixture and neat water respectively, the corresponding yields of cross-coupling heteroaryl-aryls were satisfied. The tert-butyl substituted ligand di-tert-butylphosphino in combination with POPd was found to be more active than the same family derived catalysts dipalladium complexes POPd1 and POPd2, and other two kinds of Pd-catalysts Pd(PPh3)4 and Pd2(dba)3. The mechanism of Suzuki cross-coupling reaction between heteroaryl bromides and phenylboronic acid in water was proposed with respect to the key role of phase transfer catalyst on the transmetallation step. Compared with other solid phase transfer catalysts, TBAB was tested as the ideal one. The alkalinity of base and the molar proportion between POPd and TBAB were investigated in water and alcoholic solvents. Notably, in the presence of TBAB adding alcoholic solvents into water enhanced the yields of target products. However in terms of the liquid phase transfer catalyst of PEGs, mixing water into PEGs could slightly decrease the yields with respect to the water free PEGs bulk phase, which was probably due to the homogenous liquid conditions in pure PEGs and weak interactions between PEGs and heteroaryl bromide molecules in water depending on their molecular chain lengths.

Kinetics of Oxidation of Benzyl Alcohol with Solid Phase Transfer Catalyst

Kinetics of Oxidation of Benzyl Alcohol with Solid Phase Transfer Catalyst