Polymer bound homogeneous catalysis in supercritical fluids.

摘要

Homogeneous catalysts are usually metal salts or metal complexes that are soluble only in organic solvents. Thus, organic synthesis with homogeneous catalysis is usually carried out in an organic toxic solvent. Currently, large-scale industry is facing environmental restrictions in the use of conventional solvents. The recovery of the catalyst after the completion of the reaction is an additional problem.; The use of toxic solvents can be alleviated by the use of supercritical fluids (SCFs). The use of SCFs as non-toxic solvents is promising. The most common SCF is CO₂. It has low critical properties, is inexpensive, non-flammable, non-toxic, and readily available. However, the main disadvantage is that conventional catalysts are not soluble in supercritical carbon dioxide (scCO₂).; In this study, a novel homogeneous rhodium catalyst that is bound to a copolymer backbone, which is soluble in scCO₂, was used. The polymer consists of fluoroacrylate branches and catalytic sites. Fluoroacrylate branches are soluble in scCO₂, hence scCO₂ was selected as the reaction medium. Since the catalyst is bound to a copolymer backbone, the catalyst was separated from the main stream by using a membrane reactor. The main objective of this research was to use scCO₂ as the reaction medium in the evaluation of the effectiveness of a novel rhodium catalyst in homogeneous organic synthesis. The aim of our approach was to obtain a solvent-free product and the intact recovery of the catalyst. Solubilities determinations were carried out using a gravimetric method. This catalyst was highly soluble in scCO₂ at the conditions studied. In order to evaluate the activity of the catalyst, two reactions were studied: hydrogenation and hydroformylation of 1-octene. The hydroformylation reaction of 1-octene was studied at two different temperatures and pressures. The reaction was enhanced with pressure at constant temperature. Branched aldehydes were the most abundant products with some isomerization and hydrogenation at some reaction conditions. To investigate the intact recovery of the catalyst, different reactor designs were studied. The catalyst was successfully recovered after the completion of the reaction, and several cycles were repeated with no loss of activity in the hydrogenation reaction of 1-octene.