Second-Generation meta-Phenolsulfonic Acid–Formaldehyde Resin as a Catalyst for Continuous-Flow Esterification

A second-generation m -phenolsulfonic acid–formaldehyde resin (PAFR II) catalyst was prepared by condensation polymerization of sodium m -phenolsulfonate and paraformaldehyde in an aqueous H 2 SO 4 solution. This reusable, robust acid resin catalyst was improved in both catalytic activity and stability, maintaining the characteristics of the previous generation catalyst ( p -phenolsulfonic acid–formaldehyde resin). PAFR II was applied in the batchwise and continuous-flow direct esterification without water removal and provided higher product yields in continuous-flow esterification than any other commercial ion-exchanged acid catalyst tested.