Bifunctional covalent organic framework as a heterogeneous acid photocatalyst for solvent-free microwave-assisted synthesis of isobornyl methacrylate

Abstract

Isobornyl methacrylate (IBOMA) is a bio-based specialty monomer with broad applications in coatings, adhesives, and dental materials. However, its conventional synthesis via the acid-catalyzed esterification of camphene with methacrylic acid suffers from poor catalyst recyclability, corrosive waste generation, and low energy efficiency. This study reports the first application of a sulfonated covalent organic framework, TpPa–SO3H, as a bifunctional heterogeneous catalyst for solvent-free IBOMA synthesis under combined visible-light irradiation and microwave heating. TpPa–SO3H was synthesized via both solvothermal and microwave-assisted routes, yielding chemically identical frameworks, with the microwave variant exhibiting a 45% greater total pore volume at 0.518 vs. 0.357 cm3 g−1. Under conditions optimized by the Box–Behnken response surface methodology using 5 wt% catalyst at 80 °C, 60 min, and a camphene-to-methacrylic acid molar ratio of 1 : 3, a maximum IBOMA yield of 90.97% was achieved. The catalyst retained above 80% yield over five reuse cycles, and E-factor analysis demonstrated 38- to 76-fold lower waste generation than with H2SO4, p-TsOH, and betaine hydrochloride. An environmental impact assessment further showed that the microwave-synthesized catalyst achieved a global warming potential of 0.0265 kg CO2 eq per kg IBOMA, which was 18–71% lower than that of three homogeneous acids, establishing TpPa–SO3H as an efficient and environmentally favorable catalyst for bio-based monomer synthesis.