Bifunctional crystalline microporous organic polymers: Efficient heterogeneous catalysts for the synthesis of 5-hydroxymethylfurfural

Abstract

Developing efficient catalysts for the synthesis of 5-hydroxymethylfurfural (HMF) from biomass resources is very demanding as it is an important renewable platform chemical for the synthesis of biofuels, polymers and fine chemicals. Here, we have designed two new crystalline microporous bi-functional porous organic polymers through the extended aromatic substitution reaction under refluxing conditions. Porous polymers containing sulfonic acid and secondary amine groups are two reactive catalytic centres for carrying out the bi-functional heterogeneously catalysed reactions. Bifunctionalized porous polymers POPDS and POPSDS are synthesized through the reaction of 2,2'-benzidinedisulfonic acid and 4,4'-diaminostilbene-2,2'-disulfonic acid with cyanuric chloride, respectively. The materials were characterized thoroughly using powder X-ray diffraction, N-2 sorption, FTIR, solid state C-13 CP MAS NMR spectroscopy, FE-SEM, HR-TEM, XPS and TG/DTA analysis. These two crystalline porous polymers possesses good surface acidic and basic sites, and having flower-like and spherical particle morphologies. POPDS and POPSDS exhibited superior catalytic activity for the conversion of different small carbohydrates to 5-hydroxymethylfurfural (HMF) under microwave irradiation. Moreover, the recyclability tests of these catalysts revealed good durability up to sixth consecutive reaction cycles, suggesting the future potential of these catalysts in the sustainable synthesis of HMF.