Development of hydrogelator-based gel-entrapped base catalysts (GEBCs) as heterogeneous basic catalysts for the synthesis of 3-acetylcoumarins

Abstract

New gel entrapped base catalysts (GEBCs) have been prepared by entrapping some organic and inorganic bases into a solid aqueous gel matrix. Sodium alginate, gelrite and carboxymethyl chitosan were studied for the preparation of GEBCs. The phase behaviour of binary systems (gelator + water) is well studied, but ternary systems (gelator + water + base) are not much studied. Addition of a base to a (gelator + water) system drastically affected the behaviour of the gel. The phase behaviour of ternary systems (gelator + water + base) was studied by developing the corresponding ternary phase diagrams. From this study, the promising homogeneous viscous phases were converted into hard, irreversible gel beads by cross-linking the gelator with divalent cations Ca²⁺, Ba²⁺ and Sr²⁺. These gel beads were studied for base entrapment efficiency and leaching of the base. The GEBCs were used for the condensation of salicylaldehydes and methyl/ethyl acetoacetate to obtain 3-acetylcoumarins.