Solventless green synthesis of 4-O-aryloxy carbonates from aryl/alkyl-oxy propanediols and dimethyl carbonate over nano-crystalline alkali promoted alkaline earth metal oxides

Abstract

4-O-(Alkyl/aryl)-oxy-1,3-dioxolane-2-ones find wide applications such as additives, solvents in lithium ion batteries and building blocks in the synthesis of chiral oxazolidinone derivatives. Traditional processes to synthesize 4-O-(alkyl/aryl)-oxy-1,3-dioxolan-2-ones include the use of isocyanates and phosgene derivatives as carboxylating agents which are very toxic, highly hazardous and require longer reaction times. In the present work, a green and solventless process was developed to synthesize 4-O-(aryl/alkyl)-oxy-1,3-dioxolan-2-ones by reacting 3-(aryl/alkyl)-oxy-1,2-propanediol with dimethyl carbonate using alkali promoted MgO catalyst prepared by a combustion synthesis (CS) method. The self propagating CS method is the most effective to prepare highly active oxide nanoparticles considering the cost of synthesis and simplicity. A series of alkali promoted MgO catalysts with different alkali promoters were prepared using the CS method. Catalysts with different alkali promoters were screened to study their efficacy, among which lithium metal was found to be the best promoter with 0.1% as optimum loading on MgO. The resulting catalysts were characterized by CO₂-TPD, FTIR, XRD, BET, etc. The effects of various parameters such as molar ratio, speed of agitation, catalyst loading and temperature were studied. The reaction mechanism followed a Langmuir–Hinshelwood–Hougen–Watson (LHHW) model with strong adsorption of both reactants leading to zero order kinetics with 28 kcal mol⁻¹ as the apparent activation energy. Complete conversion of 3-O-(aryl/alkyl)-oxy-1,2-propanediol with 100% selectivity towards 4-O-(aryl/alkyl)-oxy carbonates was achieved with different aryl/alkyl substituents. The process gave 88.66% atom economy with an E-factor of 0.3 in 1 h at 140 °C.