Selective acetalization of ethylene glycol with methyl 2-napthyl ketone over solid acids: Efficacy of acidic clay supported Cs_2.5H_0.5PW₁₂O₄₀

Abstract

Catalytic conversion of biomass to value added products is relevant with regard to several industries. Biomass derived ethylene glycol has many applications. Acetalization is used to synthesize valuable chemicals and also occasionally to protect carbonyl groups of aromatic molecules in organic transformations. Acetalization of ethylene glycol to cyclic dioxolane has many applications in fragrance, cosmetics, food and beverage additives, pharmaceuticals, detergents, and lacquer industries. The current work reports synthesis of 2-methyl-2-napthyl-1,3-dioxolane by acetalization of ethylene glycol with methyl 2-napthyl ketone using several heterogeneous solid acid catalysts including 20% (w/w) Cs_2.5H_0.5PW₁₂O₄₀/K-10 (Cs-DTP/K-10), UDCaT-4, UDCaT-5 and K-10 clay. Among them, 20% (w/w) Cs-DTP/K-10 catalyst was found to be the most efficient catalyst giving 87% conversion of methyl 2-napthyl ketone with 100% selectivity toward 2-methyl-2-napthyl-1,3-dioxolane. Effects of several reaction parameters were studied and optimized. The optimum reaction conditions were: 110 °C, molar ratio of methyl 2-naphthyl ketone to ethylene glycol 1:2, catalyst loading 0.02 g/cm³, speed of agitation 800 rpm, and time 3 h. Reaction mechanism and kinetic model were developed. The methodology was extended to different substrates, and catalyst reusability was also studied. The catalyst was well characterized by various techniques such as XRD, BET, FTIR, TPD and SEM. It is robust and recyclable.