Sulfonated Expanded Polystyrene Waste Promotes the (+)-Citronellal Cyclization Reaction: A Sustainable Alternative Process for Biomass Valorization

Abstract

In this work, sulfonated expanded polystyrene waste (WEPS), obtaining from recycling of the expanded polystyrene (EPS) waste by low-cost sulfonation reaction, were successfully applied as environmentally benign acid solid in the liquid-phase cyclization of (+)-citronellal (1), under mild reaction conditions. (-)-Isopulegol (2) and (+)-neoisopulegol (3) were obtained with a total yield equal to 80%. Products 2 and 3 have direct industrial application in the composition of fragrances and flavorings. (-)-Isopulegol is also used as a synthesis intermediate of (-)-menthol. It was not observed the leaching of acid sites from WEPS to reaction solution, thereby, this process presented heterogeneuos nature. The WEPS was stable in the reaction medium and presented little significant loss of its performance in consecutive reactions of its reuse. In addition, WEPS showed better performance than commercial resin Amberlyst-15, in the same reaction conditions. The use of WPES as acid solid in reactions of industrial interest is an attractive, low-cost and environmentally friendly alternative for application of this material, obtained by recycling EPS waste, for adding value to natural ingredients obtained from biomass.