Clay-supported bio-based Lewis acid ionic liquid as a potent catalyst for the dehydration of fructose to 5-hydroxymthylfurfural

Abstract

Caffeine and halloysite nanoclay mineral that are bio-based compounds were utilized to synthesize a novel Lewis acid heterogeneous catalyst. To this aim, halloysite was functionalized with 2,4,6-trichloro-1,3,5-triazine and reacted with caffeine, which was then converted to ionic liquid via a reaction with ZnCl2. The catalyst was applied for promoting the dehydration of fructose to 5-hydroxymethylfurfural. To investigate the effects of the reaction variables, response surface methodology was used. The product was achieved in 98.5% in 100 min using a catalyst loading of 30 wt% at 100 °C. Moreover, the catalyst was recyclable up to six runs with slight zinc leaching. Comparison of the catalytic activity of the catalyst with that of halloysite and a control catalyst with one caffeine-based Lewis acid ionic liquid confirmed the superior activity of the former and the important role of 2,4,6-trichloro-1,3,5-triazine for increasing the number of the grafted caffeine and thus the acidic sites of the catalyst. A plausible reaction mechanism was proposed, and the activity of the catalyst for other carbohydrates was also studied. According to the results, this catalyst catalyzed the reaction of other substrates to furnish 5-hydroxymethylfurfural in low to moderate yields. According to the kinetic studies, the activation energy was estimated to be 22.85 kJ/mol.