Transition-metal-free decarboxylation of D-glucaric acid to furan catalyzed by SnCl4 in a biphasic system

As a useful chemical, furan can be produced from bio-based chemicals, such as furfural and furoic acid (FA). There were few reports on the preparation of furan from bio-based C6 aldaric acids. Herein, a new method was developed to produce furan from D-glucaric acid (GA) without transition metals, and nearly 80% yield of furan was produced in the water/toluene biphasic system with SnCl4 at 200 degrees C in 2 h. 3-Hydroxy-2-pyrone (3-HP) and FA were proved to be the key intermediates in the formation of furan from GA, and the reaction pathway was proposed to be GA -> 3-HP -> FA furan based on the kinetic study, model substrate reaction, and isotope labeling experiments. SnCl4 gave the highest furan yield among the common acid catalysts, and the contrast experiments suggested that H+, Cl- and Sn4+ all have promoting effect on GA conversion to furan. This method was also applicable with other C6 aldaric acids.