Biomass valorization derivatives: Clean esterification of 2-furoic acid using tungstophosphoric acid/zirconia composites as recyclable catalyst

Abstract

2-Furoic acid esters, which are biomass derived, are used in the flavoring and fragrance industry or as synthesis intermediates in the pharmaceutical industry. A series of zirconia samples modified with different contents of tungstophosphoric acid (TPA) and two different preparation methods (ZrPEGTPA30T100, ZrPEGTPA60T100, ZrTPA30PEGT100, and ZrTPA60PEGT100) were synthesized from zirconium propoxide via sol–gel reactions using polyethylene glycol as template. They were characterized by different physicochemical techniques (BET, FT-IR, 31P MAS NMR and potentiometric titration), and their activities were tested in the synthesis of n-butyl-2-furoate as the model compound, among which ZrTPA30PEGT100, (mesoporous acid zirconia modified catalyst) was the most active catalyst. The effect of various parameters such as catalyst loading, mole ratio of 2-furoic acid to n-butanol, and temperature was studied under optimized conditions. Several other alkyl 2-furoates were produced from esterification of 2-furoic acid with different alcohols using these catalysts, and the effect of alcohol structure over the conversion reaction was considered. The use of a solid acid catalyst made the procedure environmentally benign. The catalysts ZrPEGTPA30T100 and ZrTPA30PEGT100 were reused without appreciable loss of the catalytic activity (three runs). The methodology represents a green and efficient alternative for the conversion of bio-based 2-furoic acid into valuable esters.