Conversion of cellulose to glucose and levulinic acid via solid-supported acid catalysis Jessica Hegner, Kyle C. Pereira, Brenton DeBoef * , Brett L. Lucht * Department of Chemistry, University of Rhode Island, Kingston, Rhode Island 02881, United States article info Article history: Received 17 December 2009 Revised 22 February 2010 Accepted 23 February 2010 Available online 1 March 2010 abstract Cellulose is hydrolyzed to glucose, which is further converted to levulinic acid in the presence of surface- supported Brønsted and Lewis acid catalysts. Nafion catalysts, in particular, have the potential to be recy- cled or applied to a continuous flow reactor for the synthesis of these biofuel precursors. Ó 2010 Elsevier Ltd. All rights reserved. Cellulose, the principle structural component of plants, is the most abundant organic compound on earth. It is a biopolymer that consists of glucose units joined by b(1?4) linkages. This bond, by itself, is not partially strong, as it can be readily hydrolyzed by sim- ple acids such as HCl or by cellulolytic enzymes. However, the cel- lulose polymer, as a whole, is very robust. The individual glucose monomers are so densely packed together by an extensive network of hydrogen bonds that enzyme catalysts and most aqueous sol- vents cannot penetrate the structure. Consequently, cellulose is virtually insoluble in water and is generally regarded as a difficult material to work with. The development of methods for hydrolyz- ing raw biomass from renewable, non-food bearing plants, either to glucose or directly to biofuels, is highly desirable. These difficult transformations are not readily feasible using the current best technology, which employs cellulolytic enzymes, as they require water solvents and mild conditions under which cellulose is not readily soluble. Herein, we report an improved chemical method to convert raw cellulose to biofuel precursors. The chemical conversion of cellulose to fuel feedstocks has re- ceived significant attention recently. 1 A method for converting C6-sugars such as glucose and sorbitol to fuels suitable for use in automobiles and aircraft has recently been reported. However, the process employs a Pt–Re catalyst on a graphite support, and is energy intensive, requiring temperatures >500 K and pressures of 27 bar. 2–4 While sugars are cheap and readily available com- modities, their refinement from biomass adds to the overall energy consumption of the process. Reducing conditions have also been applied to the conversion of cellulose to sugar alcohols. Either plat- inum or ruthenium catalysts at high temperatures and under high- pressure of H 2 can convert cellulose to a mixture of polyols, whose main component (80%) was sorbitol. 5 The current best method for converting biomass to a fuel was reported in 2008. The process employs refluxing HCl (a Brønsted acid) in the presence of LiCl, resulting in an 80% conversion. The primary product of the reaction is 5-(chloromethyl)furfural, which is not a biofuel, but this intermediate can be readily converted to 5-(ethoxy)furfural, which can be used as a diesel additive. 6 Ionic liquids have been used to dissolve cellulose 7 and even raw wood chips. 8 These solvents have the added benefit that they are generally considered to be ‘green’ due to their low vapor pressure. These solvents have been used with Brønsted acid catalysts to convert fructose to hydroxymethylfuran. 9 Recently, Schüth and co-workers degraded cellulose in [BMIM][Cl], an imidazolium- based ionic liquid, with an Amberlyst catalyst. A combined yield of less than 4% was observed for the production of both mono- and disaccharides. 8 Subsequently, Binder and Raines described a reaction medium containing dimethylacetamide, LiCl, CrCl 2 , and an ionic liquid that is capable of processing both sawdust and corn stover to furfurals in good yields. 10 Minimal attention has been given to the use of solid-supported acid catalysis for the depolymerization of cellulose in water. Recent reports describe the hydrolysis of cellulose by acid-modified amor- phous carbon, 11 layered transition metal oxides, 12 or Amberlyst re- sin. 8 These surface acidic species were quite efficient for the conversion of cellulose into smaller, water-soluble b(1?4) glucans, but conversion to glucose or other small biofuel precursors was limited. In this Letter we report the chemical conversion of cellulose to glucose and levulinic acid by hydrolysis of silica-supported acid catalysts under relatively mild conditions. The reaction is catalyzed by both Nafion and FeCl 3 supported on amorphous silica. 13 Nafion SAC 13 (Nafion polymer on amorphous silica), in particular, has the potential to be recycled or applied to a continuous flow reactor, providing that residual, unreacted cellulose can be removed from the system. Our initial experiments were conducted with cellobiose as a substrate (Scheme 1). Cellobiose is a water-soluble single repeat unit of cellulose and is frequently used as a cellulose model compound. A Teflon-capped glass reaction flask was charged with 0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2010.02.148 * Corresponding authors. Tel.: +1 401 874 9480; fax: +1 401 874 5072. E-mail address: blucht@chm.uri.edu (B.L. Lucht). Tetrahedron Letters 51 (2010) 2356–2358 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet