Russian Chemical Bulletin, International Edition, Vol. 62, No. 3, pp. 1—, March, 2013 1 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 0829—0834, March, 2013. 1066-5285/13/6203-1 © 2013 Springer Science+Business Media, Inc. Conversion of carbohydrates to 5-hydroxymethylfurfural: the nature of the observed selectivity decrease and microwave radiation effect* E. A. Khokhlova, V. V. Kachala, and V. P. Ananikov N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., 119991 Moscow, Russian Federation. Fax: +7 (499) 135 5328. E-mail: val@ioc.ac.ru The special NMR monitoring technique showed that conversion of glucose and fructose to 5-hydroxymethylfurfural in ionic liquids is highly selective and the formation of by-products, mainly oligomers, is related to further dehydration of 5-hydroxymethylfurfural. The replace- ment of usual heating by microwave irradiation provides high conversion of glucose (93%) and good yield of 5-hydroxymethylfurfural (85%) at 80 °C within 2.5 min. Key words: ionic liquids, carbohydrates, 5-hydroxymethylfurfural, biomass, biofuel, micro- wave irradiation, glucose, fructose. Since the problem of environmental pollution and po- tential exhaustion of natural resources was aggravated in the last decades, considerable attention has been devoted to chemical and biotechnological processing of plant bio- mass. 1,2 Being a renewable natural resource, biomass ac- cumulates the solar energy, which historically stipulated its use for electrical power and heat generation by direct combustion. However, currently another area is being ac- tively explored, in particular, conversion of biomass to liquid fuel and important intermediates, which may serve as the feedstock for chemical industry. 3,4 The major structural components of plant biomass are oligomeric and polymeric carbohydrates. Direct sub- jection of these materials to chemical reactions is highly inefficient and uneconomic. A promising way of chemi- cal utilization of carbohydrate materials comprises cata- lytic hydrolysis and dehydration, leading to 5-hydroxy- methylfurfural (5-HMF) (Scheme 1). 5—7 Thus, an in- dividual chemical compound of a particular structure can, in principle, be obtained from a complex mixture of biomass raw materials. It is known that 5-HMF is a full-value participant of the production of food sup- plements, pharmaceuticals, polymers, motor fuel addi- tives, and precursors of biofuels, and also a promising in- termediate for chemical industry. 8 According to the re- sults of analytical estimates, 5-HMF was proposed as a chemical platform for the sustainable chemical industry of the 21st century. 1—8 Therefore, an important research challenge is to con- vert plant hexose carbohydrates (D-fructose, D-glucose and so on) and hexose-containing materials, which are the major components of biomass, to 5-HMF. The most dif- ficulty is associated with particularly the second stage of this process (dehydration of hexoses), whereas the first stage (hydrolysis) is rather thoroughly studied. 9 The key issue is to attain high yield and selectivity of the formation of 5-HMF, and this requires suppression of a variety of side reactions. Imidazolium ionic liquids with halide anions have proved to be good solvents for cellulose biomass and carbohydrates. Moreover, recently it was shown 9—12 that 5-HMF is directly formed in ionic liquids with good selec- tivity. Currently, a large number of reactions catalyzed by mineral acids, 13—15 various metal salts, 14,16—18 and sulfon- ated ion exchange resin (Amberlyst-15) 19 have been studied, and this confirmed the efficiency of using ionic liquids as * Dedicated to the Academician of the Russian Academy of Sciences I. P. Beletskaya on the occasion of her anniversary. Scheme 1