Ionic liquids (ILs) are composed only of ions. Of special interest to this review are those where at least one ion (the cation) is organic and whose melting points are below or not far above room temperature. ILs are designated as "green" solvents because they have extremely low vapor pressure, are non-inflammable, and thermally and chemically stable. Therefore, many of them can be, in principle, recycled into the process indefinitely. The objective of the present review is to discuss different aspects of the use of ILs in carbohydrate chemistry, in particular, dissolution and functionalization of simple sugars, cyclodextrins, cellulose, starch, and chitin/chitosan. The molecular structure and synthesis of ILs most frequently employed in carbohydrate chemistry are discussed with an emphasis on imidazolium and pyridinium cations with different counterions. The physicochemical properties of ILs that are relevant to the dissolution and functionalization of carbohydrates, in particular their polarities and hydrogen-bonding abilities, are discussed. Dissolution of simple saccharides and biopolymers in ILs is presented with an emphasis on the mechanism of carbohydrate--IL interactions. Finally, the very interesting novel applications of the solutions obtained are addressed. These include, inter alia, spinning of the dissolved biopolymer into fibers, extrusion into slabs and rods, formation of matrixes for a myriad of substrates, including biomacromolecules, formation of nanocomposites, and functionalization to produce important derivatives. The use of ILs in many branches of science is expanding fast; it is hoped that this review will draw the attention of researchers to the "window of opportunities" that these green solvents open into carbohydrate chemistry.

Organic chemistry Z 0200 Applications of Ionic Liquids in Carbohydrate Chemistry: A Window of Opportunities -[177 refs.]. -(EL SEOUD, O. A.; KOSCHELLA, A.; FIDALE, L. C.; DORN, S.; HEINZE, T.; Biomacromol. 8 (2007) 9, 2629-2647; Inst. Quim., Univ. Sao Paulo, 05513 Sao Paulo, Brazil; Eng.) -Lindner 46-241

The question posed in the title has been addressed by studying the swelling of celluloses at 20°C by twenty protic solvents, including water; linear-and branched-chain aliphatic alcohols; unsaturated aliphatic alcohols, and alkoxyalcohols. The biopolymers investigated included microcrystalline cellulose, MC, native and never-dried mercerized cotton cellulose, cotton and M-cotton, and native and never-dried mercerized eucalyptus cellulose, eucalyptus and M-eucalyptus, respectively. In most cases, better correlations with the physico-chemical properties of the solvents were obtained when the swelling was expressed as number of moles of solvent/ anhydroglucose unit, nSw, rather than as % increase in sample weight. The descriptors employed in these correlations included, where available, Hildebrand's solubility parameters, Gutmann's acceptor and donor numbers, solvent molar volume, V S , as well as solvatochromic parameters. The latter, employed for the first time for correlating the swelling of biopolymers, included empirical solvent polarity, E T (30), solvent ''acidity'', a S , ''basicity'', b S , and dipolarity/ polarizability, p S * , respectively. Small regression coefficients and large sums of the squares of the residues were obtained when values of nSw were correlated with two solvent parameters. Much better correlations were obtained with three solvent parameters. The most statistically significant descriptor in the correlation equation depends on the cellulose, being p S * for MC, cotton, and eucalyptus, and V S for M-cotton and M-eucalyptus. The best correlations were obtained with the same set of four parameters for all celluloses, namely, solvent pKa (or a S ) b S , p S * , and V S , respectively. These results indicate that the supra-molecular structure of the biopolymer, in particular the average sizes of crystallites and micro-pores, and the presence of its chains in parallel (cellulose I) or anti-parallel (cellulose II) arrangements control its swelling. At least for the present biopolymer/solvent systems, use of solvatochromic parameters is a superior alternative to Hildebrand's solubility parameters and/or Gutmann's acceptor and donor numbers. The relevance of these results to the accessibility of the hydroxyl groups of cellulose, hence to its reactivity, is briefly discussed.

The swelling of microcrystalline, native and mercerized cotton and eucalyptus celluloses by 16 aprotic solvents was investigated. The number of moles of solvent/anhydroglucose unit, nSw, correlates well with solvent molar volume, basicity and dipolarity/polarizability. Swelling is sensitive to cellulose crystallite size, surface area and the presence of its chains in parallel or anti‐parallel arrangements. Use of solvatochromic parameters is a superior alternative to the use of other descriptors, such as Hildebrand's solubility parameters and Gutmann's donor numbers. The calculated nSw for 28 protic and aprotic solvents correlated well with their experimental counterparts, although hydrogen bond donation by the solvent was not included.magnified image