Biopolymers are an important area of research as a replacement for petroleum derived products. In the US, 331 million barrels, or 4.6 % of the total US petroleum consumption, were used to make polymers in 2006 (329 million as feedstock, 2 million for energy) [119]. By displacing the need for petroleum, production of biopolymers could lessen global oil demand. While cellulose, starches, and other naturally occurring biopolymers can be difficult to work with due to their chemical and physical properties, chemical modification of these naturally occurring poly­mers allows for a wide range of properties to be achieved [120]. See Table 8.1 for representative examples. Additionally, modification of biopolymers can be used to aid in analytical methods by making otherwise insoluble polymers such as cellulose soluble in a wide range of solvents [130]. Smaller molecules of interest can also be manufactured through the chemical modification of monosaccharides. In many cases, it is even possible to couple the use of ILs and enzymes to effect a biocatalytic change while maintaining the advantages of an IL system [131]. Because ILs have the ability to solubilize unmodified biomass, they are

Table 8.1 Biomass modification reactions in ionic liquids

Cellulose——— OH

well suited to the task of chemical modification of lignocellulose for a wide variety of applications. ILs are particularly well suited to chemical modification of carbo­hydrates because, generally, the sugars or biopolymers are more hydrophilic while the reactants for derivatization are more hydrophobic. The ILs are often able to solubilize both reactants and, in the case of smaller molecules, the amphiphilic product. Research into modification of biomass in ILs is also important because there is significant work focusing on using enzymes in IL based systems, which could lead to other enzymatic processing of biomass in ILs.

The modification of monosaccharides with laurates is a common method for the production of surfactants. Glucose modification with vinyl laurates in ILs has been studied by Lee et al. using 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIMTfO) and 1-butyl-3-methylimidazolium bis(trifluorosulfonyl)imide (BMIMTf2N). Using lipase enzymes, Lee and coworkers demonstrated that a super saturated solution of glucose in a mixture of BMIMTfO and BMIMTf2N, along with ultrasound treatment produces a better conversion and yield in less time than subsaturation solutions in a pure IL without the ultrasound [121—123]. This reaction, producing sugar esters with lipase enzymes, has been demonstrated in other ILs, such as BMIMBF4 and BMIMPF6 [124].

Modification of larger saccharide chains requires ILs that are better suited to biomass solvation. Unfortunately, the ILs that solvate cellulose and lignocellulose are also destructive to enzymes [132]. Consequently, most of the research in the modification of cellulose and lignocellulose uses non-enzymatic catalysts or no catalysts at all. Success has been seen in acetylation, carbanilation, sulfation,
succinilation (Table 8.1), and benzoylation of cellulose chains in imidazolium based chlorides and bromides along with choline chloride ILs [125—129]. There has been work in combining the enzymes and ILs that will dissolve biomass. Zhao and coworkers developed ILs with Me(EtO)n— substituted imidazolium and alkylammonium (where n = 2-7) cations coupled with an acetate anion that are both effective for solubilizing cellulose and as a solvent for lipase catalyzed esterification. These ILs can dissolve cellulose up to 10 wt%, and support enzy­matic esterification with methylmethacrylate with yield up to 66 % [71].