Cellulosic hydroxyls with organic

Previous work by us has led to the synthesis of silicon, germanium and tin polyethers utilizing Interfacial systems (for instance 5-9). The tin-cotton products should possess an analogous structure from previously reported similarities in reactivity of soluble cellulosic hydroxyls with organic acid chlorides... 

Table 5.3 Main changes observed in cellulosic fibres after esterification of the hydroxyl groups with organic acids... 

Cellulose is the most abundant organic material found in nature (13). It is the primary component of plant cell walls and is therefore a large constituent of fruits and vegetables. Since cellulose is safe for human consumption, it is commonly used as an additive in food products. Cellulose and chemical derivatives of cellulose are also widely used as excipients in pharmaceutical applications. The biocompatibility of cellulose coupled with a molecular structure that is conducive to chemical modification, has made cellulose a staple of pharmaceutical formulations. Each anhydroglucose unit of the cellulose backbone contains three hydroxyl groups that provide reactive sites for chemical substitution. Thereby, cellulose can be chemically modified in a variety of ways to yield materials with differing properties useful for diverse pharmaceutical applications. 

Cellulose, whose repeat structure features three hydroxyl groups, reacts with organic acids, anhydrides, and acid chlorides to form esters. Plastics from these cellulose esters are extruded into film and sheet and are injection molded to form a wide variety of parts. Cellulose esters can also be compression molded and cast from solution to form a coating. The three most industrially important cellulose ester plastics are cellulose acetate (CA), cellulose acetate butyrate (CAB), and cellulose acetate propionate (CAP), with structures as shown in Fig. 2.2. 

Additionally, cellulose sulfonates can also function as a protecting group to prevent reaction of the C6 hydroxyl during esterification reactions (Fig. 8). Cellulose tosylates with degrees of substitution from 0.38 to 2.30 have been reported. Although an effective synthetic tool, the expense of organic solvents utilized and the cost and corrosive nature of tosyl chloride have limited the use of this methodology on a commercial scale. 

Hydroxyethylcellulose (HEC) and hydroxypropylcellulose (HPC) are prepared by nucleophilic ring opening of ethylene oxide and propylene oxide, respectively, by the hydroxyl anions on the anhydroglucose ring of cellulose. Reactions are conducted commercially in caustic aqueous slurry processes (72). Laboratory methods recently have been reported for preparation of cellulose ethers, esters, and carbamates imder homogeneous reaction conditions in organic solvents (88-91). Such solvents may lead to development of new commercial processes for cellulose derivatives with more imiform substitution. 

Fischer esterification of hydroxyl groups with simultaneous hydrolysis of amorphous cellulose chains using organic acids, such as acetic and butyric acid, mixed with hydrochloric acid to extract CNs has become a viable one-pot reaction methodology that allows isolation of functionalized CNs in a single-step process [25, 26]. Figure 11.4 schematically illustrates the reaction during the process of extraction and... 

Cellulose, whose repeat structure features three hydroxyl groups, reacts with organic acids, anhydrides, and acid chlorides to form esters. Plastics from these cellulose esters are... 

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