Esterification, of cellulose

Cellulose acetate is the most important ester derivative of cellulose. It is produced by acetylation of cellulose using acetic anhydride in acetic acid in the presence of a strong acid catalyst (usually sulfuric acid). In Eq. 9-29 the symbol is a general means of representing a polymer molecule minus the functional group of interest and —OH specifically 

Partially acetylated cellulose (i.e., cellulose with less than three ester groups per repeat unit) is produced by an indirect route. Direct synthesis yields an inhomogeneous product due to insolubility of cellulose in the reaction mixture. Some chains are completely acetylated while others may be completely unreacted. A partially acetylated product is usually produced by controlled hydrolysis of the triacetate. The triacetate is soluble in the reaction mixture and complete solubility ensures that the final product will be more homogeneous. Hydrolysis of the triacetate is carried out by controlled reversal of the esterification reaction by the addition of water or dilute acetic acid. 

Various ether derivatives of cellulose, including some that are water-soluble, are important [Heinz and Liebert, 2001 Just and Majewicz, 1985 Zhang, 2001]. Methyl cellulose and car-boxymethyl cellulose (R = CH3 and CH2COOH, respectively) are synthesized by reaction of cellulose with sodium hydroxide followed by the appropriate alkyl halide  

Hydroxyethyl cellulose is produced by using ethylene oxide in place of the halide. Applications for these products include lacquers, additives for detergents, food, drilling muds, and paints. 

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Cellulose triacetate is obtained by the esterification of cellulose (qv) with acetic anhydride (see Cellulose esters). Commercial triacetate is not quite the precise chemical entity depicted as (1) because acetylation does not quite reach the maximum 3.0 acetyl groups per glucose unit. Secondary cellulose acetate is obtained by hydrolysis of the triacetate to an average degree of substitution (DS) of 2.4 acetyl groups per glucose unit. There is no satisfactory commercial means to acetylate direcdy to the 2.4 acetyl level and obtain a secondary acetate that has the desired solubiUty needed for fiber preparation. 

Eastman uses acetic anhydride primarily for esterification of cellulose, producing acetic acid as a byproduct. This acetic acid is used to convert the methanol into methyl acetate in a reactor-distillation column in which acetic acid and methanol flow countercurrently. 

Uses Solvent for cellulose ethers modifying esterification of cellulose acetate ingredient of metal polishes and shoe polishes manufacture of aniline, benzidine, quinoline, azobenzene, drugs, photographic chemicals. 

Nitrocellulose is obtained by esterification of cellulose with nitric acid. This process is described simply as nitration or more exactly O-nitration. The nitration of cellulose can be expressed by means of the following equation ... 

The investigations of Lunge and Bebie [15] made it clear that dinitrogen tetroxide, present in the mixed arid up to 6%, had no adverse influence on the degree of esterification of cellulose. It is known that dinitrogen tetroxide reacts in the presence of sulphuric acid so as to form one molecule of HN03 from one molecule of dinitrogen tetroxide ... 

Heinze et al. found that DMSO in combination with tetrabutylammonium fluoride trihydrate dissolved cellulose (degree of polymerization < 650) within 15 min at room temperature [38]. They also demonstrated that homogeneous esterification of cellulose is possible in this solvent system. The applicability of this new solvent system to cellulose grafting has recently been proved by adoption of cyclic compounds such as lactones and N-carboxy a-amino acid anhydrides (NCAs) [39]. e-Caprolactone was facilely graft-polymerized on cellulose at a graft rate of 65% (per trunk weight of 100), and NCAs at over 100%, in the respective homogeneous reaction systems at < 60 °C. 

Catalysis, enzyme-substrate and intermediate compound theory in homo-and heterogeneous, V, 51 Catalysts, for acetonation, III, 51 for acetylation of starch, I, 284, 286 Bourguel s, II, 109, 110, 113 for esterification of cellulose, I, 312 in oxidation of carbohydrates by halogens, III, 177... 

The influence of sulphuric acid in O-nitration processes, as for example in the esterification of cellulose with a mixture of sulphuric and nitric acids, appears to be somewhat different. This will be dealt with in the chapter on esters (Vol. II). 

The formylation method is based on the determination of the ratio of the extent of esterification of cellulose by formic acid after a given time interval to that of soluble starch for the same... 

Philipp et al. [177,178] studied the esterification of cellulose dissolved in N2O4-DMF solution, which is known to form nitrite derivatives preferentially at the C6 position. Sulfation was shown to occur mainly at the 6-OH group presumably as a result of a transesterification reaction. Such a process, however, did not occur in phosphorylation, which appeared to take place directly on the 2-OH and 3-OH groups. 

A relatively novel class of derivatives is obtained by the covalent incorporation of organometallic moieties into cellulose. For example, cellulose ferro-cenyl derivatives have been prepared by esterification of cellulose with an intermediate derived from ferrocene carboxylic acid and triphenyl phosphite in the presence of pyridine [84]. An enzymatically cleavable cellulose ester has been developed [85], and prodrugs have been coupled to the hydroxyl or carboxyl functions of C-terminal aromatic amino acids of cellulose peptide derivatives for controlled release applications [86]. 

The esterification of cellulose by propiolk acid proceeds only in the presence of a catalyst and at a sufficiently high concentration ctf acid (>80%). 

It is natural that with the growing interest in cellulose acetate, chemists have investigated other organic cellulose esters. Cellulose formate, the ester of the lowest member of the fatty acid series, has been studied. sufficiently to show that it is unlikely to be of commercial im-portance. It is difficult to produce a high degree of esterification of cellulose with this acid, and the ester which is obtained is very limited in solubility, and is highly unstable toward moisture and elevated temperatures. 

Various details of procedure are known for the esterification of cellulose with acetic anhydride in acetic acid. solvent. The factors of pretreatment, catalyst concentration, acetylation temperature and time of reaction are kept in balance in order that products of satisfactory appearance and the desired range of viscosity will be obtained. Modifications of this general formula usually involve the use of different solvents to replace part or all of the acetic acid. 

Partial esterification of cellulose with p-toluenesulfonyl chloride may be accomplished in the presence of pyridine, or by reaction with alkali cellulose. The tosyl (p-toluenesulfonyl) group has been shown to react quite readily with the primary hydroxyl group of cellulose but much more slowly with the secondary groups. The reaction in the presence of pyridine must be carried out at low temperatures to prevent the introduction of nitrogen and halogen from side reactions. ... 

The field of monosaccharides, disaccharides and polysaccharids contains many industrial examples of semi-synthesis, which have entered chemical history, such the hydrolysis of starch to form D-glucose, the esterification of cellulose, the chemistry of rayon and, more recently, advances in the chemistry of carbohydrate surfactants (ref.83). 

Esterification of cellulose with phosphoric acid yields a product which is not inflammable, but is of no use because the loss of tensile strength is excessive. The loss of strength is avoided if the esterification is carried out in the presence of urea (Brit. Pat. 604197) or cyanamide (Brit. Pat. 634690). The treated fabrics, however, are rather brittle and the flame-resisting effect does not stand up to repeated washings. 

The various ways in which esters of cellulose and phosphorous adds can be synthesized are esterification of cellulose with free acids alcoholysis, with cellulose, of the esters and amides of phosphoric adds and esterification with mixed anhydrides of phosphoric adds and carboxylic adds. 

The main use of methyl chlorides is for the production of higher chlorinated methanes. It also is used as a solvent and for many chemical reactions. It is used in the methylation or esterification of cellulose, which is used as industrial gum. Chloroform also is used in the esterification of alcohols. The scheme is as follows ... 

The vitality of this field is further demonstrated by a continuous search for original ways of exploiting vegetable oils. Examples include self-healing elastomers in which fatty acids play a central role [46] the esterification of cellulose with fatty acids to give thermoplastic materials [47] the synthesis of a saturated aliphatic diisocyanate from oleic acid and its subsequent use in the preparation of fully biobased polyurethanes in conjunction with canola oil-derived polyols [48] and novel elastomers from the concurrent cationic and ring-opening metathesis polymerization of a modified linseed oil [49]. 

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