Secondary cellulose acetate Preparation

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. 

Cellulose acetate [9004-35-7] is the most important organic ester because of its broad appHcation in fibers and plastics it is prepared in multi-ton quantities with degrees of substitution (DS) ranging from that of hydrolyzed, water-soluble monoacetates to those of fully substituted triacetate (Table 1). Soluble cellulose acetate was first prepared in 1865 by heating cotton and acetic anhydride at 180°C (1). Using sulfuric acid as a catalyst permitted preparation at lower temperatures (2), and later, partial hydrolysis of the triacetate gave an acetone-soluble cellulose acetate (3). The solubiUty of partially hydrolyzed (secondary) cellulose acetate in less expensive and less toxic solvents such as acetone aided substantially in its subsequent commercial development. 

Hydroxy-containing polymers such as poly(methyl-methacrylate-co-hydroxyethyl methacrylate) [65,66] or secondary cellulose acetate [67,68] were used for this purpose. Vanadium (V) 8-hydroxy quinoline-hydroxy-ethyl methacrylate adduct, prepared by condensation of the latter with a VOQ2OH complex, is polymerized to... 

In the preparation of secondary cellulose acetate rayon cotton linters, waste cotton or high-grade wood pulp is purified by boiling with alkali followed by hypochlorite bleaching. After purification the cellulose is dried... 

Secondary cellulose acetate (D.S. 2.4) is prepared by interrupting the acetylation reaction leading to CTA by adding water in the form of aqueous acetic acid of 50-75% concentration (as noted above). This also decreases the level of combined sulfuric acid which improves the stabihty of the cellulose acetate. Magnesium ions are added to produce insoluble sulfeles further improving the stability of the product. The hydrolysis rate is controlled by temperature, catalyst concentration and to a smaller extent by the water content. The amount of water influences the ratio of primary to secondary hydror l groups in the hydrolyzed cellulose acetate. 

The preparation of secondary cellulose acetate might be represented as... 

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

Acetone-soluble cellulose acetate is prepared by deacetylating cellulose triacetate. The product formed directly is unsatisfactory. Thus the distribution of free hydroxyls and acetate groupings is of primary importance. Cramer and Purves118(b) studied the distribution by tosylation and found that the acetyl removal from primary and secondary hydroxyl groups occurs at approximately the same rate, but that the number of... 

Use of the tosyl derivative of cellulose for theoretical study is important. Cramer and Purves have prepared tosyl derivatives of acetone-soluble cellulose acetate. By treatment with sodium iodide, which replaces tosyl groups in the primary position by iodine, they have been able to measure the proportions of primary and secondary hydroxyl groups present in the original product. 

Nail lacquers, or naU polishes, consist of resin, plasticizer, pigments, and solvents. The most commonly used resin is nitrocellulose or cellulose acetate butyrate, prepared by esterification of celluloses with nitric acid, with a degree of substitution between 1.8 and 2.3 nitrate groupings per anhydroglucose unit. Ethyl acetate, butyl acetate, isopropyl alcohol, and toluene are typical solvents. Toluenesulfonamide-formaldehyde resin [25035-71-6] and similar polymers, for example, the terpolymer of 2,2,4-trimethyl-1,3-pentanediol, isophthalic acid, and trimeUitic anhydride, are the resins of choice as secondary film formers for optimal nail adhesion. Other resins, such as alkyds, acrylates, and polyamides, can also serve as secondary film formers. 

The primary OH group can be selectively blocked by the bulky triphenyl-methyl (trityl) moiety, followed by esterification at the secondary OH groups and removal of the protecting trityl group. Thus 2,3-di-O-acetyl cellulose has been obtained by this procedure. Moreover, regioselectively substituted mixed cellulose esters, acetate/propionate, were prepared by subsequent acy-... 

There is no satisfactory commercial means to directly acetylate to the 2.4 acetyl level and obtain a secondary acetate that has the necessary solubility for fiber preparation. Since cellulose is highly crystalline and its polymer chains are held tightly together in an ordered manner through extensive hydrogen bonding, it is insoluble in the reaction medium until almost complete acetylation is achieved. Thus, commercially, cellulose is fully acetylated to triacetate and then hydrolyzed back to secondary acetate of 2.4 DS. Careful hydrolysis is nearly random yielding uniform polymer. 

Prepared by acetylation of cellulose with acetic anhydride/acetic acid in the presence of sulfuric acid. Acetylation is normally carried out fully to produce a product known as primary acetate, which approaches the triacetate stoichiometry, and which may then be partially hydrolysed to secondary acetate (DS value 2.2-2.5). Used in manuf. of textile fibres, cigarete filters and lacquers, including photographic films. World production 740000 t in 1987. 

Attempts were made to isolate the TBG. A preliminary purification from serum by ion-exchange chromatographic analysis on a Dowex-I column equilibrated with acetate buffer (pH 4.5) was followed by repeated ammonium sulfate precipitation, chromatographic analysis on dimethylaminoethyl-cellulose resin, and electrophoresis on cellulose columns. These attempts finally yielded a preparation homogeneous on electrophoresis and in the ultracentrifuge. The amino acid composition and the secondary structure of TBG is not known, and it is still debated whether it is a lipo-or glycoprotein. 

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