Cellulose triacetate Preparation

Deacetamidocolchicine (18) was prepared by the classic syntheses of Eschenmoser (38) and van Tamelen (39). The racemate was resolved by medium-pressure liquid chromatography on swollen, microcrystalline cellulose triacetate prepared at 5°C, and the enantiomers were collected at -70°C (32). The (-)-enantiomer with the same biaryl configuration as natural (aS,7S)-colchicine (1) was eluted first and found to be essentially optically pure. Thermal racemization of the optical isomers gave the ther-... 

Cellulose Triacetate. Cellulose triacetate is prepared according to the following reaction ... 

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. 

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. 

Polymer Plasticizer. Nylon, cellulose, and cellulose esters can be plasticized using sulfolane to improve flexibiUty and to increase elongation of the polymer (130,131). More importantly, sulfolane is a preferred plasticizer for the synthesis of cellulose hoUow fibers, which are used as permeabiUty membranes in reverse osmosis (qv) cells (131—133) (see Hollow-FIBERMEMBRANEs). In the preparation of the hoUow fibers, a molten mixture of sulfolane and cellulose triacetate is extmded through a die to form the hoUow fiber. The sulfolane is subsequently extracted from the fiber with water to give a permeable, plasticizer-free, hoUow fiber. 

Perchloric acid is a weU-known acetylation catalyst, especially in the fibrous method of preparing cellulose triacetate. Unlike sulfuric acid, perchloric acid does not combine with cellulose (78), ie, it does not form esters, and therefore virtually complete acetylation (DS 3.0, 44.8% acetyl) occurs. However, the extremely corrosive nature of perchloric acid and explosive nature of its salts have precluded its use industrially as an acetylation catalyst. 

The first practical CSP derived from polysaccharides is cellulose triacetate (21, Figure 3.10) prepared by Hesse and Hagel in 1973.94,95 Since this derivative was prepared by the heterogeneous acetylation of native microcrystalline cellulose (Avicel) in benzene, it has been postulated that its structure is closely related to that of native cellulose (form I). This has been called microcrystalline cellulose triacetate (CTA-I). CTA-I shows characteristic chiral... 

Fluorescent cellulose triacetate membranes were prepared by incorporation of pyrene-butyric acid (219), and were applied to in situ detection of ground water contamination by explosives, based on fluorescence quenching by the nitro groups LOD 2 mg/L of DNT (220) and TNT (221) and 10 mg/L for RDX (276) the response follows the Stern-Volmer law for DNT and TNT442. 

In principle, molecular sieve carbons (MSC) can be achieved by the pyrolysis of thermosetting polymers such as polyvinylidene chloride, polyfurfuryl alcohol, cellulose, cellulose triacetate, polyacrylonitrile and phenol formaldehyde (Koresh 1980). An example is given by Trimm and Cooper (1970,1973) for the preparation of MSC (mixed with metallic compounds) for catalyst systems. A mixture of furfuryl alcohol, platinum oxide and formaldehyde was heated to 40°C and additional formaldehyde was added to ensure the... 

Cotmnercial cellulose triacetate samples were fractionated by both fractional precipitation and preparative gel permeation chromatography (GPC). The triacetate fractions were characterized by vlsco-metry, high speed membrane osmometry (HSMO) and GPC. A fair agreement has been found between the molecular weights of various triacetate fractions determined by the three procedures. 

Choice of Solvent. JJ-Methylpyrrolidone (NMP) was initially used as the mobile phase but proved to be unsatisfactory because of (i) high solution viscosities, (il) exceedingly small differences in refractive index between NMP and cellulose triacetate solutions, (ill) erratic base line. In view of this dichloromethane was employed. Some additional benefits derived from this mobile phase are (i) a decrease in elution volume due to low solution viscosities, (il) fast solvent recovery due to low boiling point of dichloromethane and (iii) ease of obtaining preparative GPC cuts of cellulose triacetate. 

Preparative GPC of Cellulose Triacetate Sample. A 1% (m/V) solution of cellulose triacetate (medium) prefiltered through porosity 3 glass sinter was fractionated by repeated injection through the column set described above. Seven cuts covering the entire elution curve were collected. The flow rate, injection time and the experimental conditions were identical to those stated above. 

Narrow Molecular Weight Triacetate Fractions. Narrow molecular weight cellulose triacetate fractions were obtained by both fractional precipitation and preparative GPC as described above. The number average molecular weight (1 ) of the various fractions and cuts was determined by high speed membrane osmometry. A linear dependence of GPC elution volume on log molecular weight for all cellulose triacetate fractions was found in both methylpyrroli-done and dichloromethane. 

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... 

Analytical methods can be transferred easily to the preparative scale in polysaccharide-based CSPs, and these compounds have been used in preparative chromatography. Cellulose triacetate, which has good loading capacity, has been used for preparative separation at the industrial scale [70,85]. Moreover, the low cost of cellulose triacetate synthesis makes CTA ideal for preparative chromatography. 

Shin et al. [88] Ornithine Kuruma prawn Ornithine carbamyl transferase, nucleoside phosphorylase and xanthine oxidase/in membranes prepared from cellulose triacetate, glutaraldehyde and 1,8-diamino-4-am i nomethyl octane Oxygen electrode ... 

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