Trifluoroacetic acids, cellulosics

Many ceUulosic derivatives form anisotropic, ie, Hquid crystalline, solutions, and cellulose acetate and triacetate are no exception. Various cellulose acetate anisotropic solutions have been made using a variety of solvents (56,57). The nature of the polymer—solvent interaction determines the concentration at which hquid crystalline behavior is initiated. The better the interaction, the lower the concentration needed to form the anisotropic, birefringent polymer solution. Strong organic acids, eg, trifluoroacetic acid are most effective and can produce an anisotropic phase with concentrations as low as 28% (58). Trifluoroacetic acid has been studied with cellulose triacetate alone or in combination with other solvents (59—64) concentrations of 30—42% (wt vol) triacetate were common. 

Aqueous salt solutions such as saturated 2inc chloride [7646-85-7] or calcium thiocyanate [2092-16-2] can dissolve limited amounts of cellulose (87). Two non-aqueous salt solutions are ammonium thiocyanate [1762-95-4]— uoamonia. and lithium chloride /744Z-4/A/—dimethyl acetamide [127-19-5]. Solutions up to about 15% can be made with these solvents. Trifluoroacetic acid [76-05-17—methylene chloride [75-09-2] and /V-methy1morpho1ine N-oxide [7529-22-8]—(92—94) are two other solvent systems that have been studied (95). 

However, this method is appHed only when esterification cannot be effected by the usual acid—alcohol reaction because of the higher cost of the anhydrides. The production of cellulose acetate (see Fibers, cellulose esters), phenyl acetate (used in acetaminophen production), and aspirin (acetylsahcyhc acid) (see Salicylic acid) are examples of the large-scale use of acetic anhydride. The speed of acylation is greatiy increased by the use of catalysts (68) such as sulfuric acid, perchloric acid, trifluoroacetic acid, phosphoms pentoxide, 2inc chloride, ferric chloride, sodium acetate, and tertiary amines, eg, 4-dimethylaminopyridine. 

Fig. 7. Comparison of experimental phase boundary concentrations between the isotropic and biphasic regions for various liquid-crystalline polymer solutions with the scaled particle theory for wormlike hard spherocylinders. ( ) schizophyllan water [65] (A) poly y-benzyl L-glutamate) (PBLG)-dimethylformamide (DMF) [66-69] (A) PBLG-m-cresoI [70] ( ) PBLG-dioxane [71] (O) PBLG-methylene chloride [71] (o) po y(n-hexyl isocyanate) (PHICH°Iuene at 10,25,30,40 °C [64] (O) PHIC-dichloromethane (DCM) at 20 °C [64] (5) a po y(yne)-platinum polymer (PYPt)-tuchIoroethane (TCE) [33] ( ) (hydroxypropyl)-cellulose (HPC)-water [34] ( ) HPC-dimethylacetamide (DMAc) [34] (N) (acetoxypropyl) cellulose (APC)-dibutylphthalate (DBP) [35] ( ) cellulose triacetate (CTA)-trifluoroacetic acid [72]...

Basic Protocol 2 Determination of Noncellulosic Neutral Sugars and Cellulose Content by Trifluoroacetic Acid Hydrolysis Followed by Sulfuric Acid Hydrolysis E3.2.4... 

Several procedures have been used to hydrolyze polysaccharides in cell walls and cell wall fractions. For example, the noncellulosic polysaccharides can be hydrolyzed using 1 M sulfuric acid for 2 to 3 hr at 100°C (Selvendran and Ryden, 1990). One of the simplest procedures is that of Albersheim et al. (1967) in which hydrolysis of the noncellulosic polysaccharides is achieved by incubating in 2 M trifluoroacetic acid (TFA) at 121 °C for 1 hr. The advantage of the TFA procedure is that it is quick and the acid can be removed by evaporation in a gentle stream of air or nitrogen. However, neither the 1 M sulfuric acid or TFA procedures hydrolyze cellulose. Hydrolysis of cellulose can be achieved by an initial dispersion in 72% (w/w) sulfuric acid (Saeman et al., 1963 Selvendran et al., 1979 Fry, 1988 Harris et al., 1988 Selvendran and Ryden, 1990) followed by hydrolysis in 1 M sulfuric acid. 

DETERMINATION OF NONCELLULOSIC NEUTRAL SUGARS AND CELLULOSE CONTENT BY TRIFLUOROACETIC ACID HYDROLYSIS FOLLOWED BY SULFURIC ACID HYDROLYSIS... 

For the total hydrolysis of polysaccharides, trifluoroacetic acid (TFA) has important advantages over sulfuric acid. The reaction time is short and there is no need for conventional neutralization, as TFA is volatile and can be removed by evaporation. Several methods have been developed, depending on the substance to be hydrolyzed. Soluble saccharides (e.g., polyoses) can be hydrolyzed with diluted TFA, while cellulose, pulp, and wood need treatments with concentrated TFA in homogeneous solution. The presence of lignin impedes the hydrolysis of polysaccharides thus, especially for wood samples, an intensive treatment with TFA is necessary, and correction values have to be considered. Several application examples show that the hydrolysis with TFA enables a rapid quantitative determination of the composition of polysaccharides, pulps, and woods. 

Geddes, A. L. Interaction of Trifluoroacetic Acid with Cellulose and Re-... 

The standard procedure by Saeman et al. (I) involves manual stirring of the polysaccharide with 72% H2S04, standing at 30°C, and secondary hydrolysis at 100° or 120°C in a steam autoclave. While certain resistant polysaccharides are still incompletely depolymerized, decomposition of the more sensitive monosaccharides formed cannot be avoided. An alternative method by using trifluoroacetic acid was applied successfully for plant cell wall polysaccharides by Albersheim et al. (2) and for dissolving pulps and hemicelluloses by Fengel et al. (3). Highly crystalline cellulose was not well dissolved and not completely hydrolyzed by CFsCOOH. 

FIGURE 10 Chromatograms of enantiomeric resolution on cellulose tribenzoate CSPs. (a) ( )-//ireo-Methylphenidate on Chiralcel OB CSP, with hexane-ethanol-methanol-trifluoroacetic acid (480 9.75 9.75 0.5, v/v/v/v) as the mobile phase containing 0.2 mM benzoic acid, (b) ( H/ireo-methylphenidate on Chiralcel OB CSP, with hexane-ethanol-methanol-trifluoroacetic acid (480 9.75 9.75 0.5, v/v/v/v) as the mobile phase containing 0.2 mM phenol, (c) Ic aromatase inhibitor on Chiralcel OJ-R CSP, with acetonitrile-water (50 50, v/v) as the mobile phase, (d) lie aromatase inhibitor on Chiralcel OJ-R CSP, with acetonitrile-water (50 50, v/v) as the mobile phase. For structures of Ic and lie aromatase inhibitors, see later (Fig. 18). (From Refs. 98, 100.)... 

Without further purification, the compound is freed from the protective groups by standing for 1 hour in 80-90% trifluoroacetic acid containing some thioglycolic acid, and is subsequently precipitated by adding 150 ml of ether. Yield 3.06 g of crude peptide-trifluoroacetate. After purification on carboxymethyl cellulose, 1.45 g of the chromatographically pure peptide are obtained in the form of acetate. [a]D20 -68.6°-2° (c=0.5 in 1% acetic acid). Amino acid analysis ... 

A simple, isocratic chromatographic method for the separation, identification, and measurement of etodolac enantiomers without derivitization using chiral stationary phase columns has been reported [25]. A chiral stationary phase column packed with Chiracel OD (cellulose tris-3,5-dimethylphenylcarbamate coated on 10 pm silica gel) was used as the stationary phase. The mobile phase (85 15 v/v, n-hexane/2-propanol (containing 0.1% trifluoroacetic acid)) was pumped at 0.7 mL/min and the UV detection was set at 230 nm. The (-)-(/ )-etodolac enantiomer eluted first, indicating its stronger interaction between the stationary phase relative to the (+)-(S)-etodolac enantiomer. 

Threshold volume fractions observed for cellulose acetate (CA and CTA), ethyl cellulose (EC) and hydroxypropyl cellulose (HPC), each in various solvents, are presented in Table 3. The results depend to some extent on the solventThe data included are not exhaustive. Other cellulose esters exhibit mesomorphic behavior Chanzy et al. observed mesomorphic behavior in solutions of cellulose itself when dissolved in N-methylmorpholine N-oxide containing water at concentrations of cellulose in the range 20-55 % w/v, depending on the temperature, the water content of the solvent and the degree of polymerization of the cellulose. Solutions of cellulose in mixtures of trifluoroacetic acid with 1,2-dichloroethane or with chloroform are hkewise lyotropic at concentrations of 20% (w/v) and above according to Patel and Gilbert... 

The type 11 CSPs have been used to resolve a wide variety of pharmacologically active compounds, both with and without derivatization (9-11). Some of the compounds that have been resolved without derivatization are hexobarbital (OA-CSP) (51), glutethimide (OB, OC, OK) (51), warfarin (OB, OC) (51), compounds containing a chiral sulfur atom (OB, OC) (52), verapamil (AD) (53), propranolol (OD) (54), and flurbiprofen (AD) (55), The resolution of the latter two compounds, propranolol, an ot, p-amino-alcohd, and flurbiprofen, a carboxylic acid, is representative of new applications for the cellulosic CSPs that are primarily used with hexane alcohol mobile phases. In the case of propranolol, the mobile phase was modified with N,N-dimethyIoctyl amine, and when flurbiprofen was chromatographed, trifluoroacetic acid was used as the modifier. 

The rate of acetylation of 0-(hydrox3Tnethyl)cellulose (and other hydroxy compounds) by mixtures of carboxylic acids and their anhydrides has been found to increase greatly in the presence of trifluoroacetic acid. The acceleration is very much less with mono- and tri-chloroacetic acids, presumably because they form unsymmetrical anhydrides which are less effective acylating agents than acyl trifluoroacetates. The exceptional acylating power of the latter anhydrides is shown by their use in the synthesis of alkyl aryl ketones from polyalkylbenzenes, phenyl ethers, furan, and thiophene under mild conditions. The principle has been extended to include acids... 

Patel, D.L. Gilbert, R.D. Mesomorphic solutions of cellulose triacetate in halogenated organic acids and mixtures of trifluoroacetic acid and dichloromethane. J. Polym. Sci. Polym. Phys. Ed. 1981, 19 (9), 1449-1460. 

Modern polysaccharide columns are based on cellulose or amylose derivatives coated onto silica. Chiral discrimination and applications have been extensively documented, but the mechanism of chiral discrimination is not yet fully understood. Whereas numerous phases are available within this subset, orthogonality can generally be obtained from a set of three or four columns as a first approach to method development. A typical choice of columns would be to try a set of different amylase (Chiralpak AD and AS) and cellulose (Chiralcel OD or OJ) columns and defer more extensive method development to the subset of samples not separated by these columns. The columns specified are run in the normal-phase mode and, accordingly, mobile phases are typically mixtures of hexane with small amounts of isopropanol or ethanol to control retention. However, selectivity is changed by different polar modifiers. Tailing may be minimized by the addition of 10-50 mM trifluoroacetic acid (TFA) or triethylamine (TEA). Analogue of the columns specified (AD-R, AS-R, OD-R, and OD-J) are available for reversed-phase separation. 

The conformational distortions give rise to some flexibility of the molecules of cellulose derivatives. Tanner and Berry (1974) measured the mean square end-to-end distance of diacetate cellulose in trifluoroacetic acid... 

Complementary to the traditional xanthate system used to make viscose rayon, films, and sponges, or the use of aqueous NaOH to dissolve cellulose under limited conditions, many nonaqueous solvent systems for cellulose have subsequently been developed. Apart from trifluoroacetic acid, which is the only volatile solvent known for cellulose, the others consist of reagents that react with the hydroxyl groups of cellulose in a polar aprotic solvent, such as dimethyl sulfoxide or A,A-dimethylacet-amide (DMAC). 

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