Cellulose triacetate microcrystallin

Chiralcel CTA Cellulose triacetate, microcrystalline Amides, biaryl compounds ... 

The purpose of this study is only intended to illustrate and evaluate the decision tree approach for CSP prediction using as attributes the 166 molecular keys publicly available in ISIS. This assay was carried out a CHIRBASE file of 3000 molecular structures corresponding to a list of samples resolved with an a value superior to 1.8. For each solute, we have picked in CHIRBASE the traded CSP providing the highest enantioselectivity. This procedure leads to a total selection of 18 CSPs commercially available under the following names Chiralpak AD [28], Chiral-AGP [40], Chiralpak AS [28], Resolvosil BSA-7 [41], Chiral-CBH [40], CTA-I (microcrystalline cellulose triacetate) [42], Chirobiotic T [43], Crownpak CR(-i-) [28], Cyclobond I [43], DNB-Leucine covalent [29], DNB-Phenylglycine covalent [29], Chiralcel OB [28], Chiralcel OD [28], Chiralcel OJ [28], Chiralpak OT(-i-) [28], Ultron-ES-OVM [44], Whelk-0 1 [29], (/ ,/ )-(3-Gem 1 [29]. 

The second system studied was the separation of the chiral epoxide enantiomers (la,2,7,7a-tetrahydro-3-methoxynaphth-(2,3b)-oxirane Sandoz Pharma) used as an intermediate in the enantioselective synthesis of optically active drugs. The SMB has been used to carry out this chiral separation [27, 34, 35]. The separation can be performed using microcrystalline cellulose triacetate as stationary phase with an average particle diameter greater than 45 )tm. The eluent used was pure methanol. A... 

The competitive adsorption isotherms were determined experimentally for the separation of chiral epoxide enantiomers at 25 °C by the adsorption-desorption method [37]. A mass balance allows the knowledge of the concentration of each component retained in the particle, q, in equilibrium with the feed concentration, < In fact includes both the adsorbed phase concentration and the concentration in the fluid inside pores. This overall retained concentration is used to be consistent with the models presented for the SMB simulations based on homogeneous particles. The bed porosity was taken as = 0.4 since the total porosity was measured as Ej = 0.67 and the particle porosity of microcrystalline cellulose triacetate is p = 0.45 [38]. This procedure provides one point of the adsorption isotherm for each component (Cp q. The determination of the complete isotherm will require a set of experiments using different feed concentrations. To support the measured isotherms, a dynamic method of frontal chromatography is implemented based on the analysis of the response curves to a step change in feed concentration (adsorption) followed by the desorption of the column with pure eluent. It is well known that often the selectivity factor decreases with the increase of the concentration of chiral species and therefore the linear -i- Langmuir competitive isotherm was used ... 

A fourth method is a chromatographic resolution of a racemic mixture of organotin compounds for instance on a chiral matrix such as microcrystalline cellulose triacetate. 

Microcrystalline cellulose triacetate introduced by Hesse and HagelS1> can be used to resolve organotin compounds52, s3). Some preliminary results obtained on a rather small column (column A length 35 cm internal diameter 2 cm filled with... 

Table 6. Room temperature partial chromatographic resolution of 75 mg tetraorganotin compounds on microcrystalline cellulose triacetate (column A)...

With column B (1 = 66 cm, internal q> 2.8 cm filled with 135 g microcrystalline cellulose triacetate 43p-53n swollen in 95% ethanol dead volume V0 120 ml maximum allowed external pressure ca. 780Torr 250ml/h theoretical number of plates N = 320), racemic (67) could be partially resolved too 5S). It is interesting to note that a better resolution is obtained at lower temperatures (see Table 7). 

Fig. 4a. Resolution of racemic (67) by column chromatography on microcrystalline cellulose triacetate (column B) and by recrystallization 35) C = crystals M = mother liquor the index following C or M gives the number of recrystallizations the fraction has undergone. The value of [ot] ° is given, followed by the quantity obtained...

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... 

Figure 3.11 Compounds resolved on microcrystalline cellulose triacetate (CTA I).

Figure 3.12 Enantioseparation of TrOger s base on (a) microcrystalline cellulose triacetate (CTA I) and (b) 21 coated on silica gel. Column, 25 x 0.46 (i.d.) cm eluent ethanol-HoO (7/3) flow rate, 0.5 ml/min).

Microcrystallin cellulose triacetate (MCTA) has also been employed in the TLC analysis of flavanones. Plates were home-made by mixing 3 g of silica with 9 g of MCTA in 35 ml of ethanol and the suspension was spread on to 20 X 10 cm plates. A considerable number... 

RETENTION (hRFli hRmf AND RESOLUTION (a, Rs)h DATA FOR ENANTIOMERIC COMPOUNDS ON MICROCRYSTALLINE CELLULOSE TRIACETATE PLATES WITH SILICA GEL 60 GF254 AS BINDER (TEMPERATURE 25°C)... 

L. Lepri, M. Del Bubba and F. Masi, Reversed-phase planar chromatography of enantiomeric compounds on microcrystalline cellulose triacetate (MCTA). J. Plan. Chromatogr.—Mod. TLC 11 (1997) 108-113. 

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-... 

Stationary phase are fortuitous. In exceptional cases, where the concave adsorption isotherm crosses the convex one, even a reversal of the elution order is obtained and can be used to achieve a higher productivity as has been demonstrated by Roussel et al. [51] for the separation of the enantiomers of 3-(2-propylphenyl)-4-methyl-4-thiazolin-2-one on microcrystalline cellulose triacetate. 

The resolution of optical antipodes on polysaccharides is mainly governed by the shape and size of solutes (inclusion phenomena) and only to a minor extent by other interactions involving the functional groups of the molecules. In the case of microcrystalline cellulose triacetate (MCTA), the type and composition of the aqueous-organic eluent affect the separation because these result in different swelling of MCTA. 

A. Mannschreck, H. Roller, and R. Wernicke, Microcrystalline cellulose triacetate, a versatile stationary phase for the separation of enantiomers, Kontakte (Darmstadt) 1985 (1), 40-48 Chem. Abstr. 103, 110494(1985). 

Enantioselective packings Polar or nonpolar Packings with enantioselective cages or enantioselective surfaces, microcrystalline cellulose triacetate, cellulose ester or cellulose, carbamate/sil-ica composites, optically active poly(acrylamide)/silica composites, chemically modified silicas (Pirkle phases), cydodextrine modified silicas Operated either with normal phase or reversed phase mobile phases... 

Figure 3.25 Experimental isotherms of Troger s base enantiomers on microcrystalline cellulose triacetate. Experimental data by frontal analysis (symbols) and best quadratic isotherm (solid line). Experimental conditions column length, 25 cm column efficiency, N = 106 plates phase ratio, F = 0.515 flow velocity 0.076 cm/s, pure ethanol. Column (250 x4.6 mm) packed with cellulose microcrystalUne triacetate (CTA, 15-25ftm), previously boiled in ethanol for 30 min. (a) Isotherm data. Top line, (+)-TB, bottom line, (-)-TB. (b) Plot of q/C versus C. Reproduced with permission from A. Seidel-Morgenstem and G. Guiochon, Chem. Eng. Scl, 48 (1993) 2787 (Figs. 4 and 5).

A quadratic isotherm has been used by Guiochon et al. [77] to calculate the band profiles obtained in the case of an S-shaped equilibrium isotherm. The same isotherm has been used by Svoboda [78]. An example of an isotherm with one inflection point, accormted for by the quadratic model is shown in Figure 3.25 [79]. It corresponds to the adsorption of the (+) isomer of Troger s base on microcrystalline cellulose triacetate, while the (-) isomer follows a Langmuir behavior in... 

Figure 4.12 Competitive isotherms of the (-)- and (+)- enantiomers of Troger base on microcrystalline cellulose triacetate, with ethanol as mobile phase, (a) Single-component adsorption isotherm of (+)-TB (squares) and (-)-TB (triangles) at 40° C. Experimental data and best fit to a Langmuir, (+)-TB, and a quadratic, (-)-TB, isotherm model, (b) Competitive isotherms of (-)-TB in enantiomeric mixtures for increasing concentrations (0, 0.5,1,1.5,2, 2.5, 3 g/L) of (+)-TB, calculated with IAS theory, (c) Competitive isotherms of (+)-TB in enantiomeric mixtures for increasing concentrations (0, 0.5, 1, 1.5, 2, 2.5, 3 g/L) of (-)-TB calculated with IAS theory. Reproduced from A. Seidel-Morgenstem and G. Guiockon, Chem. Eng. Sci., 48 (1993) 2787 (Figs. 4, 6, and7).

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