Triacetyl cellulose

Diaziridines also show slow nitrogen inversion, and carbon-substituted compounds can be resolved into enantiomers, which typically racemize slowly at room temperature (when Af-substituted with alkyl and/or hydrogen). For example, l-methyl-3-benzyl-3-methyl-diaziridine in tetrachloroethylene showed a half-life at 70 °C of 431 min (69AG(E)212). Preparative resolution has been done both by classical methods, using chiral partners in salts (77DOK(232)108l), and by chromatography on triacetyl cellulose (Section 5.08.2.3.1). 

Introduction of nitrogen into the anulene ring (e.g. of 95) leads to a methano-azaanulene 107 121) with Q-symmetry which is therefore chiral (like its mono- or disubstituted derivatives)118). The low basicity of 107 (pKa 3.20) prevented its optical resolution by conventional methods (e.g. through salts with optically active acids). Excellent results were obtained, however, (as also in the case of the two isomeric carbocyclic methylesters 97 and 101 and of several derivatives of azaanulene) by chromatography on microcrystalline triacetyl cellulose in ethanol at 7 bar 1221 (see also Section 2.7.1). In many cases base line separations were accomplished to give both (optically pure) enantiomers. Enantiomeric relations were confirmed in all cases by recording the CD-spectra of both fractions. Some results of these separations are shown in Fig. 4 together with the optical rotations ([a]D in ethanol) of the enantiomers. 

Separations of [njhelicene racemates have also been attempted using n-acids, such as 2-(2,4,5,7)-tetranitrofluorenylidene-9-aminooxypropionic acid (TAPA, 112, see above) its butyric acid analogue TAB A 113 and binaphthyl-2,2-diyl-hydrogenphosphate (BPA, 115 Other employed methods were inclusion chromatography on triacetyl cellulose or helical polymers like (-l-)-poly(triphenyl-methyl-methacrylate [(-l-)-PTrMA, 776]... 

Synonyms CA Triacetate Triacetyl cellulose Classification Thermoplastic Empirical C HwO ... 

Triacetoxysilyl) ethylene Triacetoxyvinylsilane. See Vinyltriacetoxy silane Triacetyl cellulose. See Cellulose triacetate Triacetyl glycerin Triacetyl glycerol. See Triacetin... 

Triacetyl cellulose 1 -nitro-2-methyl-2-propanol, 2-trimonochloroeth-ylphosphate, butyl stearate 23... 

Regenerated cellulose Triacetyl cellulose Nitro-cellulose Celluloid... 

Acetylated cellulose plates, prepared by esterification of cellulose with acetic acid or acetic anhydride, are used for reversed-phase TLC. Plates are available with varying degrees of acetylation ranging from 10 to 40% the polarity of the layer decreases with increasing acetylation. Enantiomeric compounds were resolved by RP-TLC on microcrystalline triacetyl cellulose using 2-propanol-water (6 4) as the mobile phase (Lepri, 1995). 

Phases that have been used for the TLC separation of enantiomers include cellulose and triacetyl cellulose chemically bonded layers containing cyclodextrins... 

Lepri, L. (1995). Reversed phase planar chromatography of enantiomeric compounds on microcrystalline triacetyl cellulose. J. Planar Chromatogr.—Mod. TLC 8 467-469. 

Before synthetic chiral stationary phases were developed, attempts were made to use naturally occurring chiral materials for the stationary phase. Quartz, wool, lactose and starch were inadequate but triacetylated cellulose has met with some success. The synthetic stationary phases introduced by Pirkle are able to interact with solute enantiomers in three ways, one of which is stereochemically dependent. Typically these interactions are based on hydrogen bonding, charge transfer (rc-donoi -acceptor based) and steric repulsive types. An independent chiral stationary phase therefore consists of chiral molecules each with three sites of interaction bound to a silica (or other) support. Early work in this area demonstrated that 5-arginine bound to Sephadex would resolve 3,4-dihydroxy-phenylalanine, and that direct resolution of chiral helicenes could be accomplished with columns packed with 2-(2,4,5,7-tetranitro-9-fluorenylideneaminoxy)-propionamide or tri-P-naphthol-diphosphate amide. Amino acid esters have also been resolved with a silica bound chiral binaphthyl crown ether, but better separations are achieved with A-acylated amino acid derivatives with amino-acid derived chiral stationary phases. 

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