Natsuki Kasuya

Chiral discrimination with regioselectively substituted cellulose esters as chiral stationary phases

Four kinds of cellulose derivatives, including two regioselectively substituted cellulose esters (6-O-acetyl-2,3-di-O-benzoyl cellulose and 2,3-di-O-acetyl-6-O-benzoyl cellulose), were synthesized so that the effects of their functional group distribution on their chiral discrimination ability could be examined. The degree of substitution by functional groups appeared to have a critical effect on the separation in most cases, but the type of the functional group at the C-6 position also significantly influenced chiral discrimination when a series of neutral arylalcohol derivatives were used as racemates. Copyright 2000 Wiley-Liss, Inc.

Preparation of 6-deoxy-6-fluorocellulose

Abstract 6-Deoxy-6-fluorocellulose was prepared from cellulose 2,3-diacetate ( 1 ) or cellulose 2,3-dibenzoate ( 2 ) in various solvents, and was characterized by 19 F and 13 C NMR measurements. The best product, having ds of 0.95 at C-6 and 0.04 at C-3, was prepared from cellulose 2,3-dibenzoate in nitrobenzene. Other combinations of starting material and solvent gave a lower (≈ 0.8) ds of fluorine at C-6 and higher (≈ 0.12) at C-2 or C-3. Substitution at C-2 was observed when the combination of 1 and 1,4-dioxane, or 2 and chloroform was used. The products substituted at C-2 by fluorine were relatively resistant to acid hydrolysis.

Development of chiral stationary phases consisting of low-molecular-weight cellulose derivatives covalently bonded to silica gel

We prepared chiral supports whose chiral stationary phase (CSP), consisting of a low-molecular-weight cellulose derivative (degree ofpolymerization: 15), is covalently bonded to silica gel. The cellulose used asthe base material of the CSP was pre-hydrolysed with phosphoric acid before thecoupling reaction to unite a reducing terminal in the cellulose and anaminopropyl group on the surface of silanized silica. After substitutinghydroxyl groups in cellulose by using 3,5-dichlorophenyl isocyanate or phenylisocyanate, we tested the CSP thus obtained for its performance in chiralrecognition and found a wide range of chiral discrimination ability. We alsoconfirmed that an elution using ‘strong’ solvents as a mobile phasecould be achieved, which is difficult for the coated-type CSPs because themobile phase may dissolve the CSP. However, more enantiomeric mixtures showedlarger selectivity factors (α) when eluted on the coated-type CSPs thanonthe covalently bonded CSPs. A coated-type CSP consisting of thelow-molecular-weight cellulose phenylcarbamate, prepared as a control CSPsample, showed comparable performance with the commercial coated-type column(CHIRALCEL® OC), so the slightly poorer performance ofthe chemically bonded CSPs may be explained by the difficulty of the polymerconsisting of the CSPs in taking an optimal supermolecular structure requiredfor chiral recognition due to the fixation to the silica gel. The lowdegreeof polymerization may have an additional effect.

Synthesis and characterization of highly substituted deoxyfluorocellulose acetate

Deoxyfluorocellulose acetates were prepared from cellulose acetate (CA, degree of substitution by acetyl groups: 2.2 and 1.7) by using diethylaminosulfur trifluoride (DAST) in 1,4-dioxane or diglyme. The maximum degree of substitution of fluorine of the products was approximately 0.60, and depolymerization was not significant during fluorination. The replacement of hydroxyl groups by fluorine atoms occurred exclusively at C-6, as confirmed by carbon-13 NMR spectroscopy. In the presence of pyridine, an N-pyridinium derivative of CA was obtained instead of a deoxyfluoro derivative of cellulose.

Studies on the thermal properties and structures of deoxyhalocelluloses

The thermal properties and structures of deoxyhalocelluloses were studied using thermogravimetric and differential scanning calorimetric analyses and an X-ray diffraction method. The X-ray diffraction curves of the cellulose derivatives were obtained after subjecting them to a specific treatment that was supposed to render a specific cellulose allomorph from the amorphous state cellulose; all of the cellulose derivatives examined without such treatment exhibited no crystalline features. Only deoxyfluorocellulose was found to give a diffraction pattern similar to that of the corresponding cellulose allomorph, which was cellulose IV in this case. On the basis of the thermal analyses, it was confirmed that chlorodeoxycellulose has a flameretardant property, whereas deoxyfluorocellulose was found not to be flame-retardant. The difference is supposedly due to the difference in the bonding energy between C-Cl and C-F.

A structural study of fluorinated cellulose : crystallization of fluorinated cellulose by conversion treatments used for cellulose

Abstract A deoxyfluorocellulose derivative, with regioselective substitution mostly at the C-6 carbon atoms, has been studied by an X-ray diffraction method. The results showed that the crystallinity of the fluorinated cellulose is low but can be enhanced by a specific conversion treatment. The hydrothermally treated sample displayed a spectrum similar to that of cellulose IV.

Synthesis of novel and regioselectively mesogen-incorporated thermotropic liquid crystals from cellulose derivatives

ABSTRACT Regioselectively mesogen-incorporated cellulose derivatives, in which the hydroxy group at C-6 is displaced by a bulky and rigid mesogenic group such as {4-[(4-methoxyphenoxy)carbonyl]phenoxy}acetate or [(4′-cyanobiphenyl-4-yl)oxy]acetate, and the C-2 and C-3 groups are displaced by octanoyl or lauroyl groups, were synthesized. Thermogravimetric and differential scanning calorimetric analyses of the final products, along with polarized optical microscopic observations, revealed that the obtained cellulose derivatives have a thermotropic liquid-crystalline nature and transition from the mesomorphic to the isotropic phase over a wide range of temperatures. These derivatives could be considered to be main-chain liquid-crystalline cellulosic polymers.