Nobuyoshi Aoki

Dissolution of cellulose in lithium bromide-organic solvent systems and homogeneous bromination of cellulose with N-bromosuccinimide-triphenylphosphine in lithium bromide-N,N-dimethylacetamide

Abstract Three solvent systems, namely lithium bromide in N,N -dimethylacetamide (DMA), N -methyl-2-pyrrolidone, or N,N -dimethylformamide, are able to dissolve cellulose. No appreciable decrease in molecular weight of cellulose was observed during the dissolution into the LiBr-DMA solvent system. The homogeneous bromination of cellulose with N -bromosuccinimide-triphenylphosphine in LiBr-DMA proceeded smoothly, and the degree of substitution by bromine of 0.9 was attained under appropriate conditions. Only the 6-hydroxyl groups were replaced with bromine, even for the sample having the highest degree of substitution. The effects of reaction conditions on the degree of substitution were studied in detail.

Chlorination of cellulose with N-chlorosuccinimide-triphenylphosphine under homogeneous conditions in lithium chloride-N,N-dimethylacetamide

Microcrystalline cellulose was chlorinated with N-chlorosuccinimide-triphenylphosphine under homogeneous conditions in LiCl-N,N-dimethylacetamide. At the early stage of the reaction only replacement of the 6-hydroxyl groups with chlorine was observed, and 3-hydroxyl groups were replaced at a lower rate with Walden inversion. The effects of reaction conditions on the extent of chlorination were studied in detail. More than two equivalents of chlorination reagents per glucose residue were necessary to attain a high degree of substitution (ds) by chlorine, and the maximum ds attained was 1.86. Chlorinated disaccharides were found in the hydrolyzates of chlorodeoxycelluloses hydrolyzed under mild conditions, and their structures were studied by mass spectrometry.

Bromination of cellulose with tribromoimidazole, triphenylphosphine and imidazole under homogeneous conditions in LiBr-dimethylacetamide

Abstract The bromination of microcrystalline cellulose with tribromoimidazole, triphenylphosphine and imidazole was studied under homogeneous conditions in LiBr- N,N -dimethylacetamide. Bromodeoxycellulose samples having ds values up to 1.6 were obtained at high molecular ratios of bromination reagents to the repeating unit of cellulose (5 or higher). Recoveries of high ds samples were below 50%. 3,6-Dibromo-3,6-dideoxyglucose units were present in the samples having high ds values together with 3,6-dibromo-3,6-dideoxyallose and 6-bromo-6-deoxyglucose units. The dibromoglucose units were formed from dibromoallose units by a nucleophilic substitution of bromine atoms at C-3 with bromide ions present in the system.

Gas chromatographic—mass spectrometric study of reactions of halodeoxycelluloses with thiols in aqueous solutions

Chloro- and bromodeoxycelluloses with high degrees of substitution, prepared with halosuccinimide and triphenylphosphine under homogeneous conditions, were treated with eight thiols under moderately alkaline conditions. Bromodeoxycellulose was generally more reactive than chlorodeoxycellulose and carboxyl-bearing thiols such as mercaptoacetic acid were less reactive than neutral thiols such as benzenethiol. The maximum conversion of halodeoxyglucose units to thio derivatives was 65%. When the reaction was run at high alkalinity at 60 °C, elimination of hydrogen halide to yield 3,6-anhydroglucose and/or 5,6-glucosene units took place appreciably as a side reaction. Hydrolysates of the reaction products with thiols having no carboxyl group were analyzed by gas chromatography-mass spectrometry as trifluoroacetates and the formation of S-substituted 6-thio-6-deoxyglucose units was confirmed.

Reaction of 6-bromo-6-deoxycellulose with thiols in lithium bromide-N, N-dimethylacetamide

Nucleophilic substitution reactions of 6-bromo-6-deoxycelluloses of high degrees of substitution with eight thiols having functional groups such as carboxyl and amino groups were studied under homogeneous conditions in LiBr-N, N-dimethylacetamide in the presence of triethylamine. The reactions under the homogeneous conditions proceeded more extensively than those run under heterogeneous conditions in aqueous alkaline solutions. The reactivity of thiols was found to increase with increasing acidity of the mercapto groups of the thiols. Reaction products with 2-mercaptobutanedioic acid and with 2-mercaptobenzoic acid were soluble in alkaline and neutral water but not in 1 N HCl, while the reaction products with 2-aminoethanethiol did not dissolve even in 1 N HCl. The reaction products with cysteine showed amphoteric behavior.

Reaction of dichloroallose units in a chlorodeoxycellulose with lithium chloride under homogeneous conditions in N,N-dimethylacetamide

Abstract The reaction of methyl 3,6-dichloro-3,6-dideoxy-β- d -allopyranoside with lithium chloride in N , N -dimethylacetamide (DMA) was studied in relation to the possible conversion of 3,6-dichloro-3,6-dideoxy- d -allose units in a chlorodeoxycellulose during synthesis in a LiCl-DMA solvent system. Methyl 3,6-dichloro-3,6-dideoxy-β- d -glucoside was formed; the reaction was reversible and the equilibrium was on the glucoside side. GLC analysis of the hydrolyzates of chlorodeoxycellulose samples after treatment with LiCl showed that the dichloroallose units were partly converted into 3,6-dichloro-3,6-dideoxy- d -glucose units. A kinetic study showed that the rate of conversion of the dichloroallose unit into the dichloroglucose unit was lower than that of the dichloroalloside into the dichloroglucoside, and the amounts of the two units at equilibrium were calculated to be close to each other. Based on the values of the kinetic parameters obtained, the conversion of the dichloroallose units into the dichloroglucose units during the chlorination of cellulose in LiCl-DMA was estimated to be negligibly small under typical reaction conditions.

Synthesis of methyl 3,6-dibromo-3,6-dideoxy-β-d-allopyranoside and -glucopyranoside, and their interconversion in the presence of bromide ion

Abstract The bromination of methyl β- d -glucopyranoside with tribromoimidazole and triphenylphosphine in toluene-acetonitrile (2:1 v/v) for 4 h at 110°C gave methyl 3,6-dibromo-3,6-dideoxy-β- d -alloside in low yield, while the bromination in toluene under otherwise comparable conditions gave methyl 3,6-dibromo-3,6-dideoxy-β- d -glucoside. Examination of the time course of the reaction in toluene showed that the dibromoalloside was initially formed and was converted into the dibromoglucoside during the bromination. The rate constants of the interconversion between the dibromoglycosides in LiBr- N , N -dimethylacetamide (DMA) were about 10 3 times as large as those of the interconversion of the corresponding dichloroglycosides in LiCl-DMA. The results are discussed in relation to the presence of 3,6-dibromo-3,6-dideoxyglucose residues, in addition to 3,6-dibromo-3,6-dideoxyallose and 6-bromo-6-deoxyglucose residues, in bromodeoxycellulose samples having high ds values obtained by the bromination of cellulose with tribromoimidazoletriphenylphosphine.

Reactions of bromodeoxycellulose with various thiols in lithium bromide/N,N-dimethylacetamide

ABSTRACT 6-Bromo-6-deoxycelluloses of a high degree of substitution were treated with various thiols under homogeneous conditions in lithium bromide/N,N-dimethylacetamide in the presence of triethylamine. At high temperatures, appreciable unfavorable side reaction, dehydrobromination yielding 3,6-anhydroglucose and/or 5,6-glucosene units took place. Under favorable conditions, more than 50% of bromine was substituted with thiols. Thiols used in this work include 2-hydroxyethanethiol, 2-aminoethanethiol, 4-aminobenzenethiol, 3-mercapto-propionic acid, 2-mercaptosuccinic acid, 2-mercaptobenzoic acid and cysteine. Solubilities of the products containing carboxyl, amino and/or hydroxyl groups were studied. Aminophenylthiodeoxycellulose was treated with nitrous acid followed by diazo coupling with N,N-dimethylaniline to yield a cellulosic dye.