摘要:

The effect of Co(II) (0 to 0.25 mW CoSO4) on the degradation of methyl β-D-glucopyranoside (MBG) at 120°C in 1.25M NaOH with 0.68 MPa oxygen pressure was studied. When the Co(II) was increased from 0.00 to 0.01 to 0.05 mM the MBG half-life decreased from 12 to 6 to 1.5 hours, reflecting approximately a 0.5 order kinetic dependence on cobalt. An oxidation-reduction cycle between Co(II) and Co(III) involving oxidation of Co(II) by oxygen and oxidation of the glucoside by Co(III), hydroxyl radical, or superoxide is proposed for the degradation. At the 0.25 mM Co(II) addition level highly adsorptive Co(OH)2formed prior to reaction initiation with oxygen and removed otherwise soluble cobalt from solution. This resulted in lower rates of MBG degradation than obtained even at 0.01 mM Co(II) addition. However, Co(II) solubility could be enhanced if silicate anions or polyols (including MBG) were added to the alklaine medium prior to the Co(II) addition. In reactions initially containing 0.25 mM soluble Co(II), an adsorptive precipitate, presumably CoO(OH), gradually formed after reaction initiation with oxygen. Precipitation of the Co(III) solid coincided with a rapid decline in the rate of MBG degradation. Cobalt had little effect on the products of MBG degradation.

ISSN:0277-3813    

DOI:10.1080/02773818208085124

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The extent to which oxygen can stabilize polysaccharides against alkaline degradation was studied. The conversion of aldehyde end groups to aldonic acid groups mainly arabinonic and erythronic acids) was accelerated markedly when cellobiose, hydro-cellulose, or wood chips were treated in aqueous alkali with oxygen in the presence of anthraquinone monosulfonate. Change of the solvent to aqueous ethanol gave an even more pronounced effect without any additive. Other alcohols (methanol, n-propanol, n-hexanol, and ethylene glycol) gave a similar effect. After an oxidative pretreatment, the alkali stability of hydrocellulose (at 100 C) was increased from about 50 % to more than 90 %. When the pretreated chips were pulped in soda-AQ liquor, the rate of delignification was substantially increased. The effect of oxidation on the stabilization of wood polysaccharides, however, was small because of the low stability of the aldonic acid end groups formed at higher temperatures.

ISSN:0277-3813    

DOI:10.1080/02773818208085125

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

An increasing dry content during NO2/O2Pretreatment of wood meal led to an improved delignification during a subsequent soda cooking, both with and without addition of anthraquinone, and to an increased depolymerization of the carbohydrates during the pretreatment. The carbohydrates were stabilized towards alkaline peeling. The highest viscosity and yield compared at a given kappa number of the alkali-cooked pulp were obtained at an intermediate dry content. A pretreatment of birch meal gave rise to an enhanced yield compared at a given kappa number, while for aspen a loss was obtained. An alkaline extraction after the pretreatment led to a decreased yield of final pulp.

ISSN:0277-3813    

DOI:10.1080/02773818208085126

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The synthesis of two β-1 lignol dimers, 1,2-bis-(4-hydroxy-3-methoxyphenyl)-i,3-propanediol (Via) and l-(3-ethoxy-4-hydroxyphenyl)-2-(4-hydroxy-3-methoxyphenyl)-1,3-propanediol (VIb) was performed using the Ivan off Reaction in the key synthetic step. The erythro forms of Via and b were isolated as crystalline solids in yields of approximately 15%, while the threo isomers were obtained as oils. The ratio of threo: erythro isomers was approximately 3:1.

ISSN:0277-3813    

DOI:10.1080/02773818208085127

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Eastern black spruce, Picea mariana, chips have been treated to high yields, at temperatures from 72° to 150°C with sulphite solutions of pH 7 and total SO2 concentrations from 0.1 to 1.0 mol L-1. The rate of sulphonation of black spruce chips is directly proportional to the product of concentration of sites available for sulphonation and the total SO2 concentration. The energy of activation for sulphonation is 62.6 ± 2.3 kJ mol-1. The rate of lignin dissolution at pH 7 is dependent only upon the temperature. High total SO2concentrations are necessary for the efficient production of high strength ultra-high yields pulps. It is postulated that sulphonation at pH 7 is governed by a rate limited addition of bisulphite to quinone methide intermediates formed from phenolic lignin units.

ISSN:0277-3813    

DOI:10.1080/02773818208085128

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The title compounds were degraded in 0.099M oxygen-free aqueous NaOH at 25°, and sometimes 45°. Cellobiose degraded primarily to 3-deoxy-2-C-hydroxymethyl-D-pentonic (“isosaccharinic”) acids, plus the series of 3- to 6-carbon 3-deoxyaldonic acids and glyceric acid also produced from glucose. No disaccharide acids Indicative of a “stopping” reaction were formed. However, formation of 3,4-dideoxy-5-hexulosonic acid from cellobiose indicates that elimination of OH-3, necessary for the “stopping” reaction, did occur, but that the glucosyloxy substituent at C-4 was also eliminated in the same reaction sequence. The major products from 3, 6-anhydro-4-0-methyl-D-glucose and 3,6-anhydro-4-0-(β-D-gluco-pyranosyl)-D-glucose (3,6-anhydrocellobiose), 3-deoxy-D-hexonic acids and 3-deoxy-2-C-hydroxymethylpentonic acids, respectively, also indicate primary reaction sequences involving multiple substituent elimination. However, in contrast to cellobiose, 3,6-anhydrocellobiose also yielded a disaccharide product indicative of a “stopping” reaction. Mechanisms are proposed to account for the primary products of each substrate.

ISSN:0277-3813    

DOI:10.1080/02773818208085129

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The monosaccharide contents of solid lignosulphonate products from spent sulphite liquors were determined by capillary gas chromatography. The predominant monosaccharide was mannose in two softwood calcium bisulphite cases, and xylose in a hardwood calcium bisulphite case. Monosaccharide analysis before and after ultrafiltration of lignosulphonates showed that about 10–25% of the neutral sugars did not pass through the membranes, and presumably remained associated with the lignosulphonates. Chemical “de-sugaring” treatments removed all but traces of the monosaccharides; when hot aqueous sodium hydroxide was used for this purpose, the main products were 3-deoxy carboxylic acids derived from the hexoses.

ISSN:0277-3813    

DOI:10.1080/02773818208085130

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0277-3813    

DOI:10.1080/02773818208085123

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor