摘要:

Wheat straw, kenaf, oak, and pine were extracted to give samples with various contents of lignin, hemicellulose, and cellulose. Precise amounts of these samples were blended with KBr and pressed into discs, and their FTIR spectra were determined. Two-spectra subtraction, and combination of multiple spectra by matrix inversion and least squares matrix methods were used to give spectra of individual lignin, hemicellulose, and cellulose components in all 4 plant types. They are the most complete IR spectra available for lignin in plant matrices.

ISSN:0277-3813    

DOI:10.1080/02773818808070668

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Treatment of guaiacylglycerol- and guaiacylpropanediol-β-(2-methoxyphenyl) ethers at 160 C in 50 % alcohol containing magnesium bisulfite was found to cleave the β-aryl ether linkages in these compounds to form isoeugenol and/or eugenol in up to 60 % yield as well as comparable yields of guaiacol. The linkage in a nonphenolic model was not cleaved to a discernible extent. Both an alcohol and bisulfite were essential for this reductive cleavage which proceeded efficiently in ethanol and isopropanol but not efficiently in methanol,t-butanol or dioxane. Magnesium was a better base than sodium for the reaction.

ISSN:0277-3813    

DOI:10.1080/02773818808070669

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Under sulphite-anthraquinone cooking conditions reduced anthraquinones, such as anthrahydroquinone (AHQ) or oxanthrone, promote cleavage of the β-ether bond in the free phenolic β-ether lignin model1. This enhanced cleavage, and the products formed, can be rationalised by a mechanism involving formation of an adduct between the reduced quinone and the quinone methide3. This adduct then fragments to afford the observed products.

ISSN:0277-3813    

DOI:10.1080/02773818808070670

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A series of lignin model molecules was prepared, adsorbed and grafted (for the most appropriate one) on to bleached chemical pulp. The rates of brightness reversion of these solid materials under simulated solar light exposure were established and compared to that of bleached mechanical pulp (containing lignin). 4-hydroxy-3-metboxy acetophenone (acetovanillone or acetoguaiacone)1and 3,5-dimethoxy-4-hydroxy acetophenone (acetosyringone) both incorporating α-carbonyl and phenolic functions which have been claimed essential for an efficient coloration, did not prove to be very active in the solid state. In contrast, α-carbonyl β-O-4 and β-1 structures with whether phenolic function or not, display an intense yellowing in this medium, and mimic well the brightness reversion of bleached mechanical pulp (especially the non phenolic β-O-4 chromophore adsorbed and grafted). These results are in contrast with those found in liquid ethanolic solution where acetovanillone1(conc.=10−2M) and the α-carbonyl 4- O-methylated β-O-4 dimer3(conc.=3.7×10−3M) were shown to undergo a similar yellowing. Inter and intramolecular mechanisms were put forward to explain this difference. Moreover, the reduction of the carbonyl chromophore into benzyl alcohol appears to prevent discoloration to some extent. However, all the studied structures were found light sensitive, even the 4-O-methylated α-O-4 dimer11which contains neither carbonyl nor phenolic groups.

ISSN:0277-3813    

DOI:10.1080/02773818808070671

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Studies on the desulfonation of 2,4,6-trihydroxybenzylsulfonic acid and sodium epicatechin-(4β)-sulfonate showed that sulfonates α to a phloroglucinol ring are good leaving groups at ambient temperature and pH greater than 8.0. In contrast, hydroxybenzylsulfonic acids with resorcinol or phenol hydroxyl functionality resist desulfonation even at pH 12 and 90°C. It was also not possible to make (2,4,6-trihydroxyphenyl), (4-hydroxyphenyl)-methane or (2,4,6-trihydroxyphenyl),(2,4-dihydroxyphenyl)-methane by slow addition of 2,4,6-trihydroxybenzylsulfonic acid to alkaline solutions of phenol or resorcinol. However, facile desulfonation of 2,4,6-trihydroxybenzylsulfonic acid derivatives permits the use of condensed tannins from most conifer barks as intermediates for the formulation of water-resistant, cold-setting, wood-laminating adhesives. Under typical adhesive formulation conditions, the sulfonic acid groups on tannin derivatives from conifer barks will he displaced, resulting in water-insoluble polymers.

ISSN:0277-3813    

DOI:10.1080/02773818808070672

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Hot water extraction of Ponderosa pine bark yields condensed tannins (polymeric procyanidins, PPC's) and starch. Precipitation of the PPC's as the lead complex coprecipitates the starch, although the latter does not itself form an insoluble lead complex. Ethylene diamine tetraacetic acid (EDTA) treatment of the lead complex removes lead and yields PPC and starch which coprecipitate with ethanol from water as a starch-PPC complex, although the PPC itself is fully ethanol soluble. Chromatography of the starch-PPC complex with water on several polysaccharide media leads to elution of the starch and sorption of the PPC. Similar interactions of PPC and polysaccharides may be responsible for viscosity problems in uses of condensed tannins as tans and as adhesives. Such interactions probably occur in many plant materials.

ISSN:0277-3813    

DOI:10.1080/02773818808070673

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Cellulose is degraded by alcohols and strong acid-catalysts at 180°C to 200°C within minutes. Alkylglucosides, 5-alkoxyrnethylfurfurals, and alkyl levulinates plus alkyl formates are formed in consecutive reactions, accompanied by some humic residue. The scope of the reaction was explored by using C1-, C2-, C3-, and C4-alcanols and by combining various lignocellulosic substrates with methanol. Effects of catalysts and co-solvents were tested, resulting in more selective reactions and suppressing dialkylether formation of the solvent. Yields of 46% methyl levulinate, 44% ethyl levulinate, and 37% n-propyl levulinate (based on theory) from cellulose point to the preparative value of the reactions.

ISSN:0277-3813    

DOI:10.1080/02773818808070674

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The process of enzymatic degradation of the high-molecular hydroxyethyl-cellulose was followed by means of static low angle laser light scattering (static LALLS) which proved to be an excellent analytic method to obtain continuously an information about the decrease of the weight average molecular weight Mwwithout any manipulation of the substrate and enzyme, respectively. Moreover, due to the high sensitivity of LALLS the required substrate as well as enzyme concentration can be made much lower than needed for other physico-chemical techniques.

ISSN:0277-3813    

DOI:10.1080/02773818808070675

出版商:Taylor & Francis Group    

年代:1988

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:10.1080/02773818808070667

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor