摘要:

The significance of condensation reactions at the 5-position of the aromatic ring of lignin to the overall pulping process has been evaluated using lignin model compounds. Reactions of 5-hydroxymethylcreosol, as a model for 5-substituted lignins formed when formaldehyde is released during pulping, have shown that such groups will react viaortho-quinonemethides to give alkali-stable carbon-carbon bonded condensation products. The amount of condensation depends on the type of pulping liquor used, with less formed in the kraft and soda-anthraquinone (AQ) processes than in the soda process. In these liquors the hydrosulphide or anthrahydroquinone (AHQ) ions present can compete effectively with phenoxide ion for the reactiveo-quinonemethide intermediate.

ISSN:0277-3813    

DOI:10.1080/02773818708085279

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Unbleached kraft pulp (UKP), its residue after extraction with concentrated alkali (α-UKP), bleached kraft pulp prepared from UKP (BKP) and its residue after extraction with concentrated alkali (α-BKP) were permethylated with powdered NaOH and CH3I in their SO2-diethylamine (DEA)-dimethylsufoxide (DMSO) solutions.

ISSN:0277-3813    

DOI:10.1080/02773818708085280

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

In order to examine the stability of lignin-carbohydrate complexes (LCC) during alkaline chemical pulping, benzyl ether type LCC model compounds containing different non-phenolic units were synthesized and cooked under chemical pulping conditions. At least 80% of the starting substance was recovered unchanged, from soda, kraft and acid sulfite reactions indicating the benzyl ether linkage in this compound is stable during pulping. Furthermore, by blocking the reactive benzylic hydroxyl group, the cleavage of adjacent β-ether linkages in lignin moiety is retarded.

ISSN:0277-3813    

DOI:10.1080/02773818708085281

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Yan and Johnson's kinetic model, which has been developed for the purpose of describing wood delignification, recognizes the polymer network structure of lignin. Their model is experimentally examined with a synthetic network polymer. The starting material was functionalized monodisperse polystyrene crosslinked to yield networks in which the parameters of the theoretical equations were known. By the hydrolytic random cleavage of the crosslinks, kinetic data for this model network degradation experiment was obtained.

ISSN:0277-3813    

DOI:10.1080/02773818708085282

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Monohydric alcohols as models for cellulose were reacted with anthraquinone (AQ) and three of its alkali-soluble derivatives in 1M sodium hydroxide at 170°C. Cyclohexanol and cyclohexanemethanol were selected as soluble secondary and primary alcohols, respectively, and the steroidal alcohols, lithocholic acid and cholestan-3β-o1, as less soluble models. In every case the AQs oxidised the alcohols, although cyclohexanemethanol and the insoluble cholestanol were oxidised only to a minor extent with AQ after 6 h. The efficacy of oxidation by the quinones was in the order sodium AQ-2-sulfonate (AMS) > AQ-2-carboxylic acid > 2-hydroxy-AQ > AQ.

ISSN:0277-3813    

DOI:10.1080/02773818708085283

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The acetone-soluble lignins of steam-explodedPinus radiataand Eucalyptus regnans wood were fractionated by sequential extraction with the solvents hexane, diethyl ether, chloroform and acetone. For a given wood and SE process, the fractions showed differences in composition and in the structures of the lignin fragments present. Resin and fatty acid extractives make a significant contribution to the composition ofP. radiatasteam-explosion lignins. They can be partially removed by extraction with hexane, but a fraction may be bound to diethyl ether-soluble lignin fragments. Extractives make an insignificant contribution to the composition ofE. regnanslignin. The effect of extractives on lignin properties and utilisation of these lignins is briefly discussed.

ISSN:0277-3813    

DOI:10.1080/02773818708085284

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Substituent effects on the chemical shifts of aromatic carbons in lignin model compounds have been elucidated from13C NMR spectra of guaiacyl and syringyl type monomerio and β-O-4 model compounds and guaiacyl type β-5 model compounds. Evaluation of the observed values of substituent chemical shift (SCS) for the aromatic carbons leads to elucidation of a generalized SCS additivity rule, for estimation of the chemical shifts of aromatic carbons in ring A of β-O-4 and β-5 type substructures in model compounds and in ring B of β-O-4 substructures in lignin preparations, with errors of less than 1 ppm. The rule is applicable to substructures of both guaiacyl and syringyl types, using an appropriate parent compound as reference instead of benzene. Signals in the aromatic region of the13C NMR spectra of β-O-4 and β-5 type model compounds are reassigned on the basis of the observed SCS's as well as APT spectra of the compounds.

ISSN:0277-3813    

DOI:10.1080/02773818708085285

出版商:Taylor & Francis Group    

年代:1987

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:10.1080/02773818708085278

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor