摘要:

The quantitative reaction in an NMR tube of 1,3,2-dioxaphospholanyl chloride (I) with compounds bearing active hydrogens was explored as a simple method for derivatizing the labile centres known to occur in lignins. Derivatives of phenols, alcohols and carboxylic acids with (I) gave31P chemical shifts which appeared in different ranges of the NMR spectra. Anyorthosubstitution onto the aromatic ring of phenols significantly affected the magnitude of the31P NMR chemical shifts, whileparaand/ormetasubstituents had a much smaller effect. A clear distinction between guaiacyl, syringyl and unsubstituted phenolic hydroxyls can thus be made in mixtures of model compounds. Primary alcohols were clearly distinguished from secondary and tertiary alcohols in their derivatives with (I), while different31P NMR signals for derivatives oferythroandthreoforms of lignin-like model compounds were identified. While alcohols, phenols and simple carboxylic acids on reaction with (I) gave derivatives that were substitution products, aldehydes reacted via a distinctly different addition mechanism; ketones did not react at all.

ISSN:0277-3813    

DOI:10.1080/02773819108050267

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The hypothesis that galactose and arabinose pectic substances are disributed with lignin throughout wood cell walls was tested by analyzing a high-yield loblolly pine kraft pulp that had been separated into middle-lamella-rich and secondary-wall-rich fractions. The fractions were first treated with a polysaccharidase enzyme mixture to obtain “enzyme lignins.” The structures of the galactose and arabinose oligomers remaining attached to the lignin were determined by methylation analysis. The 1→4 linked galactose structure, characteristic of pectic materials, was present in significant amounts in the middle-lamella-rich fraction, but to only a very small extent in the secondary-wall-rich fraction. In contrast, the pectic arabinan 1→5 linked structure was a significant proportion of the arabinose from both fractions. The 1→5 linked arabinose structure can arise from a linkage of arabinoxylan to lignin through the 5 position of the arabinose substituent as well as from pectic structures. After partial acid hydrolysis, approximately half the remaining arabinose in the secondary-wall-rich fraction was attached as monomeric units to lignin through the 5 position.

ISSN:0277-3813    

DOI:10.1080/02773819108050268

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Stilbenes, representing stilbenoid structures present in residual lignins, have been synthesized by condensation of monochloroacetaldehyde diethylacetal with appropriate phenols and phenol ethers, followed by alkali- or acid-promoted rearrangement of the resulting 1,1-diaryl-2-chloroethanes. It is proposed that the mechanism of these rearrangement steps involves aryl migration with formation of intermediates of the spiro-cyclohexadienone type. The yields of individual stilbenes vary within wide ranges and are in certain cases moderate. However, the method is competitive due to its simplicity and the availability of the starting materials required.

ISSN:0277-3813    

DOI:10.1080/02773819108050269

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Reaction of (+)-catechin at pH 12 and 40 °c results in the stereoselective (if not stereospecific) formation of an enolic form of 1-[6-(3′,4′-dihydroxyphenyl)-7-hydroxybicyclo[3.3.1]nonane-2,4,9-trione-3-yl] -1-(3,4-dihyroxyphenyl)-3-(2,-4,6-trihydroxyphenyl)-propan-2-ol. The n.m.r. chemical shift assignments determined by a variety of two-dimensional experiments permit a conclusion that the compound is one of four diastereoisomers possible from reaction of the two quinone methide intermediates. Stereoselectivity in the formation of this compound can be accounted for by preference forRe-face attack on both 2-C's of the quinone methides involved in the formation of the molecule.

ISSN:0277-3813    

DOI:10.1080/02773819108050270

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Yellow birch,Betula alleghaniensis, is a dark-barked birch species that is widely utilized in the northeastern region of the United States for pulp and solid wood products. Currently, the bark is used only as a low value fuel source. In this study, the triterpenoid composition of the outer bark ofB. alleghaniensiswas investigated in order to evaluate potential for use as a resource for specialty chemicals. Seventeen triterpenoids, including four new compounds, were isolated and identified. Previously known compounds included lupeol, lupenone, betulone, betulin, betulonic acid, lupenyl formate, lup-20(29)-ene-30-ol-3-one, lup-20(29)-ene-3β,30-diol, lup-20(29)-ene-28-ol-30-al, 29-norlupan-3β-ol-20-one, lupan-20-ol-3-one, lupan-3β,20-diol, and lupan-3β-ol-29-oic acid. The four new compounds isolated from yellow birch were lup-20(29)-ene-28-ol-3-one-30-al, 29-norlupan-3,20-dione, 29-norlupan-28-ol-3,20-dione, and lupan-20,28-diol-3-one.

ISSN:0277-3813    

DOI:10.1080/02773819108050271

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

An examination of previously reported kinetic expressions describing peroxide bleaching of wood pulp under alkaline conditions reveals that the overall process can be considered as a combination of two parallel reaction routes. The first route corresponds to a reaction involving direct participation of the perhydroxyl anion in chromophore elimination. This mechanism can be identified with the classical explanation for peroxide bleaching. The second route can be associated with reactions in which chromophores are eliminated through the action of free radical intermediate species. New experimental evidence is presented to show that processes catalysed by transition metal ions can lead to enhancement of bleaching. A two stage peroxide bleaching sequence, initially under acidic conditions in the presence of chromium, followed by alkaline conditions produces an acceleration in bleaching rate, without significant additional consumption of peroxide.

ISSN:0277-3813    

DOI:10.1080/02773819108050272

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The partial solubility parameters of cellulose and AKD (Alkylketene dimer) treated paper were determined by inverse gas chromatography. The Snyder/Karger-Hansen interaction model was used, where -ΔEA= Viδld+ δlpδjp+ δjhδjh). The adsorption internal energies of a series of n-alkanes and five polar probes were measured. From the ΔEAvalues of n-decane, acetone and THF, which give the largest normalized determinant M(n), the partial solubility parameters of the stationary phases were calculated. The partial solubility parameters of cellulose were: δd= 8027; δp= 8.00; δh= 13.88; δt= 18.03 cal½/cm3/2AKD treated paper gave δd= 8.10, δp= 12.35, δh= 7.96, and δt= 16.78 cal½/cm3/2.

ISSN:0277-3813    

DOI:10.1080/02773819108050273

出版商:Taylor & Francis Group    

年代:1991

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:10.1080/02773819108050266

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor