Adrian F. A. Wallis

Changes in Cellulose Crystallinity During Kraft Pulping. Comparison of Infrared, X-ray Diffraction and Solid State NMR Results

Changes in cellulose crystallinity during kraft pulping were investigated by analysing a series of kraft pulps with yields between 96 and 47% using X-ray diffraction and infrared (IR) spectroscopy. The results were compared with those obtained for the same set of samples using solid state 13 C nuclear magnetic resonance (NMR) spectroscopy. All three methods indicated that the degree of crystallinity of the cellulose increased as kraft pulping proceeded due to preferential removal of the less ordered carbohydrates. Both X-ray and IR analyses indicated that the amount of crystalline cellulose remaining in the fibre stayed nearly constant as pulping proceeded. NMR spectroscopy, on the other hand, showed some increase in the amount of crystal interior cellulose in the early stages of pulping and evidence for damaged cellulose at yields below 57 %. The differences between the results obtained using the three methods are discussed.

Reassignment of relative stereochemistry at C-7 and C-8 in arylcoumaran neolignans

Abstract 1 H NMR spectral characteristics of synthetic trans and cis arylcoumarans and their acetates which are related to 8-5′ neolignans are given. This information is used to reassign structures to neolignans reported in nine papers, from the cis to the trans 7-aryl-8-hydroxymethyl configurations, and to neolignans in six papers in which no assignments were made. Thus far, there is no evidence for the occurrence of 8-5′ neolignans with a cis configuration in nature.

Reactivities of Guaiacyl and Syringyl Lignin Model Phenols Towards Oxidation with Oxygen-Alkali

Abstract A range of guaiacyl and syringyl lignin model phenols was treated with oxygen in 1M potassium hydroxide solution at 70°C. The reactions were monitored by high performance liquid chromatography and gas chromatography-mass spectrometry. The reactions of the phenols, which followed pseudo-first-order kinetics, were faster for syringyl than for guaiacyl phenols. For the various 4-substituted syringols the reactivities were in decreasing order CH2-syringyl > CHOH[sbnd]CH3 π C3H7 n > CH2OH > COOH > CHO > CO[sbnd]CH3. Reaction of 1-guaiacylpropane in 1M potassium hydroxide with oxygen gave products of oxidative scission of the aromatic ring and no dehydrodimer, whereas at pH 11.5 some dehydrodimer was among the reaction products. Vanillyl alcohol and syringyl alcohol yielded vanillin and syringaldehyde, respectively, as minor oxidation products. However, the reaction sites for the series of phenols were generally the aromatic rings rather than the side-chains. Oxidation of alkaline solutions of the phen...

Rapid Determination of Carbohydrates in Hardwoods by High Performance Anion Exchange Chromatography

The sugars in eucalypt and cottonwood hydrolysates were analysed by high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Reported conditions for separating softwood hydrolysates were not optimal for hardwoods because of the low mannose levels in hardwood hydrolysates. The long run times of conventional techniques also restrict sample throughput. A faster separation was obtained by introducing a controlled amount of carbonate onto the column. Apart from co-elution of rhamnose and galactose, the sugars in hardwood hydrolysates were separated in under 20 minutes using these conditions. The time between injections was reduced to approximately one third of conventional run times, and quantitation was unaffected by the fast separation. Substitution of carbonate with acetate gave better resolution of wood sugars, but significant variations in retention time made the method unreliable. Seven sugars were surveyed for their suitability as internal standards with the fast separation technique. Of these, fucose was found to be the best.

Revised structure for a neolignan from Brucea javanica

Abstract On the basis of 1 H and 13 C NMR spectral comparison with natural and synthetic compounds, the neolignan isomers isolated from Brucea javanica for which unusual 8- O -6′-structures were proposed have been reassigned to the conventional 8- O -4′-structures ( erythro and threo -guaiacylglycerol- β -coniferyl ether), respectively. Thus far, there is no evidence for the existence of 8- O -6′-neolignans in nature.

Triterpene acids from some Papua New Guinea Terminalia species

Abstract The trihydroxylated triterpene acids arjunolic acid and asiatic acid were found in ether extracts of the woods of Terminalia brassii and of T. complanata. Asiatic acid has not previously been reported as a constituent of the genus Terminalia. A similar extract of T. impediens yielded the tetrahydroxy acid terminolic acid as the major constituent; this acid was also detected as a minor constituent of T. complanata. Terminolic acid, however, does not occur in glycosidic combination in Centella asiatica, as has been recently reported.

Contribution of lignin sub-structures to nitrobenzene oxidation products

Abstract Nitrobenzene oxidation of a series of lignin model compounds with varying aromatic nuclei and sidechain structures, including diphenylmethane compounds, gave benzaldehydes and benzoic acids in a range of yields. The yields were dependent on the structure of the aromatic nucleus, and were in the order syringyl > guaiacyl > 4-hydroxyphenyl. The yields were also dependent on the benzylic group, in the order C=O > CHOH > CH2. Veratryl compounds afforded low yields of oxidation products. Lignin model 1-1′-, 1,5′-and 5,5′-diphenylmethanes gave rise to moderate yields of nitrobenzene oxidation products. However, 1,6′-diphenylmethanes gave only low yields of oxidation products, and no oxidation products were obtained from a nonphenolic 1,1′-diphenylmethane. This suggests that the assumption in the nucleus exchange-nitrobenzene oxidation method for determining lignin structures, that diphenylmethanes do not give rise to oxidation products, should be reappraised. It is proposed that a key influence on the ...

Effect of acetyl bromide treatment on the ultraviolet spectra of lignin model compounds

The effect on the UV specific absorption coefficients (SACs) at 280 nm was determined for p-Hydroxyphenols, for phenolic and non-phenolic guaiacyl models, phenolic and non-phenolic syringyl compounds. The changes in UV characteristics are discussed in terms of acetylation of hydroxyl groups and the aromatic rings. The results are consistent with the observation that whereas the UV absorption maxima of hardwood lignins have lower SACs and occur at shorter wavelengths than those of softwood lignins, they have similar wavelengths (280 nm) and SACs after AcBr treatment

Chemical cellulose from Eucalyptus Regnans wood by autohydrolysis-explosion-extraction

Eucalyptus regnans woodchips and sawdust, which were autohydrolysed at 200°C and exploded at 6·9 MPa nitrogen pressure in the Siropulper pilot plant, gave pulp yields of 68–76% with pentosan contents of 0·9–2·0%, similar to those of pulps which were not exploded. Sodium hydroxide was the most effective medium tested for extraction of lignin from the pulps, and gave pulps with kappa numbers 35–45 after extraction at 100°C with 0·33 m NaOH. At 20°C, the extraction efficacy decreased in the order 0·125 m NaOH > 50% NH3 > 0·2% Ca(OH)2. For organic solvent extractions at 60°C, the order of extraction was 70% ethanol > acetone > ethanol. The viscosities of the E. regnans cellulose samples after autohydrolysis at 200°C for 5 min and extraction were higher than those of a commercial viscose-grade cellulose, and were progressively lower for samples autohydrolysed for longer periods. However, the polydispersities of the celluloses were higher, and the α-cellulose values were lower, than the commercial cellulose. The E. regnans wood gave acetate-grade cellulose by conventional prehydrolysis-alkali pulping procedures.

Formation of Chlorinated Phenols during Bleaching of Eucalypt Kraft Pulps

Oxygen-delignified kraft pulps from mature and young eucalypt woods were treated with chlorine (C) or chlorine dioxide (D) and subsequently with alkali reinforced with oxygen, (EO) C or (EO) D . The bleaching filtrates were examined for chlorinated phenols by the in situ acetylation-gas chromatography method. A total of 43 chlorinated phenols were identified in the C-stage and/or the (EO) C -stage filtrates, whereas only four were found in the corresponding D-stage filtrates. About half of the identified compounds were chlorinated benzaldehydes and acetophenones, and 18 chlorinated phenols have not been positively identified previously. The two chloro-3,4,5-trimethoxybenzaldehydes and 2,4,6-trichlororesorcinol identified in the filtrates probably derive from extractives originally present in the wood. There was no indication of differences in the nature of the chlorinated phenols obtained from the mature and young eucalypt samples