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  • Author: K. Li x
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Summary

The reactions of the β-aryl ether lignin model 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol on heating in aqueous solution have been studied. Guaiacol, isoeugenol, vanillin, 1-(4-hydroxy-3-methoxyphenyl)-1-ethanol, 1,2-bis(4-hydroxy-3-methoxyphenyl)-1-propanol, 2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-3-methyl-2,3-dihydrobenzo[b]furan, dehydrodiisoeugenol and trans-1,2-dihydrodehydroguaiaretic acid were detected in the reaction mixtures. The formation of the products can be envisioned to proceed via homolysis of an intermediate quinone methide. When 2,6-dimethoxyphenol was present in the reaction mixtures large amounts of 1-(4-hydroxy-3,5-dimethoxyphenyl)-2-(4-hydroxy-3-methoxyphenyl)-1-propanol were formed and the yields of guaiacol and isoeugenol were comparatively high. The reaction product pattern can be explained by the occurrence of radical-exchange reactions. The presence of wood meal in the reaction mixtures resulted in an increase in the yield of isoeugenol and a lowering of the yield of dehydrodiisoeugenol. The changes in yields in this case can also be explained by radical-exchange reactions. The significance of homolytic cleavage of β-aryl ether linkages in connection with the technical processing of wood is discussed.

Summary

Refluxing of trans–2-(3,4-dimethoxyphenyl)-3-hydroxymethyl-7-methoxy-2,3-dihydrobenzo[b]furan with dioxane-water (9 : 1) in the presence of various acid catalysts led to the formation of 2-(3,4-dimethoxyphenyl)- 7-methoxy-3-methylbenzo[b]furan, the trans and cis forms of 2-hydroxy-3,3′4′-trimethoxystilbene and cis–2-(3,4-dimethoxyphenyl)-3-hydroxymethyl-7-methoxy-2,3-dihydrobenzo[b]furan. The proportions of the products were strongly dependent on the particular acid used as catalyst. HCl and to a greater extent HBr favored the formation of the 2-arylbenzofuran (phenylcoumarone) while the trans-stilbene derivative predominated in reaction products from the experiments with trifluoromethane sulfonic acid as the catalyst. Isomerization of the starting material occurred, regardless of the nature of the catalyst (small amounts of the cis-isomer formed). The number of phenylpropane units in spruce lignin attached to an adjacent unit by a β−5 linkage was estimated to be 6–9% on the basis of 1H NMR spectrometric measurements of the formation of phenylcoumarone structures on refluxing of milled wood lignin from spruce with 0.1M HBr in dioxane-water (9 : 1).

Summary

Several chiral neolignan skeletons and a benzodioxane were prepared from a tartrate derivative with the crucial chiral aryl alkyl ether formation being accomplished with cesium phenolate and 18-crown-6. These compounds have greater than 96% enantiomeric excess, and this work represents the first successful synthetic preparation of optically active 8-O-4′ type neolignan skeletons. The chiral aryl alkyl ethers were also synthesized from several protected carbohydrates, which can serve as chiral auxiliaries for a wide variety of target molecules.

Abstract

Wood products with anti-electrostatic properties have wide applications in many fields. However, wood is an insulator and does not itself have anti-electrostatic ability. This study investigated several ionic liquids as anti-electrostatic agents for wood. Ionic liquids are liquids at room temperature (or close to room temperature), possess no vapor pressure and are excellent conductors for electric current. Maple and pine veneers were either soaked in or brushed with five ionic liquids: 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-ethyl-3-methylimidazolium hexafluorophosphate. The ionic liquid-treated wood specimens were then measured for surface resistivity and volume resistivity in accordance with ASTM standards. The effects of application method (brushed vs. soaked) and storage time were investigated. All the ionic liquids studied were effective anti-electrostatic agents for pine and maple. For all ionic liquids tested, pine had lower resistivity, and thus higher anti-electrostatic ability, than maple.

Abstract

For a multivariate normally distributed n × p random matrix Y with mean μ and covariance ΣY = V 1⊗Σ1 + V 2⊗Σ2, necessary and sufficient conditions, under which Y′WY follows a Wishart distribution, are obtained, where W is a symmetric matrix, V 1 and V 2 are known nonnegative definite matrices, and Σ1 and Σ2 are unknown nonnegative definite parameter matrices. Several examples are given to illustrate our main results.