Side-chain ether groups in lignin model compounds of the general structure 1-(3$ sp prime$,4$ sp prime$-dimethoxyphenyl)-1,2-diaryloxyethane exhibited hydrolytic cleavage (the extent depending on the substituents on the 1-aryloxy groups) in aqueous 2N NaOH at 150$ sp circ$C (i.e. under wood pulping conditions). The level of hydrolysis increased in phenylpropane models (i.e. with $ gamma$-CH$ sb2$OH). Thus the commonly accepted generalization that 1,2-diethers of 3$ sp prime$,4$ sp prime$-dimethyoxyphenylpropane are stable in hot alkali is valid only for 1-alkoxy compounds. The newly observed hydrolytic cleavage is influenced by a combination of steric effects, electronic effects and solubility parameters. These observations now make it possible to consider alkaline delignification in the light of gel-degradation theory. / A series of compounds of the general structure 1-(3$ sp prime$-4$ sp prime$,dimethoxyphenyl)-1-aryl-2-guaiacyloxyethane, where the 1-aryl group bore a hydroxy substituent, also exhibited alkaline hydrolysis, at 150$ sp circ$C, at the $ beta$-carbon. The extent was greater when the 1-aryl group bore an $o$-OH than when it bore a $p$-OH. Thus, the reaction was assisted by the nucleophilic attack of the $o$-phenoxide anion on the $ beta$-carbon. / A relatively high release of guaiacol occurred on treatment of 1-(3$ sp prime$,4$ sp prime$-dimethoxyphenyl)-1-thio-2-guaiacyloxyethane with 2N NaOH at 150$ sp circ$C, and the yield of guaiacol was increased when the terminal sidechain carbon bore a $-$CH$ sb2$OH group. Analogous $ alpha$-thioaryl and $ alpha$-thioalkyl compounds also exhibited greater ether cleavage than their oxy counterparts. The hydrolysis of the $ beta$-guaiacyl group was also enhanced by the presence of $ alpha$-seleno-containing groups.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.75783 |
| Date | January 1988 |
| Creators | Mirshokraie, S. Ahmad (Seyed Ahmad) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 000665201, proquestno: AAINL46200, Theses scanned by UMI/ProQuest. |
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