31P NMR spectroscopy was further developed for the structural elucidation of lignin by undertaking a series of systematic studies. More specifically, a detailed model compound investigation showed that 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane is an additional phosphitylation reagent which may provide further quantitative structural information about lignin. Correlation analysis using the Hammet principles revealed that the 31P chemical shifts of lignin- related phenolic hydroxyls with various substitution patterns strongly depend on the nature of the substitution. Such structure-chemical shift correlations led, for the first time, the development of a set of empirical parameters that permits the accurate prediction of 31P chemical shifts of lignin-related phenolic compounds. Furthermore, the 31P NMR technique was coupled with the Mannich reaction. This unique combination allowed the quantification of various types of phenolic hydroxyls in lignin such as para-hydroxyl phenols, catechols, guaiacols, and phenols bearing C 5 or C6 substituents in a novel and nondestructive manner. / The 31P NMR technique was thus applied in order to reveal the structural changes that occur within lignin during kraft pulping and oxygen delignification. The major structural changes occurring on lignin, during the course of conventional kraft pulping were shown to be: (a) the progressive formation of carboxylic acids and condensed phenolic hydroxyl groups and (b) the progressive and stereoselective degradation of the arylglycerol-beta-aryl ether units. It was also discovered that condensed phenolic hydroxyl units are relatively stable toward oxygen delignification. Significant evidence was also supplied accounting for the enhanced delignification efficiency of modern modified pulping processes and the mechanism of xylanase prebleaching of kraft pulps. / The 31P NMR technique was also applied to examine the effect of a lignin isolation process variable (batchwise versus continuous) on the structural details of dioxane acidolysis lignin isolated from kraft pulps. The structure of the dioxane acidolysis lignin, isolated from kraft pulps using batchwise and continuous processes, was shown to have similar functional group distributions and elemental compositions. These results confirmed that the structure of residual lignin in kraft pulps is not altered significantly during a dioxane acidolysis isolation process.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34650 |
| Date | January 1997 |
| Creators | Jiang, Zhi-Hua. |
| Contributors | Argyropoulos, D. S. (advisor) |
| 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: 001618404, proquestno: NQ36991, Theses scanned by UMI/ProQuest. |
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