Alkaline hydrolysis of nonphenolic β-O-4 lignin model dimers: Further studies of the substituent effect on the leaving phenoxide

被引：0

作者：

Collier, W.E. ^{[1
]}

Fisher, T.H. ^{[1
]}

Ingram Jr., L.L. ^{[1
]}

Harris, A.L. ^{[1
]}

Schultz, T.P. ^{[1
]}

机构：

[1] Department of Chemistry, Mississippi State University, Mississippi State

来源：

| 1996年 / 50期

关键词：

Ethers - Hydrolysis - Pulp - Pulp cooking;

D O I：

暂无

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学科分类号：

摘要：

Reaction rates and activation parameters for the alkaline hydrolysis of nonphenolic β-O-4 lignin models [2-(4-substituted phenoxy)-1-(3,4-dimethoxyphenyl)-1-ethanol] were compared to 2-methoxylated B-ring analogues run earlier. The Hammett plot with the best fit used σ- values to give a ρ of 1.9 ± 0.2. while the 2-methoxyl-substituted compounds had a ρ of 2.3 ± 0.3. Compounds with a methoxyl group at the ortho position of the leaving phenoxide ion hydrolyzed slightly faster than the non-methoxylated analogues, indicating that the 2-methoxy group is a weak electron-withdrawer. The strong electron-withdrawing 4-CHO and 4-CF3 substituents gave significantly different activation parameters than the unsubstituted compound. Experiments with 18O-labeled water suggested that our earlier proposed SNAr mechanism for the alkaline hydrolysis of strong electron-withdrawing compounds is not correct. It appears that all nonphenolic β-O-4 dimers are hydrolyzed by a neighboring group mechanism.

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