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V. Sippola, T.-R. Viljava, K. Vilonen, O. Krause
New Method to Follow the Dimerisation Reaction Occuring during Oxidation of 4-Ethylguaiacol
4-Ethylguaiacol is a phenolic model compound used to study the oxidation of lignin. A new method was developed to determine 4,4?-diethyl-6,6?-biguaiacol, an unwanted side-product, in the oxidation of 4-ethylguaiacol. The sample is extracted with ethyl acetate to separate 4,4?-diethyl-6,6?-biguaiacol from the water-soluble oxidation catalyst. No other treatment is required before analysis with a standard UV-Vis spectrophotometer. The spectrophotometer is calibrated to measure concentrations of 4,4?-diethyl-6,6?-biguaiacol up to 0.3 mM. With the new method, the concentrations of 4,4?-diethyl-6,6?-biguaiacol can be reliably determined over a wide alkaline pH range. The performance of the method was demonstrated in experiments investigating the formation of 4,4?-diethyl-6,6?-biguaiacol in the autoxidation and cobalt-sulphosalen catalysed oxidation of 4-ethylguaiacol. In the conditions of the studies (1 bar oxygen pressure and 50°C), a low (0.01 mM) concentration of Co-sulphosalen clearly increased the total conversion of 4-ethylguaiacol. However, relative to autoxidation, the conversions achieved in the presence of the catalyst were just as sensitive to pH, and the yields of the undesired dimeric product, 4,4?-diethyl-6,6?-biguaiacol, were higher.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 56, 11/2002
Pages: 601 - 606