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The changes of infrared spectra of sprucewood lignin in the 1600-1800 cm-1 region during acidolysis

J. Polčin, B. Kosíková, P. Šipoš, M. Dandárová-Vašátkova, and J. Suchý

Slovak Academy of Sciences, Bratislava

 

Abstract: The structural changes of carbonyls and carboxyls in the side chains of lignin during the acidolysis of sprucewood (Picea excelsa) sawdust were studied with infrared spectrophotometry. Absorption bands at 1680 cm-1 correspond to carbonyls conjugated with benzene rings and at 1720 cm-1 to nonconjugated carbonyls and to a less degree to nonconjugated carboxyls. In protolignin and in Brauns' (Brauns and Brauns, The Chemistry of Lignin, Supplement Vol. 440, London, 1960), native, and Bjoerkman's (CA 51, 18586h) lignins, isolated under moderate conditions, carbonyls predominate in the position to the benzene ring. During acidolysis, the carbonyls switch from the α position to the β position, which occurs in compds. with a 1,2-hydroxycarbonyl structure. Switching is more rapid in MeOH than in dioxane. There is a very small amt. of coniferylaldehyde structure in native lignin, in which, during methanolysis, HCl adds to the double bonds with Cl in the α-position, which is immediately substituted with MeO. NaOH (0.1 N) decreases the amt. of carbonyls in the methanol- and dioxane lignin, which can be explained by the keto-enol tautomerism, aldol condensation, and partially by oxidative cleavage.

Full paper in Portable Document Format: 1712a891.pdf (in Slovak)

 

Chemical Papers 17 (12) 891–904 (1963)

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