Collect. Czech. Chem. Commun. 2001, 66, 1125-1139

Electrochemical Investigations of Alkaline Cleavage of Lignin Under Mild Conditions

Petr Zuman* and Elinore B. Rupp

Department of Chemistry, Clarkson University, Potsdam, NY 13699-5810, U.S.A.


At pH 8-12 and 25 °C, 10-20% of lignin undergoes cleavage producing soluble species. In suspensions of lignin it is possible to follow the concentration changes of hydroxybenzaldehydes and α,β-unsaturated carbonyl compounds. These species can be determined by the recording of polarographic current-voltage curves directly in the suspensions, where the presence of suspended and colloidal particles does not interfere with the function of the DME. The base-catalyzed cleavage follows first-order kinetics. The pH dependence indicates that the rate determining step is not a nucleophilic attack by OH-, rather the rate determining step is preceded by a rapidly established acid-base equilibrium. The cleavage of natural lignins obtained enzymatically follows a pattern similar to that of rot wood lignins and surprisingly also to that of kraft lignins. The patterns of cleavages are different from those of lignosulfonates, Klason, periodate and expansion lignin. The three dimensional (tertiary) structure of lignin seems to play a role in its reactivity.

Keywords: Lignins; Lignans; Hydrolysis; Polarography; Phenols; Aldehydes; Hydroxybenzaldehydes.

References: 22 live references.