Comparison of the Reaction Rates of the Alkali-Catalyzed Addition of Formaldehyde to Phenol and Selected Lignins

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Abstract
A comparison of the reaction rates of the alkali-catalyzed addition of formaldehyde to phenol, Kraft lignin, and steam-exploded lignin was studied by monitoring the disappearance of formaldehyde at four temperatures to determine the Arrhenius parameters. 1H-NMR spectra of acetylated lignins and their hydroxymethylated derivatives and the disappearance of formaldehyde during lignin-formaldehyde reactions were used to quantify the degree of formaldehyde substitution. The rate of the addition of formaldehyde to phenol was faster than the addition of formaldehyde to lignin, although the lignin-formaldehyde reactions were essentially complete under the reaction conditions examined. Both lignin-formaldehyde reactions had lower activation energies than the phenol-formaldehyde reaction. Kraft lignin has a faster rate of reaction with formaldehyde than steam-exploded lignin and the rate of formaldehyde addition to lignin is dependent on the reactive site availability on the lignin molecules.

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