Alkaline-catalyzed Reaction of Formaldehyde and the Methylols of Phenol; A Kinetic Study

Abstract

Previous attempts to analyze the kinetics of the phenol-formaldehyde reaction have been limited to determination of a cumulative over-all reaction rate. By means of paper chromatography it is now possible to follow quantitatively the appearance and disappearance of each individual methylolphenol in the reaction system. Mathematical analysis of the data from separate experiments involving phenol, p-hydroxybenzyl alcohol, saligenin, 2,4-dimethylol- and 2,6-dimethylolphenol, respectively, with formaldehyde at 30°, has provided individual rate constants for the reaction of each phenolic compound. Reactivities of individual positions in various phenolic nuclei may also be compared. The reactions are of second kinetic order. Significant differences in both positional and molecular reactivity were found. An ortho position in phenol is slightly less reactive than the para. In saligenin the reverse is true. Introduction of an o-methylol group enhances the reactivity of the remaining active nuclear positions. The same group in the para position retards further activity. These effects are multiplied in the dimethylol analogs. 2,6-Dimethylolphenol is, by far, the most reactive molecule present in the system. The observed differences in reactivity are attributed to the effect of hydrogen bonds in the o-methylol compounds. It was further observed that, under alkaline conditions, the formation of diphenylmethane bridges occurred only between methylol groups with loss of formaldehyde and water, not between methylol groups and free nuclear positions. The reaction appears to be first order and considerably slower than the reaction of methylolphenol formation. Deterioration of polymethylol-phenols by loss of methylol groups from the ortho position also has been observed under certain conditions. © 1954, American Chemical Society. All rights reserved.