PHENOLIC AND TANNIN-BASED ADHESIVE RESINS BY REACTIONS OF COORDINATED METAL LIGANDS .1. PHENOLIC CHELATES

Bivalent and trivalent metallic ions, respectively, accelerate and inhibit the reaction of phenols with formaldehyde. The catalytic effect of these metallic ions is equivalent, though more marked, to that of hydrogen ions, and it is due to their stronger charge. Metallic ions/phenols/formaldehyde complexes are formed. The stability of these complexes and mainly their rate of metal exchange in solution are the determining factors in the accelerating or retarding action. Identified stable chromium (III)–resorcinol–formaldehyde and chromium (III)–phenol–formaldehyde complexes have slow rates of metal exchange and inhibit the resorcinol–formaldehyde and phenol–formaldehyde reactions. The opposite is valid for lead (II), zinc (II), and other bivalent metallic ions. A scale showing the order of the accelerating effect of a series of metallic ions is given. The presence of polymeric complexes has also been observed. Copyright © 1979 John Wiley & Sons, Inc.