Calixarenes, 19. Studies of the formation of calixarenes via condensation of p‐alkylphenols and formaldehyde

Abstract

AbstractThe base‐induced reaction of p‐alkyl substituted phenols with formaldehyde yields oligomers which, in some cases, are cyclic [1,1,1,1]‐metacyclophames known as calixarenes. The present work attempts to provide insight into the mechanism of calixarene formation by studying various facets of the reaction, including the effect on the product distribution (i.e. cyclic tetramer, cyclic pentamer, cyclic hexamer, cyclic heptamer, and cyclic octamer) of (a) reactant ratios, temperature, solvent, and cation, (b) starting oligomer (i.e. monohydroxymethyl or dihydroxymethyl monomer phenol, dimer phenol, trimer phenol, or tetramer phenol), and (c) p‐alkyl group of the starting phenol. Product analyses were carried out by isolation and TLC methods in some cases and by HPLC methods in others. On the basis of the data that have been obtained it is postulated that (a) the calix[8]arenes are the product of kinetic control and are formed via a hemicalix[8]arene arising from intermolecular association between a pair of hydroxymethylated linear tetramers, (b) the calix[6]arenes are the product, in part, of template control and may be formed via a hemicalix[6]arene anion arising from intermolecular association between a pair of hemicalixarene anions from hydroxymethylated linear trimers, and (c) the calix[4]arenes are the product of thermodynamic control and can be formed via ring contraction of the calix[8]arenes and the calix[6]arenes.