Zinke Synthesis

Abstract

AbstractThis reaction is a one‐pot, three‐step process to treat the mixture ofp‐substituted phenols and formaldehyde under basic conditions to give a group of molecules of high melting points that are primarily composed of cyclic arrays of four phenolic moieties joined by alternating methylene groups attached at positionsorthoto the hydroxyl groups, and named these moleculescyclischen mehrkernmethylenephenolverbindungen. This reaction is generally referred to as the Zinke synthesis. This preparative method has subsequently been modified by different groups. In addition, Gutsche coined the name calix[n]arene to stand for these molecules. The present study focuses the structural features, modifications and applications of calix[n]arene. It has been pointed out that the Zinke–Cornforth procedure in some cases afford calix[4]arenes as major products, whereas Munch's modification can be applied to the synthesis of calix[6]arenes and calix[8]arenes. A lengthy multistep process has also been developed for the preparation of sophisticated calixarene molecules. It has been reported that the cations that complex with calix[n]arenes can be divided into two groups, alkali (or alkali‐like). The transition metal cations and the relative orientation ofparaand phenolic substituents also affects the selectivity of calix[n]arenas toward the alkali cations. It has been found that theconeconformer of calix[4]arenas shows the highest affinity for Na+, whereas the partialconeand1,3‐alternateconformers prefer K+and Cs+. All the known modification methods on calix[n]arenas have been discussed, which can be divided into nine groups. Other types of calix[n]arene analogues have been prepared, such as resorcarenes, and homo‐oxacalixarenes. The asymmetric calix[n]arenes are generally obtained by three approaches. The study finds that calixarenes arising from other aldehydes rather than formaldehyde have alkyl or aryl groups at the bridges across the aromatic annulus; and according to the orientation of these substituents, there exist four kinds of stereoisomers. This reaction has very wide applications in the preparation of calix[n]arenes.