Calixarenes
A calixarene is a macrocycle or cyclic oligomer based on a hydroxyalkylation product of a phenol and an aldehyde.
The word calixarene is derived from calix or chalice because this type of molecule resembles a vase and from the word arene that refers to the aromatic building block. Calixarenes have hydrophobic cavities that can hold smaller molecules or ions and belong to the class of cavitands known in host-guest chemistry. Calixarene nomenclature is straightforward and involves counting the number of repeating units in the ring and include it in the name. A calix[4]arene has 4 units in the ring and a calix[6]arene has 6. A substituent in the meso position Rb is added to the name with a prefix C- as in C-methylcalix[6]arene.
The aromatic components are derived from phenol, resorcinol, or pyrogallol. For phenol, the aldehyde most often used is simple formaldehyde, while larger aldehydes, like acetaldehyde, are usually required in condensation reactions with resorcinol and pyrogallol. The chemical reaction qualifies as electrophilic aromatic substitution, followed by an elimination of water, and then a second aromatic substitution. The reaction is catalyzed by acids or bases.
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