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calixarene
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()arene has 4 units in the ring and a calix()arene has 6. A substituent in the meso position Rb is added to the name with a prefix C- as in C-methylcalix()arene.
==Synthesis==
The aromatic components are derived from phenol, resorcinol or pyrogallol, For phenol, the aldehyde most often used is simply formaldehyde, while larger aldehydes (acetaldehyde, or larger) are generally required in condensation reactions with resorcinol and pyrogallol. The chemical reaction ranks under electrophilic aromatic substitutions followed by an elimination of water and then a second aromatic substitution. The reaction is acid catalysed or base catalysed.
Calixarenes are difficult to produce because it is all too easy to end up with complex mixtures of linear and cyclic oligomers with different numbers of repeating units. With finely tuned starting materials and reaction conditions synthesis can also be surprisingly easy. In 2005, research produced a pyrogallol()arene by simply mixing a solvent-free dispersion of isovaleraldehyde with pyrogallol and a catalytic amount of ''p''-toluenesulfonic acid in a mortar and pestle. Calixarenes as parent compounds are sparingly soluble and are high melting crystalline solids.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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