127679-82-7Relevant academic research and scientific papers
The first acid constant of calix[4]arenes
Backes, Michaela,Boehmer, Volker,Ferguson, George,Gruettner, Cordula,Schmidt, Christian,Vogt, Walter,Ziat, Kadija
, p. 1193 - 1200 (2007/10/03)
A series of calix[4]arenes containing a single p-nitrophenol unit (or two p-nitrophenol units) have been synthesized by fragment condensation. Their first acid constant (pKa1) has been determined in 2-methoxyethanol-water (9:1) by optical titration. Relative to the corresponding linear trimers with a p-nitrophenol in the middle, a decrease of pKa1 by 2.1 units or more is observed, which can be explained entirely by intramolecular hydrogen bonds stabilising the monoanion. In this way electron-withdrawing p-substituents in the opposite phenolic unit lead to a further decrease in pKa1, while a distortion of the cone conformation by m-methyl groups causes a slight increase. The structure of one calix[4]arene was further confirmed by single crystal X-ray analysis showing the molecule in the usual cone conformation.
A stepwise synthesis of functionalized calix [4]arenes and a calix[6]arene with alternate electron-withdrawing substituents
De Mendoza, Javier,Nieto, Pedro M.,Prados, Pilar,Sanchez, Concha
, p. 671 - 682 (2007/10/02)
Simple modifications of the TiCl4-induced cyclocondensation of phenol derivatives raise the yields of pure calix [4]arenes, even in the presence of electron-withdrawing substituents. The first example of a calix [6]arene with alternate substitu
