Synthesis of C-tetra(aryl)resorcin[4]arenes using various types of catalysts under solvent free conditions: a comparative study

Abstract

A comparative study was carried out between the methods of synthesis of C-tetra(aryl)calix[4]resorcinarenes: by means of reflux, that is to say, carrying out a cyclocondensation reaction catalyzed by hydrochloric acid between resorcinol and different aromatic aldehydes, and by means of the solvent-free method, which is part of the green chemistry methodologies, in which several catalysts were used, viz. p-toluenesulfonic acid, clinoptilolite zeolite, and silica-gel. In the calix[4]resorcinarenes obtained by both methodologies, mainly 2 types of conformers, crown and chair, were observed. The conformers were isolated and characterized via different spectroscopy techniques: FT-IR, HPLC/MS, 1H-NMR, and 13C-NMR. In these solvent-free and reflux reactions, different ratios were obtained for each of the conformers, finding diverse and unexpected ratios for the solvent-free method. On the other hand, for the solvent-free method there was a significant saving of solvent, an important factor in the care of the environment, as well as of energy and time, in addition to minimizing the significant risks involved in the handling of strong mineral acids.

Keywords

• Cyclocondensation
• Solvent-free
• Chair conformation
• Crown conformation
• Catalysis