Solvent-free synthesis of trisphenols as starting precursors for the synthesis of calix[4]arenes using sulfonated multi-walled carbon nanotubes

Abstract

The condensation of phenol derivatives (12 substrates) with 2,6-bis(hydroxymethyl)phenols (BMP) (6 examples) is reported using sulfonated multi-walled carbon nanotubes (SO₃H@MWCNTs) under solvent-free conditions as starting precursors for the synthesis of macrocyclic molecules of calix[4]arenes. The new protocol provides a series of trisphenol derivatives (21 examples) in high yields (up to 94%) and relatively short reaction times (15–120 min). Also, direct synthesis of calix[4]arenes from different trisphenols by use of the catalyst was reported (5 examples). Furthermore, the synthesized calix[4]arene was obtained using a one-pot method from simple and easily available starting materials such as p-cresol for the synthesis of 5,11,17,23-tetramethylcalix[4]arene-25,26,27,28-tetraol. Also, in this process SO₃H@MWCNTs can be reused for seven runs with almost consistent efficiency and can be recovered by easy filtration.