Counter-ion and solvent effects on the acidity of calix[4]arene and para-tert-butylcalix[6]arene

GUADALUPE GLORIA MIÑAMBRES; THOMAS SERPA JAQUES; ALICIA VIVIANA VEGLIA; MÁRCIO LAZZAROTTO; FRANCINE FURTADO NACHTIGALL

J. Incl. Phenom. Macrocycl. Chem

Springer

Año: 2014

Spectrophotometric titrations of calix[4]areneand p-tert-butylcalix[6]arene with LiOH, NaOH, KOH,tetramethylmmonium and tetrabutylammonium hydroxidesas bases were carried in ethanol 95 % and acetonitrile. Thedependence of pKa of the first deprotonation of calix[4]-arene with the nature of the cation was only modest inethanol 95 %, spanning from 8.53 pKa unit for NaOH until9.00 for LiOH, whereas in acetonitrile the proton transfer isquantitative. The first deprotonation of p-t-butylcalix[6]arene in both solvents is quantitative and the extensionof the second deprotonation is very dependent of thenature of the cation in ethanol and acetonitrile. Tetramethylammoniumhydroxide was the strongest base forboth solvents, and both deprotonations proceed quantitativelyand concomitantly in ethanol, followed by potassiumhydroxide, and the weakest base was tetrabutylammoniumhydroxide. This behavior indicates that the ability to formN?-C?H?p and K??p interactions plays an importantrole to stabilize the mono and dianion calixarene. Lithiumand sodium exhibit non-usual acid?base behavior in acetonitrile,attributed to aggregation of the species.