The problem of acidity in liquid and solid acid catalysts: A comparative study by protonation equilibria of weak bases
The protanation equilibria of nitroanilines (B + H(+) = BH(+)) in HCIO(4)/SiO(2) and CF(3)SO(3)H/SiO(2) mounted materials were studied by ultraviolet spectroscopy and the results were compared with those obtained for analogous indicators in concentrated aqueous solutions of HCIO(4) and CF(3)SO(3)H. Analogies and differences in the behaviour of indicators in the liquid and solid phase are analysed in detail by the titration curves, log [BH(+)]/[B] ratios and pK(BH(+)) values of indicators. It is shown that the equilibrium constants of indicators in the solid phase are analogous to the values estimated in concentrated aqueous acid solutions when suitable parameters to describe the properties of the medium under investigation are taken into account. The activity coefficient functions, acidity functions and protonating ability of a solvent obtained in different nonideal acid systems are discussed. Experimental data obtained by using nitroanilines in CF(3)SO(3)H/SiO(2) with added pyridine are also reported and the modifications observed on the equilibria by the titrating agent analysed.
Bibliographic Reference: Article: Organic Reactivity (1997)
Record Number: 199810121 / Last updated on: 1998-02-12
Original language: en
Available languages: en