Nitric acid equilibrium in concentrated trifluoromethanesulfonic acid studied by Raman spectroscopy

Abstract

Mixtures of CF₃SO₃H–H₂O–HNO₃ have been analysed by Raman spectroscopy and the ionic species formed in the protonation–dehydration equilibrium of nitric acid (HNO₃+ CF₃SO₃H ⇌ NO₂⁺+ CF₃SO₃^–+ H₂O) have been estimated. In the range 80–90 wt% CF₃SO₃H the titration curve of NO₂⁺ has been determined.

In the range 90–100 wt% CF₃SO₃H, linear relationships have been found, at a given acidity, in the plots of [NO₂⁺]versus[CF₃SO₃^–] using different concentrations of nitric acid. Decreasing slopes are observed with increasing acidity of the medium. The involvement of NO₂⁺·CF₃SO₃^– ion-pairs in the range above 90 wt% CF₃SO₃H is suggested, and the influence of these species on nitration rates is discussed