Possibilities of Multinuclear NMR in Determination of Acidity of Heteropoly Acid Solutions
Russian Journal of Inorganic Chemistry
, E-ISSN: 1531-8613
Boreskov Institute of Catalysis SB RAS
The N-14 and C-13 NMR parameters of the acidity indicator ortho-nitroaniline (o-NA) and the N-14 and O-17 NMR parameters of substrates in solutions of some acids and heteropoly acids (HPA) have been measured. The N-14 and C-13 NMR parameters of Hammet acidity indicators and the N-14 and O-17 NMR parameters of anions and a solvent depend on the acidity of a solution. The NMR signals of the amino nitrogen atom and the carbon atom bearing the amino group are most sensitive. Comparison of the NMR parameters of the Hammet indicator o-NA in solutions of acids and HPAs shows that the interaction of HPAs with o-NA, which is not related to acidity, additionally contributes to the NMR parameters of o-NA in HPA solutions. It has been shown that the acidity of a water-containing solution can be estimated based on the O-17 NMR parameters of water.