Determination of the pK Value of a Brønsted Acid by F NMR Spectroscopy.

Brønsted acids, such as phosphoric acids derived from chiral 1,1'-bi-2-naphthol (BINOL), are important catalysts in the formation of carbon-carbon and carbon-heteroatom bonds, for example. The catalytic activity of these Brønsted acids is strongly linked to their acidity, and as such, the evaluation of compounds to determine pK values provides insight into their catalytic activity. Herein, a F{H} NMR methodology is detailed to determine the pK of a fluorinated binaphthyl-derived phosphinic acid, rac-1, in acetonitrile and in the presence of a fluorinated sulfonamide reference compound (2-4).