PROTONATED CARBONYL GROUPS: III. ANTIPYRINE SALTS

Abstract

Salts of antipyrine (2,3-dimethyl-1-phenyl-5-pyrazolone) with halogen acids have been prepared and their infrared spectra from 4000 to 650 cm⁻¹ recorded. Stoichiometrically they are normal 1:1 salts. Identification of bands due to vibrations of the protonating hydrogen atom has been aided by replacement with deuterium atoms. It is concluded that protonation occurs at the carbonyl group from the presence of a doublet (due to correlation field splitting) at 1320 and 1220 cm⁻¹, attributed to the in-plane hydrogen-bending mode. The OH stretching vibration gives rise to bands between 2278 and 2720 cm⁻¹ in the different salts. Out-of-plane hydrogen-bending mode absorptions are observed between 840 and 770 cm⁻¹.More complex acids (HAsF₆ etc.) give the anomalous 2 base:1 acid salts, characterized by strong absorption below 1400 cm⁻¹, which probably contain strong, possibly symmetrical, hydrogen bonds.