The Structure and Properties of Phenol-2,4-disulfonic Acid Dihydrate

Abstract

The crystal and molecular structure of phenol-2,4-disulfonic acid dihydrate was determined by X-ray structure analysis. All hydrogen positions in the crystal structure were found using difference Fourier syntheses. Oxonium cations and acid anions were linked in the crystal structure by short H-bonds, and the phenol OH group participated in two weak H-bonds with sulfo group oxygens simultaneously. The IR frequency corresponding to νs, as (H3O+) vibrations decreased to 2700 cm−1 under the influence of short H-bonds between oxonium cations and anions. The contour of the corresponding absorption band became anomalously broad. A discrete maximum was observed at 3412 cm−1 on the high-frequency wing of this band; this maximum was assigned to OH stretching vibrations of the phenol group. The protonic conductivity of the compound measured by impedance spectroscopy was 2.5 × 10−6 Ω−1 cm−1 at 298 K in a vacuum, Ea = 0.37 ± 0.01 eV. An increase in the humidity of the environment to 15% at room temperature increased conductivity from 10−6 to 10−5 Ω−1 cm−1, Ea = 0.27 ± 0.02 eV.