Effect of the air humidity on the proton conductivity of some aminobenzenesulfonic acids

Abstract

Effects of environment conditions (humidity and temperature) on the proton conductivity of aminobenzenesulfonic acids: 2-amino-(orthanilic) acid (I), 3-amino-(metanilic) acid (II), 4-amino-(sulfanilic) acid (III), their general formula NH₂C₆H₄SO₃H, and 3-amino-4-hydroxobenzenesulfonic acid (IV) [NH₂(OH)C₆H₃SO₃H), as well as (for sake of comparison) inorganic aminosulfonic acid [sulphamic acid (NH₂SO₃H)] (V) are studied. All above-listed compounds are zwitter-ions: they contain a fragment NH ⁺₃ SO ⁻₃ . The presence of this structural fragment affects the thermal stability of the compounds; according to the mass-spectrometry analysis data, the decomposition of the SO₃-fragment begins at the following temperatures: (I) −339, (II) −370, (III) −320, (IV) −278, and (V) −220°C. It is shown that the increase of the environment relative humidity up to 95% results in the increase of the aminobenzenesulfonic acids proton conductivity from 10⁻⁹–10⁻⁸ to 10⁻⁵ S cm⁻¹; sulphamic acid, to 10⁻⁴ S cm⁻¹. At that, the amount of adsorbed water does not exceed 0.2 moles per 1 sulfo group in all cases. The conductance activation energy equals 0.2 eV at a relative humidity of 95%.