Solutes in sulphuric acid. Part VI. A nuclear magnetic resonance study of organic sulphonic acids and 1H nuclear magnetic resonance standards; pKBH determination of sulphonic acids

Abstract

The behaviour of some alkane- and arene-sulphonic acids in sulphuric acid as solvent has been investigated. In aqueous sulphuric acid the sulphonic acids ionize: ArSO₃H ⇌ ArSO₃^–+ H⁺. The ionization follows the H₀^a acidity function and half-ionization is observed at –5·8 > H_o^a > –6·8. In fuming sulphuric acid the sulphonic acids exhibit both protonation and sulphur trioxide complexation with formation of RSO₃H₂⁺ and RS₂O₆H respectively. The chemical shifts of some ¹H n.m.r. standards for the sulphuric acid system are reported. The preferred standards are the (CH₃)₄N⁺ ion as internal standard, and neat liquid tetramethylsilane as external standard.