THE IONIZATION BEHAVIOR OF AMIDES IN CONCENTRATED SULPHURIC ACIDS: I. A NEW ACIDITY FUNCTION BASED ON A SET OF PRIMARY AMIDE INDICATORS

Abstract

A set of eight suitably substituted primary amides of progressively weaker basicity have been prepared. Their ionization curves have been determined in sulphuric acids by spectrophotometric methods. These show good overlap and parallelism for successive indicators, enabling the pK values of the indicators to be determined by direct stepwise comparison. Using these pK values and measured ionization ratios, values of a new acidity function, H_A, have been obtained for aqueous solutions up to 82% sulphuric acid. The H_A function decreases much less rapidly than H₀ in this range, being nearly 3 log units less negative at the highest acidity studied. The reasons for this large difference are discussed. The H_A function is shown to be applicable to other amides which have not been employed as indicators.