X 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 deterlnined by direct stepwise comparison.Using these pK values and measured ionization ratios, values of a new acidity function, fI>:\, have been obtained for aqueous solutions up to 82% sulphuric acid. The H::\ function decreases much less rapidly than PI0 in this range, being nearly 3 log units less negative a t the highcst acidity studiecl. The reasons for this large difference are discussed. The $I,:\ function is shown to be applicable to other arnides which have not been elnployed as indicators.

ABSTRACT'The newly determined H. 4 scale of acidity has been tested against ionization ratio data for 33 amides. Twenty-nine of these compounds give log I vs. HA slopes of 0.9-1.1 and most are within 0.95-1.05. The average slope for these is 1.001 f 0.051. 'The H. 4 function is thus considered to be generally applicable to the ionization of this type of base, and the significance of previously reported amide p K values is discussed in the light of these results. Previously reported basicity-substituent constant relations have been reexamined using thermodynamically significant p K data and earlier conclusions confirmed. Appropriate ecluations are derived in an attempt to explain the rate-acidity dependence of amide hydrolysis directly in terms of the water activity of the reaction medium. 'The picture of the hydrolysis t r a~~s i t i o n state which results is in accord with that obtained using methods described by other workers.