The Hammett acidity function, Ho, is based upon the ionization of sub- stituted primary aromatic amines. For up to a 4 :l molar ratio of water to sulfuric acid, the amide acidity scale, HA, and the H, scale are simply related by ifA = II, - 2 log a, where oW is the activity of water. This approach has been successfully applied to benzamide and the naphthamidcs. The well-known failure of the Hammett H, function to describe the proto- tropic reaction isotherms of aromatic carboxamides can be corrected by taking account of the hydration requirements of the prototropic reactions of the carboxamides relative to the hydration requirements of the dissociations of the primary amines used as indica- tors to establish the H, scale. SCHULMAN* College of Pharmacy, University of Florida, Gainesville. Anolyticn Chimico Ado, 127 (1981) 203-207 Eisevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands Short Communication A SIMPLE RELATIONSHIP BETWEEN THE HAMME’IT ACIDITY FUNCTION, H, AND THE THERMODYNAMIC pK, VALUES OF UNSUBSTITUTED AROMATIC CARBOXAMIDES MICHAEL W.
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