, 1568 (1981).Protonation acidity constants for 27 benzamides, acetamides, and lactams have been determined. Ultraviolet, and I3C and 'H nmr, spectroscopic methods were used; almost all the spectra were found to be subject to medium effects, some quite severe, as the sulfuric acid concentration was increased. Despite this, the excess acidity (X-function) method gave accurate pKB,+ and m * values.In all cases protonation, followed by a medium shift in the spectrum of the protonated form, was the only process taking place; protonation was essentially complete in 60% H,S04. The results for the different bases are interpreted in terms of the resonance, inductive, and steric effects in operation in the acid and base forms. On a determine les constantes d'acidite de la protonation de 27 benzamides, acetamides et lactames. A cette fin on a utilise la rmn du 'H et du "C ainsi que la spectroscopie ultraviolette; lorsque la concentration en acide sulfurique augmente, presque tous les spectres subissent des effets de milieu qui sont quelquefois trbs importants. En depit decette influence, la methode d'excts d'acidite (fonction X ) donne des valeurs prkcises de pKBH+ et de m*. Dans tousles cas, la protonation, suivie d'un deplacement moyen dans le spectre de la forme protonee, est le seul processus qui a lieu; la protonation est tout a fait compl'ete dans du H,S04 a 60%. On interprbte les resultats des differentes bases en fonction de la resonance ainsi que des effets inductifs et steriques presents dans les formes acide et basique.[Traduit par le journal]
The acid-catalyzed reactions of acetamide 1, N-tert-butylacetarnide 2, and several p-substituted N-benzylacetamides (3 = H, 4 = CH3, 5 = 0CH3, 6 = C1, 7 = NOz) have been studied as a function of acidity and temperature over a wide range of aqueous sulfuric acid solutions (0-91%). Analysis of the reaction products and rate-acidity profiles revealed that four different mechanisms are operative over different acidity regions depending on the structure of the substrate. These are: two A-2 hydrolysis mechanisms with N-acyl fission of the substrate (with participation of one or several water molecules in the rate-determining step); A-l hydrolysis with N-alkyl fission; and sulfonation, followed by hydrolysis. These conclusions are supported by three complementary and detailed kinetic treatments based on the hydration parameter, transition state activity coefficient, and excess acidity approaches. The acidity domains of each mechanism have been established for each substrate. [Traduit par le journal]
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