Abstract:
The development of, and current hypotheses in, the field of protolytic reactions of organic bases in concentrated solutions of mineral acids has been reviewed.
The protonation equilibria of a series of amides and phenylureas have been studied. Both classes of compounds have been found to follow the HA acidity function. For amides the variation of pKBH+ has been found to be similar to the variation of rate constant of hydrolysis. Evidence for an A-1 mechanism for hydrolysis of acetanilide derivatives in concentrated solutions of sulphuric acid has been obtained. The rate data obtained for the hydrolysis of phenylureas and dipeptides has been treated by current criteria of mechanism. The hydrolysis of sucrose has been carried out over a wide range of acidities in hydrochloric, sulphuric, perchloric and phosphoric acids.
All available hydrolysis data on amides, both from the literature and from this investigation, has been critically examined. It has been found that the data can be divided into two mechanistic categories, one obeying the Bunnett w criteria, and the other a postulated two term mechanism.
Some of the work carried out in this investigation has been reported in the following papers -
1 solvent Effects on the Acid Catalysed Inversion of Sucrose; J.W. Barnett and C.J. O'Connor, J. Chem. Soc., B. 1971, 1163
2. The Acid Catalysed Hydrolysis of N-acetylsulphanilic acid – A changing mechanism: J.W. Barnett and C.J. O’Connor, Tetr. Letters, 1972, 2161.
3. Sulphonation or hydrolysis? Acetanilide in aqueous sulphuric acid; J.W. Barnett and C.J. O’Connor, Chem. & Ind., 7970, 1172
4. Evidence for a first-order Mechanism in Amide Hydrolysis; J.W. Barnett and C.J. O’Connor, J.C.S. Chem. Comm. 1972, 525.
5. Protonation equilibria of Ureas; J.W. Barnett and C.J. O’Connor, J.C.S. Chem. Comm., 1972, 653
6. Evidence for Differences in Interpretation of Mechanism of Acid Catalysed Hydrolysis of Aliphatic and Aromatic Amides; J.W. Barnett, C.J. Hyland and C.J. O’Connor, J.C.S. Chem. Comm., 1972, 720
7. The Acid Catalysed Hydrolysis of Acetanilide; J.W. Barnett and C.J. O’Connor, J.C.S. Perkin II, 1972, 220
8. Acid Catalysed Hydrolysis of Substituted Acetanilides; J.W. Barnett and C.J. O’Connor, J.C.S. Perkin II, 1972, 2378