Protiodeacylation of 4-substituted 1-acetyl-2,6-dimethylbenzenes in sulphuric acid: kinetics and mechanism
- 1 January 1988
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 6,p. 943-949
- https://doi.org/10.1039/p29880000943
Abstract
In 89.8%(w/w) sulphuric acid rate coefficients (104k1/s–1) for the protiodeacetylation of 4-substituted (X) 1-acetyl-2,6-dimethylbenzenes (1) were, at 25 °C; X = Br, 0.468; I, 0.509; Cl, 0.635; H, 1.345; F, 2.52; Ph, 31.5; But, 38.6; and Me, 47.2. At 25 °C the reaction of the ketone (1; X = OMe) was too fast, and at 80 °C reactions of the ketones (1; X = CONH2 or CO2H) were too slow, for convenient measurement. The carboxy nitrile (X = CN) underwent hydration to the amide (X = CONH2) rather than protiodeacylation. The rate coefficients at 25 °C of eight ketones (1) gave an accurate Hammett correlation, with σ+ constants, giving ρ=–4.64 ± 0.05. The reaction of 1-acetyl-2,4,6-trimethyl-benzene (1; X = Me) was studied of a range of acidity (73.6–99.9% sulphuric acid), and a maximum was found near 86.0% acid. Rates were also measured in D2SO4–D2O. The mechanism is discussed.Keywords
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