Constant Selectivity in Proton Exchange Reactions Between Aqueous Sulphuric Acid and Acetylenes

Chokotho, N. C. J.; Johnson, C. D.

doi:10.1002/ijch.198500129

Cited by 4 publications

(2 citation statements)

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“…This is the case in this work for 1 and 2, and probably for 3 (see Figs. 2-4), which agrees with Johnson's conclusion for 2 (9,10). However, compound 4 certainly does not have a substituent-independent slope (see Fig.…”

Section: Discussionsupporting

confidence: 88%

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The hydration of 1-aryl-3,3,3-trifluoropropynes and some other phenylacetylenes in sulfuric acid. An excess acidity analysis

Cox¹,

Grant²,

Whitaker³

et al. 1990

Can. J. Chem.

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This paper is dedicated to Professor Ross Stewart on the occasion of his 65th birthday ROBIN A. Cox, EWART GRANT, TODD WHITAKER, and THOMAS T. TIDWELL. Can. J. Chem. 68, 1876 (1990). The excess acidity method has been used to analyse the hydration kinetics of the phenylacetylenes Y-C6H4-C-C-Z in aqueous sulfuric acid mixtures; Z = CF3 (I), H (2), COC6H4-X (3), and COzH (4). All substrates gave acetophenone-type products consistent with the normal hydration mechanism involving rate-determining vinyl cation formation. Standard-state log &intercepts, and m*m* slopes, were both used in linear free energy relationship plots against the substituent u + values. Solvent isotope effects and activation parameters were obtained in some cases. The deactivating Z substituents in 1 , 3, and 4 all cause reaction to be some 100 times slower than that of the parent phenylacetylene 2. Compounds 2,3, and 4 all have p+ values of about -3.8, but 1 is more substituent sensitive, with a p+ of -5.3. A u+ value of 0.38 is calculated for the CF3C-C substituent. The p+ values were found to be acidity independent for 1 and 2, and probably for 3, but not for 4. Proton transfer at the transition state was found to be most advanced for the fastest reaction, that of 2, contrary to intuition.Key words: alkyne hydration, excess acidity, phenylacetylenes, vinyl cations, deactivated carbocations. ce n'est toutefois pas le cas avec le compose 4. Contrairement ace que l'on pouvait croire d'une faqon intuitive, on a trouvC que le transfert de proton dans l'ttat de transition est le plus avanck avec la reaction la plus rapide.

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Section: Discussionsupporting

confidence: 88%

“…[2] to the plenitude of literature information available for 2 (6)(7)(8)(9)(10)(11)(12)(13)(14) are listed in Tables 2 and 3. Results obtained by different authors are in complete agreement, and so all data for the same compound were treated together, regardless of source.…”

Section: Resultsmentioning

confidence: 99%