Bevan, Morfydd Ann (1954)
Carbinol ionisation in sulphuric acid.
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The evidence in support of the production of carbonium ions from triarylcarbinols under the influence of certain ionising solvents has been summarised. The concept of the "acidity function" of solutions outside the range covered by the terra "dilute aqueous solutions" has been discussed, including the acidity function, H0, introduced by Hamnett to cover the ionisation of simple Bronsted bases, and the new acidity function, J0, for the ionisation of secondary bases, as typified by the triarylcarbinols. The two methods by which J0 can be evaluated have been considered, together with the use of this acidity function for the interpretation of reaction mechanisms involving analagous ionisations for the production of reaction intermediates. The ionisation of some triarylcarbinol indicators in sulphuric acid-water mixtures has been studied, both colorimetrically and from absorption spectra data, the preparation of two new indicators being described. The influence of medium composition and of added salts on the absorption spectra of the triaryl. Carbonium ions has been studied. The acidity function J0 has been computed for the range 52-90% sulphuric acid by the stepwise indicator method. A method of determining the difference in basic strengths of two indicators whose ranges of ionisation just fail to overlap, involving the observed influence of added salts, has been postulated and used for the construction of the J0 scale. The influence of added salts has also been correlated with their influence on the velocities of nitration reactions. The discrepancies between the J0 scales obtained by the stepwise indicator method and by calculation from the H0 scale by the method of Gold and Hawes have been discussed.
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Institution: University of London, Royal Holloway College (United Kingdom).