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Dawson, Bernard Ernest (1956) The kinetics and mechanism of the reactions between substituted benzaldehydes and 5:5-dimethyl-cyclo-hexanedione-1:3 (dimedone). Doctoral thesis, Sir John Cass College.
The reaction between dimedone and substituted benztaldehydes has been shown to be of first order with respect to both dimedone and the aldehyde, the reaction rate depending on pH and the temperature. The Arrhenius constants for nine such reactions have been determined over the temperature range 25° - 50°C.. A study of the correlationship of these factors has shown that these reactions are of three types: those which give parallel increases of PZ and EA; and those which possess approximately the same PZ factor; and those which involve the use of aldehydes which exhibit intra-molecular hydrogen bonding or some other steric effect. It has been shown that the effects of substituents in the aldehydes can be estimated in terms of the change in free energy needed to form the transition state, and that the order of this effect appears to be related to the half-wave potential of the corresponding aldehyde. A reaction mechanism, based on the type suggested by Lapworth(7a) to account for the formation of oximes in acid solution, is postulated and this has been used to derive a rate equation which agrees reasonably well with the experimental data.
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