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Saxby, M. J. (1958) The kinetics of cyclisation of o-aroylbenzoic acids by sulphuric acid. Doctoral thesis, Sir John Cass College.
The kinetics of ring closure of o-benzoylbenzoic acid to anthraquinone have been investigated in mixtures of sulphuric acid and water over a range 77% w/w to 100% w/w and in sulphuric acid/acetic acid over the range 66% w/w to 100% w/w.
The kinetic investigations were extended to p-alkylbenzoyl-o-benzoic acids in an attempt to elucidate the mechanism of the reaction. The cyclisation of p-toluyl-o-benzoic acid was investigated in both mixtures of sulphuric acid/water and in sulphuric acid/acetic acid whilst the other alkylaroylbenzoic acids were examined in the non-aqueous mixtures only. In addition, the kinetics of cyclo-dehydration of both p-chlorobenzoyl-o-benzoic acid and benzophenone- 2,4-dicarboxylic acid to the corresponding anthraquinones were investigated in the non-aqueous solvent.
The method of analysis adopted for all the investigations was based upon the extent of ultra-violet spectra of the appropriate anthraquinone dissolved in concentrated sulphuric acid; an arithmetical correction being made for the absorption due to the unreacted aroylbenzoic acid.
Since the thermodynamic and electrical properties of solutions of sulphuric acid are not well known, it has not been possible to obtain any formal correlation of the specific rate with any common measure of solvent acidity. Further it has been demonstrated that the rate of cyclisation of o-benzoylbenzoic acid in mixtures of sulphuric acid/water bears no simple relationship with Hammett's acidity function.
Values of the energies and entropies of activation have been calculated for the reactions and their principal features have been discussed in terns of a transition state.
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