The base-catalysed ring fission of a series of substituted 2,2-dihydroxyindane-1,3-diones and phenalene-1,3-dione has been studied in 30% (v/v) dioxane-water. The reaction proceeds in two distinct steps. The first is a relatively fast base-catalysed ring fission to give substituted o-carboxyphenylglyoxals, and the second is a rearrangement of the latter resulting in formation of substituted o-carboxymandelic acids. Rate coefficients for the ring fission of a limited series of substrates have been determined at 25.0 ЊC. The reaction is first order in the mono-anion of the substrate alone. The Hammett reaction constants, , have been obtained from both the kinetic and product studies. The rate-and product-determining step appears to be an intramolecular nucleophilic attack. The rate coefficients for the rearrangement have been determined for all substrates at 25.0, 35.0 and 45.0 ЊC. The activation parameters have been calculated. The kinetic solvent isotope, solvent and salt effects have been studied. The effects of the 5-substituted and 5,6-disubstituents on the rates have been correlated using a modified Hammett equation giving a reaction constant, , equal to 3.4 at 25 ЊC.
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