Mechanism of Isotopic Exchange of Trisacetylacetonatoaluminum with Acetylacetone-14C in Organic Solvents

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Abstract
The kinetic study concerning isotopic exchange of acetylacetone (acacH) and trisacetylacetonatoaluminum [Al(acac)3] (Bull. Chem. Soc. Jap., 41, 384 (1968)) has been extended to solutions in various organic solvents. Similar catalytic actions of water and acid were observed, and the concentration of acacH did not affect the rate, so that the kinetic formula is expressed by R=[complex](k_1+k_2[H_2O]+k_1’[acid]+k_2’[acid][H_2O]) The rate constants and activation parameters are listed in Table 1. The k1 values are zero in non-polar solvents such as toluene and xylenes, whereas the k2 values are greater in these solvents than in polar solvents such as tetrahydrofuran and ethylacetate. The activation enthalpy is practically constant in these solvents, regardless of the participation of catalysts. The third and the fourth term seem to represent acid-catalysed reaction paths involving different proton carriers. The whole result appears to support our previous tentative conclusions that the exchange proceeds via an intermediate in which one of the acetylacetonate ligands is present as unidentate, and that the ease with which the free end recombines with the aluminum ion is responsible in determining the reaction rates.