Kinetics of Isotopic Exchange between Acetylacetone-14C and Tris-acetylacetonatoaluminum in Tetrahydrofuran

TLDR: In this paper, the exchange rate of trisacetylacetonatoaluminum [Al(acac)3] and acacH with the aid of acetylacetone-14C was investigated.

Abstract: Tris-acetylacetonatoaluminum [Al(acac)3] is precipitated crystalline from tetrahydrofuran (THF) solution containing an excess of acetylacetone (acacH) by adding chilled petroleum ether. This fact enables a kinetic study of isotopic exchange of acac− between [Al(acac)3] and acacH with the aid of acetylacetone-14C. The exchange rate is independent of the concentration of acacH and dependent on that of water. The rate formula at 25°C is as follows: R=[Al(acac)_3](6×10^-5+2.0×10^-2[H_2O]) mol l^-1min^-1 This exchange reaction is catalysed by acids; the stronger the acid, the greater the catalytic effect. One of the acetylacetonate ligands would be present with one end free, and break of the remaining bond of unidentate acetylacetonate seems to be the rate determining step. Water can occupy the vacant coordination site of aluminum ion to retard recombination of the unidentate ligand. The donation of proton to the free end of acetylacetonate appears to impede the recombination, too, and facilitate the exchange....