Acetylacetone ions, decomposition

The nickel complex, Ni ( 5115)2, has been made by the action of the Grignard reagent on nickel (II) acetylacetonate (217) or from potassium cyclopentadienyl and the ammine [Ni(NHs)el (S N)2 in liquid ammonia (58). It forms dark emerald-green crystals which sublime at 80-90° and which, when heated in nitrogen, melt, with decomposition and the formation of a nickel mirror, at 173-174°. It is only slowly oxidized in air, and cold water neither attacks nor dissolves it it is, however, readily soluble in organic liquids. Oxidation of the compound yields an orange-yellow solution containing the ion [Ni( 5H5)2]+, which is stable for a short period in weakly acidic media, and which may be precipitated as the reineckate or tetraphenylborate. 

The decomposition rate constant kd for pure benzoyl peroxide in styrene polymerizations is 1.33x10" s at 90°C, while that for the benzoyl peroxide-N,N-diethylaniline redox system is 1.25x10" L/mol-s at 60°C and 2.29x10" L/mol-s at 30°C [15]. The redox system thus has a much larger decomposition rate. Peroxide decomposition is also accelerated in the presence of transition metal ion complexes such as copper (II) acetylacetonate and ammonium salts [17,18]. 

Despite the recent interest in the preparation and properties of thermally stable metal chelates, only a few attempts have been made to study in a systematic manner the chemical reactions that take place when metal chelates are thermally decomposed. The thermal stabilities of the acetyl-acetonates of a number of metal ions were compared by measuring the increase in pressure caused by the formation of volatile decomposition products in a closed system containing the metal acetylacetonate and nitrogen gas. A comparison of the data obtained at 191°C indicated that the rate and extent of decomposition were dependent on the nature of the metal ion. The acetylacetonates of Zr(IV), Co(III), Fe(III), and Mn(III) had the lowest thermal stability whereas the Li(I), Mg(II), Be(II), Cu(II), Ni(II), Ga(III), and Cr(III) chelates were among the most stable (44)- In contrast, acetylacetone itself does not decompose under the same conditions (4 ). 

Hiatt, Irwin and Gould [328] studied the decomposition of terU mXyX hydroperoxide in the presence of cobaltous and cobaltic stearates (St), octanoates (Oct) and acetylacetonates as well as iron phthalocyanine. They found that the acetylacetonates of Ni(II), Co(III) and Fe(III) were inert toward terUh xiyX hydroperoxide at room temperature. In chlorobenzene or alkanes at 25-45 °C, half lives for decomposition of O.IM ferf-butyl hydroperoxide by 10 M catalyst ranged from 1-10 min with the active catalysts. Products included approximately 88% tert-huXyX alcohol, 11% di-rer -butyl peroxide, 1% acetone and 93% O2. These authors reported that in general, the choice of metal ion, as long as it can undergo a facile one-electron redox reaction, had little effect on products or reaction rates [328]. 

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