The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Steric effects on the formation constant of metal chelates of β-diketones》. Authors are Guter, G. A.; Hammond, G. S..The article about the compound:2,6-Dimethyl-3,5-heptanedionecas:18362-64-6,SMILESS:CC(C)C(CC(C(C)C)=O)=O).SDS of cas: 18362-64-6. Through the article, more information about this compound (cas:18362-64-6) is conveyed.
Formation constants for the chelates of bivalent ions of Cu, Ni, Mg, Co, and Mn, with acetylacetone, dipivaloylmethane, and diisobutyrylmethane were determined by potentiometric titration with KOH solution Titrations of solutions of metal ion, β-diketone, and KClO4 in 1:3 water-dioxane were performed under N. For acetylacetone, diisobutyrylmethane, and dipivaloylmethane, the metal ion, log K1, and log K2, are listed: Cu(II), 11.57, 9.64, 12.29, 9.99, 13.91, 11.55; Ni(II), 8.24, 6.39, 8.73, 7.56, 9.90, 9.10; Co(II), 7.86, 6.19, 8.37, 7.31, 9.60, 8.77; Mn(II), 6.81, 5.18, 7.23, 6.07, 8.34, 7.44; Mg(II), 6.13, 4.52, 6.45, 5.44, 7.44, 6.59. Stabilities of each series of chelates increase in the order acetylacetone, diisobutyrylmethane, dipivaloylmethane. The effect of the larger alkyl groups is more pronounced in the Cu chelates, which are of square planar configuration, than in the other chelates, which probably are of tetrahedral configuration. Acid dissociation constants of the β-diketones were determined at 25° (the diketone, solvent, method, and pKa are given): dipivaloylmethane, 1:1 dioxane-water, spectrophotometric absorption at 294 mμ, 13.23; dipivaloylmethane, water, spectrophotometric absorption at 294 mμ, 11.77; acetylacetone, 3:1 dioxane-water 0.05 molar KClO4, potentiometric titration, 11.27; diisobutyrylmethane, 3:1 dioxane-water 0.05 molar KClO4, potentiometric titration, 12.48; dipivaloylmethane, 3:1 dioxane-water 0.05 molar KClO4, potentiometric titration, 14.48. β-diketones may assume structures I or II in oxo form. Extent of enolization is related to the size of the R groups, and increases in the order acetylacetone, dipivaloylmethane, diisobutyrylmethane. II, in which the steric hindrance to rotation between the R groups is min., and the repulsion between the carbonyl dipoles is maximum, can be stabilized through enolization to III. Mol. models of dipivaloylmethane and diisobutyrylmethane can be constructed in form II, but not in form I. Correlations were observed between the pKa of the β-diketone, the kinetics of its enolization, and the kinetics of hydrolysis of esters of corresponding structure. Li is quantitatively and selectively separated from sq. solutions of alkali metal hydroxides by extraction with 0.1N solutions of dipivaloylmethane in ether. The small size of the Li atom compared with the Na and K atoms permits Li to replace the H atom as a shield between O atoms of dipivaloylmethane. Ether acts as solvent for chelated Li because of relatively large organic portion of mol.
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Reference:
Thiazole | C3H3NS – PubChem,
Thiazole | chemical compound | Britannica