Aluminium-27 nuclear magnetic resonance studies of the hydrolysis of aluminium(III). Part 6. Hydrolysis with sodium acetate

Abstract

If acetate anions are added to aluminium salt solutions, they are protonated by the strong acid [Al(H₂O)₆]³⁺ which itself polymerises to form the dimer cation [(H₂O)₄Al(µ-OH)₂Al(H₂O)₄]⁴⁺ which loses two further protons. This is the only hydrolysis product detected and no evidence was obtained for the presence of the tridecameric polymeric cation in such solutions. If acetate is added to the extent that the ratio [MeCO₂^–]/[Al³⁺] is greater than 1.5, then acetate groups become attached to the dimer cation to form a complex which is presumably the precursor of the dialuminium dihydroxo tetra-acetate which is known to precipitate from aluminium acetate solutions. Changes in the ²⁷Al linewidths of the species observed provide a useful measure of the rates of the exchange processes present.