Interactions of Cu (II) with Hydroxy Salicylic Acids

Chemistry Department, Marathwada University, Aurangabad Manuscript received 16 December 1972; accepted 28 May 1973 The interactions between Cu2+ and 4-hydroxy, 5-hydroxy and 6-hydroxy salicylic acids have been investigated in aqueous medium and — 0.1 M ionic strength by Calvin-Bjerrum potentio­metric titration technique. It was observed that Cu2+ forms 1 : 1 and 1 : 2 complexes with these ligands in the pH ranges of 4-6 and 7-8 respectively. The complexation occurs by the reactions (1) Cu2++ H2L-\(\rightleftharpoons\)CuHL+H+ and (ii) CuHL+H2L-\(\rightleftharpoons\) Cu(HL)22-+H+, (the ligand being H3L). The stability constants of these complexes are determined and their relation with ligand basicities are discussed. The possibility of a different type of 1 : 1 complex between Cu2+ and 6-hydroxy salicylic acid by the reaction Cu2+-+ CuHL\(\rightleftharpoons\)Cu2L-H+ is proposed. Evidence for such reaction is given by conductometric and potentiometric measurement