Studies on the Kinetics and Mechanisms of Reactions of Dimethylglyoxime with Iron(II), Cobalt(II) and Copper(II) Ions in Ethanol-Water Media

Laboratory of Chose Professor of Chemistry, Inorganic Chemisty Division, University College of Science,
92 A. P. 0. Road, CalCutta-700 009

Reactions of dimethyiglyoxime with iron(II), cobalt(II) and copper(II) ions in (20%, v/v) ethanol—water media have been studied by stopped-flow spectrophotometry. The results indicate that in all the cases the initial reaction is a rather fast formation of the bis(dimethylglyoximato) complex of M(II) followed by further reaction in a slower step which involves oxidation of the cobalt(II) complex to a cobalt(III) species by the free ligand in solution, transformation of the copper(II) complex to a copper(I) species in an intramolecular process and formation of Fe(dmgH\()^-_3\) from Fe(dmgH)₂ respectively. In the case of copper(II), the initial reaction is too fast for the stopped-flow range but in the other two cases rates of formation of the his-complexes, M(dmgH), (M = Co^II, Fe^II), could be studied and results indicated T_L/k_obs=1/\(\propto\)  + [H⁺]β T_L, where  and β are constants.

In presence of excess dimethylglyoxime, Fe(dmgH)₂. is converted to Fe(dmgH)^-₂ in a slow step and the observed pseudo-first order rate constant corresponds to 1/k_obs= 1/\(\propto\).' + [H+]/β' T_L. Cu(dmgH)₂, formed initialfy In a fast proeess transforms intramolecularly to a copper(r) species and the c:obalt(n) complex is slowly oxidised to a coball(III) complex by excess ligand. The rates of these slow reactions are independent of pH and ligand concentration, Both these reactions have been followed by stopped-How spectropbotometry.