Equilibrium and catalytic studies of some cobalt (II) chelate oxygen carriers

Abstract

The cobalt (11) chelates of ethylenediamine, diethylenetriamine, triethylenetetraamine, and tetraethylenepentaamine in aqueous solution are studied by potentiometric pH and oxygen absorption measurements. The chelates formed by the 1:1 molar ratios of diethylenetriamine and triethylenetetraamine to cobalt (II) and by the 2:1 molar ratio of ethylenediamine to cobalt (II) absorb one mole of oxygen per two moles of metal chelate and also form an even numbered polymer via the loss of one proton per two metal chelates. The tetraethylenepentaamine cobalt (11) chelate, however, also absorbs one mole of oxygen per two moles of metal chelate, but no additional proton loss is observed. The formation and oxygen equilibrium constants for these polyamine-cobalt (11) chelates are reported. Both the chelates formed by 1:1 and 2:1 molar ratios of glycylglycine to cobalt (11) in aqueous solution are found to undergo reversible oxygenation. Potentiometric pH studies indicate that the 1:1 chelate in alkaline solution undergoes amido proton ionization with the simultaneous absorption of one mole of oxygen per two moles of metal chelate. An additional loss of one proton per two metal chelates indicates the formation of an even numbered polymer. In case of the 2:1 chelate only one glycylglycine per cobalt atom undergoes amido proton ionization as one mole of oxygen is absorbed per two moles of metal chelate. The 1:1 solution of diglycylethylenediaminetetraacetic acid (DGENTA) to cobalt (II) reversibly absorbs one mole of oxygen per two moles of metal chelate with ionization of both amido protons. The formation and oxygen equilibrium constants for the Co(II)-DGENTA system are reported. ...