Structure and behavior of organic analytical reagents : Dimethylglyoxime and its oxygen monomethyl ether

The titration procedure described in previous papers of this series has been applied to a study of some metallic chelates of dimethylglyoxime and of its O-monomethyl ether. Evidence is presented for the existence of dimethylglyoxime chelates with Zn (II), Pb (II), Cd (II), and La (III) in addition to the known Cu (II), Ni (II), and Co (II) complexes. Formation constants are calculated for these complexes, and for those of dimethylglyoxime O-monomethyl ether, on the basis of their most probable structures. The results indicate that the famed specificity of dimethylglyoxime fur nickel does not lie in any special stability of this chclate. but in some other factor, possibly solubility. A comparison of the chelates of dimethylglyoxime with those of its O-ether is discussed in terms of such structural factors as hydrogen bonding and steric hindrance. Heat content and entropy changes have been calculated for the chelation of dimethylglyoxime with Cu (II) and Ni (II) ions.