STUDY OF THE PROPERTIES OF PYRIDINE-2-AZO-PARA-PHENYLTETRAMETHYLGUANIDINE AS A METAL-ION COMPLEXING AGENT

Pyridine-2-azo-p-phenyltetramethylguanidine (PAPT) was synthesized and the properties of this compound examined. The dissociation constants of the conjugate acids in H2O are pK(a)' H2O = 10.41 +/- 0.06, and pK(a)" H2O = 2.62 +/- 0.02 at 25-degrees-C at I = 0.1, and in acetonitrile are pK(a)' = 18.0 +/- 0.2 and pK(a)" = 10.4 +/- 0.2. The properties of metal-ligand chelates in acetonitrile have been examined and the stability constants for Ni2+, Co2+, and Zn2+ complexes measured. The rates of reaction of PAPT with Ni2+, Co2+, and Zn2+ in acetonitrile have been determined and the activation parameters measured for the complex formation of LNi2+. The stability constants for both complexing centres of PAPT have been calculated. The C-13 NMR spectra for PAPT and LNi2+ are quoted. The expected enhancement of the metal ion complexing ability of PAPT due to the strongly electron-releasing nature of the tetramethylguanidinyl group was not found.