Acid dissociation constants of pyridine-2-aldoxime and its affinity for various metal ions were determined by means of potentiometric titrations. Stable chelates were formed with the following metal ions, listed in order of stability: ferric > cupric > cobaltous > ferrous > nickelous > mercuric > zinc > cadmium >manganous. Calcium and magnesium ions showed no evidence of chelate formation. T h e unusually high stabilities of the cobaltous and ferrous chelates suggest that the oxime exhibits a specific affinity for these ions. All of the 1 : 1 chelates showed a strong tendency to hydrolyze, as indicated by results obtained from titrations of solutions containing the reactants in a 1 : 1 ratio. Colored species were formed in the ferrous, ferric, cobaltous, nickelous, and cupric systems. I n particular, the ferrous chelate formed an intense red solution, suggesting possible application of the oxime as an analytical reagent for ferrous ion.
HE CHELATING ability of the oxime group has
Tbeen recognized for some time; however, relatively little work on the stability of oxime chelates has been reported in the literature. A notable exception is dimethylglyoxime which, because of its analytical applications, has been the subject of extensive investigations (1-3).
Recently a few papers have appeared which were particularly concerned with oxime chelation. Murmann has calculated stability constants of chelates of 2-methyl-2-amino-3-butanone oxime and some of its derivatives (4). Proposed chelate structures demonstrated formation of hydrogen bonded species, similar to those observed for dimethylglyoxime chelates. Banerjea and Tripathi noted the intense colors of cuprous and ferrous chelates of methyl-2-pyridyl ketoxime and described the use of this oxime as an analytical reagent for these metals ( 5 ) . During the course of the present investigation, a paper by Krause and Busch was published, which described in detail the isolation of and formulas for nickelous, palladium, and platinum chelates of pyridine-2-aldoxime (6). The primary purpose of this investigation was to study the ability of pyridine-2-aldoxime to form chelates with selected metal ions. These metal complexes may be of value in the treatment of poisoning by organophosphate anticholinesterases. Wagner-Jauregg and associates (7) demonstrated that the hydrolysis rate of diisopropylphosphorofluoridate (DFP) is greatly accelerated in the presence of various cupric chelates; the cy,cu'-dipyridyl chelate, which is related structurally t o pyridine-2-aldoxime, showed the strongest catalytic activity. A similar study by .~