Document Type



The reaction of 3,5-dimethylpyrazole with cobalt (II) ion in aqueous solution was first observed by Fischer in 1925 (1). He investigated a series of organic compounds as precipitants for the common metal ions and noted that aluminum, cobalt, iron, and zinc (among others) formed precipitates with 3,5-dimethylpyrazole. Surprisingly enough, preciphation was not observed with copper and nickel. A reagent capable of differentiating between cobalt and nickel was thus potentially available. In 1930, Heim (2) used 3,5-dimethylpyrazole for the determination of cobalt ion in solutions of cobalt salts after separation of interfering ions. The blue-violet precipitate formed in basic solution was filtered, washed, dried, and weighed as Co(C5H7N2)2 . More recently, the use of the reagent as a precipitant for cobalt has been advanced (7). Procedures are outlined for the determination of cobalt in organic compounds after destruction of the organic matter by sulfuric acid and peroxide oxidation. Present interest in the cobalt-3,5-dimethylpyrazole system was concerned with the possible colorimetric determination of the metal ion with the reagent. Solubility of the colored material in a nonaqueous medium with retention of coloration would form the basis of such a method. Solubility to yield a colored solution (the precipitated species would remain as an undissociated species) might be expected from the similarity to the cobalt (1) acetylacetonate complex which is soluble in most organic solvents.

Publication Date


Journal Title

Proceedings of the Iowa Academy of Science





First Page


Last Page



©1957 Iowa Academy of Science, Inc.



File Format




To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.