INVESTIGATION OF COMPLEX COMPOUNDS OF BENZIDINE AND p-ANISIDINE WITH CERTAIN SALTS OF DIVALENT COPPER

I. I. Molodykh, A. I. Borodulina

(Presented by Prof. B. V. Tronov, Doctor of Chemical Sciences)

The aim of this work was to synthesize and investigate complex compounds of benzidine and anisidine with salts of divalent copper, descriptions of which we have not encountered in the literature. For the synthesis of the complex salts, crystalline hydrates of the following salts of divalent copper were taken: chloride, nitrate, sulfate, and acetate. The complex compounds were obtained by mixing cold saturated solutions of the components; the copper salts were dissolved in water, and benzidine and anisidine in alcohol, with the exception of the preparation of cupric nitrate anisidine and cupric acetate anisidine, where anisidine was dissolved in water.

With copper chloride, sulfate, and nitrate, benzidine gives complexes of molecular composition 1:1. In compounds of benzidine with copper acetate, as well as in all anisidine complexes, there were two molecules of amine per one molecule of the copper salt.

All the complexes form rather readily and precipitate from aqueous-alcoholic or aqueous solutions as intensely colored crystalline substances (see table). In air they are unstable and gradually decompose. With increasing temperature, decomposition proceeds more rapidly. Under strong heating the complexes first blacken; then their organic portion burns out, and the metal remains in the form of the corresponding oxide. Especially vigorous combustion of the organic portion of the complex is observed in the cupric nitrates of both benzidine and anisidine.

Owing to the instability of the complex compounds toward heating, their melting temperatures could not be determined.

With respect to water, the complexes obtained behave differently. The most stable are cupric sulfate benzidine and cupric sulfate anisidine. They do not dissolve in water and are not decomposed by water. The remaining complexes dissolve in water with decomposition. Their solubility in alcohol is also different. Thus, cupric sulfate benzidine and cupric nitrate benzidine are the most difficult to dissolve in alcohol, while the remaining complexes are fairly readily soluble.

In ether, all benzidine complexes are difficultly soluble. Of the anisidine complexes, cupric sulfate anisidine is difficultly soluble in ether, while the other three—cupric chloride, cupric nitrate, and cupric acetate anisidine—are readily soluble.

The solubility of the complexes we obtained in dilute acids is different. Some of them dissolve under ordinary conditions, others upon heating (see the appended table).

Table 1

Conclusions

1. The complex compounds of benzidine and p-anisidine with the copper salts studied by us precipitate from aqueous-alcoholic or aqueous solutions of the components in the cold, in the form of intensely colored crystals or powders.

2. All these substances are unstable and gradually decompose in air.

3. The solubility of these substances in various solvents differs. Some of them, such as cupric sulfate benzidine, are almost insoluble in water, alcohol, and ether.

4. The intense coloration of the indicated complexes and their low solubility provide grounds for investigating the possibility of using them in analytical chemistry.