Complex Compounds of Phloroglucinoquinoline with Salts of Various Metals

MOLodykh I. I. and KOZLOVSKAYA G. V.

In the study of complexes of hydroquinone and resorcinquinoline with mineral salts [1], it turned out that some of them, namely complexes with the chlorides of mercury and bismuth, possess high therapeutic properties when used for the treatment of certain skin diseases. This circumstance prompted us to continue work on the study of ternary complexes that include phenols. In the present work, phloroglucinoquinoline served as the organic part of the complex; we found no description in the literature of a method for its preparation.

Phloroglucinoquinoline was obtained by us in the following way: freshly distilled quinoline was heated on a gas burner and phloroglucinol was gradually introduced with stirring by a glass rod, in a weight ratio corresponding to one mole of phloroglucinol to three moles of quinoline. After half an hour of heating, the liquid was left overnight in a cool place. During the night the whole mass crystallized. In attempts to obtain the complex in other stoichiometric ratios, either an excess of quinoline remained or not all the phloroglucinol entered into the reaction.

Phloroglucinoquinoline is a white crystalline substance with a yellowish tint, with a melting point of 102°. It dissolves very readily in alcohol, somewhat less readily in ether, is insoluble in water, and is noticeably insoluble in benzene and chloroform, but becomes whiter. For the complex obtained, the following structural formula may be proposed:

Further complication of this complex by the addition of molecules of mineral salts proceeds at the expense of two electrons of the quinoline nitrogen, with whi...

which then enters into a complex bond with one or another metal, for example:

[[chemical structural diagram showing several quinoline rings coordinated through nitrogen/oxygen atoms to metal chlorides, with labels including CdCl₂]]

The likelihood of such a formula is supported by the fact that salts of the type \( \mathrm{C_9H_7N \cdot ZnCl_2} \) [4], \( \mathrm{C_9H_7N \cdot HgCl_2} \) [2], \( \mathrm{C_9H_7N \cdot CdCl_2} \) [3], and others exist. In addition, as is known, nitrogen in ammonia and amines very readily enters into complex bonding with metals, forming compounds more stable than those in which this bond in the molecule is effected through oxygen.

Experimental Part

The complexes were obtained by mixing an alcoholic or ethereal solution of phloroglucinoquinoline with an alcoholic solution of the corresponding mineral salt. The crystalline product that separated was filtered off on a Büchner funnel, washed with alcohol, dried in a desiccator, and then subjected to analysis. If the complex did not separate immediately after the solutions were combined, the mixture was evaporated on a water bath until crystallization began.

In preparing the complexes, various stoichiometric ratios of the components were taken; as a result, it was established that most of them have a composition corresponding to three molecules of the mineral salt per one molecule of phloroglucinoquinoline. Because of the infusibility of the complexes, it was not possible to determine the melting points by the usual capillary method.

1. The complex \( (\mathrm{C_9H_7N})_3\,\mathrm{C_6H_3(OH)_3 \cdot 2CoCl_2} \) separates, after the concentrated alcoholic solutions of the components are combined and briefly heated on a water bath, in the form of small blue crystals. It is readily soluble in water, but with decomposition. On heating it is somewhat volatile. It contains no water of crystallization.

Analysis of the Complex

Since this complex differs in composition from the others, its analysis was carried out a second time.

Chlorine was determined by Volhard’s method, cobalt as \(\mathrm{Co_3O_4}\).

2. Complex \((\mathrm{C_9H_7N})_3\,\mathrm{C_6H_3(OH)_3}\cdot 3\,\mathrm{MnCl_2}\,15\,\mathrm{H_2O}\) is obtained by mixing alcoholic solutions of the components. On evaporation on a water bath the mixture darkens. The salt crystallizes in light-brown crystals with a pink tint. It is soluble in water and readily soluble in alcohol.

Analysis of the complex

Determination of water of crystallization:

which corresponds to 15 molecules of water.

3. Complex \((\mathrm{C_9H_7N})_3\,\mathrm{C_6H_3(OH)_3}\cdot 3\mathrm{ZnCl_2}\) separates in the form of fine white crystals after cooling a mixture of alcoholic solutions of phloroglucinoquinoline and zinc chloride. It is soluble in water and alcohol.

Analysis of the complex

The lowered percentage in the determination of chlorine can be explained by a slight hydrolysis of the complex during washing of its crystals with 80% alcohol.

4. Complex \((\mathrm{C_9H_7N})_3\,\mathrm{C_6H_3(OH)_3}\cdot 3\,\mathrm{CdCl_2}\). When alcoholic solutions of the components are mixed, a white crystalline mass precipitates, with considerable heating occurring. The complex is sparingly soluble in cold water. It is decomposed by boiling water.

Analysis of the complex

1. Complex \((\mathrm{C}_9\mathrm{H}_7\mathrm{N})_3\mathrm{C}_6\mathrm{H}_3(\mathrm{HO})_3\cdot 3\mathrm{HgCl}_2\) is precipitated when alcoholic solutions of the components are mixed, in the form of a white microcrystalline precipitate. The compound is volatile on heating; it is sparingly soluble in water, and dissolves in dilute acids.

Analysis of the complex

1. Complex \((\mathrm{C}_9\mathrm{H}_7\mathrm{N})_3\mathrm{C}_6\mathrm{H}_3(\mathrm{OH})_3\cdot 3\mathrm{CuCl}_2\) is precipitated when an ethereal solution of phloroglucinoquinoline is mixed with an alcoholic solution of cupric chloride, in the form of a voluminous amorphous olive-colored precipitate. It is soluble in water and alcohol. Volatile on heating.

Analysis of the complex

1. Complex \((\mathrm{C}_9\mathrm{H}_7\mathrm{N})_3\mathrm{C}_6\mathrm{H}_3(\mathrm{OH})_3\cdot 3\mathrm{SnCl}_2\) is obtained in the form of yellow brittle needles by mixing an ethereal solution of phloroglucinoquinoline with an acidified alcoholic solution of stannous chloride. It is soluble in water with slight hydrolysis.

Analysis of the complex

1. Complex \((\mathrm{C}_9\mathrm{H}_7\mathrm{N})_3\mathrm{C}_6\mathrm{H}_3(\mathrm{OH})_3\cdot 3\mathrm{SnCl}_4\) is obtained by heating on a water bath a mixture of an alcoholic solution of phloroglucinoquinoline with an aqueous solution of stannic chloride until crystallization begins. After cooling, a white, yellowish-tinged microcrystalline precipitate separates, soft to the touch. The complex is soluble in water and alcohol without noticeable hydrolysis.

Analysis of the complex

1. The complex \((\mathrm{C}_9\mathrm{H}_7\mathrm{N})_3\mathrm{C}_6\mathrm{H}_3(\mathrm{OH})_3 \cdot 3\mathrm{FeCl}_3\) is obtained by mixing an ethereal solution of phloroglucinoquinoline and an alcoholic solution of ferric chloride, in the form of a gelatinous brown mass, completely soluble in hot alcohol, from which it is again separated only with difficulty. The complex has a sharp odor, which intensifies on standing. Soluble in water and alcohol.

Analysis of the complex

1. The complex \((\mathrm{C}_9\mathrm{H}_7\mathrm{N})_3\mathrm{C}_6\mathrm{H}_3(\mathrm{OH})_3 \cdot 3\mathrm{BiCl}_3\). On mixing an ethereal solution of phloroglucinoquinoline with an alcoholic acidified solution of \(\mathrm{BiCl}_3\), a bulky white precipitate separates, with heating of the whole mass. The precipitate was washed with a mixture of alcohol and ether in order to avoid hydrolysis. It is strongly hydrolyzed by water. Soluble in dilute acids.

The complex darkens somewhat on storage.

Analysis of the complex

In addition to those described, complexes of phloroglucinoquinoline were obtained with the following compounds: uranyl nitrate \(\mathrm{UO}_2(\mathrm{NO}_3)_2\)—light yellow; antimony chloride \(\mathrm{SbCl}_3\)—white; bismuth nitrate \(\mathrm{Bi}(\mathrm{NO}_3)_3\)—white; aluminum chloride \(\mathrm{AlCl}_3\)—a yellowish jelly; manganese nitrate \(\mathrm{Mn}(\mathrm{NO}_3)_2\), pinkish-brown; arsenic chloride \(\mathrm{AsCl}_3\)—yellow. These complexes could not be purified sufficiently well, either because of strong hydrolysis during washing or because of high solubility, which made it necessary to evaporate almost all the solvent.

Conclusions

1. Triple complexes of certain mineral salts with phloroglucinoquinoline have been obtained and studied; their general formula is \(\mathrm{R}\cdot 3\mathrm{MeX}_2\) and \(\mathrm{R}\cdot 3\mathrm{MeX}_3\). The complex with cobalt chloride is an exception: its composition is expressed by the formula \(\mathrm{R}\cdot 2\mathrm{MeX}_2\).

2. The complexes obtained are decomposed more or less readily by mineral acids and are partially or completely hydrolyzed by water.

3. The complexes are stable in the dry state. On heating or during prolonged storage they acquire a rather sharp odor. Some of them are volatile. Most are difficult to melt.

4. The investigations carried out have made it possible to propose a scheme for the structure of the complexes obtained, based on the electronic theory.

References

1. Izvestiya TII, issue III, p. 133, 1942.
2. Borsbach E.—Berichte, Vol. 23, 451, 1890.
3. Hofmann A.—Lieb. Ann., Vol. 47, 83, 1843.
4. Schiff H.—Lieb. Ann., Vol. 131, 112, 1864.