Intracomplex Organosilicon Compounds Based on Derivatives of 8-Hydroxyquinoline

L. I. Aristov, N. M. Rovkina

(Presented by the scientific seminar of the organic departments)

Intracomplex compounds of silicon have been insufficiently studied. Hardy notes that silicon tetrachloride is capable of forming acetylacetonates, binding three molecules of acetylacetone into a complex [1]. Hexachlorodisiloxane is also capable of reacting with acetylacetone, forming an intracomplex compound of tricyclic structure [2]. 8-Hydroxyquinoline has been used in analytical practice for the quantitative determination of silicon present in natural and synthetic compounds [3, 4].

The reaction of alkylchlorosilanes with 8-hydroxyquinoline and its derivatives has not been studied, although the formation of chelate-like compounds of dialkyldiaryl-dichlorosilanes with 8-hydroxyquinoline and its derivatives is possible, since silicon in these compounds has a coordination number equal to six. Therefore it was of interest to study the properties of intracomplex compounds of this type.

As starting components for obtaining an intracomplex compound we used dimethyldichlorosilane and 5-hydroxymethyl-8-hydroxyquinoline. The preparation of an organosilicon complex whose terminal groups contain $-\mathrm{CH_2OH}$ residues is of interest for the purpose of subsequently carrying out syntheses of polymeric materials. In obtaining an intracomplex compound, the solvent is of great importance, since many organic solvents (alcohols, bases) interact with dimethyldichlorosilane. Among many solvents, dioxane proved suitable for carrying out the reaction. The latter dissolves the methylol derivative of 8-hydroxyquinoline well, but dissolves the intracomplex compound that forms poorly. Study of the properties of the complex obtained showed that the complex is formed with a composition of $1:2$, and its structure may be represented by the following scheme:

\[ \left[ \begin{array}{c} \text{5-hydroxymethyl-8-oxyquinolinato ligand} \end{array} \!\!-\! \mathrm{O}\!\to\!\mathrm{Si}(\mathrm{CH_3})_2 \!\leftarrow\!\mathrm{N} \!-\! \begin{array}{c} \text{5-hydroxymethyl-8-oxyquinolinato ligand} \end{array} \right]\cdot 2\mathrm{HCl} \]

Confirmation of this scheme of the structure of the complex compound is provided by the following experimental facts: elemental analysis of this compound; the yellow color of the compound, which is also characteristic of intracomplex compounds of 8-hydroxyquinoline with dimethyldichlorosilane; the presence of free oxy groups and their ability to interact with difunctional compounds (dicarboxylic acids, amino acids); the solubility of the complex in water and its acidic reaction (pH = 4) with a universal indicator.

Experimental Part

5-Oxymethyl-8-hydroxyquinoline. In five liters of distilled water, 70 g of caustic potassium is dissolved and 280 g of 8-hydroxyquinoline is introduced.

To the resulting solution of the potassium salt of oxine, 250 ml of a 26% formaldehyde solution is added. The contents are left to stand at room temperature for 24–36 hours until the odor of formaldehyde disappears.

The solution is then acidified with a weak (10%) solution of acetic acid to a neutral reaction. The precipitated cream-colored solid is filtered off, washed with warm water, and dried. Yield 276.9 g—82% based on oxine. For purification, the product is transferred to a flask with 0.5 l of benzene. In the cold, unreacted 8-hydroxyquinoline and the 7-oxymethylene derivative dissolve in benzene. This purification is repeated twice. The precipitate insoluble in benzene is dried. Its final purification is carried out by recrystallization from aqueous acetone or dioxane. Benzene, toluene, and xylene are not suitable solvents for recrystallization, since upon heating considerable resinification of the methylol derivative of 8-hydroxyquinoline occurs. The substance has a melting point of 130°C; calculated: N—8.2%; C—68.5%; H—5.14%; OH—19.43%; found: N—7.49%; C—68.51%; H—5.23%; OH—19.63%.

Intracomplex compound. In a three-necked flask equipped with a reflux condenser, dropping funnel, and stirrer, 15 g of the monomethylol derivative of 8-hydroxyquinoline is dissolved, with heating, in 250 ml of dioxane. With stirring, 5.52 g of dimethyldichlorosilane (component ratio 2:1), dissolved in 25 ml of dioxane, is gradually added from the dropping funnel. A yellow precipitate forms. The precipitate is filtered off, washed with fresh portions of dioxane, and dried. Yield 98% based on the starting product. The resulting substance has no definite melting point; at 240°C it changes color, and at higher temperature it resinifies. Calculated: N—5.86%; OH—7.1%; Si—5.86%; Ce—14.8%. Found: N—5.97%; OH—7.1%; Si—5.83%; Ce—15.3%.

When the intracomplex compound is kept for 8 hours at 100°C, it loses 0.36% in weight; at 150°C the losses amount to 11.3%; at 200°C for 6 hours the losses amount to 21.8% by weight.

The solubility of the complex at 20°C in organic solvents is characterized by the following data: benzene—10.62%; toluene—20.65; m-xylene—10.9; methanol—67.8; ethanol—37; butanol—23; acetone—24; dichloroethane—17; chloroform—9.9; dioxane—10.8; dimethylformamide—49.2; ether—15.2%; i.e., the best solvents are methanol and dimethylformamide. The complex compound dissolves in water.

Conclusions

1. It has been shown that dimethyldichlorosilane forms, with 5-hydroxymethyl-8-hydroxyquinoline, an intracomplex compound of composition 1 : 2 and of moderate thermal stability. Some properties of the organosilicon intracomplex compound have been studied.

References

1. Hardy, Chem. Alstr. 3554 (1947).
2. Reinboldt H, Wissfeld W, J. prakt. Chem. 142, 23 (1935).
3. M. I. Volynets, Zavodskaya laboratoriya 1621 (1936); L. B. Ginzburg, ibid., 1041 (1938).
4. A. P. Kreshkov, V. A. Bork, A. V. Myshlyaeva, G. D. Nassonova, Analysis of Organosilicon Compounds. Goskhimizdat, 1954.