Full Text
Reports of the Academy of Sciences of the USSR
1963. Volume 150, No. 2
CHEMISTRY
Corresponding Member of the Academy of Sciences of the USSR G. A. RAZUVAEV, L. M. BOBINOVA
ON THE REACTIONS OF METHYLTITANIUM TRICHLORIDE WITH METALLIC MERCURY AND MERCURIC CHLORIDE
At present, the study of the properties of organotitanium compounds is attracting considerable interest, since it has been established that in Ziegler–Natta catalysts alkyl radicals are transferred from Al to Ti with the formation of a catalytic complex containing alkyl derivatives of titanium. True organotitanium compounds having Ti—C bonds, owing to their thermal instability, became known only comparatively recently. In 1952 the first representative of this class of compounds—phenyltitanium triisopropylate—was synthesized (¹). In subsequent years reports appeared in the literature (²–⁴) on the synthesis of alkyl derivatives of titanium with the general formula \(R_nTiI_{4-n}\), where R = CH₃, C₂H₅, C₄H₉. In 1959 Berman and Bestian (⁵), and somewhat later Fries (⁶), synthesized alkyltitanium trichlorides and studied some of their properties. These compounds are thermally extremely unstable and can be stored only at temperatures not higher than −70 to −80°.
Contradictory opinions have been expressed concerning the mechanism of decomposition of the indicated organotitanium compounds. Berman and Bestian showed that decomposition of \(CH_3TiCl_3\) without solvent proceeds with the formation of trichlorotitanium, methane, and liquid polymethylene. On decomposition of the organotitanium compound in a solution of hydrocarbons or carbon tetrachloride at 70–100°, the same decomposition products were isolated, with a small admixture of ethane (about 5% in hydrocarbon) or methyl chloride (1% in \(CCl_4\)). It was suggested that decomposition of methyltitanium trichloride under the described conditions proceeds mainly without liberation of free radicals. But the authors also allow for the possibility of a free-radical process, for example, during decomposition in diethyl ether or in a mixture of carbon tetrachloride with diethyl ether, when a noticeable increase in the content of ethane and methyl chloride, respectively, was observed in the decomposition products. As a result of studying the decomposition process of \(CH_3TiCl_3\) in solutions of heptane and cyclohexane with the use of labeled atoms, Fries concluded that in the thermal and photochemical decomposition of alkyltitanium trichlorides free radicals are not formed. Ethane and methyl chloride, detected in the decomposition products, in the author’s opinion are the result of side bimolecular disproportionation reactions:
\[ 2CH_3TiCl_3 \to 2TiCl_3 + C_2H_6 \]
\[ CH_3TiCl_3 + TiCl_4 \to CH_3Cl + 2TiCl_3 \]
As is known (⁷), metallic mercury is used as a scavenger of free radicals in the study of the decomposition of many organometallic compounds. It seemed of interest to us to study the decomposition process of methyltitanium trichloride on the surface of metallic mercury.
Methyltitanium trichloride was synthesized from dimethylaluminum chloride and titanium tetrachloride in hexane solution by the method described in the literature (²). The product was purified from impurities of titanium tetrachloride and organoaluminum compounds by distillation under vacuum in the presence of diphenyl oxide and by recrystallization from hexane. The pure preparation obtained was stored in hexane solution at a temperature of about −70°.
At room temperature, in an atmosphere of nitrogen carefully purified from oxygen and moisture, \( \mathrm{CH_3TiCl_3} \) (1.2 g) in hexane solution was added to metallic Hg (50 g) in \( \mathrm{CCl_4} \) with vigorous stirring. Very rapid decomposition of the organotitanium compound was observed, with separation of a brown precipitate characteristic of trivalent titanium chloride, and darkening of the reaction mass. The reaction mixture was kept for 6 hours at room temperature, and then heated to 35–40° for 5 hours. In the precipitate isolated from the reaction solution, the presence of trivalent titanium was determined (by titration with ferric ammonium alum). In the solution, after distillation of the solvent, an organomercury compound volatile with steam was found. After its decomposition with concentrated hydrochloric acid or a mixture of nitric and sulfuric acids, and passage of hydrogen sulfide through the resulting solutions, a black precipitate of mercury sulfide was obtained.
In the interaction of methyltitanium trichloride (0.05 mole) with metallic mercury (0.45 mole) in \( \mathrm{CCl_4} \) (50 ml) at a temperature of \(-5 \div -6^\circ\), rapid decomposition of the organotitanium compound also occurred, with precipitation of a brown precipitate. The reaction mixture was kept for 4.5 hours at the indicated temperature, and then for 4 hours at room temperature. From the reaction mixture, along with titanium trichloride, the following products were isolated and identified: \( \mathrm{TiCl_4} \) (0.012 mole).
\[ \begin{aligned} \text{Found, \%:}\quad & \mathrm{Cl}\ 74.3;\quad \mathrm{Ti}\ 25.1\\ \text{Calculated, \%:}\quad & \mathrm{Cl}\ 74.8;\quad \mathrm{Ti}\ 25.2 \end{aligned} \]
\( \mathrm{CH_3HgCl} \)—(0.0052 mole) (m.p. 170°, a sample mixed with the pure substance melted without depression).
\( \mathrm{C_2Cl_6} \)—(0.0013 mole), m.p. 184–186° (in a sealed capillary) (proved by a mixed-melting-point test with an authentic pure substance).
\( \mathrm{CH_3Cl} \)—(0.0024 mole). In the precipitate, the presence of calomel was determined by reaction with concentrated ammonia. During the decomposition process, the evolution of gaseous products was observed. To identify the gaseous products, \( \mathrm{CH_3TiCl_3} \) (0.008 mole) was reacted with metallic Hg (0.004 mole) in an ampoule at room temperature. After completion of the reaction, the ampoule containing the reaction mixture was cooled in liquid nitrogen, and after the ampoule was opened the gaseous products were collected in a burette over metallic mercury. Chromatographically it was found that the gaseous products consisted mainly of methane (0.005 mole), with a small admixture of ethylene and methyl chloride.
On the basis of the results obtained, it may be assumed that during the decomposition of methyltitanium trichloride on the surface of metallic Hg in \( \mathrm{CCl_4} \), in addition to the decomposition of alkyltitanium trichloride in carbon tetrachloride described in the literature, a second process takes place with liberation of free radicals, which is confirmed by the formation of methylmercury chloride, methyl chloride, hexachloroethane, and calomel. In addition, the presence of mercury considerably accelerates the decomposition process of the organotitanium compound.
It was noted (\(^{8}\)) that, under the action of air, decomposition processes of some organic mercury compounds (diisopropyl- and dicyclohexylmercury) and reactions of their interaction with \( \mathrm{CCl_4} \) or \( \mathrm{CHCl_3} \) readily occur.
When the decomposition of \( \mathrm{CH_3TiCl_3} \) (0.02 mole) was carried out in the presence of metallic Hg in \( \mathrm{CCl_4} \), in an atmosphere of dry air, at room temperature, a considerable decrease in the content of compounds of trivalent titanium and \( \mathrm{CH_3HgCl} \) (0.001 mole) in the reaction mixture was observed, which indicated the predominance, in an air atmosphere, of the oxidation reaction of the organotitanium compound.
We also studied the interaction of methyltitanium trichloride with mercuric chloride. When \( \mathrm{CH_3TiCl_3} \) (1.7 g) was mixed with \( \mathrm{HgCl_2} \) (8.0 g) in benzene (30 ml), first at room temperature (1.5 hours), and then with heating to 60–65° (for 4.5 hours), a change in color was observed.
the solution from orange to light yellow, and no brown precipitate characteristic of titanium trichloride was detected. In the reaction mixture, \( \mathrm{TiCl_4} \) (1.5 g), \( \mathrm{CH_3HgCl} \) (0.6 g), and calomel were identified.
In this case, exchange of methyl radicals between the starting products takes place.
Received
2 II 1963
References
- D. E. Hergman, W. K. Nelson, J. Am. Chem. Soc., 74, 2693 (1952).
- Belg. Patent No. 553, 477, 1957.
- French Patent No. 1 157 195, 1958.
- C. Bawn, J. Gladstone, Proc. Chem. Soc., 1959, 227.
- C. Beerman, H. Bestian, Angew. Chem., 71, 618 (1959).
- H. D. Vries, Rec. trav. chim. Pays-Bas, 80, 866 (1961).
- У. Уотерс, Химия свободных радикалов, ИЛ, 1948, p. 16.
- Г. А. Разуваев, Г. Г. Петухов et al., ДАН, 135, 87 (1960).