Chemistry

V. A. PONOMARENKO, G. V. ODABASHYAN
and Corresponding Member of the Academy of Sciences of the USSR A. D. PETROV

SYNTHESIS OF ORGANOSILICON MONOMERS FROM METHYLCHLOROSILANE

Investigations in recent years in the field of organosilicon compounds containing Si—H bonds have made it possible to outline new routes (addition reactions, telomerization, thermal condensation, etc.) for obtaining a number of the most important organosilicon monomers: ( \mathrm{C_6H_5SiCl_3} ), ( \mathrm{CH_3Si(C_6H_5)(Cl_2)} ), ( \mathrm{CH_3Si(Cl)_2CH=CH_2} ), ( \mathrm{(C_2H_5)_2SiCl_2} ), ( \mathrm{(C_6H_5)_2SiCl_2} ), ( \mathrm{(C_6H_5)SiHCl_2} ), ( \mathrm{CH_3Si(CH_2CH_2CF_3)Cl_2} ), and many others ((^1)). For their preparation, mainly only halosilicon hydrides containing one Si—H bond were used: ( \mathrm{Cl_3SiH} ), ( \mathrm{CH_3SiCl_2H} ), ( \mathrm{C_2H_5SiHCl_2} ), ( \mathrm{C_6H_5SiHCl_2} ), and certain others. The use of dichlorosilane ( \mathrm{Cl_2SiH_2} ), containing two reactive Si—H bonds together with two chlorine atoms, opened up new and very promising possibilities for the synthesis of a wide variety of organosilicon monomers ((^2)).

Developing the studies we had begun on the synthesis of monomers based on silicon hydrides, in the present work we used methylchlorosilane ( \mathrm{CH_3SiH_2Cl} ), which is readily obtained in good yield by disproportionation of ( \mathrm{CH_3SiHCl_2} ) in the presence of cyanamide catalysts ((^3)). Carrying out reactions at one or both Si—H bonds of methylchlorosilane made it possible to hope to realize a nonmetalorganic scheme for the synthesis of a number of organosilicon monomers:

[
\mathrm{CH_3SiH_2Cl + RCl \xrightarrow[-HCl]{} (CH_3)(R)SiHCl \xrightarrow{CH \equiv CH}
Cl{-}Si(CH_3)(R)CH_2CH_2Si(CH_3)(R){-}Cl}
\tag{1}
]

[
\mathrm{CH_3SiH_2Cl + CH_2{=}CHX}
\begin{matrix}
\nearrow \ \mathrm{XCH_2CH_2SiHCl(CH_3)} \xrightarrow{CH \equiv CH}
\mathrm{Cl{-}Si(CH_3)(CH_2CH_2X)CH_2CH_2Si(CH_3)(CH_2CH_2X){-}Cl}
\[6pt]
\searrow \ \mathrm{ClSi(CH_3)(CH_2CH_2X)_2}
\end{matrix}
\tag{2}
]

where ( \mathrm{R} )—( \mathrm{C_6H_5} ), ( \mathrm{CH_2=CH{-}} ), ( \mathrm{X} )—( \mathrm{H} ), ( \mathrm{CH_3} ), ( \mathrm{CF_3} ), etc.

To carry out scheme (1), the reaction of thermal condensation of methylchlorosilane with chlorobenzene and vinyl chloride at temperatures of 550–650° and atmospheric pressure was chosen; this reaction had previously been studied by us with dichlorosilane ((^2)). In comparison with dichlorosilane, methylchlorosilane enters into the thermal-condensation reaction with ( \mathrm{C_6H_5Cl} ) and ( \mathrm{CH_2=CHCl} ) with greater difficulty; the yield of products from reaction at the first Si—H bond in this case, under identical conditions, is considerably lower. In this respect the same picture is observed as in the reactions of ( \mathrm{Cl_3SiH} ) and ( \mathrm{CH_3SiHCl_2} ) with chlorobenzene ((^4)).

In addition, whereas in the thermal condensation of dichlorosilane with chlorobenzene up to 10% of the product of interaction through two Si—H bonds was isolated, in the case of methylchlorosilane we were unable to isolate methyldiphenylchlorosilane.

Table 1

Addition of silicon hydrides CH₃SiH₂Cl, (CH₃)(C₂H₅)SiHCl, and CH₃(C₆H₅)SiClH to unsaturated compounds in the presence of 0.1 M chloroplatinic acid solution in isopropyl alcohol

Unlike scheme (1), scheme (2), as is evident from the data in Table 1, is carried out considerably more easily. Methylchlorosilane reacts almost as readily with ethylene and propylene as dichlorosilane does. This applies equally to reaction through one and through two Si—H bonds of methylchlorosilane. The (CH₃)(C₂H₅)SiHCl formed in fairly good yield in the reaction with acetylene is readily converted, in the presence of H₂PtCl₆, into CH₃(C₂H₅)(Cl)SiCH₂CH₂Si(Cl)(C₂H₅)CH₃. (CH₃)(C₂H₅)SiHCl also reacts with CH₂=CHCF₃ under the same conditions, giving a fluorine-containing compound of the RR′R″SiCl type.

Methylchlorosilane adds to trifluoropropylene with more difficulty than to propylene. In this respect CH₃SiH₂Cl behaves similarly to Cl₂SiH₂.

As a result of the work carried out, it was possible to outline a completely nonmetal-organic scheme for the synthesis of such alkyl-(aryl)-silane- and disilane chlorides as (CH₃)(R)SiHCl, (CH₃)(R)₂SiCl, (CH₃)(R′)(R″)SiCl, (CH₃)(Cl)(R)SiCH₂CH₂Si(R)(Cl)(CH₃), where R, R′, and R″ are the groups CH₂=CH—, C₆H₅—, C₂H₅—, C₃H₇—, CF₃CH₂CH₂—, and others.

Experimental Part

1. Preparation of methylchlorosilane. CH₃SiClH₂ is obtained by disproportionation of CH₃SiCl₂H* in the presence of dimethylcyanamide (³). Into a flask of a rectification column packed with nichrome packing (35–50 theoretical plates), 200 g of CH₃SiCl₂H and 14 g of previously activated dimethylcyanamide were placed. Methylchlorosilane was taken off continuously and condensed in a trap cooled with solid CO₂ and acetone. The reaction time was 5–6 h. The starting CH₃SiCl₂H and CH₃SiCl₃ were distilled from the same flask. To the residue containing the catalyst and a little CH₃SiCl₃, a fresh portion of CH₃SiCl₂H was added, and the reaction was repeated in exactly the same way

* For the rearrangement it is necessary to take methyldichlorosilane carefully purified from Cl₃SiH.

as described above. The yield of methylchlorosilane was 50–60% of theory. In all, from 700 g of CH₃SiHCl₂, 290 g of pure CH₃SiH₂Cl was obtained. The catalyst does not lose its activity upon repeated repetition of the experiment.

1. Addition of CH₃SiClH₂ and CH₃(C₂H₅)SiClH to unsaturated compounds. The conditions and results of all experiments on the catalytic addition of methylchlorosilane and methylethylchlorosilane to unsaturated compounds in the presence of chloroplatinic acid are given in Table 1, and some physical constants of the substances obtained in Table 2.

2. Preparation of methylphenylchlorosilane CH₃(C₆H₅)SiClH. A mixture of 24.2 g (0.3 mole) of methylchlorosilane and 39.5 g (0.35 mole) of chlorobenzene was passed, over 2 h 40 min, through a glass tube with an internal diameter of 23 mm and a reaction-zone length of 600 mm, heated to 635–645°.

Table 2

Physical properties of the compounds obtained

* These substances were obtained for the first time.
** M.p. 59–60°.

From the resulting condensate the following were isolated by rectification: 7 g of CH₃SiClH₂, b.p. 8–10°; 8 g of CH₃SiCl₂H, b.p. 39–42°; 9.4 g of C₆H₆, b.p. 78–79.5°; 15 g of C₆H₅Cl, b.p. 128–129.5°; 7.4 g (15.5%) of CH₃(C₆H₅)SiClH, b.p. 176° (740 mm); $d_4^{20}$ 1.0540; $n_D^{20}$ 1.5171; $MR$ found 44.99, calculated 45.22; 7.1 g (yield 12.5%) of CH₃(C₆H₅)SiCl₂, b.p. 197° (740 mm); $d_4^{20}$ 1.1814; $n_D^{20}$ 1.5194; $MR$ found 49.13 (calculated 49.16); 4.1 g—residue boiling above 197°.

1. Preparation of methylvinylchlorosilane CH₃(CH₂=CH)SiClH. A mixture of 23.2 g (0.3 mole) of methylchlorosilane and 41.5 g (0.66 mole) of vinyl chloride was passed, over 3 h, through a glass tube with an internal diameter of 23 mm and a reaction-zone length of 600 mm, heated to 550–560°. From the resulting condensate, 3.7 g (11.5%) of CH₃(CH₂=CH)SiClH was isolated, b.p. 60.5° (761 mm); $d_4^{20}$ 0.9125; $n_D^{20}$ 1.4140; $MR$ found 29.21 (calculated 29.70).

Zelinsky Institute of Organic Chemistry
Academy of Sciences of the USSR

Received
11 IX 1959

REFERENCES

1. Proceedings of the Second All-Union Conference on the Chemistry and Practical Application of Organosilicon Compounds, vol. 1, Leningrad, 1958.
2. A. D. Petrov, V. A. Ponomarenko, G. V. Odabashyan, DAN, 126, No. 5, 1009 (1959).
3. D. L. Bailey, G. H. Wagner, US patent 2732280 (1956); RZhKhim., 67177 (1957).
4. A. D. Petrov, V. F. Mironov et al., Izv. AN SSSR, OKhN, 1958, No. 8, 954.