Abstract Generated abstract
This study examines complex formation between several chlorosilanes, including methyltrichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, and silicon tetrachloride, and a range of alkali, ammonium, and tetrasubstituted ammonium halides. Interactions were assessed by chemical analysis, visual observation of salt dissolution and phase behavior, and measurements of electrical conductivity under anhydrous argon. Complex formation was found mainly with tetrabutylammonium chloride and bromide, depending on cation size and anion radius, with methylchlorosilanes giving conductive layered systems of approximately 3:1 chlorosilane to salt composition, while phenyltrichlorosilane showed distinct solution behavior. Solvent extraction and electrolysis experiments indicated unequal binding of chlorosilane molecules in the trimethylchlorosilane complex, anodic dissolution of silicon in several systems, and both similarities and differences relative to known organoaluminum complexes.
Full Text
Chemistry
N. M. Alpatova, A. I. Gorbanev, Yu. M. Kessler, and L. G. Lozhkina
Physicochemical Study of Complexes between Alkyl-(Aryl)-Chlorosilanes and Halides of Tetrasubstituted Ammonium
(Presented by Academician A. N. Frumkin, 7 X 1961)
A number of authors ($^{1-7}$) have obtained interesting results concerning electrically conducting complexes of organoaluminum compounds with halides of alkali metals and tetrasubstituted ammonium, as well as with hydrides of alkali metals. An analysis of the literature data on the properties of halide compounds of Al and of the tetrahalides of elements of the fourth group shows that there is a certain similarity between them with respect to a number of properties. At the same time, the compounds of alkylaluminum display a similarity with respect to analogous properties with aluminum halides. On this basis we proposed that organoelement compounds of Si and Ge may form complexes analogous in their properties to the complexes of organoaluminum compounds.
The present work is devoted to the study of complex formation between CH$_3$SiCl$_3$, (CH$_3$)$_3$SiCl, C$_6$H$_5$SiCl$_3$, as well as SiCl$_4$ and NaCl, NaF, KF, CsCl, CsF, NH$_4$Cl, (CH$_3$)$_4$NCl, (C$_2$H$_5$)$_4$NBr, (C$_4$H$_9$)$_4$NCl, (C$_4$H$_9$)$_4$NBr, (C$_4$H$_9$)$_4$NJ, and ethylpyridinium bromide. The nature of the interaction of the organosilicon compound with the added salt was determined by chemical analysis and by measuring the electrical conductivity of the products obtained, and also visually, by observing dissolution of the salt.
The composition of the products obtained was determined by analysis for hydrolyzable chlorine ($^9$), and in some cases for the total Cl content by argentometric titration ($^{10}$).
The synthesis and measurements were carried out in an atmosphere of “pure” argon, dried by passage through P$_2$O$_5$. The synthesis was carried out in an apparatus with a reflux condenser and a magnetic stirrer. Heating was 35–40°, and the synthesis time was 3–12 hr, depending on the substance and the degree of dispersion of the salt. After synthesis the product was transferred into an apparatus for measuring electrical conductivity, which made it possible to separate the layers and to measure the electrical conductivity of each layer in the isolated state and in their joint presence. The reproducibility of the measurements of specific electrical conductivity in different experiments was ±10%, owing to the high viscosity of the substances obtained and the difficulty of complete separation.
The main results of the study are given in Table 1. For the remaining salts listed above, no interaction with the compounds was established. As a typical result for them, Table 1 gives the data for CsF.
The data on specific electrical conductivity and composition in the case of the interaction of (CH$_3$)$_3$SiCl and CH$_3$SiCl$_3$ with tetrabutylammonium chloride and bromide refer to liquids supercooled to room temperature. In the case of CsF, the values of the specific electrical conductivity of the liquid phase after contact with the salt are given. The data obtained show that, in the case of halides of tetrasubstituted ammonium salts, interaction takes place provided that the alkyl radical is sufficiently long. In addition, the capacity for complex formation of tetrasubstituted ammonium halides increases as the radius of the anion decreases. CH$_3$SiCl$_3$ and (CH$_3$)$_3$SiCl are similar in their behavior. In these compounds (C$_4$H$_9$)$_4$NCl
Table 1
| No. | Organosilicon compound | Hydrolyzable Cl, %: theoretical | Hydrolyzable Cl, %: experimental | \(\chi\) | CsF | \((\mathrm{C_2H_5})_4\mathrm{NBr}\) | \((\mathrm{C_4H_9})_4\mathrm{NJ}\) | \((\mathrm{C_4H_9})_4\mathrm{NBr}\) | \((\mathrm{C_4H_9})_4\mathrm{NCl}\) |
|---|---|---|---|---|---|---|---|---|---|
| 1 | \((\mathrm{CH_3})_3\mathrm{SiCl}\) | 32.63 | 32.20 | \(3.4\cdot10^{-7}\) | Does not dissolve | Does not dissolve; \(\chi=8.9\cdot10^{-7}\) | \(\chi=1.1\cdot10^{-5}\) | Complex forms; \(\chi_k=5\text{–}6\cdot10^{-4}\); \(\chi_{\mathrm{bc}}=2.5\cdot10^{-5}\) | Complex forms; \(\chi_k=6.0\cdot10^{-4}\); \(\chi_{\mathrm{bc}}=3.4\cdot10^{-5}\) |
| 2 | \(\mathrm{CH_3SiCl_3}\) | 71.15 | 70.30 | \(1.9\cdot10^{-7}\) | Does not dissolve | \(\chi=1\cdot10^{-5}\) | Complex forms; \(\chi_k=3\cdot10^{-4}\); \(\chi_{\mathrm{bc}}=1.6\cdot10^{-5}\) (second layer) | Complex forms; \(\chi_k=4.2\cdot10^{-4}\); \(\chi_{\mathrm{bc}}=4\cdot10^{-5}\) | |
| 3 | \(\mathrm{SiCl_4}\) | \(<1\cdot10^{-7}\) | Does not dissolve; \(\chi<1\cdot10^{-7}\) | Salt decomposes | Complex forms; \(\chi_k=3.4\cdot10^{-4}\); \(\chi_{\mathrm{bc}}<1\cdot10^{-7}\) | Complex forms; \(\chi_k=1.15\cdot10^{-4}\); \(\chi_{\mathrm{bc}}<1\cdot10^{-7}\) | |||
| 4 | \(\mathrm{C_6H_5SiCl_3}\) | 50.28 | 50.45 | \(<1\cdot10^{-7}\) | Does not dissolve; \(\chi<1\cdot10^{-7}\) | Does not dissolve; \(\chi=1\cdot10^{-7}\) | Salt dissolves; \(\chi=7.4\cdot10^{-5}\) | Salt dissolves; \(\chi=2.7\cdot10^{-4}\) |
Note. In all cases, the values of electrical conductivity \(\chi\), in \(\Omega^{-1}\cdot\mathrm{cm}^{-1}\), refer to room temperature, except for complexes with \(\mathrm{SiCl_4}\), for which \(\chi\) was measured at \(55^\circ\mathrm{C}\).
dissolves with the formation of two layers. One of the layers approximately corresponds in its composition to a ratio of organosilicon compound to salt of \(3:1\). At room temperature these complexes are viscous supercooled liquids, colorless or slightly yellowish. The second layer is a mobile colorless liquid consisting of the organosilicon compound with a small amount of dissolved salt. Its composition for \((\mathrm{CH_3})_3\mathrm{SiCl}\) and \(\mathrm{CH_3SiCl_3}\) corresponds to a ratio of organosilicon compound to salt of \(\sim 40:1\).
When \((\mathrm{C_4H_9})_4\mathrm{NBr}\) is dissolved, analogous phenomena are observed. In the case of \((\mathrm{C_4H_9})_4\mathrm{NJ}\), complexes could not be obtained. During the synthesis only a slight yellowing of the organosilicon compound is observed, with some increase in its electrical conductivity. \(\mathrm{SiCl_4}\) behaves analogously to \(\mathrm{CH_3SiCl_3}\) and \((\mathrm{CH_3})_3\mathrm{SiCl}\), but the complexes formed are rather high-melting.
The properties of phenyltrichlorosilane (PhTCS) differ sharply from the properties of the organosilicon compounds described above. Tetrabutylammonium chloride and bromide dissolve in this compound without separation into layers, forming a yellow-colored solution, and have a considerable temperature coefficient of solubility; moreover, the solubility of the chloride is considerably higher than in methyl derivatives of silicon, while the electrical conductivities are lower. The electrical-conductivity values given in Table 1 refer to a PhTCS-to-salt ratio equal to \(5.4:1\) in the case of the chloride (unsaturated solution) and \(45:1\) in the case of the bromide (saturated solution at room temperature).
Subsequently, the system $(\mathrm{CH}_3)_3\mathrm{SiCl}$—$(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ was chosen as the principal object of investigation. It was established that the composition of the layers practically does not depend on the holding time or on temperature. Table 2 gives data on the effect of temperature on the composition
Table 2
| 25° | 30° | 35° | 45° | |
|---|---|---|---|---|
| Amount of hydrolyzable Cl in the complex, % | 17.63 | 17.75 | 17.60 | 17.58 |
| Amount of hydrolyzable Cl in the upper layer, % | 30.76 | 30.59 | 30.79 | 30.67 |
| $\chi$, ohm$^{-1}\!\cdot$cm$^{-1}$ of the complex | $6.2\cdot10^{-4}$ | $8.0\cdot10^{-4}$ | $9.5\cdot10^{-4}$ |
of the substance formed and on the specific electrical conductivity of $(\mathrm{CH}_3)_3\mathrm{SiCl}$—$(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$. The independence of the composition of the complex from temperature is also indicated by the fact that the electrical conductivity of the complex at different temperatures in the presence of the second layer coincides with the electrical conductivity of the isolated complex.
Investigation of the behavior of the complexes $[(\mathrm{CH}_3)_3\mathrm{SiCl}]_3(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ with respect to various solvents (Table 3) showed that the strengths of the bonds of the three molecules of $(\mathrm{CH}_3)_3\mathrm{SiCl}$ in it are not identical: one molecule is bound more strongly than the other two.
Table 3
| Solvent | $(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ | $(\mathrm{CH}_3)_3\mathrm{SiCl}$ | Complex $[(\mathrm{CH}_3)_3\mathrm{SiCl}]_3\cdot(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ |
|---|---|---|---|
| Heptane and cyclohexane | Does not dissolve | Mixes in all proportions with formation of a nonconducting solution | The solvent leaches out 2 molecules of $(\mathrm{CH}_3)_3\mathrm{SiCl}$; the remaining 1:1 complex is insoluble in heptane and cyclohexane |
| Benzene | At room temperature only traces dissolve; the solubility increases rapidly with increasing temperature | Analogous to heptane | The complex dissolves with formation of an electrically conducting solution. $\chi=1.12\cdot10^{-5}$ ohm$^{-1}\!\cdot$cm$^{-1}$ (1 mole of complex per 100 moles of solvent) $\chi=7.5\cdot10^{-4}$ ohm$^{-1}\!\cdot$cm$^{-1}$ (1 mole of complex per 10 moles of solvent) |
| Toluene | At room temperature only traces dissolve; upon heating the solubility increases | Analogous to heptane | The complex dissolves with formation of an electrically conducting solution $\chi=0.71\cdot10^{-5}$ ohm$^{-1}\!\cdot$cm$^{-1}$ (1:100) $\chi=5.25\cdot10^{-5}$ ohm$^{-1}\!\cdot$cm$^{-1}$ (1:10) |
Next, electrolysis was carried out of the systems $\mathrm{CH}_3\mathrm{SiCl}_3$—$(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$, $(\mathrm{CH}_3)_3\mathrm{SiCl}$—$(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$, $\mathrm{CH}_3\mathrm{SiCl}_3$—$(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NBr}$, and of solutions of $(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ and $(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NBr}$ in $\mathrm{C}_6\mathrm{H}_5\mathrm{SiCl}_3$. The electrolysis was carried out with a Pt cathode and a Pt or Si anode, at room temperature without stirring. In all cases no deposition of silicon on the cathode could be observed ($D_k=0.25$–$10$ A/dm$^2$).
Dissolution of low-resistance $p$-type Si was observed in the case of the systems $\mathrm{CH}_3\mathrm{SiCl}_3$—$(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$, $(\mathrm{CH}_3)_3\mathrm{SiCl}$—$(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$, and in solutions of $(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ in $\mathrm{C}_6\mathrm{H}_5\mathrm{SiCl}_3$. For example, in the complex $[(\mathrm{CH}_3)_3\mathrm{SiCl}]_3(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ at $D_a=4$ A/dm$^2$ silicon dissolves with a current efficiency close to 100% (calculated as $\mathrm{Si}^{+4}$). The current density can be varied from 1 to 15 A/dm$^2$. The Si anode also dissolves in benzene solutions of the complex $[(\mathrm{CH}_3)_3\mathrm{SiCl}]_3(\mathrm{C}_4\mathrm{H}_9)_4\mathrm{NCl}$ (1 mole of complex per 10 moles of benzene).
The results obtained, in addition to being of independent interest, indicate a certain similarity between the compounds studied and analogous Al compounds. These include, above all, the very fact of complex formation, which until now had been considered unlikely for alkyl derivatives of silicon. Further similarity is manifested in dissociation during complex formation, in the leaching of two molecules of $(\mathrm{CH}_3)_3\mathrm{SiCl}$ by aliphatic solvents, in the dependence of complex formation on the radius of the anion and the size of the cation, and in the anodic behavior during electrolysis. At the same time, substantial differences also occur, as, for example, in the cathodic behavior of the complexes during electrolysis.
Institute of Electrochemistry
Academy of Sciences of the USSR
Received
2 X 1961
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