Phenylchlorosilanes

Alternatives to the methyl chloride dkect process have been reviewed (31). Processes to make phenyl and ethyl siUcones have employed dkect-process chemistry. Phenyl chloride has been used in place of methyl chloride to make phenylchlorosilanes (15). In addition, phenylchlorosilanes are produced by the reaction of benzene, HSiCl, and BCl (17,31). EthylsiUcones have been made primarily in the CIS, where the dkect process is carried out with ethyl chloride in place of methyl chloride (32). Vinyl chloride can also be used in the dkect process to produce vinylchlorosilanes (31). Alternative methods for making vinylchlorosilanes include reaction of vinyl chloride with HSiCl or the platinum-catalyzed hydrosilylation of acetjdene with HSiCl. ... 

In the case of phenylchlorosilanes some modifications are made to the process. Chlorobenzene is passed through the reaction tube, which contains a mixture of powdered silicon and silver (10% Ag), the latter as catalyst. Reaction temperatures of 375-425°C are significantly higher than for the chloro-methylsilanes. An excess of chlorobenzene is used which sweeps out the high boiling chlorophenysilanes, of which the dichlorosilanes are predominant. The unused chlorobenzene is fractionated and recycled. 

DOT regulations for shipment, 6 30 It molecular formula, 6 291t toxicity, 6 302t Phenylchlorosilane(s), 22 551 in TD resin preparation, 22 588 Phenyldiazonium chloride, 21 250 Phenyldichlorostibine, 3 68 Phenyldiethanolamine, physical properties of, 2 124t... 

It was reported that the reaction of poly(phenylhydrosilane) (Mw = 3004, Mw/Mn = 1.79) with CCI4 under room light selectively affords poly(phenylchlorosilane) along with CHCI3 and CH2CI2 as by-products (Reaction 8.9) [21]. The replacement of Si—H moieties by Si—Cl is found to be >84% or >95%) for reaction periods of 28 h and 5 days, respectively. Vapour... 

Poly(phenylchlorosilane) can be considered as a versatile synthon for the preparation of a variety of functionalized polysilanes. Indeed, its reactions with MeOH or MeMgBr afforded polysilane containing Si—OMe or Si—Me moieties, respectively, whereas its reaction with LiAlH4 regenerated the starting poly(phenylhydrosilane) [21,22]. 

The main raw stock for the direct synthesis of methyl-, ethyl and phenylchlorosilanes is correspondingly methylchloride, ethylchloride and chlorobenzene, as well as copper-silicon alloy or mechanical mixture of silicon and copper powders (so-called contact mass). 

For the direct synthesis of phenylchlorosilanes, copper content in contact mass should be significantly bigger than for the synthesis of methyl-and ethylchlorosilanes. Good yields of phenylchlorosilanes are attained if catalysed by silver (10% of silicon), but owing to its high cost and scarcity, industrial preference is given to copper. 

Apart from antimony, there are other good promoters of the direct synthesis of methylchlorosilanes, which increase the yield of dimethyldichlorosilane, such as arsenic and zinc chloride. If it is necessary to increase the yield of alkylhydridechlorosilanes, one should use univalent copper chloride, cobalt, and titanium. The addition of tin or lead into contact mass increases the yield of dimethyldichlorosilane up to 70% the yield of ethyldi-chlorosilane is increased to 50-80% when contact mass receives 0.5-2% of calcium silicide (Ca2Si). In the synthesis of phenylchlorosilanes effective promoters are zinc, cadmium, mercury or their compounds. In particular, the introduction of zinc oxide (up to 4%) into contact mass may increase the diphenyldichlorosilane content up to 50%, and the introduction of a mixture of zinc oxide and cadmium chloride, even up to 80%. 

Thus, we can make the following important conclusion the composition of a complex reactive mixture in the direct synthesis of methyl-, ethyl- and phenylchlorosilanes noticeably changes depending on the introduction of promoting additives into contact mass. Since the demand for the products of direct synthesis wavers quite considerably (depending on the monomer market condition), it is very important for industry to know how this or that promoter affects the yield of each polymer. 

It follows from all the above-mentioned facts that the direct synthesis of methyl-, ethyl and phenylchlorosilanes is a complex heterophase process which depends on many factors and forms a compex reactive mixture. For example, in the direct synthesis of methylchlorosilanes there are about 130 compounds found and characterised. This does not mean, however, that in this or other definite synthesis all the 130 products are formed. The composition of the mixtures formed and the transformation degree of alkyl-chlorides and chlorobenzene in the synthesis of methyl-, ethyl and phenylchlorosilanes depend on the synthesis conditions, the type of the reactor used and many other factors. In spire of the complexity of the process and the variety of its products, the reaction of direct synthesis can nevertheless be directed (towards a preferential formation of a main product), changing the conditions for the preparation of contact mass, introducing various promoters into contact mass and changing the reaction conditions. 

Similarly to methyl- and ethylchlorosilanes, the process of phenylchlorosi-lane production by the copper-catalysed reaction of chlorobenzene and silicon is very complex. Unlike the processes mentioned, the direct synthesis of phenylchlorosilanes is carried out at higher temperatures (500-650 °C, depending on the activity of contact mass), which is largely due to the high temperature of chlorobenzene dissociation. 

The mechanism of phenylchlorosilane formation has not been fully established either however, similarly to methyl- and ethylchlorosilanes, it is most probable that initially intermetallic compound Cu3Si in contact mass interacts with chlorobenzene. To intensify the reaction and increase the output of the target product, the reaction is fed with hydrogen chloride in addition to chlorobenzene. 

The liberated active copper catalyses the direct synthesis of phenylchlorosilanes ... 

Thus, the direct synthesis of phenylchlorosilanes produces a complex mixture, which, apart from phenyltrichlorosilane, diphenyldichlorosilane, phenyldichlorosilane and triphenylchlorosilane, also contains silicon tetrachloride, trichlorosilane, benzene, solid products (diphenyl and carbon) and a gaseous product (hydrogen). It also forms high-boiling polyolefines, which are part of tank residue and can deposit on contact mass, reducing its activity. It should be kept in mind that the production of phenylchlorosilanes requires silicon with a minimal impurity of aluminum, because the aluminum chloride formed contributes to the detachment of the phenyl group from phenylchlorosilanes at higher temperature. The harmful effect of aluminum chloride is counteracted by the addition of metal salts to contact mass, which form a nonvolatile and nonreactive complex with aluminum chloride. 

The same method can be used for baking contact mass after the synthesis of phenylchlorosilanes after that, the mass can be sent to metal recycling plants to extract copper for copper extraction. 

The direct synthesis of phenylchlorosilanes forms a condensate of the following average composition, (%) ... 

C (a mixture of benzene and chlorobenzene). This fraction can be further used to prepare the reactive mixture for phenylchlorosilane synthesis by high-temperature condensation. 

C (intermediate), containing a mixture of silicon tetrachloride and benzene. It can be used in phenylchlorosilane synthesis by high-temperature condensation to suppress the secondary process of reduction. 

To increase the diphenyldichlorosilane content in the condensate, it is advisable to conduct the direct synthesis of phenylchlorosilanes not with copper-silicon alloy but with a mechanical mixture of silicon and copper powders, promoted by zinc oxide. The introduction of zinc oxide seems to inhibit the undesirable reactions of diphenyl and benzene formation, creating favourable conditions to attach phenyl radicals to the silicon atom, i.t. to form diphenyldichlorosilane. 

Besides, it is advisable to carry out the direct synthesis of phenylchlorosilanes not in hollow reactors in the fluidised layer, but in mechanically agitated reactors where the contact time of chlorobenzene and contact mass increases approximately 10-fold this seems to have a favourable effect on the yield of diphenyldichlorosilane. Thus, the direct synthesis of phenylchlorosilanes with the mechanical mixture of silicon and copper promoted by zinc oxide and cadmium chloride produces a condensate, which after the separation of unreacted chlorobenzene contains 25-30% of phenyltrichlorosilane and 50-55% of diphenyldichlorosilane. This condensate is rectified to extract phenyltrichlorosilane by the technique described above at the third rectification stage it yields diphenyldichlorosilane. 

Phenylchlorosilanes (except for triphenylchlorosilane) are colourless, transparent liquids, which fume in air and are easily hydrolysed. They have a specific chloroanhydride odour. Triphenylchlorosilane has the form of... 

Phenylchlorosilanes are widely used in the manufacture of various silicone oligomers and polymers. For example, phenyltrichlorosilane, phenyldichlorosilane and diphenyldichlorosilane are used in the synthesis of polyalkylphenylsiloxanes to produce plastics and varnishes. 

Diphenyldichlorosilane is used to obtain elastomers and liquids, and triphenylchlorosilane is used for liquids. Some properties of phenylchlorosilanes are given in Table 5. 

Assessing on the whole the method of the production of alkyl- and aryl-chlorosilanes based on the interaction of alkyl- and arylchlorides with free silicon (i.e. direct synthesis), we should say that this method in comparison with metalorganic synthesis is more efficient, especially for the production of methyl- and phenylchlorosilanes. As for unsaturated chlorosi-lanes (vinyl- and allylchlorosilanes) and organochlorosilanes with higher radicals (hexyl-, heptyl-, octyl- and nonylchlorosilanes), no direct synthesis technique has yet been developed. 

Halogenated organochlorosilanes, especially chlorinated methyl- and phenylchlorosilanes of the common structure... 

In the absence of catalysts phenylchlorosilanes do not chlorinate even at increased temperature (150-200 °C). It should be kept in mind, however, that the replacement chlorination of phenylchlorosilanes depending on the conditions of the reaction (the presence of a catalyst and its composition, the effect time of chlorine, temperature) is accompanied by breaking up the Si—Car bond ... 

However, similarly to phenylchlorosilane chlorination, one cannot fully exclude the by-processes of bond breaking. The breaking-up occurs at Si— Car bonds ... 

Table 9. Physicochemical properties of chlorinated methyl-, phenyl- and methyl-phenylchlorosilanes...

Polyphenylsiloxanes are produced from alkoxyphenylsilanes, triacetoxy-phenylsilane, pure phenyltrichlorosilane or undistilled phenylchlorosilanes. Depending on the functionality of the parent monomer and the preparation technique, polyphenylsiloxanes can be branched or ladder. Often, to improve the properties of polyphenylsiloxanes, they are modified with various organic substances (by mechanical mixing or chemically). 

Some brands of polydimethylphenylsiloxane varnishes can be produced from raw phenyl rather than phenyltrichlorosilane, a nonrectified mixture of phenylchlorosilanes (the phenyltrichlorosilane content is at least 77-80%, the chlorine content is 43-47%), using the semicontinuous technique. 

Phenylchloro silane s (phenyltrichlo -rosilane, phenyldichlorosilane, di-phenylchlorosilane, etc.) are transparent, yellowish motile liquids. They are easily hydrolysed, releasing hydrogen chloride. Expl.lim. =0.8-77.5% (vol.). MAC=1 mgfri3. 

For example, silver is known to be a preferred catalyst for the direct synthesis of phenylchlorosilanes from chlorobenzene and silicon,18 and since silver chloride readily is reduced by silicon it may be inferred that the sequence of reactions is the same as that for copper. Other metals may exercise catalytic effects on the reaction through entirely different mechanisms, of course. 

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