Phenylchlorosilanes. synthesis

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. 

Summary The efficiency of the effect of ultrasound irradiation on the reaction mixture for vinyl- and phenylchlorosilane synthesis is determined by ultrasound irradiation (USI) frequency as well as by the exposure time and the origin of starting organohalide. In the case of vinylmagnesium chloride, the formation period of the major reaction product under continuous USI exposure shortened 2.3-fold. When USI affected the synthesis during half the reaction period, the latter duration shortened by 1.4 times. In the case of phenylmagnesium chloride the process period also shortened by 2 and 1.2 times respectively for irradiation times that were 100 and 50 % of the reaction time. 

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 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, (%) ... 

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 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. 

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. 

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. 

As outlined in the previous chapters, the preparation of silicone polymers involves first the preparation of organosilicon halides or esters, secondly the hydrolysis of an appropriate mixture of these intermediates, and finally the condensation or rearrangement of the polymers to achieve the desired molecular arrangement. Only in the first step is there a choice of preparative methods the second and third steps are carried out in much the same way, regardless of how the intermediates were made. From the standpoint of synthesis, the problem therefore comes down to the preparation of the methyl-, ethyl-, and phenylchlorosilanes or ethoxysilanes. Of these the methyl compounds are the most important, because they are used directly for the water-repellent treatment and are the only intermediates required for the oils, elastomers, and some types of resin. 

The most straightforward solution to the problem of producing methyl-, ethyl-, and phenylchlorosilanes would be to adapt the classical laboratory methods of synthesis to large-scale operation. A logical choice would be the Grignard reaction, long a laboratory favorite because it is so universally applicable. For the preparation of dimethyl silicone from inethyl chloride by the Grignard method, the steps would be ... 

The phenylchlorosilanes and phenylmethylchlorosilanes also required in the manufacture of silicones, currently only produced to a limited extent by direct synthesis, are preferably produced by the reaction ol chlorobcn/enc with hydrogen-containing silanes according to the equations ... 

For the synthesis of phenylchlorosilanes, a reagent such as HSiCh (silicochloToform), obtained by the previous reaction, and benzene can be used. When this mixture is heated in the presence of a catalyst, the following reaction takes place ... 

The direct process is also quite versatile and can be fine-tuned to prepare other types of chlorosilanes also. Ethylchlorosilanes could also be similarly prepared analogous to the synthesis of methylchlorosilanes. Preparation of phenylchlorosilanes required a slight modification of the catalyst. Addition of a mixture of HCl and MeCl to silicon affords mixtures of methylchlorosilanes along with MeSiHCU- Simultaneously, along with Rochow, but independently, Richard Mueller in Germany had also come out with a direct process, initially for preparing HSiCls, and later for methylchlorosilanes [7]. 

The direct synthesis also works with methyl bromide, but methyl fluoride and methyl iodide do not react satisfactorily. Phenylchlorosilanes, however, can be prepared starting from chlorobenzene. Other related reactions include ... 

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