Silicol

Organosilicon polymers. Silicon resembles carbon in certain respects and attempts have been made to prepare polymers combining carbon and silicon units in the molecule with the object of increasing the heat resistance of polymers. It has been found that the hydrolysis of a dialkyl-dichlorosilicane or an alkyltrichlorosilicane, or a mixture of the two, leads to polymers (Silicones), both solid and liquid, which possess great thermal stability. Thus dimethyldichlorosilicane (I) is rapidly converted by water into the silicol (II), which immediately loses water to give a silicone oil of the type (III) ... 

Phosphine, which is produced in small quantities in the Silicol process for making hydrogen, has under certain conditions a deteriorating effect on cotton fabrics, not as an immediate action but as a secondary reaction. The examination of a balloon envelope which burst at Milan in 1906 showed that at some spots the material could be easily torn, while over the greater portion it... 

Remembering that the temperature of the caustic soda solution used in the silicol process is above 100" C., frequently rising to 120° C., it was thought that a higher temperature might perhaps produce the suspected reaction ferro-silicon was accordingly heated in an atmosphere of steam in an electric resistance furnace to a temperature of 300° C., but still no hydrogen was produced. Consequently it was concluded that the explanation of the smaller consumption of caustic soda than would be anticipated from theoretical considerations must be explained on some basis other than the reaction of silicon with water. 

Description of Silicol Plant.—The essentials of a lilicol plant are shown in the diagram (Fig. 3). The... 

The plant is dien ready for operation, and silicol is cautiously fed into the generator by means of the hand-operated feed worked from F. 

The Silicon Content of the Perro SiIicon.— The grade of ferro-silicon used in this process is very important, as low-grade material does not yield anything like the theoretical quantity of hydrogen which should be obtained from the silicol present. This arises to a slight extent from the protective action of the impurities, which enclose particles of silicon and therefore prevent the caustic soda from attacking it. 

The ratio of silicol to caustic soda should be such that the ratio of pure silicon to pure sodium hydrate is as I to 172, but this figure is capable of modification to a slight extent, depending on the temperature of the mixture, which is naturally higher in krge plants than in small ones. 

Experiment. Strength of Soda Solution, Batio of Silicon to pure Caustic Yield m Cubic Feet per lb of Silicol. 

Theoretically the maximum possible yield under these conditions of temperature and pressure would be 35 4 cubic feet per lb of silicol of this purity... 

Since the caustic soda in the solution would be regenerated after it had reacted with the silicol, it would be available for reacting with yet more silicol, and would consequently reduce the quantity of caustic soda used in the process. 

About 32 lb. of mineral gfrease are advocated per 1000 lb. of silicol used. However, if the caustic soda solution is strong, i.e. about 25 percent, sodium hydrate, and the generator is wide, giving a large surface and a shallow depth to the caustic soda solution, no grease need be used at all. 

DEHP, which is an abbreviation for di(2-ethylhexyl) phthalate, is a manufactured chemical that is commonly added to plastics to make them flexible. Other names for this compound are dioctyl phthalate (DOP) and bis(2-ethylhexyl) phthalate (BEHP). (Note that di-n-octyl phthalate, however, is the name for a different chemical.) Trade names used for DEHP include Platinol DOP, Octoil, Silicol 150, Bisoflex 81, and Eviplast 80. DEHP is a colorless liquid with almost no odor. It does not evaporate easily, and little will be present in the air even near... 

The dialkyldihalosilanes react with alcohols to form esters of the type R2Si(OR )2> and they also hydrolyze to form dialkylsilanediols or dialkylsilicols, R2Si(OH)2. These silicols condense intermolecu-larly to form polymeric organosiloxanes. The rate of condensation is... 

In general, the alkylalkoxysilanes behave like the alkylchloro-silanes in that they hydrolyze to form the various silicols or their dehydration products. It is not necessary to go through the separate classes of compounds, for their reactions and derivatives may be inferred from the known properties of the halides and the previously discussed properties of the silicon esters. Some of the representative compounds are listed in the index which follows this chapter,66 and a list of alkyltrialkoxysilanes is given in Krause and von Grosse.67... 

Such organosiloxanes commonly are formed from the corresponding organosilanediols by a process of intermolecular condensation, as has been described in the discussion of the silicols ... 

It is necessary that the silicol condense at a rate comparable to that for orthosilicic acid, since otherwise the latter will condense only with itself and will precipitate as silica before it can be included within the siloxane network. It also is found by experiment that only a rather small proportion of SiX4 may be included in the mixture of intermediates if the precipitation of silica is to be avoided. However, the mere fact that appreciable amounts of silica can be combined chemically within the polysiloxane structure is strong evidence in support of the theory of intermolecular condensation as given here, and at the same time it illustrates the close chemical similarity between silica and the organosiloxanes. 

Modification of the properties of the phenyl silicones is possible through chlorination of the aromatic nucleus.43 One or more chlorine atoms may be substituted for hydrogen in each ring, as by chlorination of the phenylchlorosilane with iron powder as a carrier. The chloro-phenylchlorosilane is then hydrolyzed, and the resulting silicols are condensed by heat, just as is done with unsubstituted phenylchloro-silanes. The product is a brittle fusible resin, but it melts at a higher temperature than phenyl silicone and is less flammable. If an average of three chlorine atoms has been introduced into each phenyl nucleus, the product will not bum at all. 

Silicol. A hydroxyl derivative of a silane a compound containing at least one Si—OH bond. 

Structure of silica colloids. Present ideas on the state of silica in aqueous solutions are examined in detail in the review by Sretenskaya (1970), where it is mentioned that one of the most typical features is the tendency to polymerize, i.e. to convert from a molecularly dispersed to a colloidally dispersed state. Polymerization is based on the process of condensation of silicol groups Si(OH)4 with liberation of water and as a result formation of the siloxane bonds Si-O-Si. 

This reaction requires a sealed tube and a temperature of 380° C. Triethylchlorosilicane boils at 143° to 145° C, has density at 0° C. 0 9249, is only slowly decomposed by water, and with silver nitrate precipitates silver chloride. Tiiethyl silicol is formed by the action of ammonia, and triethyl silicon oxide is produced with water. 

Tripropylbromosilicane. — When 1 mol. of tripropylsilicane is treated with 1 mol, of bromine and cooled, hydrobromic acid is evolved. The reaction is allowed to finish on the water-bath and goes smoothly, giving a good yield. On fractionation the product obtained is a yellow, fuming oil, B.pt. 213° which decomposes slowly in the air, evolving hydrobromic acid. With water it slowly changes, while aqueous ammonia completely converts it to tripropyl silicol, B.pt. 205° to 208° C., and a little tripropylsilicon oxide. 

Benzylethylpropylchlorosilicane is produced from benzylethyl-silicon diehloride (1 mol.) and propyl magnesium bromide (1 mol.). It is a colourless, fuming, mobile liquid, which generally becomes pink, and is immediately decomposed by water, yielding the corresponding silicol and oxide. It boils at 172° to 176° C. at 50 mm., and the yield is 50 to 60 per cent, of the theoretical. 

Benzylethylisobutylsilicoi is formed when the corresponding chloride is treated with water. It boils at 162 to 164j C. at 25 mm. In each case, when the chloride, oxide, or silicol is sulphonated, the product is a mixture from which the dZ-acid, sulphobenzylethylisobutylsilicyl oxide is isolated as its l-menthylamine salt ... 

Diphenylethylsilicyl oxide, [(C(jH5)2(C2H5)Si]20, M.pt. 65 6° C., is prepared from diphenylethylsilicyl chloride by decomposition with water. The silicol is first formed, and this passes into the corresponding oxide. 

Benzylethylbutylsilicyl oxide is formed by the action of water on the corresponding chloride. It is a colourless, viscous liquid, insoluble in water, soluble in alcohol, and boils at 250° to 252° C. The silicol is first formed, but soon passes into the oxide, probably due to traces of impurity, such as hydrochloric acid. 

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