Chlorosilanes, such as Tetrachlorosilane, are compounds in which silicon is bonded to from one to four chlorine atoms with other bonds to hydrogen and/or alkyl groups. Chlorosilanes react with water, moist air, or steam to produce heat and toxic, corrosive fumes of hydrogen chloride. They may also produce flammable gaseous H2. They can serve as chlorination agents. Chlorosilanes react vigorously with both organic and inorganic acids and with bases to generate toxic or flammable gases. Tetrachlorosilane is incompatible with alkali metals and dimethyl sulfoxide.
. Silicon tetrachloride (SiCl4) may be used as an intermediate in the manufacture of high purity silicon. High purity silicon derived from silicon tetrachloride may find major applications in the semiconductors industry and photovoltaic cells.
. High purity SiCl4 may be used to manufacture of optical fibers.
Tetrachlorosilane is a colorless, fuming liquid with a pungent odor. Tetrachlorosilane is decomposed by water to hydrochloric acid with evolution of heat. Tetrachlorosilane is corrosive to metals and tissue in the presence of moisture. Tetrachlorosilane is used in smoke screens, to make various silicon containing chemicals, and in chemical analysis.
Distil it under vacuum and store it in sealed ampoules under N2. It fumes in moist air and is very sensitive to moisture. It is soluble in organic solvents. It is a strong irritant. [Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 682-683 1963.]
Silicon tetrachloride is prepared by heating silicon dioxide and carbon in a stream of chlorine:
SiO2 + C + 2Cl2 → SiCl4 + CO2
Also, the compound may be prepared by heating silicon with chlorine or dry hydrogen chloride:
Si + 2Cl2 → SiCl4
Si + 4HCl → SiCl4 + 2H2
Colorless fuming liquid; suffocating odor; density 1.52 g/mL; freezes at –68.9°C; boils at 57.7°C; vapor pressure 235 torr at 25°C; critical temperature 235°C; critical pressure 35.45 atm; critical volume 326 cm3/mol; decomposes in water forming silicic acid and HCl; soluble in benzene, toluence, chloroform, and ether.
Silicon tetrachloride was first prepared by Berzelius in 1823. It is used widely in preparing pure silicon and many organosilicon compounds such as silicone. It also is used to produce smoke screens in warfare.
Behavior in Fire: Contact with water in foam applied to adjacent fires will produce irritating fumes of hydrogen chloride.
Silicon tetrachloride decomposes in water forming silicic acid (precipitated silica) and hydrochloric acid:
SiCl4 + 3H2O → H2SiO3 + 4HCl
Reactions with alcohols yield esters of orthosilicic acid. For example, with ethanol the product is tetraethyl orthosilicate or tetraethoxysilane, Si(OC2H5)4:
SiCl4 + 4C2H5OH → Si(OC2H5)4 + 4HCl
An important class of organosilicon compounds known as silicones that are used as lubricants, resins, elastomers, and antifoaming agents in high-vacuum diffusion pumps are synthesized from silicon tetrachloride. Silicon tetrachloride reacts with Grignard reagents, RMgCl to form monoalkyltrichlorosilanes, RSiCl3, dialkyldichlorosilanes, R2SiCl2, trialkylmonochlorosilanes, R3SiCl, and tetraalkylsilanes, R4Si:
SiCl4 + RMgCl → RSiCl3 + MgCl2
SiCl4 + 2RMgCl → R2SiCl2 + 2MgCl2
SiCl4 + 3RMgCl → R3SiCl + 3MgCl2
SiCl4 + 4RMgCl → R4Si + 4MgCl2
The alkylchlorosilanes on hydrolysis form various types of silicones. For example, hydrolysis of trialkylmonochlorosilanes yields sylil ethers, R3SiOSiR3, which form silicones:
2R3SiCl + H2O → R3SiOSiR3 + 2HCl
Silicon tetrachloride reacts with diethylzinc to form tetraethylsilane. This compound was synthesized by Friedel and Crafts in 1863, the first organosilicon compound:
SiCl4 + 2Zn(C2H5)2 → Si(C2H5)4 + 2ZnCl2
Silicon tetrachloride reacts with alkyl chloride and sodium to form thesame tetraalkylsilane:
SiCl4 + 4C2H5Cl + 8Na → Si(C2H5)4 + 8NaCl
Silicon tetrachloride reacts with acetic anhydride to form silicon tetraacetate (tetraacetoxysilane). This reaction was discovered by Friedel and Ladenburg in 1867:
SiCl4 + 4(CH3CO)2O → (CH3COO)4Si + 4CH3COCl
Silicon tetraacetate can also be made by the reaction of silicon tetrachloride with sodium acetate. In general any carboxylate salt of silicon can be prepared from silicon tetrachloride by this reaction:
SiCl4 + 4CH3COO Na → (CH3COO)4Si + 4NaCl
Ladenburg in 1873 synthesized phenyltrichlorosilane, C6H5SiCl3 by heating silicon tetrachloride with diphenylmercury:
SiCl4 + (C6H5)2 Hg → C6H5SiCl3 + C6H5HgCl
Silicon tetrachloride undergoes addition with olefinic and acetylenic unsaturated hydrocarbons. In these addition reactions, one chlorine atom adds to one carbon atom of the double or triple bond while the rest of the unit —SiCl3 attaches to the other carbon atom forming a silicon—carbon bond:
SiCl4 + H2C=CH2 → ClCH2—CH2SiCl3
SiCl4 + HC≡CH → ClCH=CHSiCl3
Silicon tetrachloride is reduced to metallic silicon when heated with sodium, potassium, and a number of metals:
SiCl4 + Mg → Si + MgCl2
It reacts with carbon monoxide to form a compound with a silicon carbon bond:
SiCl4 + CO → ClC(=O)SiCl3
Reaction with excess amine forms amine derivatives of silicon:
SiCl4 + HN(CH3)2 → Si[N(CH3)2]4 + 4HN(CH3)2•HCl
Clear colorless liquid
Inhalation causes severe irritation of upper respiratory tract resulting in coughing, choking, and a feeling of suffocation; continued inhalation may produce ulceration of the nose, throat, and larynx; if inhaled deeply, edema of the lungs may occur. Contact of liquid with eyes causes severe irritation and painful burns; may cause permanent visual impairment. Liquid may cause severe burns of skin. Repeated skin contact with dilute solutions or exposure to concentrated vapors may cause dermatitis. Ingestion causes severe internal injury with pain in the throat and stomach, intense thirst, difficulty in swallowing, nausea, vomiting, and diarrhea; in severe cases, collapse and unconsciousness may result.
The vapors are very toxic and irritating to the eyes, throat, and mucous membrane.