THE CHEMISTRY OF SILICON

Silicon (from L. silex, flint), the fourteenth element in the periodic table, is a congener of carbon, in group IV. Silicon plays an important part in the inorganic world, similar to that played by carbon in the organic world. Most of the rocks that constitute the earth s crust are composed of the silicate minerals, of which silicon is the most important elementary constituent. 

The importance of carbon in organic chemistry results from its ability to form carbon-carbon bonds, permitting complex molecules, with the most varied properties, to exist. The importance of silicon in the inorganic world results from a different property of the element —a few coiiipounds are known in which silicon atoms are connected to one another by covalent bonds, but these compounds are relatively unimportant. The characteristic feature of the silicate minerals is the existence of chains and more complex structures (layers, three-dimen sional frameworks) in which the silicon atoms are not bonded directly to one another but are connected by oxygen atoms. 1 he nature of these structures is described briefly in later sections of this chapter. 

Elementary Silicon and Silicon Alloys. Silicon is a brittle steel-gray metalloid, with m.p. 1420 C, b.p. 2600° C, and density 2.42 g/cm. It can be made by the reduction of silicon tetrachloride by sodium  

The element has the same crystal structure as diamond, each silicon atom forming single covalent bonds with four adjacent silicon atoms which sufround it tetrahedrally. 

Silicon contaminated with carbon can be obtained by reduction ot silica, SiOs, with carbon in an electric furnace. An alloy of iron and silicon, called ferrosilicon, is obtained by reducing a mixture of iron oxide and silica with carbon. 

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Compare and contrast the chemistry of silicon, germanium, tin and lead by referring to the properties and bond types of their oxides and chlorides. 

The chemistry of silicon in very low oxidation states is one of the most fascinating research areas, which can be located between molecular compounds of silicon and elemental (perhaps amorphous) silicon [190-194]. Most interesting results have recently been obtained by structural investigations of siliddes in Zintl phases. However, compounds of silicon with negative oxidation states and very low coordination numbers of 1, 2, and 3 are so far only known in the composite of a crystal lattice. 

H. Kwart and K. King, d-Orbitals in the Chemistry of Silicon, Phosphorus, and Sulfur, Springer-Verlag, Berlin, 1977. 

Noll, W. The Chemistry of Silicones Academic Press New York, 1968. 

Hofler, F. The Chemistry of Silicon-Transition-Metal Compounds. 50, 129-165 (1974). 

E. G. Rochow, The Chemistry of Silicon, Pergamon Press, Oxford, 1973. 

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

The unique surface characteristics of polysiloxanes mean that they are extensively used as surfactants. Silicone surfactants have been thoroughly studied and described in numerous articles. For an extensive, in-depth discussion of this subject, a recent chapter by Hill,476 and his introductory chapter in the monograph he later edited,477 are excellent references. In the latter monograph, many aspects of silicone surfactants are described in 12 chapters. In the introduction, Hill discusses the chemistry of silicone surfactants, surface activity, aggregation behavior of silicone surfactants in various media, and their key applications in polyurethane foam manufacture, in textile and fiber industry, in personal care, and in paint and coating industries. All this information (with 200 cited references) provides a broad background for the discussion of more specific issues covered in other chapters. Thus, surfactants based on silicone polyether co-polymers are surveyed.478 Novel siloxane surfactant structures,479 surface activity and aggregation phenomena,480 silicone surfactants application in the formation of polyurethane foam,481 foam control and... 

Lewis, L. N. From Sand to Silicones An Overview of the Chemistry of Silicones. In Silicones and Silicone-Modified Materials Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. ACS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 11-19. 

The potential sites of cleavage in the hydrolytic degradation of the trisiloxane surfactant, M2D-C3-0-(E0)n-CH3 (1) are illustrated in Fig. 5.5.3. The Si-0 bond (c) is a likely site of cleavage according to the chemistry of silicones and the relative instability of this bond to hydrolysis [23]. 

Rochow, E.G. 1951. An Introduction to the Chemistry of Silicones. Wiley, New York. 

Hofler, F, The Chemistry of Silicon-Transition-Metal Compounds. 50, 129-165 (1974). Hogeveen, H., and van Kruchten, E. M. G. A. Wagner-Meerwein Rearrangements in Long-lived Polymethyl Substituted Bicyclol3.2.0]heptadienyl Cations. 80, 89-124 (1979). 

The British scientist wondered whether he could produce similar substances based on a silicon framework. His efforts inadvertently planted the seeds of an idea that has since blossomed in the mind of many science fiction writers an alien world may exist where everything is based on the chemistry of silicon instead of carbon. Kipping, however, by his own admission, did not think that he had come up with anything dramatic. He produced a variety of oils and gunks, which he... 

Die Chemie der MetaLl-Organische Ver-bindungen," Gebr Bomtrsfger, Berlin(1937) 4)E. G.Rochow, "The Chemistry of Silicones," Wiley,NY( 1946), 32 5)H.W.Post, "Silicones and Other Organic Silicon... 

Rochow, E. G. The chemistry of silicon. In Pergamon texts in inorganic chemistry. 

Nevertheless, mechanistic investigations on the addition reaction to disilenes and silenes advanced considerably in recent years. In this chapter, the author tries to survey the progress achieved recently. The author will not try to review all aspects of the chemistry of silicon unsaturated species since many extensive reviews on this topic are already available6-12. 

The author wishes to thank his colleagues for their indispensable contributions to the studies on the chemistry of silicon-silicon and silicon-carbon double bonds. Their names are cited in the references. The author also wishes to thank the Ministry of Education, Science, and Culture (Specially Promoted Research 02102004) and the Japan Society for the promotion of Sciences (RFTF95P00303) for financial support. 

Recent advances in the chemistry of silicon-heteroatom multiple bonds... 

Recent advances in the chemistry of silicon-heteroatom multiple bonds 1065 B. Theoretical Calculations 1. Silanones and silanethiones... 

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