Organosilicon compounds reactivities

In this section, the reactivities of organosilicon compounds for the Friedel-Crafts alkylation of aromatic compounds in the presence of aluminum chloride catalyst and the mechanism of the alkylation reactions will be discus.sed, along with the orientation and isomer distribution in the products and associated problems such as the decomposition of chloroalkylsilanes to chlorosilanes.. Side reactions such as transalkylation and reorientation of alkylated products will also be mentioned, and the insertion reaction of allylsilylation and other related reactions will be explained. 

II. Subvalent and Unsaturated Organosilicon Compounds Formation and Reactivity... 

Chemical reactivity of unfunctionalized organosilicon compounds, the tetraalkylsilanes, are generally very low. There has been virtually no method for the selective transformation of unfunctionalized tetraalkylsilanes into other compounds under mild conditions. The electrochemical reactivity of tetraalkylsilanes is also very low. Kochi et al. have reported the oxidation potentials of tetraalkyl group-14-metal compounds determined by cyclic voltammetry [2]. The oxidation potential (Ep) increases in the order of Pb < Sn < Ge < Si as shown in Table 1. The order of the oxidation potential is the same as that of the ionization potentials and the steric effect of the alkyl group is very small. Therefore, the electron transfer is suggested as proceeding by an outer-sphere process. However, it seems to be difficult to oxidize tetraalkylsilanes electro-chemically in a practical sense because the oxidation potentials are outside the electrochemical windows of the usual supporting electrolyte/solvent systems (>2.5 V). 

Although carbon and silicon both belong to the same group of periodic table and many of the silicon compounds resemble carbon compounds, but the chemical reactivity of silicon in organosilicon compounds is more comparable to that of hydrogen because many nucleophilic displacements at... 

The reactivity of organosilicon compounds is influenced by the more electropositive nature of the silicon atom as compared to carbon and hydrogen and also by the availability of empty d orbitals, although the latter point has now become controversial. On this basis Si-0 and Si-F bonds are stronger than the C-0 and C-F bonds. The Si-H bonds are weaker than C-C and H-C bonds. 

Some Applications of Organosilicon Compounds to Organic Synthesis Why Silicon Compounds are Reactive... 

W. Ando and Y. Kabe, Highly Reactive Small-ring Monosilacycles and Medium-ring Oligosilacycles, in The Chemistry of Organosilicon Compounds, Vol. 2, Z. Rappoport and Y. Apeloig, Eds., John Wiley Sons, Inc., Chichester, UK, 1998, Part 3, p. 2401. 

It is quite surprising that the influence of 7r-complex formation on the reactivity of Si—C bonds has been so little investigated to date, in spite of the importance of such studies for the purpose of regulating the chemical behavior of organosilicon compounds. 

An organosilicon compound (tetramesityldisilene) containing a silicon to silicon double bond has been synthesized. It is a crystalline solid, mp 176C, and has reactive properties similar to olefins. Compounds of the type are silylenes. 

The photochemistry of organosilicon compounds has been extensively studied, since many types of interesting reactive intermediates such as silylenes, silenes, disilenes and silyl... 

Because of their chemical inertness, low surface tension and antisurfactant activity polyorganosiloxane (silicone) oils have found varied applications in medicine. These have included use as an artificial lubricant for arthritic joints191, as a means of soft tissue augmentation, and as an additive in creams and oils for burn treatment. Di-methylpolysiloxane fluids have been injected as replacement for aqueous and vitreous humour in eyes. Reactive organosilicon compounds comprise a new class of potential prophylactic and therapeutic agents192. Protection against atherosclerosis... 

In 1981, West et al. synthesized the first stable disilene 1 via the dimerization of the corresponding silylene generated by the photolysis of a trisilane and characterized the structure by conventional spectroscopies [Eq. (2)].5 Availability of 1 and other stable disilenes has stimulated theoretical and experimental studies of various aspects of disilenes such as their bonding and structure, spectroscopic properties, reactivities, applications to the synthesis of novel types of organosilicon compounds, etc. 

This reaction made numerous silicon compounds available and even today is still of great importance. Kipping expected to find an analogy between silicon and carbon compounds, but his later papers reveal his disappointment in the lack of versatility and limited reactivity of silicon compounds. Kipping was rather pessimistic about the further development of organosilicon chemistry, being so much influenced by ideas of carbon chemistry that he underestimated the importance of the formation of the siloxanes from the silicon halides, as now evidenced in the industrial applications of organosilicon compounds. 

The reactions of silicon halides with organomagnesium or organolithium compounds for the synthesis of organosilicon compounds are oversimplified in Eqs. (3) and (4). If several reactive groups are attached to the silicon atom, as in C2H5SiCl3, the reaction cannot be controlled so as to yield a particular substitution product, since all possible substitutions will occur simultaneously. All that can be done is to favor the yield of the desired compound by manipulation of reaction conditions. 

Intermediate. A reactive compound containing an essential grouping which, by further processing or reaction, is conveyed to the finished product here, a reactive organosilicon compound of relatively simple structure which is used in the preparation of organosilicon polymers. 

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