HAROLD HAUSMAN
T.
This fact is of the greatest importance in dealing with HE recent advances in t h e knowledge and applications of the silicon polymers make it worth whiie the silicon organics. to outline the chemistry of these compounds in a more SILANES AND NON-CARBON DERIVATIVES systematic manner. To help preserve uniformity in the literature of these substances, the nomenclature Silanes (Hydrides). If the two oxygens in silica are reused follows, as far as possible, that proposed by Sauer placed by four hydrogens, we have the first of a group of noninorganic silicons which can be used as starting (1). This review is far from complete-.especially as re- materials in further syntheses. These are the silanes, gards patents, only a few of which are mentionedand or saturated hydrides, having the general formula: some of the matter discussed is still controversial. Si,Hz.+z. They are analogous in structure to the Nevertheless, it is hoped that a clear picture is repre- alkanes or paraffin hydrocarbons. sented of their behavior as well as of the possibilities The silanes are colorless gases, soluble in alcohol, of obtaining oily, vitreous, plastic, and other polymeric benzene, and carbon tetrachloride. They ignite exsubstances with properties generally intermediate be- plosively when exposed to air (oxygen) even a t low tween those of inorganic and organic materials, and temperatures. Although practically insoluble in water that further interest will be stimulated in this newcontained in a quartz vessel, they are rapidly attacked and old-field. by alkali--even by the small amount of alkali leached For the organic compounds of silicon have been out by water from ordinary glass. For these reasons known for more than one hundred years, many of them special apparatus had to be devised for their isolation having been prepared with the expectation that they and study ( 2 ) . would be analogous to those of carbon. It was found, As usually prepared-by.the action of acid on maghowever, that silicon differs from carbon in a t least one nesium silicide--the silanes are part of a mixture of hyimportant respect-namely, the great strength of the drides formed in the reaction, "unsaturated," nonsilicon-to-oxygen bond as compared to the linkages of volatile hydrides being obtained as well. The latter silicon and other elements. This is manifested in the have formulas varying from SiH, to (SiH,.& and tendency of these two elements to form alternate links are yellow to brown amorphous substances, unafof silicon and oxygen atoms in linear or cyclic structures. fected by water, insoluble in organic solvents, and are Thus, it has not been possible to build long-chain com- converted into silicates by alkalies with the evolution pounds having many silicon atoms joined to one an- of hydrogen. These can also be prepared by the action other as in the case of carbon; chains having more of sodium amalgam on SiHaC1, SiH~cln,and SiHCls: than five consecutive silicon atoms are highly - . unstable SiHCb 3Na (SiH). f 3NaCl and most readily subject to hydrolysis. 16
+
-
The Wurtz reaction, therefore, cannot be applied in the case of the silane halides containing hydrogen (3). A better yield of the saturated hydrides has been obtained by allowing magnesium silicide to drop into a liquid ammonia solution of ammonium bromide, giving a mixture of gases consisting of hydrogen, SiH, (silane), and Si2Hs(disilane), as well as small amounts of SipHs (trisilane) (4). Silane Halides. The hydrogens in the silanes can be re~lacedbv haloeens. eivine halides of the tmes: H~SG, H~SX'~, H S & , gcd ~ i They . can be prepared by direct halogenation of the hydrides, but the reaction is too violent even at room temperature. A smoother reaction is obtained by using gaseous HX in the presence of AIXs as a catalyst. As in the case of carbon compounds, a mixture of various halides results. They can also be obtained by the action of higher silanes on chloroform or carbon tetrachloride in a vacuum, using AIXaas catalyst (5). These halogenated products are colorless gases or liquids which are stable in a vacuum, but very sensitive t o water, fuming in air. Hydrolysis of the halides gives a number of oxygen derivatives which, together with others, will be considered separately. The halides also react readily with ammonia, giving volatile and nonvolatile polymers of their respective "amines:" [SiH2(NH)]., [Si(NH)2]., [SiH(N)]., and [SiN& These ammonia derivatives, unlike their carbon analogs, do not add HX to form ammonium salts (6).
-.
fected after 200 hours at 75 atm. and 400°C. (at higher temperatures condensation begins to take place) (9). The aromatic groups may be sulfonated and nitrated, but the phenyl-silicon bond is broken by PCls or bromine. By use of the Grignard reagent, or by the Wurtz reaction, mixed aliphatic-aromatic silanes have been obtained (10) : (CIH.),SiCI
-
+ CH8MgBr
/CHrCH2 C1 CH1 >i< 'WH-CH, CI
(CbHs)rSiCH.
+ 2CHaMgBr
-
,CH-CHj.
