Organic Derivatives of Silicon

Although silicon, next to oxygen, is the most abundant of the earth’s elements, it plays, so far as is known, a very insignificant part in the chemistry of living organisms. I t occurs, it is true, in a combined state in many plants, often in considerable proportions, but apparently only in the form of silica and mineral silicates, the exact functions of which have not been determined. In the animal world the presence of silicon compounds seems to be unknown except for the interesting case recorded by Drechsel (1897), who isolated from feathers a compound which was believed to be an ester of orthosilicic acid of the composition Si(0 C34H 590 )4. I t is not surprising, therefore, th a t owing to the great lack of materials which offered facilities to the investigator, the development of the chemistry of silicon has been comparatively very slow in many directions; so long as silica and the intractable mineral silicates were the only available sources of th a t element little could be done. The discovery of silicon tetrachloride by Berzelius in 1823 might have led to an immediate advance, but it was not until 23 years later tha t this compound was used by Ebelmen for the preparation of the first organic silicon compound, ethyl orthosilicate, Si(OEt)4. This ester, produced by the interaction of alcohol and the tetrachloride, was, however, completely decomposed by water and seemed to be of such little use for the pre­ paration of other substances th a t a further 17 years elapsed before any progress was made. In 1863 Friedel and Crafts prepared the first compounds, in which carbon and silicon atoms were directly united, by the action of the zinc alkyls on silicon tetrachloride; the tetra-alkylsilicanes so obtained, unlike the esters, were extraordinarily stable, and therefore, like the latter, but for a different reason, seemed to offer few facilities for their further investigation. During the following decade Friedel and Ladenburg and Ladenburg alone, by very troublesome methods, obtained various new types of organic silicon compounds: ethyl orthosilicate, treated with sodium and zinc ethyl, gave successively the derivatives SiEt(OEt)3, SiEt2(OEt)2,