METAL-ORGANIC COMPOUNDS. 2l3- Tetraethyl Silicate, Si(OC 2 H 5 ) 4.
To about 20 g. of silicon tetrachloride (No. 51) in a small flask
allow 1.1 times its weight of absolute alcohol to flow slowly from a
dropping funnel. The alcohol must have been boiled with quick-
lime for several hours immediately beforehand and then distilled
out of contact with moisture. During the operation hydrogen
chloride escapes in quantity; it is not necessary to cool the mix-
ture since it becomes warmed but little.
Purify the crude product by distilling it from a small round-
bottomed flask and through a fractionating tower containing a
13 cm. column of glass beads. Use an air condenser consisting
of a tube 40 cm. long and 1 to 1.5 cm. in diameter, which is loosely
slipped over the side-arm of the tower; a cork connection is unneces-
sary. Collect two fractions during the first distillation — the first
one, which is large in quantity, between 160° and 175°, and the
second, which is smaller, between 175° and 185°. On the second
fractionation, collect a small amount of first runnings and then
portions from 167° to 170° and from 170° to 180°, respectively.
Finally, after cleaning and drying the apparatus, distil the
fraction boiling between 167° and 170° again, whereby nearly
all goes over between 168° and 169°. Yield, 13-15 g.
Small amounts of higher boiling by-products are formed and
consist of esters of metasilicic and polysilicic acids.
Tetraethyl silicate is a colorless liquid having a typical etherial
odor; it is immiscible with water, but it dissolves in dilute alcohol
and gradually undergoes hydrolysis in that solution.METAL-ORGANIC COMPOUNDS.
The metal in the metal-organic compounds is bound directly to hydro-
carbon radicals or to carbon monoxide: Zn(C 2 H 5 ) 2 , zinc ethyl (No. 159);
Pb(C 6 H 6 ) 4 , lead tetraphenyl (No. 160); Ni(CO) 4 , nickel carbonyl (No. 161).
The low boiling-points of these compounds, which would scarcely lead one to
suspect the presence of a metal, permit in most cases a ready determination
of the vapor density and thus of the molecular weight. In this respect, as
in fact in almost their entire chemical behavior (e.g. the ready solubility in
organic solvents), these compounds show themselves to be closely related to
the purely organic compounds. It is, therefore, not surprising that the
theory which has found its most specific application, as well as its greatest
success, in the field of organic chemistry — namely the valence theory in its