A Manual of the Chemistry of the Carbon Compounds

176 THE CBEM8TRY OF
Olefines may also be produced by synthesis. Thus pentem C6Hj0
has been obtained by the action of zinc-ethyl upon allyl iodide
CSH5I :u
+ 2C8H6I = 2C6H10 + Znl,
By heating monobroinethene with ziuc-ethyl, butene C4H8 is produced
:—
2(C2HsBr) + (CjH^Zn = 2C4H8 + ZnBr,
Olefines also occur amongst the products of destructive distillation
of many organic bodies, and are found therefore in coal-tar, woodtar,
&c.
In their physical properties the olefines have great resemblance to
the paraffins. The lowest members of the series are gaseous at the
ordinary temperature; most of the others are liquids having a faint
ethereal and garlic-like smell; and the highest members consist of
crystalline solids.
The olefines contain two carbon atoms linked together by two
combining units of each atom. The number of isouierides which
according to theory may exist is larger than that of the paraffins, as
the double linking of two carbon atoms can take place between
different atoms in the carbon chain. Thus we know only two
hydrocarbons C4H10, but three having the formula C,H8:—
C iin ==: C H —v g
CHS—CH=CH—CH8
The most characteristic property of the olefines is that they combine
directly with one molecule of another element or compound, as
with the hydvacids of the chlorine group, ethene and bydnodic acid
yielding ethyl iodide:—
CH2I
The olefines containing more than two atoms of carbon yield by
this reaction secondary or tertiary compounds :—
i H ° (11 ?'
II J I
cu. CH.