A Manual of the Chemistry of the Carbon Compounds

72 THE OUBMIStHY OF
have been oalled hydrides; methane being considered as methyl
hydride -J > and hexane as hexyl hydride ° jf • But from
these names it might appear that the paraffins contain one atom of
hydrogen combined with carbon in a manner different from that in
•which the remainder of the hydrogen is attached to the carbon, which
is not the case; for on further action of chlorine on the monochlorides
•we obtain chlorides of dyad, triad, &c. radicals, propane for instance
yielding :—
Pronyl Chloride. Prommo Dielilorido. I'roneuyl Trichloride.
b3HrCl CsHuCla C5H6C1S
And therefore propane might he called propene hydride and propenyl
hydride, as well as propyl hydride.
A second general method to obtain paraffins is to act with a metal
upon an iodide of an alcohol radical; in this reaction the radicals
are set free, but as a monad radical, as we have seen, cannot exist in
the free state, two of them are linked together by the two free combining
units. Thus by heating dry methyl iodide and zinc to 150°,
ethane is formed :—
2CHS + Zn = C2H0 + Znr2
Sodium acts violently upon a mixture of ethyl and amyl iodide, the
hydrocarbon C7H10 being formed:—
C2H6I + C6HUI + Na2 = C7HW + 2NaI
The paraffins formed by this synthetical process have beon called
alcolwl radicals, because it was formerly believed that their constitution
was different from the so-called hydrides; they were regarded as
the free radicals, of which two were united to form a molecule, just as
the molecule of hydrogen consists of two atoms. But we now know
that hydride of ethyl is identical with dimethyl; both possessing the
same physical and chemioal properties, and yielding by the action of
chlorine Us the first product, ethyl chloride.
In ethyUamyl one atom of carbon iu the ethyl group is linked to
one atom of carbon in aruyl, exactly iu the same manner as all the
other carbon atoms are attached to each other, and thus on acting
with chlorine on this hydrocarbon, wo obtain hcjityl chloride C7H,6C1,
and not, as might have been expected according to the old theory, a
mixture of ethyl chloride and amyl chloride.
A third general method of obtaining paraffins consists in the
decomposition of an alkaline salt of a fatty acid by the galvanic
current. When an acid or a salt is decomposed by electrolysis, the
basic hydrogen or the metal is set free from the — pole, and the
remainder of the compound from the •+• pole. The first action of a
galvanic current upon a concentrated solution of potassium acetate is
consequently to resolve the salt into K and O4H302. But as this
decomposition takes place in presence of water, the latter is acted