Organic chemistry in our life. Part II
This material is a violent explosive, and is prepared by
steeping cotton-wool for a few minutes in a cold mixture of the
strongest nitric acid with two or three times its weight of
concentrated sulphuric acid. When thoroughly freed from
acid by washing, gun-cotton is comparatively quite safe to
handle, and may even be set fire to without anything more
violent than a rather quick combustion taking place ; but
when subjected to the shock set up by exploding a small
charge of fulminate embedded in the gun-cotton, the molecules
of the latter break down suddenly, and a powerful explosion
results; the rearrangement of atoms which then occurs may
be roughly represented by the following equation :
C i2 H u4( N 3)c = 3N 2 + 7H.O + 9 CO + 3 C0 2 Gun-cotton.
Pyroxylin is a less highly nitrated cellulose, chiefly the
tetra-nitrate ; it is prepared with a somewhat weaker nitric
acid. Its solution in a mixture of alcohol and ether is the
collodion which is largely used in photography (wet-plate
process), and in surgery for covering wounds with a thin
flexible film which prevents access of air.
The Allyl Compunds
The allyl compounds may be regarded as being derived from
the hydrocarbon propylene, C 3 H G , and their starting-point
allyl alcohol stands to propylene in the same relation as
ethyl alcohol does to ethane.
Propylene has the formula CH 2 : CH . CH 3, and from this
three alcohols might be derived :
1. CH(OH) : CH . CH 3 , a secondary alcohol,
2. CH 2 : C(OH) . CH ;i , a tertiary
3. CH 2 : CH . CH,(OH), a primary
Of these, the third formula represents allyl alcohol, which
in many respects behaves like any other primary alcohol,
but differs from methyl alcohol and its homologues in being
unsaturated. On the one hand, as a primary
alcohol, it yields an aldehyde and then an acid when oxidised,
while as an unsaturated compound it is able to combine
directly with chlorine or bromine. Allyl Alcohol, C 3 H 5 .OH, is obtained by distilling a
mixture of glycerine, C 3 H 5 (OH) 3, with formic acid (oxalic acid
may be substituted for this, but as it decomposes under these
conditions into formic acid and CO 2 , the reaction is practically
the same). The formic acid is oxidised to CO 2 and water:
Glycerine. Formic acid. Allyl alcohol.
The following is the usual method for preparing allyl
alcohol :
Four parts of glycerine and one of crystallised oxalic acid are placed in
a retort and gradually heated. At first much CO2 is evolved, and dilute
formic acid distils over. When the temperature of the mixture reaches
190 the receiver is changed, and impure allyl alcohol is obtained as the
distillate. This is purified by fractional distillation, and freed from water
by treatment with anhydrous baryta. Pure allyl alcohol boils at 96.
Allyl alcohol is a colourless liquid which, like all the allyl
compounds, has an irritating, unpleasant smell. As an un-
saturated body it combines directly with C1 or Br 9 to form
derivatives of propyl alcohol: C 3 H 5 . OH + Br 2 = C 3 H 5 Br . OH.
Allyl alcohol. Dibromo-propyl alcohol
As a primary alcohol allyl alcohol yields, when carefully
oxidised, first an aldehyde allyl aldehyde or acrolein and
then an acid acrylic acid: CH 2 : CH . CH 2 OH + O = CH 2 : CH . CHO + H 2 O
Allyl alcohol. Acrolein.
CH 2 : CH . CHO + O = CH 2 : CH . CO 2 H. Acrolein.