A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 361
It is very characteristic of this acid that the presence of mere
traces of certain impurities prevents the crystallization and lowers
the melting-point, Tims, on oxidizing toluene with dilute nitric acid,
a benzoio acid is obtained containing nitrobenzoic acid. By distilling
it with steam, the latter acid is almost entirely left behind; only a
trace, so small that it cannot be detected by combustion-analysis, is
carried over; yet the benzoic acid can,even by repeated recrystalli?»tion,
only be obtained in warty crusts or flakes. But on heating it
with tin and hydrochloric acid, the nitro-acid is converted into amidobenzoic
acid, which on cooling remains in solution, whilst pure
benzoio acid crystallizes in the characteristic needles. Before these
facts were known, it was believed that several isomerio benzoio acids
existed.
Most benzoates are soluble in water; the neutral solutions give
with ferric chloride a reddish precipitate of ferric benzoate. This reaction
is made use of for the separation of iron from manganese, and
for the detection of benzoic acid.
Silver benzoate is very sparingly soluble in cold water, and crystallizes
from a boiling solution in small shining plates.
Methyl Benzoate C6HB.C0¥CH8 is readily formed by passing hydrochloric
acid gas into a solution of benzoio acid in methyl alcohol. It
is a limpid liquid, possessing a frograut odour, and boiling at 199°.
Alkalis decompose it into benzoic acid and methyl alcohoL As this
compound has such a high boiling-point, it can easily be obtained
pure by using impure methyl alcohol; and it is therefore used for
preparing pure methyl alcohol, as tho benzoic acid can easily be
recovered and employed again foe the same purpose.
Ethyl Benzoate CflELCOyCjHj is produced by the action of hydrochloric
acid on an alcoholic solution of the acid, and by adding
benzoyl chloride to ethyl alcohol. It is an aromatic liquid, boiling
at 213°.
Benzoyl Chloride COHB,COC1 is prepared hy distilling the acid with
phosphorus trichloride, and also formed by the action of chlorine on
benzaldehyde. It is a limpid liquid, boiling at 199°, and possessing a
very pungent smell. Water acts on it as on other aoid chlorides;
and on heating it with phosphorus pentachloride it is converted into
benzenyl tridileride CgH6.CCl8.
Benzoyl Muoride C6HS,COF,—To obtain this compound, benzoyl
chloride and dry potassium hydrofluoride are heated in a platinum
retort;—
HKF9 + 200H6.COQ *> HC1 + KC1 + 2C6H6.COF
It is an oily liquid, boiling at 162°, and possessing a very irritating
smelL Water decomposes it readily into hydrofluoric acid mid
benzoic acid,
Benzoyl Oxide or Benzoic Anhydride (CjH^CO^O is prepared by
heating dry sodium benzoate with benzoyl chlondo, or with phosphorus
oxychloride;—