Process for the Production of Benzoic Acid from Coal Tar Oil.
Year: 1899

page_text: Date of Application, 14th Apr., 1899-Accepted, 8th July, 1899
COMPLETE SPECIFICATION.
Process for the Production of Benzoic Acid from Coal Tar Oil.
We, AKTIEN-GESELLSCHAFT FÜR THEER-UND ERDOL-INDUSTRIE, of Berlin,
Flottwellstrasse No. 7, and DR. GUSTAV KRAEMER, Chemist, of Flottwellstrasse
No. 7, Berlin, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement:-
The lighter fractions of coal tar give, on suitable fractional distillation, a
distillate in which mostly carbolic acids are contained, and which is consequently
called carbolic oil or creosote oil. According to the present invention there is
obtained from this tar oil fraction by suitable treatment with alkaline reagents,
benzoic acid in the form of a salt, from which latter the free acid can be separated
by precipitation by means of any acid more powerful than it is itself, in the known
manner. It is distinguished from the benzoic acid obtained artificially from
toluene by its high degree of purity.
In practically carrying out the process, the light and middle oil of coal tar is
so fractionated in the known manner in suitable column apparatus that a fraction
is produced that boils between 160° C. and 240° C. or preferably between narrower
limits, such as is employed as raw material for the production of phenol and
cresol. By washing with dilute soda lye of about 11 specific gravity in the
cold, these substances are removed. The remaining oil which boils between the
same above named limits is then placed in a double walled vessel provided with
a stirrer and heated by open and closed steam, which vessel is combined with a
condenser and receiver in such manner that the escaping gases and vapours can
be collected.
Caustic soda solution of 1'4 specific gravity is then added to the extent of about
twice the quantity necessary for the saponification of the benzonitrile contained
in the oil; the stirrer is set in motion and a little steam is passed in to heat the
mixture so long as ammonia is evolved in notable quantity. After some hours
this part of the process is finished and there are then in the receiver the lower
boiling constituents of the oil and a somewhat concentrated solution of ammonia.
The stirrer is stopped and the contents of the vessel are transferred to a separating
tank wherein the lower, alkaline layer is separated from the upper oily layer.
The alkaline liquid is then treated with carbon dioxide or a mineral acid until
the excess of caustic soda is saturated. By this means traces of phenol and a
small quantity of resinous and oily matters are separated and may be skimmed
from the nearly colourless, aqueous layer. This latter is a solution of an almost
chemically pure sodium benzoate from which benzoic acid is precipitated by adding
a more powerful acid than it is itself to the solution, which is preferably first
heated. When the liquid is cold the benzoic acid is in the form of beautiful white
crystals and is easily separated.
The obtainment of benzoic acid from the oil may be effected also by heating
with another alkali and even with lime or baryta; the use of bases which are but
little soluble is not, however, to be recommended.

page_text: Having now particularly described and ascertained the nature of this invention.
and in what manner the same is to be performed, we declare that what we claim
is:-
Process for the production of benzoic acid from the light oils and middle oils
of coal tar by first removing therefrom the phenoles contained therein by washing
in the cold by means of dilute soda lye, and then treating them with alkalies, in
particular soda, until the saponification of the benzonitrite is completed, sub-
stantially as described.
1
11
1000
ABEL & IMRAY,
Agents for the Applicants.