A Process for the Preparation of Phenylestersalicylic Acid or Salol from Salicylic Acid.
Year: 1891

page_text: Date of Application, 22nd Aug., 1891-Accepted, 26th Sept., 1891
COMPLETE
SPECIFICATION:
A Process for the Preparation of Phenylestersalicylic Acid or Salol
from Salicylic Acid.
I PAUL ERNERT.of the firm Wierss and Ernert, Ludwigshafen on the Rhine, in
the German Empire, Chemists do hereby declare the nature of this invention and
in what manner the same is to be performed to be particularly described and ascer-
tained in and by the following statement :--
In chemical literature (see Beilstein Org page 951 chapter 2 vol. II.) it is stated
that salicylic acid sublimates undecomposed when carefully heated but is partly
decomposed when rapidly distillated into carbonic acid and phenol, a similar
decomposition slowly taking place by heating this compound with water in a
closed tube.
These statements are so far inaccurate, that is to say wrong, that it does not
depend upon a careful or rapid heating but upon the temperature at which the
salicylic acid is heated. Salicylic acid sublimates only below the melting point,
above which decomposition always takes place being very trifling at a temperature
slightly above such melting point and increasing in proportion with the increase of
temperature.
I have discovered that salicylic acid heated to a high temperature is decomposed
into salol with the separation of water and carbonic acid if during the heating the
water formed is distilled off and the access of air is carefully avoided.
Hitherto salol was prepared by treating salicylic acid and phenol with water
extracting means. That the formation of salol which occurs according to my
invention should have been hitherto overlooked may be explained by the fact that
little or no salol is obtained by heating under ordinary circumstances salicylic acid
to a high temperature, as this salol or the intermediate products causing its forma-
tion are again decomposed by the previously separated water or by the action of
the air and as moreover small quantities of salol are hardly noticeable as they are
readily solved in phenol and do not separate alone. Under these circumstances it
is questionable whether the phenol appearing in the ordinary heating of salicylic
acid is a direct product of decomposition. Should this hypothesis be assumed, the
formation of salol according to my invention can be explained inasmuch as the
phenol produced under the given conditions from the decomposition of a molecule of
the acid with an immediate separation of water is combined with a second molecule
of the acid according to the equations

page_text: undecomposed salicylic acid is retained, thus forming salol, in the following manner
for example
OTT
COOL
In this assumption the formation of anhydride within the hydroxyl groups
appears probable, as an addition of phenol does not increase the production.
Under the conditions above set forth the theoretic yield of salol can be easily
reached approximately so that 2 kilos. of salicylic acid produce without the use of
phenol and water extracting means from 1, 4-1, 5 of salol.
For this purpose the operation is conducted as follows. Pure or even crude
salicylic acid is heated for about 4 hours in a bath at a temperature from 220° to
230° C. The flask of glass or other suitable material containing the acid is
provided with a narrow neck projecting a suitable distance out of the bath and
having such a temperature, that the ascending steam may not run in a condensed
form down the bottom of the vessel but reach a small bulb or receptacle connected
to the neck and resembling those used in apparatus for carrying out fractional
distillation the water running out from this bulb through an outlet pipe. Should
the neck of the flask not be maintained at a temperature considerably above
that required for the above object, which may occur through cooling, no other
substance will escape from the neck of the flask besides the water and the carbonic
acid evolved. To prevent the access of air the flask is filled before heating with
an inert gas, such as carbonic acid, a feeble current of this gas being conveyed
during the heating operation through the water bulb in the direction of the outlet
pipe. The salol formed is washed with water or if required with a solution of soda
and is crystallized by means of alcohol or other suitable solvent.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
The hereinbefore described process for the preparation of phenylestersalicylic
acid or salol by heating salicylic acid at a high temperature (preferably at 230° C.)
while distilling off the water formed and excluding the air.
Dated this 22nd day of August 1891.
H. GARDNER,
Patent Agent, 166, Fleet Street, London, Agent for the said P. Ernert.