An Improved Method of Manufacturing Potassium Salicylate and Salicylic Acid.
Year: 1893

page_text: Date of Application, 9th Sept., 1893-Accepted, 4th Nov., 1893
COMPLETE SPECIFICATION.
An Improved Method of Manufacturing Potassium Salicylate and
Salicylic Acid.
I, SIEGFRIED MARASSE of 19 Schulzendorferstrasse, Berlin, N., in the Empire
of Germany, Doctor of Philosophy, 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 :-
In the ordinary process for manufacturing salicylic acid commercially, the latter
is derived from the phenolates of the alkalies or alkaline earths. These phenolates
have to be absolutely freed from the presence of water, which requires laborious and
troublesome treatment, previous to subjecting them to the action of dry carbonic
acid gas in open or closed vessels, under increased temperature.
On the other hand, according to an observation, published by Drechsel in the
"Zeitschrift für Chemie" for the year 1865, page 580, salicylic acid is found to
generate "slowly and in small quantities" if a mixture of phenole, bicarbonate of
potassium (KHCO,) and water is placed in a glass tube, sealed up by melting and
kept therein for several days at a temperature of 160° C.
Moreover from experiments made by Senhofer, Brunner and Sarlay, described in
the "Wiener Akad. Berichte" (volume 80, pages 504 to 524 and vol. 84 pages 323
and 331) appears, that, where phenoles containing over one atom of oxigen are heated
for fourteen hours with carbonate of ammonia or bicarbonate of potash in aqueous
solution-the mon or dicarboxilic acid of the respective phenole is produced.
But no such action takes place on phenole itself C.H.O.
These investators emphasize repeatedly the fact, that from phenole proper under
action of carbonate of ammonia and water-they always attained "only traces" of
salicylic aci
Conseqntly owing to the extremely insignificant results neither the process,
described by Drechsel nor that of Senhofer, is useful in a manufacturing sense for
producing the far most important aromatic oxicarbon acid namely." salicylic
acid."
By the improved process hereinafter described a complete reaction is attained,
without the necessity of producing and drying phenolates.
Phenole is intimately mixed with neutral carbonate of potassium or potashes and
this mixture is placed in a closed receptacle and subjected to the action of the
necessary quantity of carbonic acid under increased temperature.
The most advantageous temperature lies between 130° and 160° C.
It is especially important, that an excess of potash be used, to prevent the
mixture from caking, when warmed and thus excluding the carbonic acid wholly or
in part from entering freely to act on the mixture.
As soon as such temperature as is advantageous for the reaction is reached,
the carbonic acid will act extremely readily, as will be seen from the pressure
guage.
When after cooling, the receptacle is opened, the phenole will be found to have
been almost completely converted into salicylate of potash.
The reaction, in which intermediate products are apparently non-existant takes
place according to the following equation:
OH
2 C.H.OH + K,CO, + CO, = 2 CH
+ H₂O.

page_text: From the aforesaid it results, that this improved process is new and essentially
distinct from the previously known processes, in the following three points.
I. The production of salicylic acid according to the improved process, takes
place under separation of water, as is apparent from the equation of the reaction.
The process even permits also water to be added or to be present in the reagents,
without the formation of salicylic acid being prevented provided always that a
sufficient quantity of potash is present to prevent the mixture from becoming
coherent or caking.
In the previous manufacturing method the presence of water as mentioned, in the
first instance must be carefully avoided.
II. As it is observed and stated by Baumann (Berichte der Deutschen Chem.
Gesellschaft, vol. 10 page 686, that after a boiling for 14 hours of phenole with a
solution of potash under developement of carbonic acid, potassium phenolate will be
formed, it might consequently be presumed, that also in the before described process
the formation of potassium, phenolate would precede the generation of salicylic
acid. That this however does not occur and that in a closed receptacle the
reaction, observed by Baumann does not take place is proved by the following
experiment:
If potassium phenolate in a closed vessel and in presence of water is subjected to
the action of a small quantity of carbonic acid, phenole will be set free and
carbonate of potassium formed. This separation occurs at low as well as at higher
temperatures.
In the improved method in which water is generated without doubt only carbonate
of potash comes into simultaneous action with the carbonic acid. It is by the
simultaneous action of the potash and the carbonic acid in common upon the phenole
in the presence of the porous quality of the mixture of the phenole and potash, that
the ready formation of the salicylic acid rests.
III. An important feature of the improved process is the intimate mixture of the
phenole with potash, the latter being added in excess to such a degree, that the
mixture even in warm temperature preserves its quality of dry powder and may
consequently be easily penetrated by the carbonic acid gas in all parts.
This intimate mixture is the preliminary condition for-as regards quantity-
the almost complete possible output of salicylic acid.
This fact also distinguishes the new process from that of Drechsel, where likewise
after warming, there are present potash, phenole, water and carbonic acid,
independent from another. However the carbonic acid is not found present in
opposition to a porous mixture, but to two layers of liquid, which do not penetrate
each other, the one being a watery, the other an oily substance, which prevents
them from acting upon one another. The only layer separates the carbonic acid
from the watery layer and through the warming being continued for days, the
carbonic acid will only generate a very slight amount of salicylic acid. In the
improved process the salicylic acid is removed in the known manner from
the mixture after treatment by precipitation by an admixture of a mineral acid and
is purified by re-crystallyzation and admixture of animal charcoal.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is :-
The improved process of producing salicylic acid, or its potassium salt consisting
in exposing a mixture of phenole and excess of carbonate of potassium or potashes
to carbonic acid in a closed vessel under action of heat, whereby the mixture
although in a warmed condition is prevented from caking by excess of potash.
1000
R. HADDAN,
Herbert Haddan & Co.,
18, Buckingham Street, Strand, London, Agent for Applicant.