An Improved Method or Process of Preparing Oxalic Acid and Oxalates.
Year: 1897

page_text: Date of Application, 10th Nov., 1897
Complete Specification Left, 8th Aug., 1898-Accepted, 5th Nov., 1898.
PROVISIONAL SPECIFICATION.
An Improved Method or Process of Preparing Oxalic Acid and
Oxalates.
I, Dr. MARTIN GOLDSCHMIDT, of 1, Carmerstrasse, Charlottenburg, in the German
Empire, Chemist, do hereby declare the nature of this invention to be as
follows:-
The industrial preparation of oxalic acid and its salts is effected, as is known, by
the action of potash on sawdust. (See, for example, Lehrbuch der organ, Chemie,
Victor Meyer, und Paul Jacobson, Vol. I, p. 645).
After I had discovered a method or process of preparing formates, which is
extremely simple and well suited for technical purposes, and consists in allowing
carbon monoxide to act on caustic alkalis or alkaline earths under pressure at an
elevated temperature, (See British Patent, No. 17066 of 1895) it suggested itself
to me to test the practicability of the proposal, first made by Merz and Weith and
supported by experiments (See Berichte d. Chem. Ges., Vol. 13, p. 721), to utilize
the conversion of formates into oxalates for technical purposes.
Merz and Weith established, in a series of brilliant experiments, that it is
possible to transform formates into oxalates by heating to 440° C. (Berichte d.
Chem. Ges. Vol. 15, p. 1509). The yield is in many cases cousiderable, but never
reaches that indicated by theory; in the best of the numerous experiments made
by them, they obtained 71 per cent. of the amount to be expected theoretically
(Berichte, Vol. 15, p. 1510, Experiment No. 12 of the tables).
In order however generally to obtain a, to some extent, satisfactory yield, Merz
and Weith must employ a forced (Berichte, Vol. 13, p. 720), a fierce (Berichte
Vol. 15, p. 1508), and a very rapid (Berichte, Vol. 15, p. 1510) heating.
They state especially that sodium formate, at 360° C., is principally con-
verted into carbonate, and at 440° C., principally into oxalate (Berichte, Vol.
15, p. 1509). Obviously the heating must be carried as rapidly as possible past
the dangerous point 360° C. since otherwise the undesirable formation of carbonate
takes place. Merz and Weith, in their experiments always employ comparatively
only very small quantities of the substance. In one case they take 2 grams
(Berichte, Vol. 13, p. 720), and further on also they worked, as clearly follows from
their description and the drawing of the apparatus used (Berichte, Vol. 15, p.
1508), with only inconsiderable quantities. With these small quantities by weight,
they also were able to obtain quite well the forced, fierce, very rapid heating speci-
fied. The said authors themselves, however, have doubts whether such a peculiar
method of heating would be also possible with considerable quantities such as are
required for technical purposes; they frequently give expression to this doubt
(Berichte d. Chem. Ges. Vol. 15, p. 1513) but content themselves finally by saying
that with the exercise of an intelligent interest on the technical side, the solution
of the problem does not appear to be in any way improbable" (Berichte d. Chem.
Ges., Vol. 15, p. 1513).
As a matter of fact however, it is not likely that an apparatus could be con-
structed in which it would be possible to heat a larger quantity of substance-

page_text: representing about 100 kilograms-from the ordinary temperature up to 440° C.
without allowing the material heated to gradually pass through all degrees of heat
from the original temperature up to the temperature of 440° C. In the present
case, consequently, the ominous temperature of 360° C. will undoubtedly also be
gradually reached and only gradually exceeded, and the consequences of this tem-
perature will undoubtedly make themselves felt.
I have repeated the experiments of Merz and Weith and confirmed them in every
respect, and have not succeeded in producing a quantity of oxalate which could
possibly be considered a technical application of this process, when employing only
a few hundred grams of formate by heating the same. I mention this, together
with peculiar phenomena, which were brought about by the extremely bad thermal
conductivity of the formate and the partial overheating caused thereby, principally
because of the circumstance that it is likewise quite impossible to heat only 100
grams in a forced and flerce manner and very rapidly.
After this I undertook experiments in another direction, which were guided by
the following considerations:-
:-
The sodium formate at 360° C. is mainly converted into carbonate, and at 440° C.
mainly into oxalate.
(b)
2 NàCOOH =
Na₂C₂O + H₂
To me another course of the reaction seems probable especially as the
heretofore generally accepted hypothesis construed the very noticeable phe-
nomenon that, at a high temperature, a less energetic decomposition takes
place than at a lower temperature. At a lower temperature the formate should
give carbon monoxide and hydrogen; at higher temperatures however, only
hydrogen.
I believed myself to be justified in adopting the opinion that the reaction,
under all circumstances-even at higher temperatures-takes place in a different
manner to that indicated by the generally accepted hypothesis, i.e. according to
equation (a), and that the formation of sodium oxalate takes place in a secondary
reaction, in which the carbon monoxide generated, at the moment at which it is
formed, attaches itself to the already formed soda, thus
(c) Na₂CO + CO = Na₂C₂O
I consider myself to be the more justified in forming this opinion by reason of
the well-known enormous affinity or combining power of carbon monoxide, (for
example, Beilstein, Org. Chemie, II Edition, Vol. 1, p. 87).
The hypothesis that the carbon monoxide, on heating the formate, first fixes
itself to the previously-formed soda, is also in the fullest accordance with
the fact that, in all the experiments which were made by Merz and Weith, there
is not a single one in which very considerable quantities of alkali carbonate were
not formed. The generally accepted equation (b) does not offer any explanation
of this fact.
If however the opinion of the inventor as to the course of the decomposition
of the formate be correct, it is not impossible that the addition of already prepared
carbonate to the formate to be converted into oxalate, would increase the
yield of oxalate, for there would then be a carbonate already present, to which
the carbon monoxide could fix itself as it is set free. The combination with the
carbonate can then take place immediately, as soon as the formate gives off
carbon monoxide, whilst otherwise a certain quantity of carbon monoxide first

page_text: escapes until sufficient soda is formed as is required for fixing the carbon
monoxide.
As was established by a suitable experiment, the at first extremely surprising
result was obtained, viz. --that the mixture of soda and sodium formate, even
without forced, fierce heating, gave the quantitative yield of oxalate. Moreover,
it was generally unnecessary to raise the temperature to 440°, the reaction being
perfectly complete at 360° C.
Remarkable as these last facts at first appeared, their explanation is equally
simple, formate is decomposed at 360° C. into carbon monoxide and carbonate.
The nascent carbon monoxide has the property of fixing itself to the carbonate
or, which is the same thing, of being absorbed by the carbonate. The capacity
of the carbonate for absorbing carbon monoxide is very great at 440° C. At
360° C. this capacity of absorption already exists, although in a less degree than
at 440° C. If however, one absorbent absorbs less strongly than another, it is
necessary, in order to effect complete absorption, to use larger quantities of this
less strongly absorbing substance. At 360° C. consequently, larger quantities
of soda must be prosent for the complete absorption of the carbon monoxide,
than are necessary at 440° C. and inversely, Merz and Weith, who did not
have sufficient soda, must endeavour to attain the temperature of 440° C. as
rapidly as possible, in order that the CO shall not
the air.
pass unabsorbed into
By the addition of soda consequently, the forced, fierce, very rapid heating is
rendered unnecessary, and thus the technical preparation of oxalates from formates is
rendered possible in a very simple and beautiful manner.
The formate is simply very intimately mixed with soda (4 parts of crystallized
sodium formate and 5 parts of soda have been found advantageous), and the
mixture (contained, when in small quantities, in glass flasks or retorts, and, when
in larger quantities, in iron vessels preferably provided with stirrers to ensure
uniform heating), is heated in a bath (lead) to from 400 to 410 degrees C.
Exclusion of the air is advantageous, since this permits the escaping hydrogen to
be carried off and allowed to pass through water so that the course of the
reaction can be observed, the said hydrogen being, if desired, still further used or
collected.
The formation of oxalate by heating formate takes place fairly rapidly after
starting; it should be completed in about 30 to 45 minutes. The evolution of
hydrogen is sometimes very rapid. When this ceases, the reaction is complete.
The mass produced in the reaction then contains oxalate and carbonate, the
separation of which can be effected very easily by reason of the great difference
which exists between the solubilities of the two salts in water.
For this purpose,
water, preferably at a temperature of 33° C., is employed, since this, as is known,
possesses the highest capacity of dissolving soda, and of this water a quantity about
double that of the soda present is employed. The solution of soda so obtained,
which is absolutely colourless, and does not contain a trace of colouring or dirty
matter (as it does in the manufacture of oxalates from saw-dust or shavings), is
evaporated to dryness. The dry soda can be used as above mentioned in further
operations. The sodium oxalate (after being freed from soda) which is likewise
perfectly white, can be further manufactured into oxalates and oxalic acid in the
known manner used in oxalic acid works, by means of milk of lime. The manufac-
ture of oxalic acid can also be combined with the manufacture of formates protected
by ny aforesaid former patent, in the simplest manner; it is therefore possible to
convert the carbon monoxide into a solid either in the form of formic acid or of
oxalic acid.
The advantages which therefore result from heating a mixture of carbonate and
formate for obtaining an oxalate, over the open heating of forinate, and which
render possible the preparation of oxalates from formates for technical purposes for
the first time, are briefly the following, viz. :-
(1). Increase in the yield to the quantity obtainable theoretically.

page_text: (2). The necessity is obviated of using forced and fierce heating, for industrial
manufacture, which if it became general, could only be effected by the most
complicated apparatus ;
(3). The application of a lower temperature with all the economies resulting
therefrom;
(4). The overheating due to the bad thermal conductivity of the formates and the
disadvantages incidental thereto are avoided.
D. YOUNG & Co.,
11 and 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.
An Improved Method or Process of Preparing Oxalic Acid and
Oxalates.
I, Dr. MARTIN GOLDSCHMIDT, of 1, Carmerstrasse, Charlottenburg, in the
German Empire, Chemist, 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 industrial preparation of oxalic acid and its salts is effected, as is known, by
the action of potash on sawdust. (See, for example, Lehrbuch der organ. Chemie,
Victor Meyer und Paul Jacobson, Vol. I, p. 645).
After I had discovered a method or process of preparing formates, which is
extremely simple and well suited for technical purposes, and consists in allowing
carbon monoxide to act on caustic alkalis or alkaline earths under pressure at an
elevated temperature, (See British Patent, No. 17066 of 1895) it suggested itself to
me to test the practicability of the proposal, first made by Merz and Weith and
supported by experiments (See Berichte d. Chem. Ges., Vol. 13, p. 721), to utilize
the conversion of formates into oxalates for technical purposes.
Merz and Weith established in a series of brilliant experiments, that it is possible
to transform formates into oxalates by heating to 440° C. (Berichte d. Chem.
Ges., Vol. 15, p. 1509). The yield is in many cases considerable, but never reaches
that indicated by theory; in the best of the numerous experiments made by them,
they obtained about 71 per cent. of the amount to be expected theoretically
(Berichte, Vol. 15, p. 1510, Experiment No. 12 of the Tables).
In order however generally to obtain a, to some extent, satisfactory yield, Merz
and Weith must employ a forced (Berichte, Vol. 13, p. 720), a fierce (Berichte,
Vol. 15, p. 1508), and a very rapid (Berichte, Vol. 15, p. 1510) heating. They
state especially that sodium formate, at 360° C., is principally converted into
carbonate, and at 440° C., principally into oxalate (Berichte, Vol. 15, p. 1509).
Obviously the heating must be carried as rapidly as possible past the dangerous
-point 360° C. since otherwise the undesirable formation of carbonate takes place.
Merz and Weith in their experiments always employ comparatively only very small
quantities of the substance. In one case they take 2 grams (Berichte, Vol. 13, p. 720),
and further on also they worked, as clearly follows from their description and the
drawing of the apparatus used (Berichte, Vol. 15, p. 1508), with only inconsiderable
quantities. With these small quantities by weight, they also were able to obtain quite
well the forced, fierce, very rapid heating specified. The said authors themselves,
however, have doubts whether such a peculiar method of heating would be also
possible with considerable quantities such as are required for technical purposes;
they frequently, give expression to this doubt (Berichte d. Chem. Ges.

page_text: Vol. 15, p. 1513) but content themselves finally by saying that "with the exercise
of an intelligent interest on the technical side, the solution of the problem does
not appear to be in any way improbable" (Berichte d. Chem. Ges., Vol. 15,
p. 1513).
As a matter of fact however, it is not likely that an apparatus could be
constructed in which it would be possible to heat a larger quantity of substance
representing about 100 kilograms-from the ordinary temperature up to 440° C.
without allowing the material heated to gradually pass through all degrees of heat
from the original temperature up to the temperature of 440° C. In the present
case, consequently, the ominous temperature of 360° C. will undoubtedly also be
gradually reached and only gradually exceeded, and the consequences of this
temperature will undoubtedly make themselves felt.
I have repeated the experiments of Merz and Weith and confirmed them in every
respect, and have not succedeed in producing a quantity of oxalate which could
possibly be considered a technical application of this process, when employing only
a few hundred grams of formate by heating the same. I mention this, together
with peculiar phenomena, which were brought about by the extremely bad thermal
conductivity of the formate and the partial overheating caused thereby, principally
because of the circumstance that it is likewise quite impossible to heat only
100 grams in a forced and fierce mauner and very rapidly.
After this I undertook experiments in another direction, which were guided by
the following considerations :-
The sodium formate at 360° C. is mainly converted into carbonate, and at
440° C. mainly into oxalate. Consequently at 360° a reaction takes place accord-
-DOOKS IOr example, nichter, mo
p. 426 Victor Meyer and Jacobson, Vol. 1, p. 644)
(b)-2NaCOOH
=
COMIGNSTON verungen, fo1,
NCO + H₂
To me another course of the reaction seems probable, especially as the heretofore
generally accepted hypothesis construed the very noticeable phenomenon that, at a
high temperature, a less energetic decomposition takes place than at a lower
temperature. At a lower temperature the formate should give carbon monoxide
and hydrogen; at higher temperatures however, only hydrogen.
I believed myself to be justified in adopting the opinion that the reaction, under all
circumstances even at higher temperatures-takes place in a different manner
to that indicated by the generally accepted hypothesis, i.e. according to equation (a),
and that the formation of sodium oxalate takes place in a secondary reaction, in
which the carbon monoxide generated, at the moment at which it is formed, attaches
itself to the already formed soda, thus
(c) Na2CO3 + CO
== Na2C2O4
I consider myself to be the more justified in forming this opinion by reason of
the well-known enormous affinity or combining power of carbon monoxide, (for
example, Beilstein, Org. Chemie, II. Edition, Vol. 1, p. 87.)
The hypothesis that the carbon monoxide, on heating the formate, first fixes
itself to the previously-formed soda, is also in the fullest accordance with the fact
that, in all the experiments which were made by Merz and Weith, there is
not a single one in which very considerable quantities of alkali carbonate
were not formed. The generally accepted equation (b) does not offer any explana-
tion of this fact.
If however the opinion of the inventor as to the course of the decomposition of
the formate be correct, it is not, impossible that the addition of already prepared
:

page_text: carbonate to the formate to be converted into oxalate, would increase the yield of
oxalate, for there would then be a carbonate already present, to which the carbon
monoxide could fix itself as it is set free. The combination with the carbonate can
then take place immediately, as soon as the formate gives off carbon monoxide,
whilst otherwise a certain quantity of carbon monoxide first escapes until sufficient
soda is formed as is required for fixing the carbon monoxide.
As was established by a suitable experiment, the at first extremely surprising
result was obtained, viz. that the mixture of soda and sodium formate, even
without forced, fierce heating, gave the quantitative yield of oxalate. Moreover, it
was generally unnecessary to raise the temperature to 440°, the reaction being
perfectly complete at 360° C.
Remarkable as these last facts at first appeared, their explanation is equally
simple, formate is decomposed at 360° C. into carbon monoxide and carbonate.
The nascent carbon monoxide has the property of fixing itself to the carbonate or,
which is the same thing, of being absorbed by the carbonate. The capacity of the
carbonate for absorbing carbon monoxide is very great at 440° C. At 360° C.
this capacity of absorption already exists, although in a less degree than at 440° C.
If however, one absorbent absorbs less strongly than another, it is necessary, in order
to effect complete absorption, to use larger quantities of this less strongly absorb-
ing substance. At 360° C. consequently, larger quantities of soda must be present
for the complete absorption of the carbon monoxide, than are necessary at 440° C.
and inversely, Merz and Weith, who did not have sufficient soda, must endeavour
to attain the temperature of 440° C. as rapidly as possible in order that the CO
shall not pass unabsorbed into the air.
By the addition of soda consequently, the forced, fierce, very rapid heating is
rendered unnecessary, and thus the technical preparation of oxalates from formates is
rendered possible in a very simple and beautiful manner.
The formate is simply very intimately mixed with soda (4 parts of crystallized
sodium formate and 5 parts of anhydrous sodium carbonate or an equivalent
proportion of crystallized soda have been found advantageous), and the mixture
(contained, when in small quantities, in glass flasks or retorts and, when in larger
quantities, in iron vessels preferably provided with stirrers to ensure uniform
heating), is heated in a bath (lead) of from 400 to 410 degrees C. Exclusion of the
air is advantageous, since this permits the escaping hydrogen to be carried off and
allowed to pass through water so that the course of the reaction can be observed,
the said hydrogen being, if desired, still further used or collected.
The formation of oxalate by heating formate takes place fairly rapidly after
starting; it should be completed in about 30 to 45 minutes. The evolution of
hydrogen is sometimes very rapid. When this ceases, the reaction is complete.
The mass produced in the reaction then contains oxalate and carbonate, the separation
of which can be effected very easily by reason of the great difference which exists
between the solubilities of the two salts in water. For this purpose, water, preferably
at a temperature of 33° C., is employed, since this, as is known, possesses the
highest capacity of dissolving soda, and of this water a quantity about double that
of the soda present is employed. The solution of soda so obtained, which is
absolutely colourless, and does not contain a trace of colouring or dirty matter (as
it does in the manufacture of oxalates from saw-dust or shavings), is evaporated to
dryness. The dry soda can be used as above mentioned in further operations.
The sodium oxalate (after being freed from soda) which is likewise perfectly white,
can be further manufactured into oxalates and oxalic acid in the known manner
used in oxalic acid works, by means of milk of lime. The manufacture of oxalic
acid can also be combined with the manufacture of formates protected by my afore-
said former patent, in the simplest manner; it is therefore possible to convert the
carbon monoxide into a solid either in the form of formic acid or of oxalic
acid.
The advantages which therefore result from heating a mixture of carbonate and
formate for obtaining an oxalate, over the open heating of formate, and which

page_text: render possible the preparation of oxalates from formates for technical purposes
for the first time, are briefly the following, viz. —
(1). Increase in the yield to the quantity obtainable theoretically;
(2). The necessity is obviated of using forced and fierce heating, for industrial
manufacture, which, if it became general, could only be effected by the most
complicated apparatus;
(3). The application of a lower temperature with all the economies resulting
therefrom;
(4). The overheating due to the bad thermal conductivity of the formates and
the disadvantages incidental thereto are avoided.
Having now particularly described and ascertained the nature of my said in-
vention, and in what manner the same is to be performed, I declare that what I
claim is :-
The preparation of oxalates by heating a mixture of formates with carbonates.
ted the 8th day of August 1898.
D. YOUNG & Co.,
11 and 12, Southampton Buildings, London, W.C.,
Agents for the Applicant.