Note: Descriptions are shown in the official language in which they were submitted.
34~
It is known to prepare oxalic esters by oxidative
reaction of carbon monoxide and monobasic alcohols with oxygen
and also with quinones, preferably in a substantially anhydrous
medium, anhydrous for the presence of dehydrating substances,
and catalized by Redox-systems in general consisting of the
finely subdivided metal or of soluble salts or complexes (citrates,
kelates) of a noble metal of the Pt group, such as, for instance,
Pd, Os, and of a salt and/or a complex of another metal more
electropositive than the previous ones, such as Fe, Co, Ni, Cu,
Mn, etc., such as chlorides, acetates, etc., possessing several
oxidative states.
The reaction is preferably conducted in the presence
of co-catalysts and/or complexing agents consisting of soluble
salts of alkaline metals (e.g., LiCl, KCl, etc.).
Nevertheless, processes of this type, because of the
simultaneous occurrence of secondary reactions leading to the
formation of carbonates, CO2, esters-(acetates, phormiates,
etc.), cannot be considered fully satisfactory from the indus-
trial point of view owing to the low yields and for the rela-
tively burdensome separation, purification, etc. operationsinvolved.
Moreover, the use of gaseous C0 ~ 2 mixtures with
the corresponding risk of explosions constitutes a further
serious obstacle to an industrial application.
On the other hand, also, the other processes of the
prior art, for instance, by dehydrogenation of the sodium for-
miate, subsequently converted to calcium oxalate, acidified,
- etc., or by oxidation of the propylene with HNO3 catalized by
Fe, Cr, etc., do not insure best results owing to the consid-
erable technological and operational difficulties involves
which make them little acceptable economically, especially for
the mass production.
- 1 - q~
^ -
1~13~
An object of this invention is that of providing a
simple and economical process for the preparation of esters of
oxalic acid that are free of the drawbacks of the art, and, in
particular, securing high yields and purity of the products,
representing a real progress over the technique of the art.
This and still other objects, which will appear more
clearly to the skilled in the art from the following description,
are reached according to this invention by a process for the
preparation of esters of oxalic acid, characterized in that the
oxalic acid esters are obtained by reacting a copper (II) com-
pound of the formula Cu(OR)X wherein R represents an alkyl
radical having from 1 to 8 carbon atoms, preferably an alkyl
radical having from 1 to 4 carbon atoms: X represents a chlorine
or bromine atom, preferably chlorine, with carbon monoxide in
the presence of at least a palladium salt or a zero-valent pal-
ladium compound, possibly in a substantially anhydrous medium,
at a temperature comprised between about 20 and 200C.
The process may be schematically represented by the
following equation :
COOR
(1) 2Cu(oR)x + 2coPd salt ~ ~ + 2 CuX
: COOR
wherein R and X have the above given meaning.
The invention should be considered so much the more
surprising, inasmuch as it represents a considerable overcoming
of a prejudice existing in the technique of the prior art, which
is quite explicit in teaching that copper compounds of the type
- 30 used in this invention, by reaction with CO lead, in the absence
of Pd and in similar parametric conditions, exclusively and
quantitatively to the corresponding diester of the carbonic acid,
according to the equation:
(2) 2 Cu(OR~X + CO ` CO(OR)2 + 2CuX,
-- 2 --
15 ~34~i~
wherein R and X have the already given meaning a prejudice
that obviously would have dissuaded the expert in the art to
undertake further research in that direction.
Oxalic esters are, at any rate, obtained by the reaction
of carbon monoxide with the alcoxy-cupric Cu(OR)X salt, wherein R
and X have the previously given meaning, in the presence of a
Pd-based catalyst, possibly in an inert solvent.
Catalysts that may be used in accordance with this
invention are Pd salts soluble in the reaction medium or mix-
tures thereof such as halides, sulphates, nitrates, acetylace-
tonate, acetates, etc., preferably Pd (acetylacetonate)2. It is
also possible to use metal Pd or complexes of zero-valent Pd
which are well known to the technician, such as Pd on carbon,
or Pd complexes with binders such as phosphines, dibenzylidene-
acetone, etc.
The molar ratio of palladium with respect to the
Cu(OR)X copper compound is preferably comprised between 0.0001
and 0~1 mols of Pd per 1 mol of the copper compound. Ratios
different from these are acceptable but are not necessary.
The inert reaction medium preferably consists of mono-
functional RO~ alcohols, wherein R has the meaning already given,
still preferably of methyl or ethyl alcohol, and/or of aliphatic
or aromatic hydrocarbons that are inert at the reaction condi-
tions, or mixtures thereof.
Just for indicative purposes, there have proved quite
effective mixtures containing up to 75-95% of benzene and 25-5%
of alcohol. Other inert solvents may be benzene, acetone,
ethylacetate, tetrahydrofurane.
The carbon monoxide, which may be by itself or in the
form of a synthetic gas combined with H2, is fed at a partial
pressure comprised between 1 and about 100 atm.
The useful reaction temperature ranges from 20 to
l~i3~
about 200C, but preferably is comprised between 50 and about
120C.
The reaction times may vary, depending on the temper-
ature and the pressure employed, within wide intervals.
Whenever desired, the use of C0 in admixture with
inert gases is admissible.
The yields in ester according to reaction (1) of this
process are practically quantitative with respect to the C0 and
the cupric compound, while Pd acts exclusively as the catalyst.
The separation of the reaction product from the solvent
and from the catalyst may be easily achieved by distillation,
etc., according to known techniques. From the ester the acid
is easily obtainable by hydrolysis according to conventional
methods.
The distillation residue, containing the CuX salt and
the catalyst, may be used for further reactions after the pre-
liminary regeneration of the cupric Cu(OR)X compound, according
to known methods, for instance, by oxidation with air and/or
oxygen in an ROH alcoholic medium, wherein R and X have the
repeatedly indicated meaning.
The Cu(OR)X compound may also be obtained accordiny
to another known method in the form of a complex with basic
organic binders, such as, for instance, pyridine and picoline,
and used as such, without any difficulty in the process reaction.
Because of the milder operational conditions, the
invention appears to be particularly convenient.
Other advantages consist in the selectivity for the
desired products and in the reasonable reduction of the opera-
tional risks of explosivity, in the absence of C0 + 2 mixtures.
Finally, of particular interest is the possibility of
using the mixtures of C0 and hydrogen, as such, produced during
the preparation of the synthesis gas, without thereby reducing
-- 4 --
1~34~
the effectiveness of the process.
The invention will now be described in more detail by
the following examples given for mere illustrative purpose not
limiting the wider scope of the invention.
Example 1
Into a stainless steel autoclave of 1 lt holding
capacity, fitted with a glass vial, were loaded: 30 ml of
methanol, 0.15 g of Pd(acetylacetonate)2 and 3.06 g of Cu(OCH3)Cl.
Thereupon there were loaded 100 atm. of CO, and the
temperature was brought up to 45C. The reaction mass was then
kept over 6 hours under stirring at the same temperature of 45C.
The raw reaction mass was then distilled, and there were o~tained
1.39 grams of methyl oxalate having a boiling point of 65-67C/12
mmHg and a melting point of 53C. The yield reckoned on the
reacted Cu(OCH3)Cl turned out to be 100%.
Exam~le 2
Proceeding in the same way as in Example 1, into the
autoclave were loaded : 25 ml of benzene, 5 ml of methanol, 3.43
grams of Cu(OCH33Cl, and 0.15 g of Pd(acetylacetonate)2. Under
the same operational conditions as in Example 1 there were ob-
tained 1.56 grams of methyl oxalate. Yield reckoned on the
reacted Cu(OCH3)Cl was 100%.
Example 3
Proceeding as in Example 1, into the autoclave were
loaded: 30 ml of methanol, 0.15 g of Pd(acetylacetonate)2, 3.15 g
of Cu(OCH3)Cl. Then there were fed 100 atm. of C0; thereafter
the autoclave wa~ left over 5 hour~ at room temperature. Th~reby
were obtained 1.43 g of methyl oxalate. The yield on the reacted
Cu(OCH3)Cl amounted to 100%.
Example 4
Proceeding as in Example 1, into the autoclave were
loaded: 30 ml of methanol, 0.15 g of Pd(acetylacetonate)2, and
~il3~
2.91 g of CU(OCH3)Cl. Thereupon there were fed 100 atm. of CO,
leaving then the autoclave at room temperature over 4 hours.
Thereby were obtained 1.08 g of methyl oxalate. The yield on
the reacted Cu(OCH3)Cl was 82%.
Exam~le 5
Proceeding as in Example 1, into the autoclave were
loaded: 30 ml of methanol, 0.15 g of Pd(acetylacetonate)2, and
3.12 g of Cu(OCH3)Cl. Thereupon into the autoclave were fed 12
- atm. of CO and the autoclave was then left at room temperature
over 11 hours. Thereby were obtained 1.41 grams of methyl
oxalate. The yield on the reacted Cu(OCH3)Cl was 100%.
Example 6
Proceeding as in Example 1, into the autoclave were
loaded:3 ml of methanol, 30 ml of C6H6 , 0.15 g of Pd(acetylace-
tonate)2 and 2.88 of Cu(OCH3)Cl. Thereupon there were fed 50 atm.
of CO and 50 atm. of H2, then bringing the temperature up
to 45C. The autoclave was then left at this temperature over
6 hours. There were obtained 1.10 g of methyl oxalate. The
yield calculated on the reacted CU(OCH3)Cl proved to be 85%.
Example 7
Proceeding according to Example 1, the autoclave was
loaded with: 2 ml of methanol, 30 ml of benzene, 0.15 g of
Pd(acetylacetonate)2, and 3.28 ~ of Cu(OCH3)Cl. Thereupon into
the autoclave were fed 5~ atm. of CO and 50 atm. of H2 and then
the whole was brought up to a temperature of 60C. The autoclave
was then left at this temperature over 2 hours. Thereby were
obtained 1.488 g of methyl oxalate. The yield, calculated on
the reacted Cu(OCH3)Cl was 100%.
Example 8
Proceeding as in Example 1, the autoclave was loaded
with: 30 ml of benzene, 0.15 g of Pd(acetylacetonate)2 and 2.88 g
of Cu(OCH3)Cl. Thereupon into the autoclave were fed 50 atm. of
~34~
C0 and the temperature was brought up to 45C. Then the auto-
clave was left at this temperature over 6 hourq. Thereby were
~btained 0.466 grams of methyl oxalate.
ExamDle 9
It was proceeded as in Example 8, except that the
temperature in the autoclave was 70C. There were obtained
, 1.174 g of methyl oxalate.
Exam~le 10
; It was proceeded as in Example 8, except that the
reaction time was 2 hours, Thereby were obtained 1.020 g of
methyl oxalate.
- Exam~le 11
It was proceeded in the same way as in Example 8.
except that instead of be~zene there was used acetone. There
were obtained 0.646 g of methyl oxalate.
. Exam~le 12
It was proceeded as in Example 8, except that instead
J of benzene there was used ethylacetate. There were obtained
0.656 g of methyl oxalate.
Example 13
.
It was proceeded as in Example 8, except that instead
of benzene there was used tetrahydrofurane. Thereby were ob-
tained 0.692 grams of methyl oxalate.
Exam~le 14
Proceeding as in Example 1, into the autoclave were
loaded : 30 ml of benzene, 2 ml of methanol, 0.15 g of Pd(acetyl-
acetonate)2 and 2.94 g of Cu~OCH3)Cl. Into the autoclave were
then loaded 50 atm. of C0 and the temperature was brought up to
60C. The autoclave was then left at this temperature over 2
30 hours. Thereby were obtained 1.390 g of methyl oxalate. The
yield on the reacted Cu~OCH3)Cl was 100%.
'lil34~
Example 15
Proceeding as in Example 1, but in the absence of
solvents, into the autoclave were loaded: 0.60 g of Pd(acetyl-
acetonate)2, 2.3 g of Cu(OCH3)Cl. The autoclave was then loaded
with 100 atm. of CO and the temperature was brought up to 60C.
The autoclave was then left at this temperature over 6 hours.
There were obtained 0.330 grams of methyl oxalate.
Example 16 (comparison example in the absence of catalysis)
Proceeding as in Example 1, the autoclave was loaded
with : 40 ml of methanol, 2.88 g of Cu(OCH3)Cl. Thereupon there
were fed in 100 atm. of CO and the temperature was brought up to
50C. It is then left at this temperature for 4 hours. No trace
of oxalate could be found.
Example 17
3.8 g of Cu(OCH3)Br were prepared "in situ" from
CuBr2 (5 grams) and CH30Na (1.2 grams) in 30 ml of methanol.
0.15 g of Pd(acetylacetonate)2 were then added. The autoclave
was then pressurized with CO at 50 atm. and was maintained at
45C over 6 hours, under stirring. Thereby were obtained 0.558
grams of methyl oxalate.
Exam~le 18
Proceeding as in Example 1, into the autoclave were
loaded: 2.9 g of Cu(OCH3)Cl, 30 ml of benzene, 2 ml of methanol,
and 0.15 g of Pd(acetylacetonate)2 and this mixture was then
maintained under stirring at 60C over 3 hours and under a pres-
sure of 5 atm. of CO. Thereby were obtained 0.93 g of methyl
oxalate.
Example 19
Into a glass flask, fitted with a magnetic stirrer,
were loaded 2.9 g of Cu(OCH3)Cl, 20 ml of benzene, 10 ml of
methanol and 0.15 g of Pd~acetylacetonate)2. The flask was
then degassed with a flow of CO and put into communication with
li~34~)
a C0 loaded buret. Stirring was then kept on over 10 hours main-
taining the reaction mixture at a temperature comprised between
50 and 60C. Thereby were obtained 0.54 grams of methyl oxalate.
Example 20
3.82 g of Cu(OC4Hg)Cl were prepared "in citu" from
3 g of CuC12 and 2.1 g of C4HgONa in 50 ml of butanol. The mass
was then diluted with 30 ml of benzene and additioned with 0.15
grams of Pd(acetylacetonate)2, whereupon one proceeded as in
Example 1, under a pressure of 50 atm. of C0 over 3 hours at
60C. There were thus obtained 1.65 g of butyl oxalate.
