CA1113490A

CA1113490A - Process for the preparation of esters of oxalic acid

Info

Publication number: CA1113490A
Application number: CA275,911A
Authority: CA
Inventors: Giovanni Agnes; Guglielmo Rucci; Giuseppe Bimbi; Franco Guerrieri
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1976-04-12
Filing date: 1977-04-07
Publication date: 1981-12-01
Also published as: NL187265B; FR2348185A1; DE2716170C2; BE853505A; FR2348185B1; JPS52125112A; NL7703845A; IT1059066B; DE2716170A1; ES457704A1; JPS6045173B2; GB1567377A; NL187265C

Abstract

ABSTRACT OF THE DISCLOSURE:

The present invention concerns a process for the preparation of an ester of oxalic acid. More particularly, the present invention relates to a catalytic process for the prep-aration of esters of oxalic acid by the reaction of carbon mon-oxide with alcoxyl copper salts in the presence of palladium salts. The esters prepared according to the present invention may be converted to the acid according to traditional techniques (e.g. hydrolysis. The acid or the oxalic esters are of consider-able industrial interest. Oxalic acid may find its use in the field of the textile industry as an auxiliary stripping agent in the dyeing of wool, as bleaching agent for natural fibres or as pickling agent for metal surfaces, especially for copper. In industry, it is also known for its use as dehydrogenating agent in condensation reactions. Finally, the esters are known solvents, such as, for instance, the diethylester for cellulose.

Description

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.

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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, 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 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.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Process for the preparation of esters of oxalic acid by oxidative reaction in the presence of palladium based catalysts, characterized in that the oxalic esters are obtained by the reaction of a copper (II) compound, having the formula Cu(OR)X, wherein R represents a radical selected from among alkyls having from 1 to 8 carbon atoms, and X is chosen from between chlorine and bromine atom, with carbon monoxide in the presence of a catalyst selected from the group consisting of Pd salts, metal Pd and zero valent Pd complexes, at a temperature comprised between 20° and about 200°C.

2. Process according to claim 1, characterized in that the catalyst consists of a Pd containing component selected from the group consisting of Pd halides, Pd nitrate, Pd acetate, Pd sulphate and Pd acetylacetonate, Pd on carbon and Pd com-plexes with phosphines and/or with dibenzylidene-acetone.

3. Process according to claim 1, characterized in that the catalyst consists of Pd acetylacetonate.

4. Process according to claim 1, characterized in that the copper (II) compound is Cu(OR)X, wherein R is a radical selected from the group consisting of alkyls having from 1 to 4 carbon atoms and X is either a chlorine or a bromine atom and preferably R is methyl and X is a chlorine atom.

5. Process according to claim 1, characterized in that the reaction is conducted in a substantially anhydrous medium selected from the group consisting of monofunctional alcohols of formula ROH, wherein R is an alkyl having from 1 to 4 carbon atoms, benzene, acetone, ethylacetate, tetrahydrofurane and/or mixtures thereof.

6. Process according to claim 1, characterized in that an anhydrous medium is selected from the group consisting of methyl and ethyl alcohol.

7. Process according to claim 1, characterized in that the molar ratio of Pd in respect of the copper compound Cu(OR)X is comprised between 0.0001 and 0.1 mols of Pd per 1 mol of copper compound.

8. Process according to claim 1, characterized in that the reaction is conducted between about 50° and 120°C.

9. Process according to claim 1, characterized in that the reaction is conducted under partial CO pressures comprised between atout 10 and 100 atm.

10 . Process according to claim 1, characterized in that the carbon monoxide is fed in admixture with gases inert under reaction conditions, preferably in admixture with H2 coming from the industrial preparation of the synthesis gas.