DE2936700A1 - METHOD FOR SELECTIVE CATALYTIC HYDRATION OF OXAL ACID DIESTERS - Google Patents

Description

DR. STEPHAN G. BESZiDES PATENT ADVOCATE

-ζ-

AUTHORIZED REPRESENTATIVE AT THE EUROPEAN PATENT OFFICE

PROFESSIONAL REPRESENTATIVE ALSO BEFORE THE EUROPEAN PATENT OFFICE

DACHAU NEAR MÖNCHEN

PO Box 1 168

MDNCHENER STRASSE 8OA Federal Republic of Germany TELEPHONE: DACHAU 4371 Postal checking account Munich (BLZ 700 100 BO)

Account No. 1 368 71

Bank account no. 906 370 at the district and city Sparkasse Dachau Indersdorf (BLZ 700 515 40)

(VIA Bayerische Landesbank

Girozentrale. Munich)

P 1 240

description

for patent application

MONTEDISON S.p.A.

Milano, Italy

concerning

Process for the selective catalytic hydrogenation of oxalic acid diesters

The invention relates to a process for the selective catalytic hydrogenation of oxalic acid diesters. In particular it relates to a process for the selective catalytic hydrogenation of oxalic acid diesters, by which it is possible, both the semi-hydrogenated products glycolic acid ester and the fully hydrogenated product ethylene glycol selectively to obtain.

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293670Q

Glycolic acid, for its part, is known from the glycolic acid esters by conventional methods such as hydrolysis.

The products to be manufactured glycolic acid esters and from them glycolic acid and ethylene glycol are important Compounds with widely known technical or industrial applications of considerable Interest.

Glycolic acid and its esters are used as agents in the dyeing and tanning of hides, in the field of Dyeing of textiles, soldering or welding and in the fields of adhesives and detergents.

Ethylene glycol, in turn, is a well-known technical or industrial mass product and its applications of those for coolants, e.g. for engines, and hydraulic fluids or pressure fluids, for example for brakes, to those for polyester fibers in the textile field, for solvents, for example for cellulose esters and resins, as well as for paints, resins and adhesives.

Therefore, several processes for the production of glycolic acid or glycolic acid esters and in particular of ethylene glycol, for example for the production of glycolic acid from formaldehyde and carbon dioxide in an acidic medium and for the production of ethylene glycol from ethylene oxide, are known.

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Processes for the production of ethylene glycol by catalytic hydrogenation of oxalic acid diesters have also been specifically developed described.

So is the hydrogenation of oxalic acid diesters or of glycolic acid and its esters up to Achievement of ethylene glycol in the presence of catalysts based on copper and zinc chromates and -chromites, based on copper and aluminum, based on copper oxides and oxides of others Metals and based on Raney nickel at high temperatures of the order of 3OO ° C and below Known hydrogen pressure in the vapor phase. These procedures the temperatures are essentially in the vapor phase and under severe or drastic operating conditions and pressures performed. As a result, these procedures are in reality because of the troublesome and laborious Operating conditions and low yields, which also adversely affect the economy, of limited Interest.

Process for the hydrogenation of oxalic acid diesters in the liquid phase for the optional and selective production of glycolic acid esters and ethylene glycol were against it not yet described.

The invention is based on the object, while eliminating the disadvantages of the prior art, a simple and Economical process for the selective catalytic hydrogenation of oxalic acid diesters, which is optionally selective predominantly leads to ethylene glycol or selectively predominantly to glycolic acid esters.

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The above has surprisingly been achieved by the invention.

The invention is a method for selective catalytic hydrogenation of oxalic acid diesters of the general formula

OO Il Il

B ₁ -OCCOB ₂ I,

where B ^. and Bp independently of one another for alkyl radicals with 1 to 8 carbon atoms, alkoxy radicals with Λ to 6 carbon atoms or aralkyl radicals, preferably substituted with 1 to 6 carbon atoms, amino groups, carboxyl groups and / or cyano groups, optionally substituted by 1 or more alkoxy radicals which are inert under the fieaktionsbedingungen Phenylalkyl radicals with alkyl parts with 1 to 3 carbon atoms, in particular benzyl radicals, are represented by gaseous hydrogen in the presence of at least 1 catalyst, which can also be one based on Raney nickel, which process is characterized in that the hydrogenation in a temperature of about 40 to 25O ° C is carried out, wherein a catalyst based on ruthenium, nickel and / or Raney nickel is used.

It is thus possible, through a suitable choice of the operating conditions, to produce the products of the partial hydrogenation of the Oxalic acid diesters, namely the corresponding glycolic acid esters in which only 1 of the ester groups of the oxalic acid diester is hydrogenated, as well as the product of complete hydrogenation, namely ethylene glycol, to be selectively obtained.

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The general reactions of the process according to the invention can be _{represented by the following reaction schemes for the case that R ^ «R 2} (in this case this is denoted by R in the following):

030013/0776

OO

Il 11 * ♦ ι * Il

a) HOCCOH + 2H ₅ rOCC-OH + B-OH

^{2 H} 2

"■ * ■ 0

b) ROCCOR + AH _{2 Ηο} _ _c _ _c _ ₀ Η + 2 R-OH

H ₂ H ₂

In these, R can have the meanings of R ,. or Rp have, where preferred meanings are the alkyl radicals with 1 to 8 carbon atoms and alkoxy radicals with 1 to 6 Are carbon atoms. In the event that R- is different from R ^ is, mixtures of corresponding glycolic acid esters are obtained in the reaction a).

As a by-product of reactions a) and b) is a Alcohol of the general formula R-OH is obtained, which is separated off and subjected to a conventional carbonylation process can be returned to an integrated cycle to achieve oxalic acid diesters in the circuit.

The inventive method brings the special The advantage is that there is a high selectivity for the hydrogenation of the oxalic acid diester when im essentially predominantly glycolic acid esters or ethylene glycol results.

Another advantage of the process according to the invention is the reaction conditions, which in comparison are milder than those of the prior art and in any case of considerable interest to the art.

The preferred oxalic acid diester is oxalic acid dimethyl ester, oxalic acid diethyl ester, oxalic acid di (n-butyl) - -ester or oxalic acid di (2-methoxyethyl) ester used, as these were found to be the most effective.

The catalysts specified above can either be in the form of the metals as such or in the form of salts or derivatives other than salts can be used. Advantageously, as a catalyst on the basic

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location of ruthenium and / or nickel metallic ruthenium and / or metallic nickel and / or 1 or more of the Chlorides, nitrates, carbonates, oxides, hydroxides and / or salts with organic acids, in particular acetates and / or Acetylacetonate, the same or the same are used.

The weight ratio of the active part of the catalyst to the oxalic acid diester is necessary for proper hydrogenation not critical in the process according to the invention. It is but advantageous, the molar ratio of the active part of the catalyst to the oxalic acid diester to 1: 1 000 to 1: 10 to choose.

The metals and metal compounds serving as catalysts can be used alone or on conventional supports, in particular carbon, silicon dioxide, kieselguhr or aluminum oxide or a mixture thereof, while the catalysts can be applied to the supports by conventional methods, for example by impregnation or precipitation. Preferably, the catalyst used is one which advance in a stream of hydrogen at a temperature of about 300 to 500 ⁰ C by substantially herköi
has been activated.

500 ⁰ C according to essentially conventional procedures

For example, effective supported nickel and ruthenium catalysts may have been prepared as follows: The carrier is with an aqueous solution of a nickel salt and / or ruthenium salt, such as chloride or Nitrates, impregnated, with successively 1 or more impregnations until the desired concentration of the active part is achieved on the carrier.

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leads to be. Then, the catalyst in an oven at about 120 ° C is dried and activated 2 hours at about 300 to 500 ⁰ C in a stream of hydrogen.

Similarly, the Raney nickel catalyst according to conventional Procedures, for example according to H. Adkins - Reaction of Hydrogen - Univ. of Wisconsin, 1937 edition »page 20.

The catalyst can be used depending on the operating conditions used, i.e. depending on whether in the liquid phase or working in the gas phase, in suspension or respectively can be used in fixed bed or fluidized bed. In general, in this regard, in more conventional Proceeded wisely.

The method according to the invention offers a broad one Range of possibilities of operation. As already mentioned, it can be in the liquid phase as well carried out with advantage in the gas phase by suitable choice of the temperature, the operating pressures and the catalyst will.

Thus, according to an advantageous embodiment of the method according to the invention, in the liquid phase a hydrogen pressure of at least about 10 atm at the specified temperatures. Preferably temperatures of 60 to 200 ° C and pressures of about 40 to 150 atm are used.

According to a special expedient embodiment the method according to the invention is used to control the implementation on the selective achievement of predominantly

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Glycolic acid esters worked out at temperatures of about 40 to 150 ^° C., the above pressures being used.

According to another particular advantageous embodiment of the inventive method of conversion to the selective obtaining of ethylene glycol is used for controlling primarily worked out at temperatures greater than about 13O ⁰ C, whereby the above pressures are applied.

The reaction in the liquid phase can be in the absence or be carried out in the presence of solvents. As a solvent can advantageously 1 or more mono- or polyfunctional aliphatic or cycloaliphatic alcohols with up to 10 carbon atoms or linear or cyclic ethers or polyethers or mixtures of these can be used. as aliphatic alcohols, primary, secondary or tertiary alcohols can be used. Preferably will as solvent (s) methyl alcohol, ethyl alcohol, n-propyl alcohol, n-butyl alcohol, cyclohexyl alcohol, sec-butyl alcohol, tert-butyl alcohol, on alcohol of the general formula

B ¹ - 0 1 (C \ OH II

wherein B 'is an alkyl red having from 1 to 10 carbon atoms and η and m are integers from 1 to 10, such as ethylene glycol monoethyl ether (Cellosolve), ethylene glycol, Propane-1,2-diol, propane-1,3-diol, a butylene glycol or

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Glycerin or a mixture of these is used. Preferably the [r] ether serving as a solvent is one of the general formula

Ε · · _ ο - E "'III

wherein E ¹ · and R ¹ 'are independently ■ Aklylreste or cycloalkyl radicals having up to 10 carbon atoms, in particular diethyl ether, di-n-propyl ether or ethyl n-butyl ether, a P _o lyäther of the general formula

_R i ι ₀ _ / _c ν ___ 0 - R ¹ "IV

where R ", R", m and η are as defined above, in particular a dimethyl ether of mono-, di- or triethylene glycols, the cyclic ether tetrahydrofuran, the cyclic polyether dioxane or a crown ether or a mixture of such is used.

If solvents are used, the reaction can be carried out under concentration conditions, depending on the choice will. In any case, the concentration values are not critical for the implementation.

Similarly, the reaction times can be varied within a wide range depending on the other parameters used and the stirring effect. Response times of the order of 30 minutes are sufficient.

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At the end of the reaction, the reaction products can after conventional procedures, for example by fractional distillation under reduced pressure, easily be separated.

According to another advantageous embodiment of the The process according to the invention is carried out in the gas phase at a temperature of about 80 to 200 ° C. under a hydrogen pressure at least atmospheric pressure and with contact times of at least 0.1 second. In general contact times between the oxalic acid diester and the catalyst of 0.1 to 10 seconds are used. Usually contact times of 0.5 to 1 second are sufficient.

The products obtained can also be separated during the reaction in the gas phase by conventional procedures be performed. So the vapors can be collected, condensed and distilled, if necessary under Recirculation of the hydrogen and alcohol.

The hydrogen can be used as such or in a mixture with inert gases such as nitrogen, advantageously in the range of partial pressures given above.

The invention is explained in more detail by means of the following examples.

030013/0776

example 1

It was in a stirrer with tetrafluoroethyl enrührflü ge In or -rührschaufeln and with a polytetrafluorethylene sheath for a thermocouple vertical 1 1 steel autoclave inserted a beaker, which was fixed to the autoclave walls by means of an asbestos cover.

The following materials were placed in this container brought in:

15 β (74 millimoles) di (n-butyl) oxalate

80 cm ethylene glycol monomethyl ether

(Methylcellosolve)

1 g of catalyst on ruthenium

Coal with a ruthenium content of 5% by weight, which has been activated ^{at 400 ° C. for 2 hours}

The autoclave was pressurized with hydrogen 140 atm set. It was heated to 180 ° C. and stirred at this temperature for 3 hours.

After cooling, the residual pressure was released. The solution filtered off from the catalyst was reduced under reduced pressure Distilled pressure.

The fraction passing over at 80 to 85 ° C / 15 mm Hg contained 4 g (65 millimoles) of ethylene glycol, which

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yield of 86.7% of theory, based on the amount used Oxalic acid di (η-butyl) ester, corresponds.

Example 2

The following were used in the autoclaves used in Example 1 according to the procedure described there Materials brought in:

15 6 (103 millimoles) diethyl oxalate

80 cm ethylene glycol monoethyl ether

(Ethyl Cellosolve)

2 g of ruthenium catalyst

Silicon dioxide with a ruthenium content of 5% by weight

The autoclave was pressurized to 160 atm with hydrogen and ^{stirred at a temperature of 180 °} C. for 3 hours.

The treatment described in Example 1 gave a fraction passing over at 60 to 85 ° C./15 mm Hg. It consisted of a mixture of the following composition:

2 g (32 millimoles) ethylene glycol 4 g (38 millimoles) glycolic acid ethyl ester

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This corresponds to a yield of 31 »1% of theory Ethylene glycol and a yield of 36.9% of theory of ethyl glycolate, ie a total yield of 68.0% of theory of desired products, based in each case on the diethyl oxalate used.

Example 3

The following were used in the autoclaves used in Example 1 according to the procedure described there Materials brought in:

20 g (97 millimoles) oxalic acid di (2-methoxyethyl) -

-ester

150 cm ⁵ 2- (methoxy) ethanol

2 g of the same ruthenium / carbon catalyst

as in example 1

The autoclave was pressurized to 160 atm with hydrogen and ^{heated to 170 °} C., the whole being stirred at this temperature for 1 hour.

By working as described in Example 1, 6.05 g (97 millimoles) of ethylene glycol were obtained, which is a yield of 100% of theory, based on the di (2-methoxyethyl) oxalate used.

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Example 4

The following were used in the autoclave used in Example 1 according to the procedure described there Materials brought in:

20 g (97 fiillimoles) of oxalic acid di- (2-methoxyethyl) -

-ester

150 cm * 2- (methoxy) ethanol

2 g of the same ruthenium / carbon catalyst

as in example 1

The autoclave was pressurized with hydrogen
120 atm and set to 120 ° C
Stirred for 2 booths.

120 atm and heated to 120 ° C, with the whole

By working as described in Example 1, the following products were obtained:

Traces of ethylene glycol

8.8 g (65 millimoles) glycolic acid (2-methoxyethyl) -

-ester

^ »5 g (22 millimoles) of unchanged oxalic acid

- (2-methoxyethyl) ester

This corresponds to a yield of 67.0% of theory
Glycolic acid (2-methoxyethyl) ester, based on the oxalic acid di (2-methoxyethyl) ester used.

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Example 5

There were in the autoclave used in Example 1 according to the procedure described there, the following Materials brought in:

20 g (97 millimoles) oxalic acid di (2-methoxyethyl) -

-ester

150 cnr of ethy] englyco? "Monomethyl ether

2 g of the same ruthenium / carbon catalyst

as in example 1

The autoclave was pressurized to 120 atm with hydrogen and pressurized to 170 ⁽
Was stirred for 1 hour.

120 atm and heated to 170 ° C, with the whole

By working as described in Example 1, the following products were obtained:

4.2 g (68 millimoles) ethylene glycol

3Λ B (25 millimoles) glycolic acid (2-methoxyethyl) -

-ester

This corresponds to a yield of 70.1% of theory Ethylene glycol and 25.8% of theory glycolic acid (2-methoxyethyl) ester, that is to say a total yield of 95 »9% of theory of the desired products, based in each case on the products used Di (2-methoxyethyl) oxalate.

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The catalyst coming from this run was filtered off and used both for one with the previous run The experiment was identical with regard to the operating conditions and the number of participants.

By the aforementioned usual treatment, the following products were obtained:

4 grams (65 millimoles) of ethylene glycol

3.6 g (27 millimoles) glycolic acid (2-methoxyethyl) -

-ester

This corresponds to a yield of 67% of theory Ethylene glycol and 27.8% of theory glycolic acid (2-methoxyethyl) ester, ie a total yield of 94.8% of theory of desired products, each based on the di- (2-methoxyethyl) oxalate used.

The filtered catalyst was subjected to the same number of tests 4 times in which the reactant amounts and the experimental conditions were the same as those given above. Each of these attempts delivered ethylene glycol in yields of 60 to 70% of theory and glycolic acid (2-methoxyethyl) ester in Yields of 30 to 40% of theory, based in each case on the di (2-methoxyethyl) oxalate used. this shows that there was no appreciable deterioration of the catalyst in these tests.

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030013/0776

Example 6

The following were used in the autoclaves used in Example 1 according to the procedure described there Materials brought in:

20 g (99 millimoles) of di (n-butyl) oxalate

1 g of the same ruthenium / carbon catalyst

as in example 1

The autoclave was pressurized with hydrogen to a pressure of 50 atm and heated to 1J0 ° C, the whole 2 h \ ei this temperature was stirred.

By working as described in Example 1 were receive the following products:

9.2 g (70 millimoles) of glycolic acid (n-butyl) ester

7 6 (35 millimoles) unchanged oxalic acid

- (n-butyl) ester

Traces of ethylene glycol

This corresponds to a yield of 70.7% of theory Glycolic acid (n-butyl) ester, based on the oxalic acid di (η-butyl) ester used.

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Example 7

The following were used in the autoclaves used in Example 1 according to the procedure described there Materials brought in:

15 g (73 millimoles) of di (n-butyl) oxalate

2 g of the same ruthenium / carbon catalyst

as in example 1

30 cm dimethoxyethane

The autoclave was pressurized with hydrogen 40 f-n set and heated to 1 ^ 0 C, with the whole Was stirred for 5 hours at this temperature.

Purch as described in Example 1 were working receive the following products:

8 g (61 millimoles) of glycolic acid (n-butyl) ester

2 g (10 millimoles) of unchanged oxalic acid

- (η-butyl) ester

Traces of ethylene glycol

This corresponds to a yield of 83 ~ 6% of theory Glycolic acid (n-butyl) ester, based on the oxalic acid di (η-butyl) ester used.

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-4ΤΛ -

Example 8

The following were used in the autoclaves used in Example 1 according to the procedure described there Materials brought in:

10 g (68 millimoles) diethyl oxalate

2 g of the same ruthenium / carbon catalyst

as in example 1

30 cm tetrahydrofuran

The autoclave was pressurized to 40 atm with hydrogen and the whole was kept at for 8 hours Stirred 130 ° C.

After the treatment described in Example 1, a fraction now passing over at 60 to 70 ° C./15 was obtained. It consisted of 7 g (67 millimoles) of ethyl glycolate, which is a yield of 98.5% of theory, based on the diethyl oxalate used.

Example 9

There were in a glass vial respectively a Glass vial placed the following materials:

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10 g (49 millimoles) oxalic acid di (2-methoxyethyl) -

-ester

30 cm ethylene glycol monoethyl ether

(Ethyl Cellosolve)

5 g of catalyst made of nickel

Kieselguhr (50% by weight nickel),

which for 2 hours at 400 ° C with hydrogen has been activated

The glass vial was placed in a vibrating autoclave. The autoclave was pressurized to 160 atm with hydrogen and heated to 180.degree. That Shaking was carried out for 10 hours.

By working as described in Example 1, the following products were obtained:

2.1 g (34 millimoles) ethylene glycol

3 g (15 millimoles) of unchanged oxalic acid

- (2-methoxyethyl) ester

This corresponds to a yield of 69 »4% of theory Ethylene glycol, based on the oxalic acid used - (2-methoxyethyl) ester.

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Example 10

There were 3 g of a catalyst, consisting of 5 wt .-% ruthenium on aluminum oxide, which previously has been activated by a 2 hour treatment with a hydrogen stream at 300 ° C, in a glass reaction device for the catalysis in the gas phase, which was provided with a partition frit, introduced.

The reaction device was placed in a muffle furnace maintained at a temperature of 160.degree.

There was a hydrogen flow of 5 l / hour through a. Oxalic acid diethyl ester containing ^{vessel kept at a temperature of 95 0} C allowed to bubble through. The hydrogen stream saturated with the oxalic acid diethyl ester was passed over the catalyst.

The residence time of the gas mixture in the reaction device was 0.8 seconds.

At the outlet of the reaction device there was a trap kept ^{at 0 ° C.}

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90 minutes after the start of the experiment, the 1 g of liquid separated in the trap is collected and analyzed by gas chromatography. It turned out that they consist of 0.7 g of diethyl oxalate and 0.2 g of ethyl glycolate country consisted of 0.1 g of ethyl alcohol.

Compare example

The device described in general example 9 was used introduced the following materials:

10 g (49 millimoles) oxalic acid di (2-methoxyethyl) -

-ester

30 cm ethylene glycol monoethyl ether

(Ethyl Cellosolve)

3 g conventional catalyst,

consisting of copper chromite

(The Raney nickel catalyst is after H. Adkins, Reactions of Hydrogen - University of Wisconsin, 1937 Edition »page 12 been)

The autoclave was pressurized to 160 atm with hydrogen and heated to 180 ° C, the whole Was stirred for 10 hours at this temperature.

03001 3/0776

By working as described in Example 1, the following products were obtained:

1.07 8 W millimoles) ethylene glycol

1 »3 β (^ O millimoles) glycolic acid (2-methoxyethyl)

-ester

Traces of unchanged oxalic acid

- (2-methoxyethyl) ester

This corresponds to a yield of 34.7% of the theoretical ethylene glycol and 20.4% of theory glycolic acid (2-methoxyethyl) - -ester, i.e. a total yield of 55 »1% of theory, each based on the di- (2-methoxyethyl) oxalate used.

The gases discharged from the autoclave also contained methane and carbon dioxide.

Claims

030013/0776

Claims (16)

Claims Method of selective catalytic
... hydrogenation of oxalic acid diesters of the general formula O O R ₁ -OCCOR ₂ wherein R. and Rp are independently of one another
optionally by 1 or more among the
Söaktionsbedingungen inert alkoxy groups, amino groups, carboxyl groups and / or cyano groups
substituted, alkyl radicals with 1 to 8 carbon atoms, alkoxy radicals with Λ to 6 carbon atoms or aralkyl radicals, by gaseous hydrogen in the presence of at least 1 F-italy s at or, which can also be used on the basis of Raney nickel, characterized in that the hydrogenation
at a temperature of about 4-0 to 250 C carried out, with a catalyst based on ruthenium, nickel and / or
Raney nickel used. 030013/0776 -Sf- 2.) Method according to claim 1, characterized in that that as oxalic acid diester, oxalic acid dimethyl ester, oxalic acid diethyl ester, oxalic acid diester - (n-butyl) ester or oxalic acid di (2-methoxyethyl) - -ester used. 3.) Method according to claim 1 or 2, characterized in that that there is metallic as a catalyst based on ruthenium and / or nickel Ruthenium and / or metallic nickel and / or 1 or more of the chlorides, nitrates, carbonates, Oxides, hydroxides and / or salts with organic acids, in particular acetates and / or acetylacetonates, the same or the same used. 4-.) Method according to claim 1 to 3> characterized in that the molar ratio of the active part of the catalyst to the oxalic acid diester is added Selects 1: 1,000 to 1:10. 5.) Method according to claim 1 to 4, characterized in that that the catalyst is on an inert support, in particular charcoal, silicon dioxide, Diatomaceous earth or aluminum oxide or a mixture thereof is used. 6.) Method according to claim 1 to 5 »characterized in that that one as a catalyst, which in a hydrogen stream at a Temperature of about 300 to 500 ° C has been activated is used. - 28 030013/0776 - -28 - 7 ·) Method according to claim 1 to 6, characterized that the catalyst is used in suspension. 8.) Process according to claim 1 to 6, characterized in that the catalyst is in a solid layer or used in fluidized bed. 9.) Process according to claim 1 to 8, characterized in that one is in the liquid phase under a Hydrogen pressure of at least about 10 atm works, 10.) The method according to claim 1 to 9 »characterized in that one uses a temperature of about 60 to 200 ⁰ C and a pressure of about 40 to 150 atm. 11.) Process according to claim 1 to 10, characterized in that one is used to control the implementation on the selective achievement of predominantly glycolic acid esters at temperatures of about 40 to 150 ° C works. 12.) The method according to claim 1 to 10, characterized in that one works to control the reaction to the selective achievement of predominantly ethylene glycol at temperatures of more than about 130 ^O C. 13 ·) Method according to claim 1 to 12, characterized in that that in the presence of 1 or more monofunctional or polyfunctional aliphatic or cycloaliphatic alcohols with up to - 29 030013/0776 to 10 carbon atoms or linear respectively cyclic ethers or polyethers or a mixture of such as Solvents) works. 14.) Method according to claim 1 to 13 »characterized in that that serving as a solvent [n] alcohol (s) methyl alcohol, ethyl alcohol, n-propyl alcohol, n-butyl alcohol, cyclohexyl alcohol, sec-butyl alcohol, tert-butyl alcohol, an alcohol of the general formula R '- 0 II wherein R ^{1 is} an alkyl radical having 1 to 10 carbon atoms and η and m are integers from 1 to 10, ethylene glycol, propane-1,2-diol, propane-1,3-diol, a butylene glycol or glycerol or a mixture of such used. 15.) The method according to claim 1 to 14, characterized in that that an ether of the general formula is used as the solvent R ¹ · - 0 - R ¹ III 030013/0776 where R "and R ¹ " independently of one another represent alkyl radicals or cycloalkyl radicals with up to 10 carbon atoms, in particular diethyl ether, di-n-propyl ether or ethyl-n-butyl ether, a polyether of the general formula 0 - R ¹ · 'IV where R ¹ 'and R''· are as defined above and η and m are integers from 1 to 10, in particular a dimethyl ether of mono-, di- or triethylene glycols, tetrahydrofuran, dioxane or a crown ether or a mixture of these are used. 16.) The method according to claim 1 to 8, characterized in that in the gas phase at a Temperature of about 80 to 200 ° C under a hydrogen pressure of at least atmospheric pressure as well as with contact times of at least 0.1 seconds. 030013/0776