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07-23-03 21:05
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      US Pat 5919349 Electrochemial Red. Org. Comps.
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US Patent 5,919,349

Electrochemical reduction of organic compounds


Abstract:
A process for the electrochemical reduction of an organic compound by bringing the organic compound into contact with a cathode, wherein the cathode comprises a support made of an electrically conductive material and an electrically conductive, cathodically polarized layer formed thereon in situ by alluviation.


Example 1:

Within a divided cell having an anode area and cathode area of 100 cm.sup.2 each, a filter plate was installed which was covered with a 50 .mu.m warp twill fabric of alloy steel material No. 1.4571 as the cathode. Via a separate filtrate line the filtrate can be discharged from a cavity underneath the filter fabric.

The anode employed was a titanium anode, designed to liberate oxygen and coated with Ta/Ir mixed oxide. The separating medium used was a NAFION-324 cation exchange membrane (commercially available from Du Pont). The divided cell was incorporated into a twin-circuit electrolytic apparatus equipped with pump circuits.

The conversion was carried out discontinuously in the following sequence:

1100 g of 5% strength aqueous sulfuric acid were used as the anolyte.

The catholyte was prepared by 5 g of vinclozoline (RS)-3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-oxazoline-2,4-dione! being dissolved in a mixture of 500 g of water, 375 g of methanol, 375 g of isobutanol and 65 g of acetic acid. The cathode circuit was charged with 1200 g of the catholyte batch.

According to a titrimetric assay, the catholyte batch prior to the reaction is chloride-free.

While the filtrate outlet was closed, 15 g of graphite powder were added into the circulating catholyte circuit and were dispersed in the circulation. Alluviation was effected by the catholyte circulation being shut and the filtrate outlet being opened. The pressure in the cathode compartment rose to 4.times.10.sup.5 Pa, and the filtrate throughput was 12 l/h. This was followed by 5 g of catalyst (Degussa Type E101N/D, 10% Pd on carbon) being additionally alluviated in the same manner. Over a period of 30 min, a DC current of 20 A was then imposed which required a cell voltage of 35 V at the outset and as much as 7.5 V at the end of the experiment.

According to a titrimetric assay, 850 ppm of chloride were detected in the output from the reaction, corresponding to a conversion ratio of 90%.

Analysis of the obtained product by means of gas chromatography confirmed the following conversion: ##STR9##


Example 2:

The following example, which relates to the reduction of adipodinitrile (ADN) to hexamethylenediamine (HDA), and the subsequent examples were carried out in the following apparatus.

Electrolytic cell: divided electrolytic cell of the flow-cell type

Membrane: NAFION-324

Anode: DeNora dimensionally stable anode (DSA) (anode area: 100 cm.sup.2)

Cathode: Armor chain of alloy steel material No. 1.4571 (cathode area: 100 cm.sup.2, pore size: 50 .mu.m)

Throughput: about 20 l/h through the cathode.

1200 g of 2% strength sulfuric acid were used as the anolyte.

The catholyte consisted of a mixture of 693 g of methanol, 330 g of H.sub.2 O, 22 g of NaOH, 55 g of adipodinitrile (0.509 mol) and 7.5 g of Raney nickel (BASF H.sub.1 -50).

The conversion was carried out as follows:

First the two cell compartments were charged, and then the Raney nickel was washed against the cathode over a period of 10 min.

Then the electrolysis was carried out at between 30 and 40.degree. C. with a current density of 1000 A/m.sup.2 at normal pressure. The electrolysis was stopped after 8.5 F/mol of ADN. After the NaOH had been separated off by means of electrolysis the product was isolated by distillation. 56 g (95% based on the amount of ADN used) of hexamethylenediamine were obtained.

Example 3:

The identical reaction apparatus, the identical anolyte and the identical catholyte as in Example 2 being employed, adipodinitrile was converted into 6-aminocapronitrile (ACN), the preparation of the cathode and the electrolysis being carried out in the same way as in Example 2, except that the electrolysis was terminated after only 4 F/mol of ADN. After the NaOH had been separated, followed by distillation, 38.7 g (0.34 mol, 68% of ADN) of aminocapronitrile, 16% of hexamethylenediamine and 14% of ADN were isolated. The selectivities were 79% for aminocapronitrile and 18.6% for hexamethylenediamine.

Example 4:

The next conversion was carried out employing the identical apparatus and the identical anolyte as in Example 2. The catholyte employed was a mixture of 110 g (0.92 mol) of acetophenone, 638 g of methanol, 330 g of water, 22 g of NaOH and 7.5 g of Raney nickel.

The preparation of the cathode and the conversion were carried out in the same way as in Example 2, except that the electrolysis was terminated after only 2.3 F/mol of acetophenone.

After dilution with water (1 l) the product was isolated by extraction with 5.times.200 ml of MTBE (t-butyl methyl ether), evaporation and distillation, and 101.3 g (yield: 90%, based on acetophenone) of 1-phenylethanol were obtained.

Example 5:

The reduction of 2-cyclohexanone to cyclohexanol was carried out employing the same apparatus and the same anolyte as in Example 2. The catholyte used was a mixture of 737 g of methanol, 330 g of water, 11 g of NaOH, 22 g of 2-cyclohexanone and 7.5 g of Raney nickel. The conversion was carried out as in Example 2, except that the electrolysis was terminated after 6 F/mol of 2-cyclohexanone. The output obtained was concentrated by distillation to 270 g, diluted with 500 ml of water and extracted with 5.times.200 ml of MTBE. The organic phase was then distilled, and 21.7 g of cyclohexanol were obtained, which corresponds to a yield of 95% based on 2-cyclohexanone.

Example 6:

This example was carried out in the same apparatus as in Example 2. 1100 g of 1% strength sulfuric acid were used as the anolyte. The catholyte consisted of a mixture of 418 g of methanol, 318 g of distilled water, 297 g of sodium methyl sulfate solution, 7.4% strength in methanol, 55 g of cyclohexanone oxime (0.487 mol) and 8 g of copper powder.

The conversion was carried out as follows:

First the cell compartments were charged, and then the copper powder was washed against the above cathode over a period of 10 min. Then the electrolysis was carried out at a temperature of between 30 and 50.degree. C. with a current density of 1000 A/m.sup.2 at normal pressure. An electrical charge of 12 F/mol was applied, based on the oxime used.

To work up the product, the catholyte was set to a pH of 13 with sodium hydroxide solution, the copper powder was filtered off, the filtrate was concentrated to 639 g and extracted 5 times with 100 g of MTBE each. After drying and removal of the solvent the crude product was distilled. 35.2 g of cyclohexylamine (73%, based on the oxime used) could be isolated as the reaction product.

Example 7:

This example was carried out in the same apparatus as in Example 2. 1100 g of 1% strength sulfuric acid were used as the anolyte. The catholyte consisted of a mixture of 418 g of methanol, 330 g of distilled water, 297 g of sodium methyl sulfate solution, 7.4% strength in methanol, 55 g of 2-butyne-1,4-diol (0.64 mol) and 15 g of Raney nickel (BASF H1-50).

The conversion was carried out in a manner similar to Example 6:

An electrical charge of 4.5 F/mol was applied, based on the diol used.

To work up the product, the catholyte was filtered, most of the filtrate was evaporated, and the crude product was distilled. 23 g of butanediol-1,4 and 12.4 g of 2-butene-1,4-diol could be isolated as the reaction product.

Example 8:

This example was carried out in the same apparatus as in Example 2. 1100 g of 1% strength sulfuric acid were used as the anolyte. The catholyte consisted of a mixture of 704 g of methanol, 330 g of distilled water, 11 g of sulfuric acid, 55 g of nitrobenzene (0.447 mol) and 8 g of copper powder.

The conversion was carried out in a manner similar to Example 6:

An electrical charge of 6.45 F/mol was applied, based on the substrate.

To work up the product, the catholyte was set to a pH of 13 with sodium hydroxide solution, the copper powder was filtered off, the filtrate was concentrated to 597 g and extracted 5 times with 100 g of MTBE each. After drying and removal of the solvent the crude product was distilled. 26.2 g of aniline could be isolated as the reaction product.

Example 9:

This example was carried out in the same apparatus as in Example 2, being modified in that an edge filter (pore size 100 .mu.m) made of alloy steel was employed as the cathode. 1100 g of 1% strength sulfuric acid were used as the anolyte. The catholyte consisted of a mixture of 806 g of methanol, 377 g of distilled water, 52 g of sodium hydroxide solution, 48 g of 2-thienylacetonitrile (0.391 mol) and 30 g of Raney nickel (BASF H1-50).

The conversion was carried out at 21.degree. C. and a current density of 1000 A/m.sup.2. The starting material was added in 14 batches. An electrical charge of 6.45 F/mol was applied, based on the substrate.

To work up the product, the nickel powder was filtered off, the catholyte was neutralized with sulfuric acid and the methanol removed by distillation. After the pH had been set to 13, extraction with MTBE was carried out. After drying and removal of the solvent the crude product was distilled. 37 g of thienylethylamine could be isolated as the reaction product.

Example 10:

This example was carried out in the same apparatus as in Example 2, being modified in that an edge filter (pore size 100 .mu.m) made of platinized titanium was employed as the cathode. 1200 g of 1% strength sulfuric acid were used as the anolyte. The catholyte consisted of a mixture of 651 g of ethylene glycol dimethyl ether, 651 g of distilled water, 28 g of sodium hydroxide solution, 70 g of 2-thienylacetonitrile (0.569 mol) and 50 g of Raney nickel (BASF H1-50).

The conversion was carried out at 23.degree. C. and a current density of 1000 A/m.sup.2. An electrical charge of 5.5 F/mol was applied, based on the substrate.

To work up the product, the nickel powder was filtered off, and the filtrate was admixed with 4% of sodium hydroxide and saturated with NaCl. Separation of the phases was followed by distillation. 45 g of thienylethylamine could be isolated as the reaction product.

Example 11:

This example was carried out in the same apparatus as in Example 2, being modified in that an edge filter (pore size 100 .mu.m) made of platinized titanium was employed as the cathode. 1200 g of 1% strength sulfuric acid were used as the anolyte. The catholyte consisted of a mixture of 882 g of methanol, 420 g of distilled water, 28 g of sodium hydroxide solution, 70 g of veratryl cyanide (0.395 mol) and 50 g of Raney nickel (BASF H1-50).

The conversion was carried out at 21.degree. C. and a current density of 1000 A/m.sup.2. An electrical charge of 4 F/mol was applied, based on the substrate.

To work up the product, the nickel powder was filtered off, the methanol removed from the filtrate by distillation and the remaining aqueous crude solution extracted 5 times with 100 g of MTBE each. After drying and removal of the solvent the crude product was distilled. 54.5 g of homoveratrylamine could be isolated as the reaction product

References:
U.S. Patent Documents
4217185
4584069
5164091
5620584

Foreign Documents
0 133 468
0 435 434
0 479 052
0 808 920
44 08 512

Other References

V. Anantharaman et al., "The Electrocatalytic Hydrogenation of Glucose II. Raney Nickel Powder Flow-Through Reactor Model," J. Electrochem. Soc., vol. 141, No. 10, Oct. 1994, pp. 2742-2752.
K. Park, et al., "Flow reactor Studies of the Paired Electro-Oxidation and Electroreduction of Glucose," vol. 132, No. 8, pp. 1850-1855. No date available.
K. Park, et al., "Current Efficiencies and Regeneration of Poisoned Raney Nickel in the Electrohydrogenation of Glucose to Sorbitol," Journal of Applied electrochemistry 16 (1986), pp. 941-946. No month available.
K. Otsuka, et al., "Dimethyl Carbonate Synthesis by Electrolytic Carbonylation of Methanol in the Gas Phase," Electrochemica Acta, vol. 39, No. 14, 1994, pp. 2109-2115. No month available.
85-045250/06 Abstract = EP 0 133 468, no date available.
98-001803/01 Abstract = EP 0 808 920, no date available.
Coche et al., "Electrocatalytic Hydrogenation Using Precious Metal Microparticles in Redox-Active POlymer Films", J. Org. Chem., vol. 55, No. 23, pp. 5905-5910. Abstract Only, no month available 1990


This patent was included to give examples of electrochemical reductions in organic chemistry.  We have a definite lack of electrochemical procedures.  This will help to establish a base of electrochemical knowledge to look back upon for examples.- If anybody has any patents will examples more specific to our need, please post them.

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