PREPARATION OF 4-PENTENENITRILE BY ISOMERIZATION

Abstract: Isomerization by contacting 3-pentenenitrile with a heterogeneous catalyst, preferably promoted with at least 1 group 8 noble metal, to form 4-pentenenitrile.

Description: This invention relates to a process for the selective isomerization of 3-pentenenitrile to form 4-pentenenitrile by the use of a particular class of catalysts that are not dissolved in the reaction mixture. The process requires contacting the 3-pentenenitrile with the catalyst at elevated temperatures. 3-Pentenenitrile (3PN) is produced commercially by the hydrocyanation of butadiene in the presence of nickel catalysts: CH₂=CH-CH=CH₂ + HCN → CH₃-CH=CH-CH₂-CN 3PN is a precursor for the production of the nylon intermediates, adiponitrile (by further hydrocyanation), or adipic acid and caprolactam (by carbonylation to 5-cyanovaleric acid). To form these intermediates, 3PN must first be converted to the terminal olefinic isomer, 4-pentenenitrile (4PN): CH₃-CH=CH-CH₂-CN → CH₂=CH-CH₂-CH₂-CN Some hydrocyanation catalysts are also effective for this isomerization, allowing the selective production of adiponitrile commercially by hydrocyanation of 3PN: CH₃-CH=CH-CH₂-CN → [CH₂=CH-CH₂-CH₂-CN] → NC-CH₂-CH₂-CH₂-CH₂-CN However, carbonylation catalysts are, in general, relatively poor isomerization catalysts and they are also less selective in the carbonylation of internal vs terminal double bonds. These factors lead to lower yields of 5-cyanovaleric acid and its esters in the carbonylation of 3PN. In contrast, much higher selectivity to 5-cyanovaleric acid can be obtained by carbonylation of 4PN: CH₂=CH-CH₂-CH₂-CN + CO + ROH → RO₂C-CH₂-CH₂-CH₂-CH₂-CN The present invention is concerned with the isomerization of 3-pentenenitrile to 4-pentenenitrile. U.S. Patent 3,542,847 to Drinkard et al. discloses the isomerization of 3-pentenenitrile to 4-pentenenitrile by the use of homogeneous palladium or platinum catalysts having a valence of plus 2 or less; and when the platinum or palladium is a zero valent state, an acid is preferably also present. It is also known from U.S. Patent 4,529,815 to prepare 4-pentene acid esters by isomerization of 2- and/or 3-pentene acid esters using an acidic ion-exchange resin or zeolite containing a noble metal of group 8 of the periodic table as the catalyst. There is no basis for the assumption that this process would also be useful for the isomerization of different types of compounds like nitriles. The reference does not make any sort of statements as to how the catalysts are to be prepared and therewith no statements as to the oxidation state in which the noble metal is. The point must therefore be proceeded from that it is an oxidation state of O. Perfluorinated ion-exchange resins have been previously employed as isomerization catalysts -- see, for example, U.S. Patents 4,022,847 and 4,038,213 to McClure and McClure et al. which disclose the isomerization of alkanes. The present invention is a process for the preparation of 4-pentenenitrile which comprises isomerizing 3-pentenenitrile by contacting 3-pentenenitrile at a temperature in the range of about 50° to 150°C. at a pressure of 0.01 to 49.3 bar (0.01 to 50 atmospheres) with a heterogeneous catalyst selected from the group consisting of a) acidic amorphous silica aluminates promoted with palladium, b) acid Y-zeolites promoted with palladium, and c) perfluorinated sulfonic acid ion-exchange polymers promoted with palladium, platinum or rhodium, the palladium, platinum or rhodium being present in an amount of 0.1% to 4% by weight of the catalyst and having an oxidation state of at least +2. The isomerization process of the present invention involves the use of a heterogeneous catalyst. Suitable catalysts have already been broadly described above. When the catalyst is a perfluorinated sulfonic acid ion-exchange resin promoted with palladium, platinum or rhodium, it can be prepared from a suitable perfluorinated acid ion-exchange polymer (PFIEP[SO₃H]), or a blend of perfluorinated sulfonic acid and perfluorinated carboxylic acid polymers (PFIEP[SO₃H]/PFIEP[CO₂H]). Most preferred perfluorinated sulfonic acid polymers have a number average molecular weight of at least about 5000. Preferably, the PFIEP contains a sufficient number of sulfonic acid groups to give an equivalent weight of from about 500 to about 2000, and most preferably from about 700 to about 1500. The equivalent weight, E.W., is determined by the formula: E.W. = M.W./number of acid groups, where M.W. is the molecular weight of the perfluorocarbon polymer. Although the polymer backbone will largely comprise perfluorinated carbon atoms, it is not necessary that all other atoms be excluded. For example, ether oxygen may be present in the backbone or in the side chains of the polymer. Other atoms or groups such as hydrogen, chlorine and carboxyl groups may be present in limited amounts without significantly affecting the stability or operability of the polymer under the process conditions. It is preferred that the polymer contain no greater than about 5 weight percent total of such other atoms or groups. The perfluorinated acid ion-exchange polymer may be a blend of two or more ion-exchange polymers. The preparation of blends of perfluorinated sulfonic acid and perfluorinated carboxylic acid polymers is disclosed in U.S. Patent 4,176,215, the disclosure of which is incorporated herein by reference. Preferred blends of perfluorinated sulfonic acid and perfluorinated carboxylic acid polymers include blends of tetrafluoroethylene copolymers with methylperfluoro-5-methyl-4,7-dioxanon-8-eneoate and tetrafluoroethylene copolymers with perfluoro(3,6-dioxa-4-methyl-7-octene) sulfonyl fluoride. Most preferred blends have an ion-exchange capacity of at least 0.7 meq/g. Preferably, the weight ratio of sulfonic acid polymer to carboxylic acid polymer in the blend is from about 1:1 to about 10:1. The perfluorinated acid ion-exchange polymer is ground to small particles -- usually 0.074 to 0.84 mm (20 to 200 mesh size) and is subjected to an exchange with a salt of the noble metal whereby an amount by weight of the catalyst of between about 0.1 to 4% of the noble metal is incorporated into the perfluorinated acid ion-exchange resin. The noble metal is preferably present in the oxidation state of at least +2, and is preferably +3. The noble metal acts to promote the reaction. Suitable hydrocarbon sulfonic acid ion-exchange polymers are commercially available under such trademarks as Dowex resins and Amberlyst 15 resins. Another suitable catalyst is acid Y-zeolite promoted with palladium. Zeolites are crystalline aluminosilicate compounds. Zeolites occur in nature, and also are synthesized. See Kirk-Othmer: Encyclopedia of Chemical Technology Vol. 15, page 638 through 650, John Wiley & Sons, NY (1981). Commercially available Y-zeolites sold by Union Carbide Company are satisfactory synthetic zeolites useful in the process of the present invention. Acidic amorphous silica aluminates promoted with palladium are also satisfactory catalysts for the isomerization reaction of the present invention. The aluminates can be purchased commercially as Davison Catalyst Supports (from Grace-Davision Chemical Co.). The isomerization process of this invention is carried out at temperatures between about 50°C and 150°C and at pressures between 0.01 and 49.3 bar (0.01 and 50 atmospheres) with a preferred pressure range of between 0.1 and 4.9 bar (0.1 and 5 atmospheres). The optimum operating conditions will depend upon the particular catalyst employed. Examples Example 1: Pd/HY Zeolite Catalyst (a) Catalyst Preparation To a slurry of 5 g of the NH₄Y (LZY-82, Union Carbide) Zeolite in 1000 ml water was added 0.40 g palladium tetramine nitrate. The slurry was stirred for 4 hours at ambient temperature. The Pd-Zeolite was filtered, washed with 1 liter water and suction dried. The solid was dried by heating to 100°C in flowing oxygen over 1 hour and holding at 100°C for 30 minutes. It was then calcined by heating at 500°C in flowing oxygen for 2 hours and then holding at 500°C for an additional 1 hour in vacuum. It was cooled in vacuum and maintained in an anhydrous atmosphere before use. Analysis of the solid showed 2.84 wt % Pd. (b) 3PN to 4PN Isomerization Crude 3-pentenenitrile, 3PN, was distilled under nitrogen to remove impurities. Gas chromatographic analysis of this product showed the following isomer distribution: trans 3PN 93.6 cis 3PN 3.1 trans 2PN 1.4 cis 2PN 0.3 4PN 1.5 4.0 g of the above mixture was heated to reflux (about 140°C) under nitrogen. To this was added 0.4 g of the 2.84% Palladium/Zeolite catalyst. Samples were taken at intervals and diluted with methanol to quench the reaction. Samples were then analyzed by capillary gas chromatography to determine isomer distribution. No other 3PN byproducts were observed. The following isomer distributions as a function of time were obtained: Time (Min) C2PN T2PN 4PN T3PN C3PN Δ4PN/2PN 0 0.31 1.42 1.50 93.65 3.12 - 1 0.99 1.17 9.34 77.15 11.35 18.2 5 0.94 1.18 10.90 73.70 13.28 24.1 30 1.08 1.33 10.09 74.76 12.74 12.6 The Δ4PN/2PN ratio shows that 4PN is produced 12 to 24 times faster than 2PN under these conditions. This ratio, selectivity, is the number of moles of 4PN formed , divided by the number of moles of 2PN formed during the isomerization reaction. In making this latter calculation, the number of moles of 2PN (cis + trans isomers) present in the starting mixture containing 3PN is not considered. Example 2 A. Catalyst Preparation The H⁺ form of a commercially available perfluorinated ion-exchange polymer, PFIEP, having an equivalent weight of about 1000 and a particle size of less than 0.15 mm (100 mesh) (6.9 g; 6 Meq H+) was stirred in a solution of PtCl₂ (0.2 g; 0.75 mmole) in a mixture of 50 ml acetonitrile and 100 ml distilled water. The mixture was maintained at 80°C for 2 hours. The resin was filtered, washed with 100 ml distilled water and dried in a vacuum oven at 100° under N₂ for 3 hours. The dried resin weighed 6.24 g. Analysis showed 1.56% Pt. B. Isomerization The experiment in Example 1B was repeated except that the Pd/Zeolite was replaced with 0.40 g 1.56% Pt/PFIEP catalyst. The following Table shows the amounts of 4PN and 2PN (Cis + trans isomers) at the times indicated: Time (Min) 2PN 4PN Δ4PN/2PN 0 1.73 1.50 - 1 1.95 7.23 26.0 5 1.75 8.20 33.5 30 1.86 8.27 52.0 The data shows that 4PN is formed much more rapidly than 2PN. Example 3 A. Catalyst Preparation: 0.55% Pd/HCl treated amorphous silica-aluminate (13% Al₂O₃) Commercial (Davison) Silica aluminate (10 µm powder) containing 13% alumina was treated with HCl and palladium tetraamine chloride as follows: 5 g of amorphous silica-aluminate containing 13 wt % alumina were slurried into 1000 cc water and acidified to pH 1.0 with hydrochloric acid. The slurry was stirred for 30 minutes then filtered and washed with 1000 cc distilled water. The solid was slurried into 1000 cc fresh distilled water and 0.05 g palladium tetraamine chloride was added. The slurry was stirred for 4 hours then filtered and washed with 1000 cc distilled water. The suction-dried solid was loaded into a horizontal tube furnace quartz tube and oxygen gas was flowed over it while the temperature was ramped up to 100°C at 2°C/min. The sample was held at 100°C in flowing oxygen for 30 mins and then temperature was rapidly increased to 400°C for a further 2 hours in flowing oxygen ( 50 cc/min). The oxygen flow was terminated and the tube evacuated at 400°C for a further 1 hour. The sample was cooled under vacuum then sealed and taken into an inert (nitrogen) atmosphere dry box where it was divided into 1 g lots in separate screw-capped vials. Chemical analyses showed about 0.55 wt % Pd. B. Catalytic conversion of 3PN to 4PN A 10 g sample of 3PN containing 97.2% trans 3PN, 2.0% cis 3PN and 0.8% 4PN (no 2PN) was heated to 140° under N₂. To this was added 1.0 g of the Pd/Silica-aluminate catalyst of part A. Samples were taken at intervals and analyzed by capillary gas chromatography. The following results were obtained: Time (Min) 2PN 4PN Δ4PN/2PN 0 0 0.8 - 1 0.4 3.1 5.7 5 0.4 4.6 9.5 30 1.3 9.3 6.5 Example 4 The experiment in Example 3B was repeated except that the catalyst was an amorphous silica-aluminate containing 25% Al₂O₃ and 0.6% Pd. The following results were obtained: Time (Min) 2PN 4PN Δ4PN/2PN 0 0 0.8 - 1 0.5 2.6 3.6 5 0.7 3.8 4.3 30 1.5 6.4 3.7 Example 5 The experiment in Example 3B was repeated except that the catalyst was an acid exchanged perfluorinated ion-exchange polymer, PFIEP, in the sulfonic acid form (more fully described in Example 2) containing 0.91% Pt. Analysis showed the following isomer distributions: Time (Min) 2PN 4PN Δ4PN/2PN 0 0 0.8 - 30 0.4 3.5 6.7 60 0.3 5.5 15.7 Example 6 Miscellaneous Group 8 Noble Metal Exchanged Acidic Ion-Exchange Resins The experiment in Example 3B was repeated except that different catalysts (1.0 g per 10 g T3PN) were used. Analysis after 30 minutes gave the following results: Catalyst 2PN 4PN Δ4PN/2PN Rh⁺³ on PFIEP[SO₃H] (0.85% Rh) 0.3 1.6 2.7 Pt⁺² on PFIEP[SO₃H]/PFIEP[CO₂H] (0.7% Pt) 0.4 1.9 2.7

Claims: A process for the preparation of 4-pentenenitrile which comprises isomerizing 3-pentenenitrile by contacting 3-pentenenitrile at a temperature in the range of about 50° to 150°C. at a pressure of 0.01 to 49.3 bar (0.01 to 50 atmospheres) with a heterogeneous catalyst selected from the group consisting of, a) acidic amorphous silica aluminates promoted with palladium, b) acid Y-zeolites promoted with palladium, and c) perfluorinated sulfonic acid ion-exchange polymers promoted with palladium, platinum or rhodium, the palladium, platinum or rhodium being present in an amount of 0.1% to 4% by weight of the catalyst and having an oxidation state of at least +2. The process of claim 1 in which rhodium has an oxidation state of +3. The process of claim 1 wherein the perfluorinated sulfonic acid ion-exchange polymer is a blend of perfluorinated sulfonic acid polymer and perfluorinated carboxylic acid polymer.

Inventors: BURKE, PATRICK MICHAEL, HERRON, NORMAN, WALLER, FRANCIS JOSEPH
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1988
Main classification: C07C255
IPC codes: C07B61, B01J39, B01J29, B01J31, C07C253, C07C67, C07B35, C07C255, B01J27, C07B31