Catalysts for the Hydration of Nitriles of Amides

The conversion of a nitrile to the corresponding amide is carried out on a commercial scale by sulfuric acid hydration. This process requires extensive amounts of expensive equipment, and in addition provides an undesirable source of sulfate pollution. Other methods of converting a nitrile to the amide are also known, see for example, Mahon in U.S. Pat. No. 2,421,030, Haefele in U.S. Pat. No. 3,366,639 and Watanabe in Bull. Chem. Soc. Japan, 32, 1280 (1959), 37, 1325 (1964), and 39, 8 (1966). The basic problem encountered has been the development of a suitable catalyst which would be feasible for the successful application of these operations to commercial production.

It has now been found according to the present invention that nitriles can be converted to the corresponding amide by contacting the nitrile in the presence of water with an essentially insoluble heterogeneous catalyst selected from the group consisting of reduced silver oxide, reduced nickel-chromium oxide, reduced iron-chromium oxide or mixture thereof. These catalysts are the foundation of the invention and one or more of these catalysts must be present in the catalytic hydration in at least a substantial amount, e.g., greater than 1 percent by weight of the catalyst for unsupported catalysts, and preferably more than 10 percent. By the use of these catalysts, good conversions and yields are obtained in a convenient reaction without deleteriously affecting the environment.

The important and novel aspect of the present invention is the use of the specific catalysts named above in the conversion of a nitrile to the corresponding amide by contacting the nitrile in water with the catalyst. Generically, the catalysts are prepared by forming the oxide or a mixture of oxides and then reducing the oxide when required with a suitable reducing agent. Various techniques for both of these steps in the catalyst preparation are known.

The proportions of the component metals in those catalysts containing two or more metals are not critical and may vary widely so long as any significant proportion of each is present.

The oxide or oxide mixture is suitably prepared by precipitation of the soluble components of the catalyst, preferably as the carbonate salt and decomposing the carbonate to the corresponding oxide. For example, silver oxide may be purchased commercially or prepared by adding a solution of ammonium carbonate to a solution of silver nitrate to form a precipitate of silver carbonate. This precipitate is then decomposed by heat to give the desired silver oxide. In a manner similar to those preparations described by Butts (Copper, Reinhold, New York (1954) beginning at page 842) and Adkins (Reactions of Hydrogen, U. of Wis. Press, Madison, Wis. (1937) beginning at page 12) for copper-chromium oxide catalysts, the catalysts of the invention may be prepared. By any of these preparations, the final product is the oxide or mixture of oxides. In those cases where the unreduced catalyst is employed, the catalyst is used without further treatment.

The reduced catalysts are prepared by treating the mixture of oxides with an additional step. This second step involves contacting the oxide or oxide mixture with a suitable reducing agent until a desirable catalyst is obtained. Although numerous reducing agents may be utilized in the reduction, the use of hydrogen as the reducing agent is preferred since the adverse effect on the catalyst is minimized because of the volatile by-products. The reduced catalysts may also be prepared, simultaneously decomposing the carbonate salt and reducing the oxide produced in situ, by heating the carbonate salt at a suitable temperature in the presence of a reducing agent.

The active catalysts of the invention may be used alone or mounted on a support. Representative examples of suitable supports include alumina, silica, silica gel, charcoal, magnesia, chromia, iron oxide and clays. Of course, the weight of active catalyst in supported catalysts compared to the total weight of the catalyst is proportionally smaller than those values described above for unsupported catalysts.

The catalysts of the present invention are used to convert a nitrile to the corresponding amide in either a batch or a continuous process. In either process, the nitrile and water are contacted with the catalyst under the appropriate reaction conditions and the amide product is then recovered. Since the catalysts of the present invention are essentially insoluble, heterogeneous catalysts, a continuous flow reaction is preferred.

In a continuous flow reaction, the solid catalyst of the invention is placed into a reaction chamber having an inlet for reactants and an outlet for products. The reaction chamber is maintained at the desired reaction temperature and the rate of flow of the reactants over the catalysts is controlled to give the desired contact of the reactants with the catalyst. The reactants may be fed over the solid catalyst as a gas or preferably as a liquid. The reaction product from the reactor may suitably be used as such or purified by any conventional technique.

The process of the present invention is suitably applicable to any nitrile, with aliphatic and aromatic hydrocarbon nitriles containing up to about 20 or more carbon atoms being preferred. For purpose of the invention, aromatic nitriles are defined as those nitriles having cyano groups attached to the aromatic nucleus. Representative examples of suitable nitriles include: saturated aliphatic hydrocarbon nitriles such as acetonitrile, propionitrile, pentanonitrile, dodecanonitrile, succinonitrile, adiponitrile and the like; unsaturated aliphatic hydrocarbon nitriles such as acrylonitrile, methacrylonitrile, crotonic nitrile, .beta.-phenylacrylonitrile, 2-cyano-2-butene, 1-cyano-1-octene, 10-undecenonitrile, maleonitrile, fumaronitrile and the like; and aromatic nitriles such as benzonitrile, p-toluonitrile, .alpha.-naphthonitrile, phthalonitrile and the like. Of the nitriles suitable for use in the invention, the olefinic nitriles of 3 to about 6 carbon atoms are especially preferred, with the conversion of acrylonitrile to acrylamide being of special interest.

The proportions of nitrile to water in the reactant mixture may vary widely. More important than the specific nitrile to water ratio is the extent of the interaction between the nitrile and water. A high degree of contact is desirable to assure the greatest efficiency in the reaction. For gaseous reactants, the nitrile and water are miscible in all proportions, but for liquid reactants, certain precautions may be necessary to insure that sufficient contact of the nitrile and water is maintained. The necessary contact may be realized by dissolving the nitrile in the water or by dissolving the water in the nitrile. Outside of the limits of the solubility of one of the reactants in the other, however, the reactant mixture may be agitated, a suitable solvent may be added or another means of increasing the contact of the reactants may be employed. Excess water is the preferred solvent although other inert solvents, such as dioxane, dimethyl sulfoxide, acetone, dimethyl ether of ethylene glycol or tetrahydrofuran, may also be used.

The temperature of the reaction may vary widely as different nitriles and catalysts are used in the invention. Generally, the reaction is conducted within a temperature range of about 0.degree. to about 400.degree. C. At temperatures below this range, the reaction is impractically slow. Above this range, the reaction forms an increasing amount of undesirable by-products. Within the broad temperature range, temperatures of about 25.degree. to about 200.degree. C. or more are preferred. For unsaturated nitriles which tend to polymerize, the use of a reaction temperature of less than about 200.degree. C. or the use of dilute solutions is desirable to avoid polymerization of the nitrile and possible poisoning of the catalyst.

The other reaction conditions and techniques for the use of heterogeneous catalysts are known and not critical to the invention. The important aspect of the invention is using a catalyst defined above to convert a nitrile to the corresponding amide.

In a liter of water, 48 g. of (NH.sub.4).sub.2 CO.sub.3 was dissolved, and in a second liter of water 170 g. of AgNO.sub.3 was dissolved. The carbonate solution was slowly added to the silver solution. The mixture was stirred during the addition and for 10 minutes thereafter. The precipitate was allowed to settle and the solution was decanted. The remaining solid was washed several times with water, separated by filtration and dried at 85.degree. C. in an air oven. The oxide was then simultaneously produced and reduced by passing a gaseous mixture of 20 percent hydrogen in nitrogen over a portion of the carbonate salt for about 4 hours at a rate of about 640 cc./min. and at a temperature of about 200.degree. C. One gram of the reduced silver oxide catalyst so produced was added to a glass ampoule with 5 g. of a 7 percent solution of acrylonitrile in water. The ampoule was sealed, heated at 80.degree. C. for 1 hour and quickly cooled. The contents were analyzed by gas-liquid chromatography for the remaining acrylonitrile and the presence of acrylamide. The results of this and the other parallel experiments using other catalysts are shown in Table I.

In the manner of Example 1 and from a portion of the silver carbonate salt prepared therein, silver oxide was simultaneously produced and reduced as above except at a temperature of about 100.degree. C. As in Example 1, the catalyst so produced was tested in the hydration of acrylonitrile to acrylamide. The results are given in Table I.

A portion of the silver carbonate salt produced in Example 1 was decomposed to silver oxide by heating in a muffle furnace for about 28 hours at from about 120.degree. to about 175.degree. C. The silver oxide thus produced was reduced by passing a gaseous mixture of 20 percent hydrogen in nitrogen over it for about 4 hours at a rate of about 640 cc./min. and at a temperature of about 100.degree. C. The catalyst so produced was tested as in Example 1 and the results are given in Table I.

In a manner similar to that shown in Example 1, 62.5 g. of (NH.sub.4).sub.2 CO.sub.3 was dissolved in 1 liter of water, and 146 g. of Ni(NO.sub.3).sub.2.sup.. 6H.sub.2 O and 40 g. of Cr(NO.sub.3).sub.3.sup.. 9H.sub.2 O was dissolved in a second liter of water. The carbonate solution was slowly added to the other solution with stirring. The precipitate was recovered, dried and decomposed in air at 250.degree. C. for 17 hours. A portion of the resulting oxide was reduced with hydrogen as described above at 240.degree. C. for 5 hours. The catalyst was tested as shown in Example 1 and the results are given in Table I.

In the same manner as shown above, a 1 liter solution of water containing 157 g. of (NH.sub.4).sub.2 CO.sub.3 was added to a solution of 404 g. of Fe(NO.sub.3).sub.3.sup.. 9H.sub.2 O and 40 g. of Cr(NO.sub.3).sub.3.sup.. 9H.sub.2 O in 2 liters of water. The pH was adjusted to 6 with NH.sub.4 OH and the precipitate was stirred for 15 minutes. The separated solid was decomposed at 250.degree. C. for 3 hours and reduced as described above at 325.degree. C. with hydrogen for 4 hours. The catalyst so produced was tested as in Example 1 and the results are given in Table I.

In the same manner as shown by the examples above, the catalysts are used to hydrate other nitriles, such as acetonitrile, benzonitrile, adiponitrile and methacrylonitrile, to the corresponding amide. Also in a similar manner to that shown above, the catalysts of the examples are combined with reduced copper-metal oxides, such as reduced copper-aluminum oxide, reduced copper-chromium oxide, reduced copper-cobalt oxide, reduced copper-zinc oxide or reduced copper-yttrium oxide, copper-silicon oxide and the mixtures are used to hydrate nitriles of up to 20 carbon atoms to the corresponding amide.