Abstract:
Ammonialytic cleavage of lactams to ω-aminonitriles is effectively promoted by the use of catalysts selected from among molecular sieves and alkaine earth silicates. Molecular sieves additionally reduce the formation of undesired polymer.

Description:
This application is a continuation-in-part of Ser. No. 856,807 filed Sept. 10, 1969 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the production of ω-aminonitriles from the corresponding lactams. In another aspect, it relates to catalysts for the ammonialytic cleavage of lactams to ω-aminonitriles. 
     Lactams are internal or cyclic amides. The reaction involved utilizing the catalysts according to my invention converts the lactam to an ω-aminonitrile by a cleavage reaction involving ammonia. The reaction results in the removal of the oxygen from the lactam molecule with the formation of water, the addition of another nitrogen to the molecule, thus forming a nitrile group at one end and an amino group at the other end of a chain-like molecule. There can be various substituents along the chain. 
     The ω-aminonitriles are valuable chemicals since they are readily convertible to diamines or to other compounds useful as polymer precursors. For example, commercially available nylons are essentially linear long chains of amide groups ##STR1## groups separated by usually 4 to 11 methylene ##STR2## groups. One basic method of preparation of such nylons is by condensing the diamines with dibasic acids, for example, hexamethylene diamine with adipic acid. 
     It is desirable to obtain maximum conversion of lactam to the corresponding ω-aminonitrile in order to have commercially feasible production. 
     OBJECTS OF THE INVENTION 
     It is an object of my invention to provide catalysts effective to improve the ammonialytic cleavage of lactams to ω-aminonitriles. 
     Another object is to provide for maximum effectiveness is one or more of productivity and selectivity in the conversion of lactams to ω-aminonitriles by use of proper catalysts. 
     A further object is to obtain ω-aminonitrile formation while at the same time providing minimum loss to formation of undesired polymer. 
     Other aspects, objects, and the several advantages of my invention will be apparent to one skilled in the art from the following description and from my appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     I have discovered that the use of certain silicon-containing compounds as catalysts, more particularly the alkaline earth silicates, the Type A and Type X molecular sieves, and the mordenites, serve to enhance this ammonialytic conversion reaction. 
     DESCRIPTION OF THE INVENTION 
     The ammonialytic cleavage reaction to which I have referred can be illustrated by the following: ##STR3## 
     The lactam as shown by formula (I) above is called a lactim in the tautomeric or enol form as shown by formula (II) above. The reaction perhaps may be more readily visualized as being between the enol form and the ammonia. Whether the cleavage is considered as occurring on one side or the other of the nitrogen of the lactam is immaterial. The resulting noncyclic ω-aminonitrile is represented by formula (III) above. 
     In the lactams to which my catalysts are applicable, n can be in the range of 3 to 9 inclusive in the case of application of the alkaline earth silicates and the Type X molecular sieves. The Type A molecular sieves and the mordenites are effective for a broader range of lactams wherein n can be in the range of from 3 to 19 inclusive. Carbons in the chain are counted exclusive of carbons in the R groups, if any. 
     There can be various substituents on the carbons of the lactam ring, and consequently along the ω-aminonitrile carbon chain as shown by formula (III) above. R can be hydrogen, alkyl, cycloalkyl, aryl, or combinations thereof such as alkaryl, or aralkyl and the like, having in the range of from 1 to about 8 carbon atoms, provided that not more than 10 carbon atoms are contained in the total of R groups per lactam molecule. 
    
    
     EXAMPLES 
     The examples which follow demonstrate the operability and effectiveness of the catalysts as I apply them to the ammonialytic cleavage reaction according to the process of my invention. These examples should be considered illustrative and not limiting. The examples represent a series of runs with varying catalysts and with varying reaction temperatures. The evaluation of the results of these runs was made with the aid of analysis by gas-liquid chromatography (GLC). With this procedure, the chromatography peaks corresponding to reactants and products were identified and compared with one another on the basis of area percent, the area for each effluent constituent being defined by the base line of the chromatographic curve and the chromatographic peak for that constituent. While area percent is not necessarily identical with weight percent or mole percent, it is, nevertheless, a commonly used and reliable method for comparing the relative effects of reaction variables, such as different catalysts, within a given reaction system. 
     In the examples, conversion was determined by subtracting the area percent of lactam in the effluent from the catalyst-containing reactor, based on the total area of the effluent excluding ammonia, from 100. Stream selectivity was determined by calculating the area percent of the effluent from the reactor, excluding ammonia and lactam, which was the desired ω-aminonitrile. 
     The stream from the catalyst-containing reactor was periodically subjected to gas liquid chromatography. A lack of a peak for the original lactam showed complete conversion. The formation of polymer was measured by physically distilling representative samples to determine volatiles and nonvolatiles and the weight percent of lactam converted to polymer was thus determined. The gas liquid chromatography peak for ω-aminonitrile determines the area percent of ω-aminonitrile in the stream portion made up of the ω-aminonitrile plus unsaturated nitrile. Thus the percent of polymer subtracted from 100 times the stream selectivity is equal to selectivity percent, or of the percent of lactam converted which is converted to aminonitrile. 
     A series of products formed in the ammonialytic cleavage of a lactam, including the desired ω-aminonitrile, a series of minor amounts of intermediates of an unsaturated type which can be represented by ##STR4## wherein y and z are integers such that y + z + 2 = n, as well as polymer, unconverted lactam, ammonia, and diluent if any. Where a diluent is used, the diluent was excluded in calculating conversion and the selectivities. 
     EXAMPLE I 
     A solution was prepared composed of 40 weight percent of the caprolactam and 60 weight percent of benzene as diluent. This solution was then admixed with ammonia by conducting the solution through a conduit equipped with a T connection to permit admixture of the ammonia and to permit closer monitoring of flow rates of the solution, the ammonia, and the admixture. The admixture was charged to a reactor at the rate of 0.5 ml per minute for the solution and at the rate of 1.9 grams per minute for the ammonia. The ammonia being admixed was at atmospheric pressure and at room temperature. 
     The reactor was a stainless steel reactor 1-inch in diameter containing 100 cc of magnesium silicate as the catalyst. The catalyst charged in the vertical tube reactor was retained by a plug of glass wool and some alpha-alumina at the bottom of the reactor. This run was designated Run 1. 
     The temperature of the reactor was controlled and varied by an electric furnace in which the reactor was contained. Thus, the stream of ammonia and lactam vapor mixture was passed through the catalytic reactor for about 20-30 minutes, the reaction temperature was noted, and the reactor effluent was sampled for analysis by gas-liquid chromatography. This process was repeated for several reaction temperatures, samples being taken at about 275°, 300°, 330°, 360°, 400°, and 425° C. The conversion and selectivity results obtained at each temperature in this series was plotted on a graph as a function of reaction temperature. At a point corresponding to 375° C reaction temperature, the curve indicated a 95 percent conversion and a selectivity of about 100 percent of lactam converted to omega aminonitrile. No polymer was formed. 
     The magnesium silicate used in Run 1 as an example of the alkaline earth silicates was a commercial magnesium silicate catalyst obtained from the Floridin Company of Dallas, Tex. This magnesium silicate has the formula Mg 3  Si 4  O 11 .H 2  O, classified as a talc. 
     The above example, Run 1, shows that an alkaline earth silicate was highly effective in the desired aspects of conversion and in selectivity in converting a lactam to an ω-aminonitrile. 
     EXAMPLE II 
     A solution was prepared composed of 10 weight percent dodecano-lactam and 90 weight percent of toluene as diluent. This solution was preheated at 100° C. The preheated solution was then admixed with ammonia gas at about 400 psig and about 100° C. in the same manner as described in Run 1 in Example I above. 
     The solution was charged to a catalyst-containing reactor at the rate of 8 ml per minute. The ammonia was charged at the rate of 3 ml per minute measured on the basis of volumes of liquid anhydrous ammonia. 
     The reactor was a stainless steel reactor 1.25-inch in diameter containing 250 cc of catalyst for each run. The reactor was maintained at approximately 300°-380° C. based on the temperature measured in the middle of the bed. The admixture of lactam, diluent, and ammonia being fed to the hot reactor vaporized on contact therein. The effluent from the reactor was periodically analyzed by means of a gas liquid chromatograph. Results obtained for several runs under these conditions using several catalysts are shown in Table 1 following. 
     
                       Table 1______________________________________                       Stream               Con-    Selec- Poly-                                   Selec-Run                 version tivity mer  tivityNo.  Catalyst       %       %      %    %______________________________________2    3A Molecular Sieve (.sup.a)               100     99     12   873    4A Molecular Sieve (.sup.a)               100     99     17   824    5A Molecular Sieve (.sup.a)               100     97     20   785    Mordenite(.sup.b)               100     99     20   796    α-Alumina(.sup.c)                55     95      3   92______________________________________ (.sup.a)3A, 4A, 5A are designations of various commercially available molecular sieves. The molecular sieves used in the runs were obtained fro the Linde Division, Union Carbide Corporation. The A series is a specific group of molecular sieves described hereinafter. (.sup.b)A synthetic molecular sieve Zeolon-H (trademark) from The Norton Company, Worcester, Massachusettsdescribed in the Norton Product Information Bulletin of January 28, 1966, described as M.sub.8/n. Al.sub.8. Si.sub.40 O.sub.96. 24H.sub.2 O, where M may be Sodium, hydrogen, or other exchangable cation, and n is the valence of such cation, a type of mordenite. The H designation refers to the form where M equals hydrogen. The mordenite used in this run had a pore size of about 10 A.  (.sup.c) α-Alumina, obtained from the Harshaw Chemical Company, Cleveland, Ohio, was a tableted, sintered α-alumina containing 99 percent Al.sub.2 O.sub.3, remainder moisture. 
    
     The data summarized in Example II, Table 1 above demonstrates the high conversion obtained by the catalyst according to the process of my invention as opposed to the relatively low conversion using α-alumina. 
     EXAMPLE III 
     Additional runs were made using the procedure and reactants as described in Example II above, except that the lactam diluent solution was charged to the catalytic reactor at a rate of 3 ml per minute. The ammonia was charged to the reactor at a rate of 1 ml per minute, and temperatures for the runs were approximately 400°-500° C. based on the temperature measured in the middle of the bed. The results for the several runs under these conditions are shown in the following table: 
     
                       Table 2______________________________________                       Stream               Con-    Selec-                             Pol-  Selec-Run                 version tivity                             ymer  tivityNo.  Catalyst       %       %     %     %______________________________________7    3A Molecular Sieve.sup.(a)               100     90    26    678    4A Molecular Sleve.sup.(a)               100     95    33    649    α-Alumina.sup.(b)               60      80    11    7110   Glass Beads.sup.(c)               1       Nil    1    Nil______________________________________ .sup.(a)Refer note .sup.(a) in Table 1. .sup.(b) Refer note .sup.(c) in Table 1. .sup.(c) Laboratory type soft silica glass boiling beads. 
    
     The runs shown in Table 2 of Example III demonstrate the high conversion of lactam to ω-aminonitrile in the presence of the catalysts according to the process of my invention, as opposed to the low conversion, lower stream selectivity, in a control run with α-alumina, and particularly as compared to a control run with another silicon-containing material, i.e., glass beads, which is shown to be completely ineffective. 
     The runs of Example II, Table 1, and Example III, Table 2, further demonstrate that these molecular sieves are effective to show high conversion with minimal formation of polymer. 
     EXAMPLE IV 
     In the runs summarized in Table 3 below, the procedure followed was to heat caprolactam to a molten state at a temperature of 130° C. and to hold it at this temperature while 1.9 grams of ammonia gas per minute were passed through the molten lactam, with the ammonia gas at atmospheric pressure and at room temperature. This produced a vaporous mixture of lactam and ammonia containing in the range of between 75 and 100 moles of ammonia per mole of lactam. The vaporous mixture was passed through a stainless steel catalyst-containing reactor. The reactor was 1-inch in diameter and contained 100 cc of catalyst for each run. 
     In a manner similar to that of Example I, about 5-6 runs were carried out at different temperatures for each catalyst tested, and a performance profile was plotted on a graph with conversion and selectivity plotted as functions of reactor middle temperature. To compare the effectiveness of the catalyst, the conversion and selectivity were read from each curve at a point corresponding to 375° C reaction temperature. These standardized and directly comparable data so obtained by these series of reactions are shown in Table 3 below. 
     
                       Table 3______________________________________                             StreamRun                    Conversion SelectivityNo.   Catalyst         %          %______________________________________11    4A Molecular Sieve.sup.(a)                  53         10012    13X Molecular Sieve.sup.(a)                  57         8213    γ-Alumina.sup.(b)                  90         2514    Magnesium phosphate.sup.(c)                  47         98______________________________________ .sup.(a) Refer note .sup.(b) in Table 1. .sup.(b) γ-Alumina, obtained from the Harshaw Chemical Company, Cleveland, Ohio, was in the form of 1/8-inch tablets. .sup.(c) Magnesium phosphate pelleted, laboratory grade Mg.sub.3 (PO.sub.4).sub.2 . 5H.sub.2 O. 
    
     The above runs demonstrate that molecular sieves, both Type A and Type X, are effective catalyst for caprolactam which is a lactam with a total of 6 carbon atoms, wherein n equals 5 according to formula (I) given hereinbefore. The further run in this example shows the relatively poor stream selectivity of γ-alumina catalyst, and relatively poor conversion resulting from use of magnesium phosphate as catalyst. Only the molecular sieves in these comparative runs demonstrated effectively improved conversion plus improved stream selectivity. 
     Lactams 
     The group of lactams wherein n is in the range of about 3 to 9 include the following as illustrative examples: 
     6-aminohexanoic acid lactam 
     4-aminobutyric acid lactam 
     10-aminodecanoic acid lactam 
     10-amino-3-ethyl-5-octyldecanoic acid lactam 
     4-amino-2-methylbutyric acid lactam 
     10-amino-3-cyclohexyldecanoic acid lactam 
     8-amino-4,4-dicyclopentyloctanoic acid lactam 
     10-amino-6-phenyldecanoic acid lactam 
     10-amino-4-butyl-6-phenyldecanoic acid lactam 
     6-amino-3-benzylhexanoic acid lactam 
     5-amino-4-(3-ethylcyclohexyl)pentanoic acid lactam 
     7-amino-5-(3,5-dimethylphenyl)heptanoic acid lactam 
     8-amino-3-(4-ethylcyclohexyl)octanoic acid lactam 
     8-amino-2,2,4,4,6,6,-hexamethyloctanoic acid lactam 
     9-amino-2-ethyl-3-methyl-6-phenylnonanoic acid lactam 
     5-aminopentanoic acid lactam 
     and the like. 
     Illustrative examples of lactams which can be subjected to ammonialytic cleavage with catalysts of the Type A molecular seives and mordenite molecular sieves include all of the above as illustrative examples, plus the following to further illustrate the range of n from 3 to 19: 
     20-aminoeicosanoic acid lactam 
     20-amino-2,14,15,18-tetramethyl-3,5,15-triethyleicosanoic acid lactam 
     20-amino-4-benzyleicosanoic acid lactam 
     12-aminododecanoic acid lactam 
     11-aminoundecanoic acid lactam 
     and the like. 
     Catalysts 
     To exemplify the alkaline earth silicates, magnesium silicate was used in Run 1, Example I. The alkaline earth silicates as a group are effective. These alkaline earth silicates are compounds of metals of Group II-A of the Periodic Table of the Elements as it is shown on page B-3 of the Handbook of Chemistry and Physics, 49th Edition (1968), The Chemical Rubber Company, Cleveland, Ohio. Specifically, I refer to silicates of beryllium, magnesium, calcium, strontium, and barium. 
     By the term &#34;silicate,&#34; I refer to the orthosilicates, the metasilicates, and the trisilicates, and include the hydrated, partly hydrated, and anhydrous forms of any of these silicates. 
     Nonlimiting examples of the alkaline earth silicates to which I refer are beryllium disilicate Be 4  Si 2  O 7  (OH) 2 , beryllium orthosilicate Be 2  SiO 4  ; magnesium metasilicate MgSiO 3 , magnesium orthosilicate Mg 2  SiO 4  ; calcium α-metasilicate and calcium β-metasilicate CaSiO 3 , calcium diorthosilicate Ca 2  SiO 4 , calcium trisilicate Ca 3  SiO 5  which is sometimes written 3CaO.SiO 2  ; strontium metasilicate SrSiO 3  ; strontium orthosilicate SrSiO 4  ; barium metasilicate BaSiO 3  ; as well as the hydrates such as BaSiO 3 .6H 2  O, and the like. 
     While I prefer to use the synthetically produced alkaline earth silicates, the equivalent naturally-occurring minerals also are effective. Examples of the latter include enstatite MgSiO 3 , serpentine Mg 3  Si 2  O 5  (OH) 4 , clinoenstatite MgSiO 3 , forsterite Mg 2  SiO 4 , talc Mg 3  Si 4  O 10  (OH) 2  ; phenakite Be 2  SiO 4 , phenazite Be 2  SiO 4 , bertrandite Be 4  Si 2  O 7  (OH) 2  ; wollanstonite CaSiO 3  ; and the like. 
     Natural or synthetic mixtures or a chemically combined earth silicate such as diopside CaMg(SiO 3 ) 2  or mellilite Ca 2  MgSi 2  O 7  are effective catalysts. 
     The molecular sieves or zeolites to which I refer include the zeolite A or Type A, the zeolite X, or Type X, and the mordenites. Both the A and X series are synthetic products, while mordenites are produced synthetically  and also found naturally occurring. 
     Molecular formulas for the molecular sieves or zeolites, I use the terms synonymously, have been given as follows: 
     Type A: Na 12  [(AlO 2 ) 12  (SiO 2 ) 12  ]27H 2  O 
     Type X: Na 86  [(AlO 2 ) 86  (SiO 2 ) 106  ].264H 2  O 
     Mordenite: Na 8  [(AlO 2 ) 8  (SiO 2 ) 40  ].24H 2  O 
     molecular sieves are particularly described in an article by D. W. Breck, 41 Journal of Chemical Education, page 678 and following, (December, 1964). I specifically incorporate the material of this article for detailed descriptions of the molecular sieves involved. The material following is for brief summary reference so as not to unduly lengthen this specification. 
     Molecular sieves have a three-dimensional interconnecting network structure of silica and alumina tetrahedra. The tetrahedra are formed by four oxygen atoms surrounding a silicon or aluminum cation. Each oxygen has two negative charges and each silicon atom has four positive charges. The trivalency of aluminum causes the alumina tetrahedron to be negatively charged which then requires an additional anion to balance the system. The final structure generally has sodium, potassium, or calcium in the network. These cations are the exchangeable ions of the zeolite structure. Quadrivalent silicon atoms can be replaced by trivalent aluminum atoms in various ratios which then alters the crystal structure. 
     All of the catalysts as I have described them are solid materials. The particular physical form of the catalyst is not critical, but is chosen according to suitability for a particular catalytic reactor. 
     Molecular sieves are commercially available in various physical forms such as granular, 1/8-inch to 1/4-inch pellets, beads, and finely divided forms of up to 200 mesh. 
     The alkaline earth silicates, either synthetically produced or naturally occurring, preferably are used in the form of extrudates formed into pellets or irregular lumps or granules with a particle diameter of from about 3 to 6 millimeters. The particular form of the catalyst whether in pellet or lump or granule or fine particle, as to the choice of catalyst particle size, will depend to a large extent on whether a fixed bed or fluidized bed or the like will be used in the contacting zone with the lactam vapor. 
     Conversion Process 
     The catalysts are solids. The conversion itself, the ammonialytic cleavage, usually is effected in the gaseous phase. The contacting of the gaseous phase with the solid catalyst can be any conventional means, such as by passing a gaseous stream of lactam and ammonia, optionally with a diluent, through a fixed bed catalyst, or through a fluidized bed of catalyst, or otherwise as may be convenient. 
     Thus, it is necessary, first, to produce a vaporous stream of the lactam. The ammonia portion of the vaporous stream can be added as the molten lactam is vaporized, or added separately after the lactam is vaporized, or added as a separate gaseous phase to a liquid lactam and diluent. For example, the lactam can be melted to form a molten or fluid state and ammonia gas passed therethrough, with the effluent vapors or gases forming a vaporous stream that is a mixture of ammonia vapor and lactam vapor. This stream is conducted to a contacting or reaction zone where the ammonialytic cleavage is promoted by the catalyst. If desired, the ammonia can be heated before passing through the molten lactam. 
     Alternatively, the lactam can be dissolved or dispersed in a suitable solvent, ammonia gas then passed therethrough, with the effluent gaseous stream then containing vaporized lactam, ammonia vapor, and solvent vapors. This vaporous stream is contacted with a catalyst as described hereinbefore. 
     A more usual procedure is to prepare the lactam-diluent solution or dispersion, admix therewith the ammonia to form a liquid-gas admixture, conduct the whole admixture to the hot contacting zone where the liquid is vaporized and ammonialytic cleavage then occurs in the vapor state. 
     The reaction temperatures can be in the range of about 250° to 750° C. but more preferably in the range of about 350° to 500° C. Pressures in the range of about 0.1 to as much as 1000 atmospheres can be employed in the reaction zone. More usually, the pressures are within the range of about 1 to about 100 atomspheres. Atmospheric pressure is convenient, and suitable. 
     The reaction can be effected in a time within a range of about 0.1 second to 10 hours, or more usually, times of between 1 and about 10 seconds are suitable to obtain desired degrees of conversion. 
     While a minimum reaction requirement at 1 mole of ammonia per mole of lactam is required for the ammonialytic cleavage reaction, the amount of ammonia actually employed can range from the minimum of 1 to as much as 1000 moles of ammonia per mole of lactam. Excess ammonia not consumed in the reaction can be recovered, such as by suitable condensation, and recycled for reuse. The maximum amount of ammonia employed is limited primarily by economic considerations as to quantities feasible to use and recover. More than the minimum amount of ammonia is normally employed, usually at least 10 moles per mole of lactam, since most effective cleavage is obtained thereby.