Abstract:
A process is disclosed for preparing an isomeric mixture of a monomethyl-, dimethyl- or monoethyl-substituted aniline consisting essentially of contacting at least one of said anilines with a specified zeolite at about 250°-500° C. and about 10 kPa-10 MPa of pressure.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation-in-part of application bearing U.S. Ser. No. 559,183, filed on Dec. 7, 1983, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a process for the preparation of a mixture of methyl- or ethyl-substituted anilines. 
     Methyl- and ethyl-substituted anilines are useful in a variety of applications such as in the preparation of dyes, herbicides, insecticides, plant growth agents and antiknock agents for gasoline engines. The anilines are generally prepared by nitration of the appropriate methyl benzene followed by reduction of the resulting nitro compound. This process depends upon the availability of the appropriate nitro compound which in some instances is unavailable or available only in limited quantities. For example, m-toluidine is important as an intermediate in dyes and agricultural chemicals. However, in the foregoing nitration-reduction process, only 4% of the toluidines produced are m-toluidine. 
     European patent application No. 92,103 discloses a process for preparing o-toluidine and/or m-toluidine and/or p-toluidine in two steps: (a) treatment of a toluidine isomer mixture or any undesired toluidine isomer with an isomerization catalyst from the series of the synthetic zeolites of the pentasil type, (b) isolation of the desired or one of the desired isomers from the mixture of isomers formed in step (a) through selective adsorption on a medium or large pore zeolite and subsequent desorption. 
     U.S. Pat. No. 3,868,420 discloses a process for producing phenylamines alkylated in the ortho and/or para positions by alkyl groups of 1 to 4 carbon atoms and unsubstituted on the amino group which comprises reacting a suitable phenylamine with an alkanol of 1 to 4 carbon atoms in the vapor phase at a temperature of from 350° to 450° C. in the presence of an aluminum oxide catalyst or an aluminum oxide/molybdenum oxide mixed catalyst. 
     U.S. Pat. No. 3,931,298 discloses a process for converting hydroxy-substituted aromatic compounds to the corresponding amine by reacting the aromatic hydroxy compound with ammonia in the presence of a catalytic amount of a cyclohexane and in contact with a hydrogen-transfer catalyst. U.S. Pat. No. 3,960,962 discloses a similar process wherein the catalyst comprises metallic palladium bonded to a phosphinated polystyrene resin. 
     U.S. Pat. No. 4,188,341 discloses a process for making 2,6-dimethylaniline or an N-substituted 2,6-dimethylaniline comprising reacting an enamine of a specified formula at a temperature of between -30° C. and 150° C. with acrolein in the presence of an inert aprotic solvent and heating the resulting reaction product to a temperature of between 100° and 400° C. in the presence of a hydrogen-transfer catalyst and an amine of the formula RNH 2  wherein R is --H or a specified lower alkyl. 
     Japanese Kokai No. 53-28128 discloses a process for para-methylation of anilines comprising reacting an aniline having para-hydrogens with methanol in the presence of an alkali metal synthetic zeolite catalyst, particularly NaY zeolite. Preparation of 2,4-dimethylaniline from o-toluene and the preparation of p-toluidine from aniline are specifically disclosed. 
     Inoue et al., Seikyu Gakkaishi, 15, 372 (1972) studied the methylation of aromatic compounds with methanol in vapor or liquid phase on various catalysts and specifically report the orthomethylation of aniline with methanol using 10% MgO/Al 2  O 3  catalyst to produce o-toluidine. 
     Japanese patent publication No. 28129/1978 discloses demethylation of polymethylanilines, which contain at least more than two methyl groups, in the presence of a catalyst composition of the formula A a  B b  C c  O d  wherein A is titanium; B represents more than one kind of element selected from zinc, zirconium and magnesium; C represents more than one kind of element, selected from vanadium, chromium, manganese, tin, iron, cobalt, nickel, copper, molybdenum, tungsten, barium, calcium; O is oxygen; a is 1, b is 0.05 to about 20, and c is 0 to 1.0. 
     Japanese patent publication No. 1974-[Showa-49], 29,178 discloses a process for the synthesis of toluidines rich in m-toluidine by dealkylation of xylidines having a methyl group in a meta position in the presence of a dealkylation catalyst such as silica-alumina, alumina, silica, silica-magnesia and magnesia. Matsumoto et al., Chemistry Letters, pages 435 to 438 (1978) disclose a process for preparing m-toluidine by hydrocracking 2,3-xylidine over metal oxide-supported nickel catalysts. The authors disclose that the selectivity of m-toluidine is influenced by side reactions, such as isomerization, and that the extent of isomerization can be related to the acidic character of the metal oxide carriers. 
     SUMMARY OF THE INVENTION 
     The present invention provides a process for preparing an isomeric mixture of an alkyl-substituted aniline having the formula ##STR1## wherein R is a methyl or ethyl group, n is 1 or 2 when R is methyl, and n is 1 when R is ethyl, the process consisting essentially of contacting at least one compound of formula I with a zeolite catalyst at a temperature of from about 250° to 500° C. and at a pressure of from about 10 kPa to 10 MPa, said zeolite catalyst having pores with dimensions of from about 0.5 nm to less than about 0.7 nm and having cages with dimensions no greater than about 0.7 nm, with the proviso that when R is methyl and n=2 the formula I anilines can only be 2,4- 2,5- and 3,4-dimethylanilines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The FIGURE shows the kinetic paths followed by the toluidines to reach equilibrium when isomerization is performed over the zeolite HZSM-5. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The isomerization process of this invention is represented by the reaction ##STR2## where n equals one or two, and by the reaction ##STR3## where in each reaction the product is a different isomer than the reactant. 
     In the process of the invention the total number of methyl or ethyl groups on the primary aniline is substantially conserved. Minor portions of the reactant may undergo reactions in which some of the methyl or ethyl groups are lost. However, under the conditions of this process, the major portion of the reactant undergoes the reaction indicated above in which the number of methyl or ethyl groups on the reactant aniline equals the number on the product aniline. 
     Zeolite catalysts suitable for use in the process of the invention have pores large enough to accommodate one aromatic molecule but not large enough to allow two aromatic molecules to react with each other. This condition is satisfied by those zeolites with pore aperture dimensions of at least about 0.5 nm but less than about 0.7 nm and having cages with dimensions no greater than about 0.7 nm. As used herein, &#34;pore dimensions&#34; means the aperture dimensions determined from crystal structures analyses, i.e., the crystallographic free diameters of the channels as discussed by Meier et al., &#34;Atlas of Zeolite Structure Types&#34;, published by the Structure Commission of the International Zeolite Association, 1978. The free diameter values are based on the atomic coordinates of the type species in the hydrated state and an oxygen radius of 1.35 Å (0.135 nm). 
     Suitable zeolite catalyst include HZSM-4, HZSM-5, HZSM-8, HZSM-11, HZSM-34, HZSM-35, HZSM-47, H-β, H-L, NaZSM-5, NaZSM-12, H-mordenite and H-offretite or a mixture of any of the foregoing but HZSM-5 and HZSM-8 are preferred. These zeolite catalysts can be prepared by known procedures. Zeolite HZSM-4 can be prepared according to the method disclosed in U.S. Pat. No. 3,642,434. Zeolite HZSM-5 can be prepared according to the method disclosed in U.S. Pat. No. 3,702,886. Zeolite HZSM-8 can be prepared according to the method disclosed in U.S. Pat. No. 3,766,093. The method disclosed in European patent application publication No. 14,059, particularly Example 7, can be used to prepare zeolite HZSM-11. Zeolites HZSM-34 and HZSM-35 can be prepared by the process disclosed in U.S. Pat. No. 4,086,186 (particularly Example 10) and U.S. Pat. No. 4,016,245 (particularly Example 12), respectively. The method disclosed in U.S. Pat. No. 4,187,283, particularly Example 1, can be used to prepare zeolite HZSM-47. Zeolite H-β can be prepared by the procedure disclosed in U.S. Pat. No. 3,308,069. Zeolite NaZSM-5 and zeolite NaZSM-12 can be prepared by the methods disclosed in U.S. Pat. No. 3,702,886 and European Pat. No. 18,089 (particularly Example 2), respectively. Zeolite H-offretite can be prepared by the method disclosed in British Pat. No. 1,188,043. Zeolite H-L and zeolite H-mordenite can be purchased commercially and, as used in the examples, were Linde ELZ-L and Norton Z-900H, respectively. The X-ray diffraction pattern of each zeolite that was prepared for use in the examples was compared with the known X-ray pattern of that zeolite to confirm that the desired zeolite had been prepared. 
     The toluidine isomerization can be represented as o-toluidine⃡m-toluidine⃡p-toluidine with no direct interconversion of o- and p-toluidine. For isomerization of the toluidines, depending on the reactor system employed, a solvent may be needed to feed p-toluidine, which is a solid, to the reactor system. A convenient solvent is aniline, however, any other suitable solvent can be used, such as benzene, toluene, xylene and related solvents. 
     In the process of the invention isomerization of 2,4-, 2,5-, and 3,4-dimethylanilines (DMA) occurs with interconversion between any two of these three isomers; i.e., ##STR4## The other three isomers 2,3-, 2,6-, and 3,5-dimethylanilines, are neither formed from 2,4-, 2,5-, or 3,4-dimethylaniline over the herein prescribed catalysts, nor are the 2,3-, 2,6-, and 3,5-dimethylanilines converted by these catalysts. 
     In the process of the invention at least one substituted aniline of formula I is contacted with a catalytic amount of any of the zeolite catalysts set forth herein. A temperature of from about 250° to 500° C., preferably from about 300° C. to 400° C. is employed. The process is conducted at a pressure of from about 10 kPa to 10 MPa, preferably from about 100 kPa to 1 MPa. Suitable reaction times are from about 0.1 second to 10 hours. The process of the invention can be carried out in either a liquid or gas phase and can be conducted in batch or continuous mode. 
     The invention is further illustrated by the following examples in which all temperatures are in degrees Celsius and all percentages are by weight unless otherwise stated. 
     EXAMPLES 1 to 3 
     Isomerization of toluidines when contacted with zeolite HZSM-5 was demonstrated by passing an approximately 1:1 (mole ratio) toluidine/aniline feed solution over 3 g of zeolite HZSM-5, at atmospheric pressure and various reaction temperatures, feed solution flow rates and nitrogen gas flows in a 13 cm (5 inch) long, 1 cm (3/8 inch) diameter Vycor® reactor heated with a split-tube furnace. After the process had operated for 20 minutes, the product for the next 5 minutes was collected and analyzed using a 6.1 m (20 feet) by 0.32 cm (1/8 inch) stainless steel column packed with polyethylene oxide and 1% KOH on 80/100 mesh diatomaceous earth. Elution was carried out isothermally at 200° with a nitrogen gas flow of 40 cc/minute. The retention times increased in the order aniline, ortho-, para-, and meta-toluidine. 
     Feeding each toluidine/aniline solution to HZSM-5 at increasingly severe reaction conditions (longer contact times and/or higher temperatures) results in the kinetic paths shown in the FIGURE. Except at the very highest temperatures, no more aniline is found in the product than was present in the starting material. Neither di- nor trimethylanilines are formed. The reaction conditions and results are summarized in Table I. The maximum meta distribution which this catalyst produces starting from p-toluidine is 58 mole %. The same equilibrium concentration, 17 mole % p-toluidine, 52 mole % m-toluidine, and 31 mole % o-toluidine, of the three toluidine isomers is obtained no matter which toluidine is used as the feed. There is no direct interconversion of o- and p-toluidine and the reaction may be described essentially in terms of shifts of methyl group to neighboring ring sites. The relative rates of the four reactions needed to describe this system are given in the Figure. 
     EXAMPLE 4 
     To demonstrate that aniline is not a necessary reactant in Examples 1-3, Example 3 was repeated using as the feed pure m-toluidine at a rate of 2.2 ml/hr with a N 2  gas flow rate of 10 ml/min and with a reaction temperature of 375° and atmospheric pressure. The product was analyzed using a procedure similar to that described for Examples 1-3 and found to contain 54 mole % m-toluidine, 29 mole % o-toluidine, 15 mole % p-toluidine, and 1.7 mole % aniline. 
     
                                           TABLE I__________________________________________________________________________        N.sub.2Tolu-    Feed        Gasidine    Flow        Flow            Reaction                 Product Composition (mole %)Examplein  Rate        Rate            Temp Ani-                    o-Tolu-                         p-Tolu-                              m-Tolu-No.  Feed    ml/hr        ml/min            °                 line                    idine                         idine                              idine__________________________________________________________________________1    p-tolu-    1.5 50  357  55 0.5  31   13idine       377  55 1.1  24   19            409  54 2.1  22   22            416  54 10   9.1  25    3.0 25  390  51 1.5  29   18            417  52 4.7  18   25            422  52 7.6  13   27            445  51 9.5  12   27            450  52 12   9.2  27            463  51 13   8.7  25            495  52 15   8.0  242    o-tolu-    3.0 10  365  49 48   --   1.5idine       414  49 46   0.6  3.4            415  50 43   1.3  5.6            447  50 28   5.1  16            470  50 20   7.3  21            500  51 16   8.0  243    m-tolu-    3.0 10  360  51 0.9  2.6  45idine       418  51 6.3  8.8  33            430  51 7.8  9.3  32            450  50 13   9.1  28            464  52 14   8.4  25            496  51 15   8.2  25__________________________________________________________________________ 
    
     EXAMPLES 5 to 14 
     The process of the invention was carried out using various suitable zeolite catalysts and using a procedure similar to that set forth in Examples 1-3. A feed solution of approximately 1:1 (mole ratio) p-toluidine/aniline was passed over 3 g of the catalyst at atmospheric pressure and at various reaction temperatures at a feed solution rate of 2.2 ml/hr and a nitrogen gas flow of 10 ml/min. The catalyst, reaction conditions, and results are shown in Table II. 
     EXAMPLES 15 to 20 
     Using a procedure similar to that described in Examples 1-3, a feed solution of approximately 1:1 (mole ratio) p-toluidine/aniline was passed over various amounts of different catalysts at atmospheric pressure and various reaction temperatures at a feed rate of 2.2 ml/hr and a nitrogen gas flow of 10 ml/min. The reaction conditions and results are shown in Table III. 
     EXAMPLES 21 to 23 
     Isomerization of 2,4-, 2,5-, and 3,4-dimethylanilines in the presence of zeolite HZSM-5 was effected by passing a dimethylaniline over 3 g of zeolite HZSM-5, at atmospheric pressure and various reaction temperatures at flow rate of 3 ml/hr and a nitrogen gas flow rate of 10 ml/min in a vapor phase reactor similar to that described in Examples 1-3. After the process operated for 30 minutes, the product for the next 5 minutes was collected and analyzed by gas chromatography using a procedure similar to that of Examples 1 to 3. Results are summarized in Table IV. 
     
                       TABLE II______________________________________                Product CompositionEx-                  (mole %)am-                            o-    p-    m-ple             Reaction Ani-  Tolu- Tolu- Tolu-No.  Catalyst   Temp. °                    line  idine idine idine______________________________________5    HZSM-5     300      51    --    44    5.0           400      51    15    8.3   256    HZSM-5     300      51    --    48    --           400      52    4.5   19    24           500      53    15    7.4   237    HZSM-5     300      52    --    47    0.6           400      51    13    8.1   26           500      59    13    6.3   208    HZSM-8     300      52    0.6   47    0.6           400      53    7.4   16    24           500      56    14    7.1   229    HZSM-11    300      51    --    48    --           400      51    0.5   46    1.8           500      52    12    10    2610   NaZSM-5    300      53    --    47    --           400      52    6.3   17    24           500      58    13    6.6   2011   HZSM-34    300      53    --    47    --           400      54    0.4   40    5.9           500      60    4.1   17    1912   H--β  300      53    --    47    --           400      55    0.8   40    4.7           500      62    7.7   8.2   2013   H--L       300      51    --    49    --           400      54    0.6   43    2.1           500      61    6.2   20    8.414   H--mordenite           375      51    --    43    5.3           500      52    --    45    2.6______________________________________ 
    
     
                                           TABLE III__________________________________________________________________________       Quantity  Product Composition       of   Reaction                 (mole %)Example     Catalyst-            Temp.                 Ani-                    Tolu-                         Tolu-                             Tolu-No.  Catalyst       grams            °                 line                    idine                         idine                             idine__________________________________________________________________________15   HZSM-4 1.5  300  41 0    43  0.2            400  50 0.4  44  2.1            500  50 2.3  30  1416   HZSM-11       3.0  400  47 16   11  2617   HZSM-35       1.3  400  52 --   41  1.8            500  58 2.8  28  1018   HZSM-47       1.5  300  51 0.6  49  --            400  51 0.7  48  --            500  53 0.5  43  3.219   NaZSM-12       1.4  300  48 0.9  48  --            400  42 2.2  36  2.6            500  52 3.7  26  17.120   H-offretite       1.7  300  52 --   48  --            400  52 --   42  2.8            500  60 3.2  22  14__________________________________________________________________________ 
    
     
                       TABLE IV______________________________________Ex.            Reaction  Product Composition (mole %)No.   DMA      Temp. (°)                    2,4-DMA                           2,5-DMA 3,4-DMA______________________________________21   2,4-DMA   385       88     7.6     4.5          412       69     22      9          435       57     31      11          454       52     35      13          474       47     38      15          501       40     40      2022   2,5-DMA   355       2.1    93      4.6          375       3      89      8          420       15     68      17          433       26     52      22          455       26     51      23          502       30     46      2423   3,4-DMA   380       4      14      83          420       9      32      59          455       12     39      50          487       19     43      38______________________________________ 
    
     EXAMPLES 24 and 25 
     Isomerization of an ethylaniline in the presence of zeolite HZSM-5 was effected using a procedure similar to that described in Examples 1-3. A feed solution of approximately 1:1 (mole ratio) ethylaniline:aniline was passed over 3 g of zeolite HZSM-5 catalyst at a rate of 2.2 ml/hr with a N 2  gas flow rate of 10 ml/min. The reaction conditions and results are shown in Table V. 
     
                       TABLE V______________________________________          Product Composition (mole %)Ex.  Ethylene  Reaction         EthylanilineNo.  in Feed   Temp. (°)                    Aniline                           o-   p-    m-______________________________________24   o-ethyl-  295       45     53   0.3   1.9aniline   295       45     52   0.3   2.1          300       47     45   1.1   7.1          300       48     48   0.9   5.4          330       47     32   3.5   18          360       49     22   4.8   24          390       58     12   5.9   25          400       59     11   5.9   2425   p-ethyl-  300       46     1.1  38    14aniline   300       45     1.6  27    27          330       47     3.1  24    26          360       48     3.1  13    33          390       52     7.8  8.2   31          420       60     8.1  6.2   25______________________________________