Abstract:
This invention relates to a process for the nucleochlorination of o-xylene using elemental chlorine in the presence of a Friedel-Crafts catalyst and a co-catalyst, where the co-catalysts used are benzo-fused thiazepines or thiazocines.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a process for the nucleochlorination of o-xylene to give a mixture of 4-chloro-1,2-dimethylbenzene and 3-chloro-1,2-dimethylbenzene using elemental chlorine in the presence of a catalyst and a co-catalyst.  
           [0002]    Mononucleochlorinated o-xylenes are valuable intermediates for preparing agricultural and pharmaceutical active compounds and for preparing polymer precursors.  
           [0003]    The nucleochlorination of o-xylene by elemental chorine is known. In the presence of customary Friedel-Crafts catalysts, for example, Fe, FeCl 3 , AICl 3 , SbCl 3 , or SbCl 5 , the mononucleochlorination of o-xylene produces a mixture of 4-chloro-1,2-dimethylbenzene and 3-chloro-1,2-dimethylbenzene having a product ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene of less than 1.5:1 ( U.S. Pat. No. 4,190,609). 4-chloro-1,2-dimethylbenzene is the more valuable isomer, so that a number of processes have been described for increasing the proportion of 4-chloro-1,2-dimethylbenzene.  
           [0004]    Adding simple sulfur compounds as co-catalysts can increase the proportion of 4-chloro-1,2-dimethylbenzene, for example, using Fe+S 2 Cl 2 , to a ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethyl-benzene of 1.78:1 (Chemical Abstracts CA 1988, No. 472737).  
           [0005]    U.S. Pat. No. 4,190,609 discloses a process for the nucleochlorination of o-xylene by elemental chlorine, the procedure being carried out in the presence of Lewis acids as catalysts and defined substituted thianthrenes as co-catalysts. Although by this means the ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene can be increased to 3.81:1, a disadvantage in the use of thianthrenes is that compounds of this class act in a similar manner to the corresponding dioxins, that is to say, they are toxic.  
           [0006]    EP 126 669 A1 describes the nucleochlorination of o-xylene using SbCl 3  as Lewis acid and N-chlorocarbonyphenothiazine as co-catalyst. In this process a ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene of 2.3:1 is achieved.  
           [0007]    In the presence of Lewis acid catalysts (for example, FeCl 3 ) and nitro compounds (for example, o-nitrotoluene), in contrast, an increased proportion of 3-chloro-1,2-dimethylbenzene is obtained with a ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene of 1:1.8 (Chemical Abstracts CA 1999, No. 802798).  
           [0008]    A fundamentally different process is the nucleochlorination of o-xylene by chlorine in the presence of L-zeolites as catalysts. In the presence of KL-zeolite in m-dinitrobenzene solvent, a ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene of 3.87:1 is achieved (Chemical Abstracts CA 1991, No. 514135). In 1,2-dichloroethane solvent, an isomeric ratio of up to 11.73:1 can even be achieved, but in this case over 60% of the o-xylene used is not converted (J. Catal. 150, 1994, 430-433). A disadvantage of carrying out the process in the presence of zeolites is the use of a solvent and the heterogeneous catalyst, as a result of which, during the work-up of the reaction mixture, additional distillation steps and filtration steps become necessary.  
           [0009]    The object of the present invention was to provide a process for the nucleochlorination of o-xylene using a simply handled catalyst system, in which as high a possible a ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene is to be achieved.  
           [0010]    This object is achieved in a surprisingly simple manner by using benzo-fused thiazepines or thiazocines as co-catalysts.  
         SUMMARY OF THE INVENTION  
         [0011]    The invention therefore relates to a process comprising nucleo-chlorinating o-xylene using elemental chlorine in the presence of Friedel-Crafts catalysts and with benzo-fused thiazepines or thiazocines as co-catalysts.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0012]    Suitable Friedel-Crafts catalysts for the inventive process are known. Examples that may be mentioned are antimony chlorides, antimony oxides, aluminum chloride, iron(II) chloride, iron(III) chloride, tellurium chlorides, lead chlorides, molybdenum chlorides, tin chlorides, tungsten chlorides, titanium chlorides, zinc chlorides, boron trichloride, and boron trifluoride.  
           [0013]    Elements and element compounds that form a Friedel-Crafts catalyst, that is to say, a Lewis acid, during the chlorination can also be used (precursors of Friedel-Crafts catalysts), for example, the metals or semi-metals antimony, iron, lead, tin, zinc, molybdenum, tellurium, or aluminum or their oxides, sulfides, carbonyls, or salts, for example, carbonates. Examples of element compounds coming into consideration are antimony oxides, iron oxides, iron sulfides, lead sulfides, tin sulfides, zinc sulfides, iron carbonyls, molybdenum carbonyls, and boron phosphate. Instead of the chlorides mentioned, the corresponding fluorides, bromides, and, if appropriate, iodides of the said elements can also be used.  
           [0014]    Preference is given in the inventive process to antimony chlorides, iron, iron oxides, iron sulfides, iron carbonyls, and iron(III) chloride as Friedel-Crafts catalyst. Particular preference is given to iron(III) chloride.  
           [0015]    Friedel-Crafts catalysts and/or their precursors can be used individually or as any mixtures with one another.  
           [0016]    The amount of the Friedel-Crafts catalyst or its precursor can be varied within broad limits. Thus, frequently, catalyst activity can be observed even at an addition of 0.0005% by weight. On the other hand, 5% by weight or more of the Friedel-Crafts catalyst can also be added, but such high amounts generally offer no advantages and may even be accompanied by disadvantages during work-up. Usually, the Friedel-Crafts catalyst is used in an amount of 0.001 to 1.0% by weight, preferably 0.005 to 0.5% by weight. All these figures are based on the amount of the o-xylene used.  
           [0017]    In the inventive process the co-catalysts used are thiazepines or thiazocines. Processes for preparing such compounds are known and are described, for example, in U.S. Pat. No. 4,948,886.  
           [0018]    For example, the co-catalysts used can be benzothiazepines of the formulas  
                         
 
           [0019]    where  
           [0020]    R 1 , R 2 , R 3 , and R 4  are identical or different and represent hydrogen, hydroxyl, amino, cyano, halogen, nitro, nitroso, sulfonyl, sulfoxyl, tosyl, mercapto, carboxyl, carboxyamide, carbalkoxy, dithio-carboxyl, thiocarboxyamide, dithiocarbalkoxy, or unsubstituted or substituted alkyl, aryl, heteroaryl, alkoxy, aryloxy, heteroaryloxy, acyloxy, alkylthio, arylthio, heteroarylthio, acylthio, acyl, thioacyl, or acylamino and, in addition, can together form one or more saturated or unsaturated, unsubstituted or substituted isocyclic or heterocyclic carbon rings having up to 8 carbon atoms,  
           [0021]    R 5 , R 6 , R 7 , and R 8  are identical or different and have the meanings of R 1  to R 4  except that they cannot together form rings,  
           [0022]    Y denotes hydrogen, unsubstituted or substituted alkyl, aryl, heteroaryl, acyl, thioacyl, acyloxy, arylamino, or acylamino,  
           [0023]    X 1 , X 2 , or X 3  independently of one another each denotes one of the following groups:  
                         
 
           [0024]     where  
           [0025]    R 9  and R 10  are identical or different and have the meanings of R 5  to R 8 , and  
           [0026]    Z has the meaning of Y except that Z cannot be identical to H,  
           [0027]    A denotes the anellation of an unsubstituted or substituted saturated isocyclic or heterocyclic ring having up to 8 carbon atoms,  
           [0028]    B denotes the anellation of an unsubstituted or substituted unsaturated isocyclic or heterocyclic ring having up to 8 carbon atoms, and  
           [0029]    m denotes 0 or 1.  
           [0030]    In addition, the co-catalysts can be, for example, compounds of the formula  
                         
 
           [0031]    where R 21  and R 22  independently of one another denote hydrogen, hydroxyl, amino, cyano, halogen, nitro, carboxyl, halogenocarbonyl, carboxyamide, alkoxycarbonyl, alkyl, aryl, alkoxy, aryloxy, acyloxy, alkylthio, arylthio, acylthio, acyl, thioacyl, oracylamino,  
           [0032]    R 23  represents hydrogen or chlorine and, in addition with an adjacently ring-substituted radical R 21  or R 22  and together with the substituted carbon atoms, can form an anellated saturated, unsaturated, or aromatic isocyclic or heterocyclic ring having 5 to 8 ring atoms,  
           [0033]    R 24  denotes hydrogen, alkyl, aryl, halogen, alkylthio, arylthio, alkoxy, aryloxy, amino, hydrazino, alkylhydrazino, or phenylhydrazino,  
           [0034]    m, n, and o independently of one another can have the value 0 or 1, but n and o cannot simultaneously have the value 0,  
           [0035]    R 25 , R 27 , and R 29  independently of one another denote hydrogen, alkyl, alkoxy, phenyl, acyloxy, cyano, halogen, carboxyl, alkoxycarbonyl, phenoxy, or acyl, where R 25  and R 27  or R 27  and R 29 , together with the substituted carbon atoms, can form a saturated, unsaturated, or aromatic isocyclic or heterocyclic ring having 5 to 8 ring atoms,  
           [0036]    R 26 , R 28  and R 210  independently of one another denote hydrogen, alkyl, or halogen, where R 26  and R 28  or R 28  and R 210  can together form a double bond, where, in addition, R 25  and R 26  can together designate double-bonded oxygen, sulfur, or R 211 -substituted nitrogen, where R 211  denotes alkyl, aryl, acyl, alkylamino, or arylamino.  
           [0037]    In addition, the co-catalysts used can be, for example, compounds of the formula  
                         
 
           [0038]    where  
           [0039]    R 31  and R 32  independently of one another denote hydrogen, hydroxyl, amino, cyano, halogen, nitro, C 1 -C 8 -alkyl, phenyl that is unsubstituted or substituted by R 31  and R 32  (except for repeated substitution by R 31 - and R 32 -substituted phenyl), C 1 -C 8 -alkoxy, phenoxy, C 1 -C 8 -acyloxy, C 1 -C 8 -acyl, or C 1 -C 8 -alkoxycarbonyl,  
           [0040]    R 33  represents hydrogen or chlorine and furthermore with one of the radicals R 31  or R 32  and together with the substituted carbon atoms can form an anellated saturated, unsaturated, or aromatic isocyclic or heterocyclic ring having 5 to 8 ring atoms,  
           [0041]    R 34 , R 36 , and R 40  independently of one another denote hydrogen, C 1 -C 8 -alkyl, phenyl that is unsubstituted or substituted by R 31  and R 32  (except for repeated substitution by R 31 - and R 32 -substituted phenyl), C 1 -C 8 -acyl, C 1 -C 8 -alkoxycarbonyl, cyano, halogen, carboxyl, C 1 -C 8 -alkoxy, C 1 -C 8 -alkylthio, phenylthio, benzylthio, phenoxy, or C 1 -C 8 -acyloxy,  
           [0042]    R 35 , R 37 , and R 39  independently of one another denote hydrogen, C 1 -C 8 -alkyl, halogen, C 1 -C 8 -alkoxy, or C 1 -C 8 -alkylthio,  
           [0043]    R 38  denotes hydrogen, C 1 -C 8 -alkyl, phenyl that is unsubstituted or substituted by R 31  and R 32  (except for repeated substitution by R 31 -and R 32 -substituted phenyl), C 1 -C 8 -acyl, C 1 -C 8 -thioacyl, halogeno-carbonyl, or C 1 -C 8 -alkoxycarbonyl, and  
           [0044]    p represents one of the numbers 0 or 1,  
           [0045]    wherein, in addition,  
           [0046]    the pairs of substituents R 34  and R 35 , R 36  and R 37 , and R 39  and R 40  independently of one another can denote double-bonded oxygen, sulfur, or R 38 -substituted nitrogen, and  
           [0047]    where, in addition, the substituent pairs R 35  and R 36 , and R 38  and R 39  independently of one another can form a double bond, and  
           [0048]    where, in addition, the substituent pairs R 34  and R 37 , and R 38  and R 39  independently of one another can form 3- to 5-membered alkylene, in which 1 or 2 carbon atoms can be replaced by oxygen, sulfur, or R 38 -substituted nitrogen, and  
           [0049]    where, in addition, R 40  can also have the meaning hydrazino, C 1 -C 8 -alkylhydrazino, or phenylhydrazino.  
           [0050]    In addition the co-catalysts used can be, for example, compounds of the formula  
                         
 
           [0051]    where  
           [0052]    R 41  and R 42  independently of one another denote hydrogen, cyano, halogen, carboxyl, alkoxycarboxyl, alkyl, aryl, alkoxy, aryloxy, or acyl, preferably hydrogen, methyl, ethyl, propyl, or isopropyl,  
           [0053]    R 43  represents hydrogen, alkyl, or chlorine (preferably hydrogen) and in addition with an adjacently ring-substituted radical R 41  and R 42  and together with the substituted carbon atoms can form an anellated saturated, unsaturated, or aromatic, isocyclic or heterocyclic ring having 5 to 8 ring atoms,  
           [0054]    R 44  and R 45  independently of one another denote hydrogen, alkyl, aryl, halogen, alkoxy, aryloxy, acyl, or acyloxy (preferably hydrogen, methyl, ethyl, propyl, or isopropyl) or together with the substituted carbon atoms can form a saturated or unsaturated, isocyclic or heterocyclic ring having 5 to 8 ring atoms,  
           [0055]    R 46  denotes hydrogen, alkyl, aryl, or alkyl- or aryl-substituted silyl (preferably hydrogen), and  
           [0056]    q can have the value 0 or 1.  
           [0057]    In addition, the co-catalysts used can be, for example, compounds of the formula  
                         
 
           [0058]    where  
           [0059]    R 51  and R 52  independently of one another denote hydrogen, hydroxyl, amino, cyano, halogen, nitro, alkylsulfonyl, phenylsulfonyl, alkyl-sulfoxyl, phenylsulfoxyl, tosyl, mercapto, carboxyl, halogeno-carbonyl, carboxyamide, alkoxycarbonyl, thiocarboxyamide, alkyl, aryl, heteroaryl, alkoxy, aryloxy, heteroaryloxy, acyloxy, alkylthio, arylthio, heteroarylthio, acylthio, acyl, thioacyl, or acylamino,  
           [0060]    R 53  represents hydrogen or chlorine and in addition with one of the radicals R 51  or R 52  and together with the substituted carbon atoms can form an anellated saturated, unsaturated, or aromatic isocyclic or heterocyclic ring having 5 to 8 ring atoms,  
           [0061]    R 54  denotes hydrogen, alkyl, aryl, heteroaryl, acyl, thioacyl, halogeno-carbonyl, or alkoxycarbonyl,  
           [0062]    X 51  and X 52  independently of one another represent double-bonded oxygen, sulfur, or R 57 -substituted nitrogen, where R 57  has the scope of the meanings of R 54  except hydrogen,  
           [0063]    r, s, and t independently of one another can have the value 0 or 1, and  
           [0064]    R 55  and R 56  independently of one another can be at one or two of the carbon atoms situated between the S atom and the N atom in the 8-membered ring, provided that these carbon atoms are not occupied by X 51  or X 52 , and have the scope of meanings of R 51  and R 52 , where in the case of adjacent ring substitution, with the substituted carbon atoms a saturated, unsaturated, or aromatic isocyclic or heterocyclic ring having 5 to 8 ring atoms can also be formed and, where, in addition, R 55  and R 56  together can also denote double-bonded oxygen or sulfur.  
           [0065]    Preferably, the co-catalysts used are compounds that contain a seven-membered N- and S-containing heterocycle.  
           [0066]    In particular, preferably the co-catalysts used are compounds of the formula (I) where  
           [0067]    R 1 , R 2 , R 3 , R 4 , and Y represent hydrogen,  
           [0068]    X 1  represents ═O,  
           [0069]    X 2  and X 3  independently of one another in each case denote  
                         
 
           [0070]     where  
           [0071]    R 9  represents hydrogen, methyl, ethyl, propyl, or isopropyl, and  
           [0072]    m denotes 0.  
           [0073]    Also, preferably, the co-catalysts used are compounds of the formula (VI) where  
           [0074]    R 1 , R 2 , R 3 , and R 4  are identical or different and represent hydrogen, methyl, ethyl, propyl, or isopropyl,  
           [0075]    R 7  and R 8  denote hydrogen,  
           [0076]    Y represents hydrogen,  
           [0077]    X 1  represents ═O,  
           [0078]    m denotes the number 0, and  
           [0079]    A denotes a anellation of a saturated isocyclic ring having 6 carbon atoms.  
           [0080]    In addition, preferably, the co-catalysts used are compounds of the formula (VIII), where  
           [0081]    R 21 , R 22 , R 26 , and R 28  are identical or different and represent hydrogen, methyl, ethyl, propyl, or isopropyl,  
           [0082]    R 23  represents hydrogen,  
           [0083]    R 24  denotes methylthio, ethylthio, propylthio, or isopropylthio, m and o has the value 0,  
           [0084]    n has the value 1, and  
           [0085]    R 25  and R 27  independently of one another denote hydrogen or C 1 -C 4 -alkyl, where together with the substituted carbon atoms they can form a saturated isocyclic ring having 6 ring atoms.  
           [0086]    It is also possible to use in the inventive process the co-catalysts in combination with other elements or compounds that are not described as co-catalysts.  
           [0087]    The co-catalysts can be used not only individually but also in a mixture of a plurality of them.  
           [0088]    The amounts of co-catalyst used can vary within broad limits. Amounts less than 0.0001% by weight are less advantageous, since then the co-catalytic activity decreases. Amounts even of 5% by weight or more of co-catalyst can be used, but these high amounts generally offer no advantages, but they may cause disadvantages during work-up. The co-catalysts to be used inventively can therefore be used, for example, in an amount of 0.0001 to 1.0% by weight, preferably 0.0005 to 0.5% by weight, particularly preferably 0.001 to 0.1% by weight, in each case based on the amount of the o-xylene used.  
           [0089]    The molar ratio of Friedel-Crafts catalyst(s) or precursors thereof and co-catalyst(s) can be varied within broad limits in the inventive process. A suitable molar ratio, for example, of Friedel-Crafts catalysts or precursors thereof to co-catalyst is 100:1 to 1:50, preferably 75:1 to 1:10, particularly preferably 50:1 to 1:2.  
           [0090]    The inventive process is expediently carried out in the liquid phase. If appropriate, the process can be carried out in dilution with an inert solvent.  
           [0091]    Suitable solvents are those which are not attacked by chlorine under the conditions of a nucleochlorination and are known for this purpose to those skilled in the art, such as, for example, methylene chloride, chloroform, carbon tetrachloride, and acetic acid. Preferably no solvent is employed.  
           [0092]    The amount of chlorine is preferably selected such that a degree of chlorination of not significantly higher than 1 results. For example, an amount of 0.7 to 1.1 mol of chlorine is used, preferably 0.8 to 1 mol of chlorine, based on the amount of o-xylene used.  
           [0093]    The nucleochlorination to be carried out according to the invention can in principle be carried out at temperatures from the solidification point to the boiling point of the reaction mixture. Generally, the reaction temperature is −30 to 120° C., preferably −10 to 100° C., particularly preferably 0 to 70° C.  
           [0094]    The reaction pressure can be atmospheric, reduced, or elevated and is not critical in principle. Because of the inexpensive procedure, atmospheric pressure is preferred. Elevated pressure can be indicated, for example, if the procedure is to be carried out above the boiling point of a low-boiling solvent. In this case, for example, the procedure can be carried out below the inherent pressure of the reaction mixture established by itself.  
           [0095]    The water content of the reaction mixture is not generally critical. It is preferred not to dry all starting materials specially but to use them at the low water content at which they usually occur in chemical engineering. However, it is possible to dry individual or all substances of the reaction mixture specially. Usually, the water content of the starting materials should not be above the saturation limits of the respective starting materials. Water contents in the chlorination mixture are, according to the invention, preferably up to 250 ppm, particularly preferably up to 150 ppm, very particularly preferably up to 100 ppm.  
           [0096]    For carrying out the inventive process in practice, the sequence of the addition of the individual components to the reaction mixture is arbitrary. In this case the process may be carried out either continuously or batchwise. For example, o-xylene is charged at the desired reaction temperature, Friedel-Crafts catalyst and co-catalyst are added, and the chlorine is added until the desired degree of chlorination is reached. The chlorination mixture can then be worked up directly by distillation. The catalyst components remain behind in the bottom phase.  
           [0097]    The inventive process permits the nucleochlorination of o-xylene having an increased proportion of 4-chloro-1,2-dimethylbenzene with very low amounts of Friedel-Crafts catalysts and co-catalysts being required. Since the process is preferably carried out without solvent, simple work-up is possible by direct distillation of the product mixture.  
           [0098]    The following examples further illustrate details for the process of this invention. The invention is not to be limited either in spirit or scope by these examples. Those skilled in the art will readily understand that known variations of the conditions of the following procedures can be used. Unless otherwise noted, all temperatures are degrees Celsius and all percentages are percentages by weight. 
       
    
    
     EXAMPLES  
     Example 1  
       [0099]    [0099] 100  parts by weight of o-xylene were charged into a blackened chlorination beaker. 150 ppm of FeCl 3  and 39 ppm of a co-catalyst of the formula  
                         
 
         [0100]    were then added. At 20° C., over the course of 6 h, 95 mol% of chlorine (based on o-xylene) were introduced at a uniform rate. Gas-chromato graphic analysis of the reaction mixture found 6.1% o-xylene, 63.3% 4-chloro-1,2-dimethylbenzene, 25.2% 3-chloro-1,2-dimethylbenzene, 4.9% dichlorinated o-xylenes, and 0.5% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 2.51:1.  
       Example 2  
       [0101]    The method of Example 1 was repeated, but instead of the co-catalyst used there, 44 ppm of the co-catalyst of the formula  
                         
 
         [0102]    were added. Then, at 30° C., over the course of 6 h, 95 mol% of chlorine (based on o-xylene) were added at a uniform rate. Gas-chromatographic analysis of the reaction mixture found 8.4% o-xylene, 61.2% 4-chloro-1,2-dimethylbenzene, 25.1% 3-chloro-1,2-dimethylbenzene, 4.8% dichlorinated o-xylenes, and 0.5% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was 2.44.  
       Example 3  
       [0103]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 70 ppm of the co-catalyst of the formula  
                         
 
         [0104]    were used. At 20° C., over the course of 6 h, 95 mol % of chlorine (based on o-xylene) were added at a uniform rate. Gas-chromatographic analysis of the reaction mixture found 6.1% o-xylene, 62.0% 4-chloro-1,2-dimethyl-benzene, 26.0% 3-chloro-1,2-dimethylbenzene, 5.4% dichlorinated o-xylenes, and 0.4% unknown products, corresponding to a ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene of 2.38.  
       Example 4  
       [0105]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 52 ppm of the co-catalyst of the formula  
                         
 
         [0106]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced. Gas-chromatographic analysis of the reaction mixture found 6.1% o-xylene, 67.0% 4-chloro-1,2-dimethylbenzene, 22.0% 3-chloro-1,2-dimethylbenzene, 4.4% dichlorinated o-xylenes, and 0.5% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 3.04.  
       Example 5  
       [0107]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 37 ppm of the co-catalyst of the formula  
                         
 
         [0108]    were used. Then, 95 mol % of chlorine (based on o-xylene) were added at 20° C. at a uniform rate. Gas-chromatographic analysis of the reaction mixture found 5.2% o-xylene, 63.7% 4-chloro-1,2-dimethylbenzene, 25.3% 3-chloro-1,2-dimethylbenzene, 5.2% dichlorinated o-xylenes, and 0.6% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 2.52.  
       Example 6  
       [0109]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 57 ppm of the co-catalyst of the formula  
                         
 
         [0110]    were used and instead of FeCl 3 , 280 ppm of SbCl 5  were used. At 20-25° C., 95 mol % of chlorine (based on o-xylene) were then added over the course of 6 h at a uniform rate. Gas-chromatographic analysis of the reaction mixture found 5.6% o-xylene, 69.9% 4-chloro-1,2-dimethylbenzene, 19.0% 3-chloro-1,2-dimethylbenzene, 3.9% dichlorinated o-xylenes, and 0.6% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was therefore 3.68.  
       Example 7  
       [0111]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 57 ppm of the co-catalyst of the formula  
                         
 
         [0112]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 7.5% o-xylene, 69.5% 4-chloro-1,2-dimethyl-benzene, 19.2% 3-chloro-1,2-dimethylbenzene, 3.4% dichlorinated o-xylenes, and 0.4% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 3.62.  
       Example 8  
       [0113]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 40 ppm of the co-catalyst of the formula  
                         
 
         [0114]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 7.2% o-xylene, 63.7% 4-chloro-1,2-dimethyl-benzene, 23.3% 3-chloro-1,2-dimethylbenzene, 5.1% dichlorinated o-xylenes, and 0.7% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 2.73.  
       Example 9  
       [0115]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 55 ppm of the co-catalyst of the formula  
                         
 
         [0116]    were used. Then, at 20° C., 95 mol % of chlorine (based on-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 8.0% o-xylene, 58.8% 4-chloro-1,2-dimethyl-benzene, 27.2% 3-chloro-1,2-dimethylbenzene, 5.4% dichlorinated o-xylenes, and 0.6% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 2.16.  
       Example 10  
       [0117]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 49 ppm of the co-catalyst of the formula  
                         
 
         [0118]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 6.8% o-xylene, 66.1% 4-chloro-1,2-dimethyl-benzene, 21.5% 3-chloro-1,2-dimethylbenzene, 5.1% dichlorinated o-xylenes, and 0.5% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 3.07.  
       Example 11  
       [0119]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 38 ppm of the co-catalyst of the formula  
                         
 
         [0120]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 7.3% o-xylene, 64.1% 4-chloro-1,2-dimethyl-benzene, 23.2% 3-chloro-1,2-dimethylbenzene, 4.9% dichlorinated o-xylenes, and 0.5% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 2.76.  
       Example 12  
       [0121]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 38 ppm of the co-catalyst of the formula  
                         
 
         [0122]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 9.1% o-xylene, 58.3% 4-chloro-1,2-dimethyl-benzene, 26.8% 3-chloro-1,2-dimethylbenzene, 5.2% dichlorinated o-xylenes, and 0.6% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 2.18.  
       Example 13  
       [0123]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 53 ppm of the co-catalyst of the formula  
                         
 
         [0124]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 8.6% o-xylene, 54.9% 4-chloro-1,2-dimethyl-benzene, 28.7% 3-chloro-1,2-dimethylbenzene, 7.3% dichlorinated o-xylenes, and 0.5% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 1.91.  
       Example 14  
       [0125]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 55 ppm of the co-catalyst of the formula  
                         
 
         [0126]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 7.1% o-xylene, 66.1% 4-chloro-1,2-dimethyl-benzene, 21.3% 3-chloro-1,2-dimethylbenzene, 4.9% dichlorinated o-xylenes, and 0.6% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 3.10.  
       Example 15  
       [0127]    The process of Example 1 was repeated, but instead of the co-catalyst used there, 43 ppm of the co-catalyst of the formula  
                         
 
         [0128]    were used. Then, at 20° C., 95 mol % of chlorine (based on o-xylene) were introduced over the course of 6 h. Gas-chromatographic analysis of the reaction mixture found 9.2% o-xylene, 66.2% 4-chloro-1,2-dimethyl-benzene, 19.9% 3-chloro-1,2-dimethylbenzene, 4.3% dichlorinated o-xylenes, and 0.4% unknown products. The ratio of 4-chloro-1,2-dimethylbenzene to 3-chloro-1,2-dimethylbenzene was thus 3.33.