Abstract:
A more efficient reaction mechanism is provided for producing 1,1-dichloro-1-fluoroethane (HCFC-141b) by reacting vinylidene chloride with hydrogen fluoride in the liquid phase in the presence of a catalyst and a sulfone solvent or a nitroalkane or nitroarene solvent. In particular, by using a titanium tetrafluoride catalyst in conjunction with tetramethylene sulfone solvent, most all the vinylidene chloride reagent can be converted to HCFC-141b to the virtual exclusion of unwanted, closely associated byproducts like 1,1-difluoro-1-chloroethane (HCFC-142b) and 1,1,1-trifluoroethane (HFC-143a), while reducing the production of tars to a minimum.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application has the same inventors as and is a continuation-in-part of the U.S. application with the Ser. No. 07/992,146 filed on Dec. 17, 1992 and issued on Aug. 9, 1994, as U.S. Pat. No. 5,336,816. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the production of hydrogen chlorinated fluorocarbons (HCFC&#39;s), and more specifically to a method for preparing 1,1-dichloro-l-fluoroethane also known in the trade as HCFC-141b or R-141b. 
     Because of the celebrated ozone-depleting properties of chlorinated fluorocarbons (CFC&#39;s), they are falling out of favor for such uses as solvents for cleaning circuit boards, blowing agents for the extrusion of polymer foams, and aerosol propellants. Indeed, international treaties have established strict schedules for phasing out the use of CFC&#39;s. 
     HCFC&#39;s have been found to exhibit a relatively low ozone depletion potential, and have therefore been offered as a significant alternative to the use of CFC&#39;s. They include HCFC-141b, as well as the closely related 1,1-difluoro-1chloroethane (a.k.a., HCFC-142b) and 1,1,1-trifluoroethane (a.k.a., HFC-143a). 
     HCFC-141b has been prepared by a number of known methods. For example, 1,1,1-trichloroethane may be reacted with hydrogen fluoride as follows: ##STR1## to induce a halogen exchange between the chlorine and fluorine anions. U.S. Pat. No. 3,833,676 issued to Rokuo Ukaji et al. discloses such a reaction without the use of a catalyst, while U.S. Pat. No. 4,091,043 issued to Ohsaka et al., and European Published Application No. 353,059 issued to E. I. dupont de Nemours teach the use of metal halide catalysts, including antimony pentachloride. However, this halogen exchange reaction sequence suffers from several significant problems. First, for each molecule of HCFC-141b produced, a corresponding molecule of HCl is generated, which must be recovered and disposed of. Second, the trichloromethyl group of 1,1,1-trichloroethane reacts so readily in the halogen exchange reaction that multiple fluorination almost always occurs under normal operating conditions, thereby producing: ##STR2## at the expense of the desired HCFC-141b product. This reduces significantly the yield of HCFC-141b, and poses the need to separate the unwanted HCFC-142b and HFC-143a from HCFC-141b. 
     While E. T. McBee et al, &#34;Fluorinated Derivatives of Ethane,&#34; Industrial and Engineering Chemistry (March 1947), pp. 409-12 is directed to a method of producing HFC-143a from either 1,1,1-trichloroethane or vinylidene chloride, the article also indicates that large amounts of HCFC-142b can be generated at high reaction temperatures and times as a side product. However, it also shows that no HCFC-141b was isolated. It is known, however, that vinylidene chloride will react directly with HF to produce HCFC-141b without the generation of Hcl, as follows: ##STR3## For example, U.K. Patent No. 627,773 issued to Chapman used stannic chloride at 35° C. for 1.75 hours to catalytically induce the reaction sequence, and convert 32.7% of the vinylidene chloride to HCFC-141b. A. L. Henne et al., &#34;The Addition of Hydrogen Fluoride to Halo-Olefins,&#34; Journal of American Chemical Society (1943), vol. 65, pp. 1271-72, discloses a reaction at 65° C. for 3 hours, using 4 moles of HF without a catalyst to yield a product comprising 50% HCFC-141b, a trace of HCFC-142b, 10% unreacted vinylidene chloride, 5% CH 3  CCl 3  (a.k.a., R-140), and 15% tar. Twenty percent of the product stream composition is unaccounted for. These procedures, however, give poor to moderate selectivity and conversion to HCFC-141b with relatively large amounts of tar. Indeed, the propensity of vinylidene chloride to dimerize and polymerize, as well as to over-fluorinate as in the halogen exchange mechanism, makes this route appear unattractive. 
     Efforts have also been made with varying degrees of success to use a vapor phase process for reacting vinylidene chloride with HF to produce HCFC-141b. U.S. Pat. No. 3,755,477 issued to Firth et al. discloses the use of a steam-treated chromium oxide catalyst at 80° C. to yield 46% HCFC-141b, the remainder being unwanted fluorinated products like HCFC-142b and HFC-143a. At 90°-100° C., however, no HCFC-141b was produced. U.S. Pat. No. 3,803,241 issued to Stolkin used alumina impregnated with a chromium salt solution at 198° C. to catalytically induce a vapor-phase reaction producing 98.8% HFC-143a and 0.2% each of HCFC-141b and HCFC-142b. By contrast, European Published Application No. 353,059 issued to E.I. dupont de Nemours teaches a process passing the reagents mixed in the vapor phase through an aluminum fluoride catalyst at 74°-86° C. using a molar HF/vinylidene chloride ratio of 4.3 to produce a product stream comprising 99.8% HCFC-141b, 0.1% HCFC-142b, and 0.1% unreacted vinylidene chloride with an 89.6% yield. The missing 10% of the product stream is probably tar, which would shorten the life of the catalyst. 
     Vinylidene chloride has also been reacted with HF in the liquid phase to produce HCFC-142b, as disclosed by Japanese Published Application No. 47-39086 issued to Kureha Kagaku Kogyo Co., Ltd., using a stannous chloride catalyst. Running the process at 90° C. for 60 minutes using a 6.0 HF/vinylidene chloride ratio, 96.4% of the vinylidene chloride reagent was converted to fluorochloroethanes, for a yield of 76.4% HCFC-142b, 8.0% HCFC-141b, and 12.0% HFC-143a--a high conversion rate, but an exceedingly low yield of HCFC-141b product. The disclosure also indicates that when TiCl 4  catalyst was used, 40.4% of the resulting product stream comprised HCFC-141b, while HCFC-142b accounted for 4.0%. However, identifiable organic products only accounted for 51% of the product stream leaving 49% for tar. The moderate yield of HCFC-141b product and large production of tar makes this process undesirable. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a method, which converts vinylidene chloride and HF to HCFC-141b. 
     Another object of the present invention is to provide such a method, which selectively produces HCFC-141b, with minimal formation of HCFC-142b, tar, and other undesirable byproducts. 
     Yet another object of the present invention is to provide such a method, which converts a large percentage of the vinylidene chloride to organic products. 
     Still another object of the present invention is to increase production of the HCFC-141b end product by providing a method which requires a relatively short reaction time period. 
     Yet another object of the present invention is to use reagents in the liquid phase for such a reaction in order to reduce reactor volumes and energy consumption levels required for the process. 
     Other objects of the invention, in addition to those set forth above, will become apparent to those skilled in the art from the following invention disclosure. 
     The present invention is a method for preparing 1,1-dichloro-1-fluoroethane (HCFC-141b) in high yield, comprising reacting vinylidene chloride and hydrogen fluoride in the presence of a catalyst and a solvent selected from the group consisting of: a cyclic sulfone solvent represented by the formula C x  H 2x  SO 2 , where x=3 to 7, a sulfone solvent represented by the formula RSO 2  R 1 , and a nitrated solvent represented by the formula R 2  NO 2 , wherein R and R 1  are selected from the group consisting of: 
     an aromatic ring (C 6  H 5 ), 
     an alkyl group (C y  H 2y+1 , where y=1 to 6), and 
     a fluorine; and 
     R 2  is selected from the group consisting of: 
     an aromatic ring (C 6  H 5 ) and 
     an alkyl group (C z  H 2z+1 , where z=1 to 6). 
     Briefly, the invention is directed to providing a more efficient reaction mechanism for producing HCFC-141b by reacting vinylidene chloride with hydrogen fluoride in the liquid phase in the presence of a catalyst and a sulfone solvent such as an alkyl sulfone, an aryl sulfone or an alkyl aryl sulfone or a nitroalkane or a nitroarene solvent. In particular, by using a titanium tetrafluoride catalyst in conjunction with tetramethylene sulfone solvent, most all the vinylidene chloride reagent can be converted to HCFC-141b to the virtual exclusion of unwanted, closely associated byproducts like HCFC-142b and HFC-143a, while reducing the production of tars to a minimum. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred catalyst for converting vinylidene chloride to HCFC-141b using an excess of HF is titanium tetrafluoride (TiF 4 ), although titanium may be conveniently added as a tetrahalide, or another Ti +4  derivative like titanium tetrachloride (TiCl 4 ), which will be readily converted to TiF 4  in the presence of anhydrous HF. Catalysts like boron trifluoride etherate (BF 3 ) and tin tetrachloride (SnCl 4 ) may also be used, although BF 3  is highly volatile, and therefore is readily lost from the reactor. 
     The preferred solvent for the catalyst/solvent system is a sulfone, preferably tetramethylene sulfone, also known as sulfolane: ##STR4## 
     However, any other alkyl sulfones, aryl sulfones or alkyl aryl sulfones that are stable to HF and the catalyst, having a melting point below 60° C. in the presence of HF, such as dimethyl sulfone (Me 2  SO 2 ), dibutyl sulfone (Bu 2  SO 2 ), methane sulfonyl fluoride (MeSO 2  F) and benzenesulfonyl fluoride (Ph 2  SO 2  F), may also be used. Nitroalkane solvents like nitromethane (MeNO 2 ) or nitroarene solvents like nitrobenzene (PhNO 2 ) likewise modify the activity of TiF 4 , and may be also used to good effect. 
     The catalyst/solvent system is prepared by dissolving and suspending the titanium compound in the solvent, and treating the mixture with excess anhydrous HF. While TiCl 4  comprises the titanium source of the preferred embodiment, TiO 2  or titanium tetra-alkoxide may be used if a drying agent like thionyl chloride is employed to destroy the water or alcohol formed thereby. The resulting catalyst is soluble in the solvent, and forms a complex with it. 
     The molar ratio of solvent to catalyst may range between 2 and 50, the preferred ratio being between 6 and 10. Lower ratios result in higher carbonation and tar formation, while high ratios lead to reduced reaction rates. 
     The molar ratio of vinylidene chloride to catalyst may range between 10 and 200, the preferred ratio being 20. The lower ratios result in greater byproduct formation, while the higher ratios provide unnecessarily slow reaction rates. 
     Excess HF is necessary to drive the reaction to high conversion. While a 2 to 3 molar excess with respect to the vinylidene chloride reagent is preferred, larger excesses may be used to advantage. 
     Batch reaction temperatures may range between 25° C. and 150° C. with the preferred temperature being 60°-95° C. Pressure is not a critical element of the batch reaction. Since autogenous pressure is most convenient, it is preferred. The preferred synthetic method is to run the reaction in an adiabatic plug flow reactor. 
     EXAMPLE I 
     The reactions were analyzed using a Hewlett-Packard 5890 gas chromatograph with thermal conductivity detectors, using a 30-foot, 0.5mm, DB-1 megabore capillary column. Peaks were identified with a Hewlett-Packard 5971A mass selective detector. 
     The first set of batch experiments were run in a 300 ml stirred Hastaloy C Parr autoclave fitted with a thermocouple and pressure gauge. In the bomb were placed sulfolane and TiCl 4  or anhydrous TiF 4 . The bomb was sealed and weighed. A weighed quantity of HF was then added through a dip tube at room temperature. A moderate exotherm from the solvation of HF in the sulfolane was observed. When TiCl 4  was used, pressure built up in the reactor from liberation of HCl. 
     Next, the bomb was cooled to about 10° C. When HCl was present, the bomb was vented and reweighed. To the cold mixture was added 81 ml (i.e., 97 g or 1 mole) of vinylidene chloride through the gas inlet by means of a syringe. The bomb was then placed in a preheated bath fitted with a temperature controller, and brought to the desire temperature as rapidly as possible, and maintained thereafter at that temperature. 
     Immediately after the desired temperature was reached, and periodically thereafter until the reaction was complete, a vapor sample was withdrawn by attaching a 50 ml polyethylene syringe containing 1-2g of crystalline trisodium phosphate to the gas outlet. The syringe was capped and shaken until the HF was neutralized. The vapor sample was then analyzed by gas chromatography. The sampling times were then adjusted to take into account the reaction that took place during the heating period, and to provide the best fit of the rate constant K2 for the reaction. The K2 values thus obtained were subjected to regression analysis, and are reported in Table 1. 
     The yield of crude HCFC-141b was determined by distilling the volatiles from the bomb at 60°-70° C. through a dry ice-cooled condenser into a teflon-coated separatory funnel cooled in an ice bath. The upper layer comprised HF, while the lower layer comprised HCFC-141b. The HCFC-141b fraction was separated, washed with water, dried over anhydrous, potassium carbonate, and weighed. Due to the volatility of the HCFC-141b and the HCFC-141b/HF azeotrope, and the solubility of HCFC-141b in liquid HF, there were significant losses of the product during workup. Yields of HCFC-141b in the total volatile organic product determined by gas chromatography and isolated crude yields (usually greater than 97% pure by GC) are reported in Table 1. 
     After stripping the volatiles, the bomb was weighed once again to determine the amount of HF retained by the sulfolane. This mixture was reused in successive runs until a new catalyst level was required, or the bomb seals failed. 
     Average volatile &#34;tars&#34; were estimated by combining the crude HCFC-141b from a series of runs at a single catalyst level, and distilling the HCFC-141b through an efficient packed distillation column. The pot residue was weighed, and that weight divided by the total number of runs is reported in Table 2. 
     Average nonvolatile tars were estimated by pouring the stripped sulfolane/HF catalyst residue left in the bomb after a series of runs at the same catalyst level on ice and 100 ml of 20% aqueous HCl. The mixture was then extracted three times with methylene chloride, and the aqueous layer discarded. The combined organic extract was washed three times with 10% aqueous HCl, three times with concentrated sulfuric acid, dried over anhydrous potassium carbonate, and filtered and evaporated on a Rotovap at atmospheric pressure and 60° C. The residue was weighed, divided by the number of runs represented, and reported in Table 2. 
     Thus, it can be seen that when sulfolane was not used, only 50-79% of the product stream comprised identified organic materials, the remainder being tar, although all but 1% of the vinylidene chloride was reacted. The reaction was relatively selective, with 73.1-95.3% of the product stream comprising HCFC-141b. By adding sulfolane to modify the titanium-based catalyst, however, conversions consistently ranging between 83% and 95% were obtained with HCFC-141b accounting for 95.0-98.7% of the volatile components contained in the product stream. Not only was the reaction highly selective in favor of HCFC-141b to the virtual exclusion of HCFC-142b with almost complete conversion of the vinylidene chloride reagent, but also short reaction times and relatively low temperatures were used. 
     EXAMPLE II 
     A second set of batch experiments were run using the apparatus and procedure described in Example I. The reaction was run with 2.65 moles of anhydrous hydrogen fluoride, 1 mole of vinylidene chloride, 0.05 moles of the test solvent at 60° C. The solvents used were methane sulfonyl fluoride (MeSO 2  F), benzenesulfonyl fluoride (PhSO 2  F), dibutylsulfone (Bu 2  SO 2 ), dimethylsulfone (Me 2  SO 2 ), sulfolane, nitrobenzene (PhNO 2 ), and nitromethane (MeNO 2 ). In each case the reaction was essentially complete in 40-60 minutes with about 1% vinylidene chloride present. 
     EXAMPLE III 
     Experiments were run under adiabatic continuous flow conditions. A solution of 1140 g of sulfolane and 190 g of titanium tetrachloride was carefully treated with a large excess of anhydrous hydrogen fluoride (exothermic, HCl evolution). The resulting HCl and excess HF were removed by heating the solution to 82° C. The solution was then cooled to ambient then pumped at 40 ml/min. through a 50 ml (3.5 inch long) Monel mixing chamber with 17.3 ml/min. anhydrous HF. Through a &#34;T&#34; coupling at the entrance to the reactor, 22.7 ml/min. of vinylidene chloride was added to the solution exiting the mixing chamber. The reactor was a 150 ml (8.5 inch long) insulated Monel bomb fitted with a thermocouple and back pressure regulator set at 450 psi at the exit (225-250 psi has been found to be adequate). An exotherm took place which raised the exit temperature to 117° C. The products flashed upon exiting the reactor. Gas chromatography analysis of the vapors showed a composition of 0.6% vinylidene chloride, 98.4% 1,1-dichloro-1-fluoroethane (HCFC-141b), and 0.5% 1,1-difluoro-1-chloroethane (HCFC-142b). 
     
                                           TABLE 1__________________________________________________________________________                             Percent  Percent    Initial         Temper-  Reaction                             Conversion                                      VolatileExam-    HF   Catalyst          Sulfolane               ature                    Rate                        Time to Volatile                                   Los-                                      Vinylidene                                            Product Fractionple (Moles)    (Mole %)          (ml) (°C.)                    K2  (minutes)                             Products                                   ses*                                      chloride                                            HCFC-141b                                                   HCFC-142b__________________________________________________________________________ 1  3.35 5.0    0   47   0.0313                        47   50    50 0.6   73.1   26.3 2  3.16 5.0    0   51   0.0408                        29   79    21 1.0   95.3   3.7 3  3.94 5.0     12.5               48   0.0559                        51   85    15 1.2   98.7   0.1 4  2.95 5.0     12.5               54   0.0579                        50   83    17 1.3   98.5   0.2 5  4.02 5.3   25   60   0.0727                        32   89    11 1.1   97.6   1.3 6  3.84 5.4   50   45   0.0491                        45   89    11 1.8   96.1   2.1 7  4.60 5.4   50   50   0.0682                        33   87    13 1.5   96.6   1.9 8  3.85 5.4   50   50   0.0714                        53   83    17 0.9   97.1   2.0 9  3.89 2.0   50   55   0.1617                        51   95     5 0.6   98.4   1.010  3.57 1.0   50   55   0.1790                        92   85    15 1.6   97.6   0.811  4.18 1.0   50   55   0.2324                        55   92     8 0.7   98.4   0.912  4.04 0.5   50   55   0.2623                        81   89    11 2.7   96.5   0.813  3.98 5.4   50   60   0.1053                        27   85    15 0.5   98.2   1.314  3.97 2.0   50   65   0.1884                        50   92     8 1.5   97.0   1.515  3.46 1.0   50   65   0.2084                        85   80    20 1.0   97.9   1.116  3.68 2.0   50   65   0.2577                        38   91     9 0.7   97.9   1.617  3.52 1.0   50   65   0.3214                        71   92     8 0.6   97.9   1.518  4.17 5.4   50   69   0.2457                        27   89    11 0.5   95.0   4.5__________________________________________________________________________ *These are materials that under the particular conditions were not collectable. They were primarily organic product, due to the high volatility thereof, with some tar. 
    
     
                                           TABLE 2__________________________________________________________________________            Total Total Average      No. batch            amount of                  amount of                        amount tar                              TotalCatalyst Sulfolane      runs  nonvolatile                  volatile                        per batch                              tars(Mole %) (ml) averaged.sup.1            tar (g)                  tar (g)                        run (g)                              (wt. %)__________________________________________________________________________0.5   50   8     1.2         0.2      7           18.1  2.6   2.91.0   50   8     3.1         0.4      8           19.2  2.4   2.92.0   50   8     3.1         0.4      8           14.1  1.8   2.25.4   50   8     2.4         0.3      8           15.3  1.9   2.35.3   25   10    4.4         0.4      10          20.6  2.1   2.65.0     12.5      4     *           --      4           10.8  2.7   .sup. 3.5.sup.25.00-    4    large*      5?      4           11.5  1.9   4.5-6.0.sup.2__________________________________________________________________________ *Semi-solid residue which formed a stable emulsion on workup. .sup.1 While the catalyst and sulfolane solvent in the reactor were between batch runs, additional vinylidene chloride and hydrogen fluoride reagents were introduced for each run. .sup.2 These are conservative estimates. 
    
     
                       TABLE 3______________________________________COMPARISON OF SOLVENTS AT 60° C.HG/VDC/Ti ratio 2.65/1/.05          AdjustedSolvent Time   Time     142b   141b  VDC   K2______________________________________MeSO.sub.2 F   10     7        0.0054 0.7596                                0.2337                                      0.05765   20     17       0.0195 0.9453                                0.0336   30     27       0.0451 0.9427                                0.0107   40     37       0.1036 0.8908                                0.0041   50     47       0.0976 0.8973                                0.0037   60     57       0.14   0.856 0.0024   70     67       1.1448 0.8512                                0.0023   80     77       0.1773 0.8174                                0.0024   90     87       0.19   0.8058                                0.0014   100    97       0.2554 0.7403                                0.0007   110    107      0.2571 0.7382                                0.0009PhSO.sub.2 F   10     7.4      0.0188 0.7658                                0.2154                                      0.07705   20     17.4     0.641  0.8991                                0.0368   30     27.4     0.0815 0.9008                                0.0104   40     37.4     0.1114 0.888 0.0058   50     47.4     0.2292 0.7688                                0.002   60     57.4     0.2106 0.787 0.0023   70     67.4     0.2445 0.7534                                0.0021   80     77.4     0.3561 0.6417                                0.0022   90     87.4     0.2872 0.7121                                0.0018Bu.sub.2 SO.sub.2   12     6        0.0016 0.6302                                0.3629                                      0.0937   20     14       0.0037 0.9242                                0.0673   30     24       0.005  0.9732                                0.0182   40     34       0.0049 0.9778                                0.014   50     44        0.00114                          0.9767                                0.0073   60     54       0.006  0.9857                                0.0051   70     64       0.0102 0.9809                                0.0051   80     74       0.0118 0.9793                                0.0048   90     84       0.0106 0.9827                                0.0038   100    94       0.014  0.9791                                0.0038Sulfolane   10     8.86     0.0011 0.6457                                0.3505                                      0.03848   20     18.86    0.0046 0.8612                                0.1327   30     28.86    0.0092 0.9114                                0.0641   40     38.86    0.0136 0.9569                                0.0283   50     48.86    1.0129 0.9658                                0.0193   60     58.86    0.0182 0.9617                                0.0181   75     73.86    0.025  0.9551                                0.0177   90     88.86    0.0385 0.947 0.0119   105    103.86   0.0278 0.9589                                1.0114Me.sub.2 SO.sub.2   12     6.2      0.0057 0.4938                                0.4981                                      0.04085   20     14.2     0.0078 0.8157                                0.1698   30     24.2     0.0128 0.9205                                0.0613   40     34.2     0.0142 0.9503                                0.032   50     44.2     0.0186 0.9539                                0.0229   60     54.2     0.026  0.9555                                0.0162   75     69.2     0.0306 0.9519                                0.0116   90     84.2     0.0226 0.9628                                0.01   120    114.2    0.0457 0.94  0.0058CH.sub.3 NO.sub.2    8     7.6      0.0042 0.7816                                0.2134                                      0.04197   12     11.6     0.0071 0.8332                                0.1579   16     15.6     0.0059 0.8758                                0.1172   20     19.6     0.007  0.9157                                0.0758   25     24.6     0.0075 0.9589                                0.0323   30     29.6     0.0086 0.9729                                0.0173   40     39.6     0.0095 0.9821                                0.0072   50     49.6     0.011  0.9732                                0.014   60     59.6     0.0169 0.9777                                0.004   75     74.6     0.017  0.976 0.0034   90     89.6     0.016  0.9789                                0.0033PhNO.sub.2    5     3        0.0018 0.5827                                0.4114                                      0.0878   10     8        0.005  0.9017                                0.897   15     13       1.0073 0.9572                                0.0286   20     18       0.009  0.9752                                0.0139   30     28       0.0148 0.9742                                0.0088   40     38       0.0181 0.9718                                0.0075   60     58       0.0339 0.958 0.0047   90     88       0.0416 0.9493                                0.0034______________________________________