Patent Publication Number: US-2010121116-A1

Title: Process for preparing octafluorocyclohexadiene

Description:
CROSS-REFERENCE TO RELATED U.S. APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not applicable. 
     REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process of preparing octafluorocyclohexadiene by allowing hexafluorobenzene to react with a fluorinating agent, in which octafluorocyclohexadiene can be obtained with high selectivity, and to a fluorinating agent for use in the process. 
     More particularly, the present invention relates to a process of preparing octafluorocyclohexadiene (C 6 F 8 ) by allowing hexafluorobenzene (C 6 F 6 ) to react with a fluorinating agent, and to a fluorinating agent comprising 1-10 wt % of cobalt fluoride (CoF 2 ) and 90-99 wt % of othermetal fluoride selected one at least among calcium fluoride (CaF 2 ), magnesium fluoride (MgF 2 ), aluminum(III) fluoride (AlF 3 ), sodium fluoride (NaF) and potassium fluoride (KF). 
     2. Description of Related Art Including Information Disclosed under 37 CFR 1.97 and 37 CFR 1.98 
     Octafluorocyclohexadiene (C 6 F 8 ) is a compound having a molecular weight of 224 and a boiling point of 56-58° C. It is a candidate material which can form an electrical insulating thin film in the plasma state on a silicon surface, thus, can be used for the next-generation semiconductor process. 
     U.S. Pat. No. 4,423,260 and U.S. Pat. No. 4,476,337 disclose a process of preparing octafluorocyclohexadiene (C 6 F 8 ) by allowing hexafluorobenzene (C 6 F 6 ) to react with a fluorinating agent which is obtained by dissolving NF 4 .BF 4  in a Hydrogen fluoride (HF) solution. In the process, the selectivity of C 6 F 8  is relatively as high as about 94%, but the process is not suitable as a commercial process, because it is a laboratory-scale synthesis process, and the process for preparing NF4.BF4 is so much complicated. In addition, a process of preparing C 6 F 8  using chlorobenzene as a starting material has problems in that, because hydrofluoric acid and hydrochloric acid are produced, a separate process for removing the acids is required, and a number of isomers are also produced. 
     In addition to the above-described processes, a process of preparing C 6 F 8  by allowing hexachlorobenzene (C 6 C 16 ) to react with bromine trifluoride (BrF 3 ) and antimony pentafluoride (SbF 5 ) is also known (U.S. Pat. No. 2,432,997). 
     As described above, the process of fluorinating the aromatic ring compound by substituting the chlorine atom of the aromatic ring compound with a fluorine is known as a laboratory-scale process, because it shows low selectivity and low conversion rate and causes large amounts of byproducts. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a process of preparing octafluorocyclohexadiene (C 6 F 8 ) using hexafluorobenzene (C 6 F 6 ) as a starting material, in which conversion and selectivity are low and the production of byproducts is low, and a fluorinating agent for use in the fluorination process. 
     The fluorinating agent according to the present invention is a powder and is prepared by mechanically mixing 1-10 wt % of cobalt difluoride (CoF 2 ) with 90-99 wt % of other metal fluoride selected one at least among calcium fluoride (CaF 2 ), magnesium fluoride (MgF 2 ), aluminum(III) fluoride (AlF 3 ), sodium fluoride (NaF) and potassium fluoride (KF) and allowing the mixture to react with fluorine gas, thus preparing an activated fluorinating agent. Reactivity and selectivity are vary depending on the ratio of metal fluoride added, and this fluorinating agent is suitable for selectively synthesizing octafluorocyclohexadiene (C 6 F 8 ). 
     The activation for the fluorinating agent is carried out by allowing CoF 2  and the metal fluoride to react with fluorine gas so as to activate the metal fluoride, and it proceeds according to the following reaction equation: 
       CoF 2 +1/2F 2 →CoF 3    
     Metal fluorides other than CoF 2  no longer undergo a fluorination reaction during the process of activating the fluorinating agent. 
     CoF 3  is a good fluorinating agent, but unstable compound which is reduced into CoF 2  immediately upon contact with air and is very difficult to store. 
     When C 6 F 6  is used as a starting material to prepare C 6 F 8 , with CoF 3  as a fluorinating agent to fluorinate C 6 F 6 , the reaction product will be obtained as a mixture of C 6 F 8 , C 6 F 10  and C 6 F 12  in various ratios. Particularly if only CoF 3  is used as the fluorinating agent, most of reaction product will be C 6 F 12 . 
     Herein, the reaction of C 6 F 6  is influenced by the fluorinating ability of the fluorinating agent and the reaction temperature, and the mixing ratio of metal oxides. 
     Accordingly, in order to increase the selectivity of the target compound (C 6 F 8 ), it is required to maintain reaction conditions suitable therefor. 
     The present inventors have conducted various experiments to determine reaction conditions in which the selectivity of the target compound (C 6 F 10 ) can be maximized. As a result, the present inventors have found that the fluorination rate of C 6 F 6  can be adjusted by adjusting the weight ratio of CoF 3  in the fluorinating agent, and have found reaction conditions, in which the selectivity of C 6 F 8  is high, by selecting and employing a metal fluoride as a diluting agent to adjust the content ratio of CoF 3  without adversely affecting a fluorination reaction, thereby completing the present invention. 
     Herein, the metal fluoride is preferably CaF2, MgF2, AlF3, NaF or KF. 
     In order to inhibit C 6 F 6  from proceeding to C 6 F 12  due to the high activity of CoF 3  and to control reaction conditions, the activity of CoF 3  needs to be adjusted to a low level. 
     The process of preparing octafluorocyclohexadiene using the activated fluorinating agent is characterized in that, as a method of adjusting the reactivity of the fluorinating agent in order to obtain the optimal yield, in addition to adjusting the ratio of metal fluoride added, any one of nitrogen (N 2 ), helium (He) and argon (Ar) that are inert gases is supplied together with the reactant. 
     When inert gas is introduced into the fluorination reaction of C 6 F 6 , the contact time between the raw material gas (C 6 F 6 ) and the fluorinating agent can be reduced. Thus, the fluorination reaction can be controlled through the introduction of inert gas. 
     The fluorinating agent comprises CoF 2  as an active material and metal fluoride as a diluent, and the content of the metal fluoride is preferably 90-99 wt % based on 100 wt % of the fluorinating agent. 
     Under the conditions of a fluorination reaction that uses the fluorinating agent of the present invention, the content of metal fluoride, the reaction temperature and the amount of inert gas supplied influence the fluorination reaction. If the content of metal fluoride is more than 99%, the fluorination rate will be excessively low, and if it is less than 90 wt %, the control of the reaction will be difficult. 
     The content of metal fluoride is preferable for 90-99 wt % to control the reaction rate at the reaction temperature of 60˜200° C. 
     In the preparation process of the present invention, hexafluorobenzene is used as a starting material. Hexafluorobenzene (C 6 F 6 ) is a compound which contains a fluorine atom bonded to each of six unsaturated carbons has no hydrogen. The use of benzene, chlorobenzene or hydrocarbon as a starting material is not suitable in a commercial process, not only because hydrofluoric acid (HF) is produced which needs additional process of removing the acid but also because many side products including isomers are produced, thus making a purification process very complicated. 
     In the present invention, a mixture of cobalt difluoride (CoF 2 ) and metal fluoride is charged into a reactor and activated with fluorine gas at 200-400° C., thus preparing an activated fluorinating agent. C 6 F 6  together with inert gas is supplied and allowed to react with the activated fluorinating agent at a reaction temperature of 60-200° C., thus preparing C 6 F 8 . After completion of the reaction, the fluorinating agent is activated again with fluorine gas and stands by for the next reaction. For application to a commercial process, the reaction must be continuously carried out, and thus two reactors are used such that the process of activating the fluorinating agent and the reaction process are repeatedly carried out. 
     Hereinafter, the preparation process of the present invention will be described with reference to the preparation system shown in  FIG. 1 . 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a schematic view of a diagram showing a process of preparing octafluorocyclohexadiene according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 
     Type of Reactor and Process for Activating Fluorinating Agent 
     In a horizontal-type or vertical-type reactor, a fluorinating agent obtained by mechanically mixing 1-10 wt % of powdery cobalt difluoride (CoF 2 ) with 90-99 wt % of at least one of powdery calcium fluoride (CaF 2 ), magnesium fluoride (MgF 2 ), aluminum(III) fluoride (AlF 3 ), sodium fluoride (NaF) and potassium fluoride (KF) is uniformly charged in an amount corresponding to about 70% of the volume of the reactor and is activated with fluorine gas at a temperature of 200-400° C. After completion of the activation, the remaining fluorine gas is removed while supplying inert gas into the reactor. When the introduced fluorine gas is no longer consumed in the reactor, the activation of CoF2 is ended. 
     Process for Synthesizing C 6 F 8    
     After the activation of the fluorinating agent is completed, the temperature of the reactor is lowered to 60-200° C., and the raw material C 6 F 6  is quantitatively passed through a preheater, and then sent to the reactor. The reaction product from the reactor is condensed in a trap at a temperature ranging from −10° C. to 0° C. to capture unreacted reactant and products having higher boiling points, and the remaining product is condensed in a second trap of acetone/liquid nitrogen slush at a temperature ranging from −60° C. to −80° C. 
     Hereinafter, the present invention will be described in further detail with reference to examples. 
     EXAMPLE 1 
     As shown in  FIG. 1 , 1.8 kg of a fluorinating agent consisting of 97 wt % of MgF 2  and 3 wt % of CoF 2  was introduced in a reactor A or B (3 inches×1100 mm). Then, the inside of the reactor was purged with nitrogen gas to remove water from the reactor and the powder surface. Then, the temperature of the reactor was elevated to 350° C., and fluorine gas was introduced therein to activate the fluorinating agent. After completion of the activation, unreacted fluorine gas in the reactor was removed, and the temperature of the reactor was maintained at 80-120° C. 
     Then, the raw material C 6 F 6  was quantitatively passed through a preheater 7 at a temperature of 80-120° C. and sent to the reactor. In addition, nitrogen gas was also supplied into the reactor in an amount of 5-600 mol % relative to the amount of raw material supplied. 
     The reaction of hexafluorobenzene (C 6 F 6 ) with the fluorinating agent prepared according to the above-described method was carried out in the following reaction conditions.
         Reaction conditions:   Reactor: 3 inches×1100 mm, SUS 316L   Raw material: hexafluorobenzene (9 g/min)   Supply ratio of inert gas: 250 mol % relative to the amount of raw material supplied (inert gas: nitrogen)   Reaction temperature: 80-120° C.   Reaction pressure: atmospheric pressure       

     After the hexafluorobenzene was fluorinated under the above-described conditions, the resulting gas was condensed using both trap of ice water and a trap of acetone/liquid nitrogen slush. Then, the reaction product was analyzed using gas chromatography. The analysis results are shown in Tables 1 and 2 below. 
     EXAMPLES 2 TO 6 
     Examples 2 to 6 were carried out according to the reaction conditions shown in Tables 1 and 2 in the same manner as in Example 1, except that the compositions and contents of the fluorinating agent were changed. The results are shown in Tables 1 and 2 below. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Examples 
               
            
           
           
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Fluorinating agent 
                 3% CoF 2 /MgF 2   
                 3% CoF 2 /MgF 2   
                 1% CoF 2 /MgF 2   
               
               
                 Reaction 
                 95 
                 80 
                 80 
               
               
                 temperature (° C.) 
               
               
                 Inert gas (ml/min) 
                 25 
                 25 
                 50 
               
               
                 Contact time (sec) 
                 74.5 
                 77.6 
                 72.5 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 A 
                 B 
                 A 
                 B 
                 A 
                 B 
               
               
                   
               
               
                 C 6 F 6  conversion (%) 
                 72.08 
                 84.95 
                 51.58 
                 71.62 
                 38.4 
                 51.7 
               
            
           
           
               
            
               
                 Composition (mol %) of organic compounds 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 C 6 F 8   
                 64.32 
                 60.27 
                 75.38 
                 70.52 
                 89.03 
                 85.35 
               
               
                 C 6 F 10   
                 35.57 
                 39.56 
                 24.53 
                 29.32 
                 10.97 
                 14.63 
               
               
                 C 6 F 12   
                  0.11 
                  0.17 
                  0.09 
                  0.16 
                 0   
                  0.02 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Examples 
               
            
           
           
               
               
               
               
            
               
                   
                 4 
                 5 
                 6 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Fluorinating agent 
                 3% CoF 2 /MgF 2   
                 10% CoF 2 /MgF 2   
                 1% CoF 2 /MgF 2   
               
               
                 Reaction 
                 95 
                 80 
                 80 
               
               
                 temperature (° C.) 
               
               
                 Inert gas (ml/min) 
                 100 
                 100 
                 25 
               
               
                 Contact time (sec) 
                 64 
                 64 
                 78 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 A 
                 B 
                 A 
                 B 
                 A 
                 B 
               
               
                   
               
               
                 C 6 F 6  conversion (%) 
                 29.6 
                 49.1 
                 79.2 
                 79.5 
                 51.58 
                 71.62 
               
            
           
           
               
            
               
                 Composition (mol %) of organic compounds 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 C 6 F 8   
                 29.0 
                 11.7 
                 22.52 
                 25.36 
                 70.3 
                 68.5 
               
               
                 C 6 F 10   
                 69.18 
                 87.25 
                 76.7 
                 73.69 
                 28.5 
                 31.3 
               
               
                 C 6 F 12   
                 0.17 
                 0.51 
                 0.06 
                 0.10 
                 0.09 
                 0.2 
               
               
                   
               
            
           
         
       
     
     In the results shown in Tables 1 and 2 above, as the ratio of CoF 2  had increased, the conversion of C 6 F 6  was increased, but the selectivity of C 6 F 8  was decreased. Under optimal reaction condition, the selectivity of C 6 F 8  could reach about 87%. 
     In the present invention, the two reactors A and B are connected in parallel and used alternately. Specifically, when the reaction in one reactor is completed, the remaining organic product is discharged with nitrogen, and then fluorine gas is introduced into the reactor to activate the fluorinating agent. At the same time, in the other reactor which is standing by, the reaction of the organic material with the fluorinating agent is initiated. For commercial processes, the reaction must be continuously carried out, and thus two reactors are alternatively used in order for the process for activating the fluorinating agent and the reaction process to be repeatedly carried out. 
     As described above, the process of the present invention has an advantage in that octafluorocyclohexadiene can be prepared with a selectivity of more than 87%. 
     Although the preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.