Abstract:
Fluorine-containing dimethylchlorosilanes are prepared by reacting an ethylene compound having a fluorine-containing organic group with dimethylchlorosilane in the presence of a rhodium complex, for instance RhCl(PPh 3 ) (Ph: phenyl group), as a catalyst. The use of a rhodium complex as a catalyst enables preparation in high yield of the fluorine-containing dimethylchlorosilane, which has been heretofore obtainable only in low yields.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a process for preparing fluorine-containing dimethylchlorosilanes in high yields by a reaction between an ethylene compound having a fluorine-containing organic group and dimethylchlorosilane. 
     2. Description of the Prior Art 
     It is well known that fluorine-containing dimethylchlorosilanes can be obtained by reacting a fluorine-containing alkylethylene with dimethylchlorosilane. This reaction is represented by the following reaction formula: ##STR1## wherein Rf is a fluorine-containing organic. 
     Conventionally, the above reaction has been carried out using a platinum complex or a peroxide as a catalyst. The conventional method has the problem that the desired product can be obtained only in low yield. 
     SUMMARY OF THE INVENTION 
     Accordingly it is an object of this invention to provide a process for preparing fluorine-containing dimethylchlorosilanes in high yields by a reaction of an ethylene compound having a fluorine-containing organic group, such as a fluorine-containing alkylethylene, with dimethylchlorosilane. 
     According to this invention, there is provided a process for preparing a fluorine-containing dimethylchlorosilane, which comprises reacting an ethylene compound having a fluorine-containing organic group with dimethylchlorosilane in the presence of a rhodium complex. 
     By the use of a rhodium complex as a reaction catalyst, it has become possible to obtain fluorine-containing dimethylchlorosilanes in shorter time and in higher yield, as compared with the conventional processes. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Ethylene compound 
     The ethylene compound used as a starting material in this invention has, for example, the following formula: 
     
         Rf--CH═CH.sub.2 
    
     Wherein Rf is a monovalent fluorine-containing organic group, or 
     
         CH.sub.2 ═CH--Rf&#39;--CH═CH.sub.2 
    
     wherein Rf&#39; is a divalent fluorine-containing organic group. 
     The monovalent fluorine-containing organic group Rf includes, for example, perfluoroalkyl groups having the formula: 
     
         C.sub.1 F.sub.21+1- 
    
     wherein 1 is an integer of 1 or above, preferably from 1 to 10, perfluoroalkyl ether groups having the formula: ##STR2## wherein n is an integer of 0 or above, preferably from 0 to 10, and groups which are derived from these groups by substitution of hydrogen atoms for part of the fluorine atoms in these group. 
     The divalent fluorine-containing organic groups Rf&#39; includes, for example, perfluoroalkylene groups having the formula: 
     
         --C.sub.m F.sub.2m- 
    
     wherein m is an integer of 1 or above, preferably from 1 to 10, perfluoroalkylene ether groups having the formula: ##STR3## wherein p and q are integers of 0 or above, preferably such integers that p+q is from 0 to 10, and groups which are derived from these groups by substitution of hydrogen atoms for part of the fluorine atoms in these groups. 
     Of the ethylene compounds having the monovalent or divalent fluorine-containing organic group as mentioned above, those which are particularly preferred for use in this invention include the followings: ##STR4## 
     Rhodium complex 
     Preferable examples of the rhodium complex to be used as a reaction catalyst in the process of this invention include RhCl(PPh 3 ) 3 , RhCl(CO)(PPh 3 ) 2 , [Rh(CH 3  COO) 2  ] 2 , [RhCl(C 2  H 4 ) 2  ] 2 , [RhCl(C 7  H 8 )] 2  (wherein C 7  H 8  is norbornadiene as a divalent ligand), Rh(CH 3  COCHCOCH 3 ) 3 , etc. In the above formulas, and hereinafter, Ph stands for the phenyl group. 
     The rhodium complexes are used preferably in an amount of from 1.0×10 -8  to 1.0×10 -1  mole, more preferably from 1.0×10 -6  to 1.0×10 31  3 mole, per mole of the ethylene compound. 
     Reaction 
     The reaction between the ethylene compound having a fluorine-containing organic group and dimethylchlorosilane is carried out in the presence of the rhodium complex at a pressure of preferably 2 atm or above, more preferably from 4 to 10 atm, and a temperature of from 50° to 250° C., preferably from 70° to 150° C. The reaction under these conditions is carried out, for example, in an autoclave. 
     In carrying out the reaction, it is generally desirable to use dimethylchlorosilane in an amount of from 1.0 to 5.0 moles, preferably from 1.1 to 2.0 moles, per mole of an ethylenic double bond contained in the ethylene compound. 
     The reaction proceeds according to the aforementioned reaction formula. For example, when the ethylene compound used is a monofunctional one, a fluorine-containing dimethylchlorosilane having the following general formula [I]: ##STR5## wherein Rf is a monovalent fluorine-containing organic group, is obtained in a high yield. The fluorine-containing dimethylchlorosilane thus obtained is useful as a silylating agent, a silica treating agent, a raw material for surfactants, etc. 
     When a bifunctional ethylene compound is used, on the other hand, the aforementioned reaction produces a dimethylchlorosilane having the following general formula [II]: ##STR6## wherein Rf&#39; is a divalent fluorine-containing organic group. This dimethylchlorosilane is useful as a raw material for hybrid silicones having a fluorine-modified backbone. 
     EXAMPLES 
     Example 1 
     A 300-ml autoclave equipped with a stirrer and a thermometer was charged with 179 g of n-C 4  F 9  CH═CH 2 , 98 g of dimethylchlorosilane and 0.11 g of RhCl(PPh 3 ) 3  (Wilkinson&#39;s complex), and the resultant mixture was stirred with heating at 100° C. under a pressure of 7 atm for 4 hours. 
     After the reaction, the reaction product was cooled to 25° C. and taken out of the autoclave. A quantitative analysis of the reaction product by gas chromatography gave a conversion of n-C 4  F 9  CH═CH 2  of 93% and a selectivity of 93% for dimethylchlorosilane having the following formula: ##STR7## 
     Example 2 
     The same 300-ml autoclave as that used in Example 1 was charged with 177 g of CH 2  ═CHC 6  F 12  CH═CH 2 , 122 g of dimethylchlorosilane and 0.08 g of RhCl(PPh 3 ) 3 , and the resultant mixture was stirred with heating at 110° C. and 8 atm for 6 hours. 
     After the reaction, the reaction product was quantitatively analyzed in the same manner as in Example 1. The analysis gave a conversion of CH 2  ═CHC 6  F 12  CH═CH 2  of 99% and a selectivity of 79% for the addition reaction product having the following formula: ##STR8## 
     Example 3 
     The same 300-ml autoclave as that used in Example 1 was charged with 239 g of ##STR9## 61 g of dimethylchlorosilane and 0.09 g of RhCl(PPh 3 ) 3 , and the resulting mixture was stirred with heating at 100° C. and 6 atm for 6 hours. 
     After the reaction, the reaction product was analyzed quantitatively in the same manner as in Example 1. The conversion of the HFPO trimer-ethylene was 86%, and the selectivity for the addition product having the following formula: ##STR10## was 88%. 
     Examples 4-7 
     Reactions were carried out in the same manner as in Example 1 except that 0.1 g each of other rhodium catalysts were used in place of RhCl(PPh 3 ) 3 . The results are shown in Table 1 below. 
     
                       TABLE 1______________________________________                  Conversion SelectivityExample  Catalyst        (%)        (%)______________________________________4      [Rh(CH.sub.3 COO).sub.2 ].sub.2                  87         895      RhCl(CO)(PPH.sub.3).sub.2                  88         926      [RhCl(C.sub.2 H.sub.4).sub.2 ].sub.2                  81         907      Rh(CH.sub.3 COCHCOCH.sub.3).sub.3                  82         87______________________________________ 
    
     Comparative Examples 1-8 
     Reactions were carried out in the same manner as in Example 1 except that various catalysts were used in place of RhCl(PPh 3 ) 3 . The results, such as the selectivity for the desired addition product, are shown in Table 2 below. 
     
                       TABLE 2______________________________________Compar-             Amount    Con-ative               of catalyst                         version                                SelectivityExample  Catalyst     (g)       (%)    (%)______________________________________1      H.sub.2 PtCl.sub.6.6H.sub.2 O               0.1       66     932      (t-BuO--).sub.2 --               1.2       52     893      PdCl.sub.2 (PPh.sub.3).sub.2               0.1       44     914      PtCl.sub.2 (PPh.sub.3).sub.2               0.1        5     945      Mo(Co).sub.6 0.06      36     886      IrCl(CO)(PPh.sub.3).sub.2               0.1       12     957      Ru.sub.3 (CO).sub.12               0.1       19     908      RuCl.sub.2 (PPh.sub.3).sub.3               0.1        7     92______________________________________