Abstract:
Processes for preparing hexafluoroisobutene epoxide (HFIBO) from CH2=C(CF3)2 (HFIB) are provided. The processes can be carried out in substantial absence of oxidation catalysts.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to a process for preparing 2,2-bis(trifluoromethyl)oxirane (hexafluoroisobutene epoxide, HFIBO). 
       BACKGROUND 
       [0002]    Hexafluoroisobutene epoxide (HFIBO) is a useful intermediate in the synthesis of chemical compounds containing gem-trifluoromethyl groups. 
         [0003]    It is currently known to prepare HFIBO by liquid phase oxidation of the corresponding olefin, CH2=C(CF3)2, using sodium hypochlorite under phase-transfer catalysis conditions (U.S. Pat. No. 6,653,419). 
         [0004]    EP 0 209 911 discloses a process for the oxidation of fluorinated olefins by reacting the olefin with oxygen in the presence of a catalyst. 
         [0005]    There is currently a need for a gas-phase process to prepare HFIBO, especially one that does not generate a chlorine waste stream or require the use of a catalyst. 
       SUMMARY OF THE INVENTION 
       [0006]    One aspect of this invention is a process comprising contacting hexafluoroisobutene (HFIB) with oxygen in the substantial absence of oxidation catalysts at a temperature of 200-400 oC and at a pressure of 0.01-100 megapascals. 
     
    
     DETAILED DESCRIPTION 
       [0007]    This invention is a gas-phase process for the preparation of HFIBO 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    from the readily-available olefin, CH2=C(CF3)2, and oxygen. The process is typically conducted at temperatures of 200-400 oC and pressures of 0.01-100 megapascals, in the substantial absence of oxidation catalysts. 
         [0008]    The process of this invention can be carried out in batch, semi-continuous or continuous mode. The products and unreacted olefin can be isolated by cooling. 
         [0009]    In one embodiment, the reaction is carried out in a batch, semi-batch or continuous mode at 210-290 oC and at a pressure of 0.1-100 megapascals for a sufficient time to form a reaction mixture comprising 2,2-bis(trifluoromethyl)oxirane. In another embodiment, the reaction is at 230-270 oC. In another embodiment, the reaction is conducted at pressures of 1-50 megapascals. In yet another embodiment, the reaction is conducted at pressures of 1-10 megapascals. 
         [0010]    In another embodiment, the reaction can be carried in a continuous mode, in which HFIB and oxygen are contacted in a flow system at atmospheric or sub-atmospheric conditions at 200-400 oC for 1 second to 1 hour. 
         [0011]    As illustrated in the Example below, the process of this invention produces the desired epoxide in good yield and selectivity, even in the absence of an oxidation catalyst. 
         [0012]    Typical molar ratios of oxygen to olefin range from 1:1 to 10:1. Pure oxygen can be used, or the oxygen can be mixed with other inert gases such as N2 and/or CO2. If a mixture of gases is used, oxygen typically comprises at least 15 mole % of the mixture. 
         [0013]    When the process of this invention is conducted in batch mode, the crude products are typically isolated as a liquid phase when the reactor is cooled. In other embodiments, the crude products can be collected by cooling the reaction mixture. 
         [0014]    Reaction times vary with reaction temperature and the desired conversion level. Typical reaction times for batch and semi-batch processes range from a few minutes to a few days. As noted, above, reaction times for continuous process can be 5 minutes or less, especially when the reaction is carried out at temperatures above 300 oC. Conversion rates of 40-50% are easily achieved, even at relatively high selectivity (30-50% or more) to the desired epoxide. 
         [0015]    The crude product typically contains the desired epoxide (HFIBO), as well as unreacted HFIB and hexafluoroacetone (HFA). The HFA can be removed by washing the crude product with water. The desired HFIBO can be isolated by distillation. 
         [0016]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
       EXAMPLES 
       [0017]    The following examples illustrate certain features and advantages of the present invention. They are intended to be illustrative of the invention, but not limiting. All percentages are by weight, unless otherwise indicated. 
         [0018]    HFIB is commercially available from E. I. du Pont de Nemours, Inc. (Wilmington, Del.). 
       Example 1 
       [0019]    A Hastelloy shaker tube (400 mL) was charged with 50 g of CH2=C(CF3)2 (HFIB), pressurized with 200 psi of oxygen and was kept at 230 oC for 12 h. The reaction mixture was transferred from the reactor into a cold, evacuated stainless steel cylinder and analyzed by NMR. The crude product contained 2,2-bis(trifluoromethyl)oxirane (HFIBO) (30%), hydrate of hexafluoroacetone (21%), and CH2=C(CF3)2 (49%). This corresponds to a conversion of CH2=C(CF3)2 of 51%, and a selectivity to epoxide formation of 60%. 
       Example 2 
       [0020]    Example 1 was repeated and the reaction mixtures from 2 consecutive runs were combined and washed with ice water. The water-washed reaction mixture (60 g) was analyzed as liquid by 1H and 19F NMR. The crude product contained 2,2-bis(trifluoromethyl)oxirane (HFIBO) (43%) and CH2=C(CF3)2 (57%). Signals attributable to hydrates of hexafluoroacetone were absent in the 19F NMR spectrum. The total calculated yield of epoxides for the 2 combined runs was 25% at 50% conversion of olefin.