STUDIES ON THE REACTIVITY OF TETRAFLUOROPHENYL AND PENTAFLUOROPHENYL TRIMETHYLSILYL ETHER WITH PENTAFLUOROBENZENES - CHEMISTRY AND X-RAY STRUCTURAL INVESTIGATIONS OF POLYFLUORODIPHENYL ETHERS

The introduction of tetrafluoro- and pentafluorophenoxy moieties into a variety of pentafluorobenzenes C(6)F(5)R (R = CF3 CN, NO2) is accomp lished by employing the trimethylsilyl ethers (siloxanes) 4-HC(6)F(4)O SiMe(3) (1) and C(6)F(5)OSiMe(3) (2) as transfer agents. Depending on the nature of the electrophile, the stoichiometry of the reaction, and the reaction conditions, polysubstituted polyfluorodiphenyl ethers ar e obtained. Excess C(6)F(5)R results in the formation of the 1,4-monos ubstituted benzenes (diphenyl ethers) 4-(4'-XC(6)F(4)O)C(6)F(4)R (R = CF3, X = H (3), F (4); R = CN, X = H (5), F (6); R = NO2, X = H (9), F (10)). When R = NO2, the 1,2-substituted isomers are also detected. A dditional by products that are isolable are the disubstituted benzenes 2,4-(4'-XC(6)F(4)O)(2)C(6)F(3)R (R = CN, X = H (7), F (8); R = NO2, X = H (11), F (12)). Excess 1 or 2, when reacted with C(6)F(5)R, result s in the formation of the trisubstituted benzenes 2,4,6-(4'-XC(6)F(4)O )(3)C(6)F(2)R (R = CN, X = H (13), F (14); R = NO2, = H (15), F (16)). The hydrolysis of nitrile-containing diphenyl ethers (5, 6, 13, and 1 4) under acidic conditions results in the substituted benzoic acids 4- (4'-XC(6)F(4)O)C6F4COOH (X = H (17), F (18)) and 2,4,6-(4'-XC(6)F(4)O) (3)C6F2COOH (X = H (19), F (21)). These acids are decarboxylated to fo rm the respective hydropolyfluoro aromatics (4-HC6F4)(2)O (23), 4-(C6F 5O)C6F4H (24), and 2,4,6-(4'-XC(6)F(4)O)(3)C6F2H (X = H (20), F (22)). In addition to acid 17, alkaline hydrolysis of 5 gives the alpha-hydr oxy-substituted acid 4-(4'-HC6F4O)C6F3(2-OH)COOH (25). All;aline hydro lysis under milder conditions enables the isolation of the amide 4-(4' -HC6F4O)C6F4CONH2 (26). The compounds 3, 4, 14-18, 23, and 26 have bee n characterized by single-crystal X-ray diffraction analysis. The pres ence of a hydrogen atom in 3, as well as protection of the reactive 4' -position with a trifluoromethyl group, gives 4-(4'-CF3C6F4O)C6F4Li (3 a) on reaction with n-butyllithium. In situ reactions between 3a and k etone or acid chlorides result in novel mono- or bis(perfluorodiphenyl ether)-substituted tertiary alcohols 4-(4'-CF3C6F4O)C6F4C(R)(R')OH (R /R' = CF3 (27), C6F5 (28), C6H5 (29), C3F7/C8F17 (30), C6F5/CH3 (31)), [4-(4'-CF3C6F4O)C6F4]C-2(R)OH (R = CF3 (32), C3F7 (33), C7F15 (34), i -C3H7 (35)). When R = i-C3H7, the major product is the ester [4-(4'-CF 3C6F4O)C6F4]C-2(i-C3H7)OC(O) (i-C3H7) (36). The ketone C3F7(C8F17)CO ( 37) is synthesized and characterized. Reaction of 3a with hexafluorogl utaryl chloride gives [4-(4'-CF3C6F4O)C6F4]C-2(OH)(CF2)(3)C(O)C6F4O(4 ''-C6F4CF3) (38), whereas with dimethyl carbonate or carbonyl fluoride , [4-(4'-CF3C6F4O)C6F4]2CO (39) as well as small amounts of [4-(4'-CF3 C6F4O)C6F4]3COH (40) and [4-(4'-CF3C6F4O)C6F4]3COC(O)C4H9 (41) are for med. Residual n-butyllithium cleaves the intermediate 4-(4'-CF3C6F4O)C 6F4COOCH3 to form 4-CF3C6F4C4H9 (42) and 4-HOC6F4COOCH3 (43).