Characterization and crystal structures of some fluorinated imides

The previously known, but not well-characterized, fluorinated imides, trifluoroacetyltrifluoroacetimide, HN(C(O)CF3)(2) (1), acetyltrifluoroacetimide, HN(C(O)CH3)C(O)CF3 (2), and dichlorophosphoryltrifluoroacetimide, HN(P(O)Cl-2)C(O)CF3 (3), have been shown to be moderately strong acids in aqueous solution; the first two compounds have pK(a)'s of 2.0 and 2.1 while the last compound consumes three equivalents of base per mole of imide owing to the hydrolyzable chlorine atoms. All three imides show a window of electrochemical inactivity on platinum from O to near +2.0 V. On vitreous carbon, (1) and (2) are inactive from -1.0 to + 1.5 V and (3) from -1.0 to +1.0 V (vs. SCE). (1) crystallizes in a body-centered tetragonal unit cell while (2) and (3) crystallize in monoclinic unit cells. Hydrogen-bonded chains are formed in (1) and (2) and hydrogen-bonded dimers are formed in (3). The compounds were further characterized by H-1, F-19, and C-13 NMR, FTIR, and elemental analysis. (C) 1999 Elsevier Science Ltd. All rights reserved.