l3 (I, x) with x=0, 1, 2 and CCl3CF2CCl2CF2CCl3 (II). Hydrolysis, by oleum, of compounds (I, 0) and (I, 2) leads to the corresponding diacid chlorides. Hydrolysis of (I, 1) and (II) however yields perhalogenated cyclic, six- membered stable acid anhydrides. In the second part of this work, several methods are compared for synthesizing diacid chlorides from diacids or cyclic anhydrides prepared