Perfluororganochalkogensäuren in hohen Oxidationsstufen

Perfluoroorganochalcogenic Acids in Higher Oxidation States Pentafluoroethylseleninic acid is oxidized by KMnO 4 in slightly alkaline aqueous solution to give K[C 2 F 5 SeO 3 ]. With HClO 4 the salt is converted into the free acid. Neutralisation of C 2 F 5 SeO 3 H with NaOH, Ag 2 O, NH 3 + H 2 O provides the corresponding salts. The ethyl ester is made from Ag[C 2 F 5 SeO 3 ] and C 2 H 5 I. Oxidation of C 6 F 5 TeC 6 F 5 with concd. HNO 3 yields C 6 F 5 Te(OH)ONO 2 which on controlled hydrolyses gives (C 6 F 5 ) 2 Te(OH) 2 . Strong acids like HClO 4 or H 2 SO 4 form mixed anhydrides like (C 6 F 5 ) 2 Te(OH)ClO 4 or (C 6 F 5 ) 2 Te(OH)OS(O) 2 OTe(OH)(C 6 F 5 ) 2 . For the latter compound a cyclic or noncyclic polycondensate form cannot be ruled out. Acidic 35% H 2 O 2 solution oxidizes (C 6 F 5 ) 2 Te(OH) 2 at 40°C (48 h) to give (C 6 F 5 ) 2 TeO 2 . This anhydride dissolves only in CF 3 SO 3 H forming (C 6 F 5 ) 2 Te(OSO 2 CF 3 ) 4 . It is soluble in CH 3 CN and reacts in solution with water to yield (C 6 F 5 ) 2 Te(OH) 2 (OSO 2 CF 3 ) 2. Oxidation of C 6 F 5 TeTeC 6 F 5 with concd. HNO 3 provides oligomeric [C 6 F 5 Te(O)OH] x which still contains some HNO 3 . A single‐crystal X‐ray structure determination carried out on [(C 6 H 5 ) 4 As][C 2 F 5 SeO 3 ] shows convincingly that the central selenium atom is coordinated by three equivalent oxygen atoms with d (Se‐O) = 1.614(3) Å, proving that Se has the oxidation state VI.