Cl-Initiated oxidation of N-ethyl-perfluoroalkanesulfonamides: A theoretical insight into the experimentally observed products

Abstract

Theoretical calculations at the B3LYP level of theory were performed to investigate the Cl-initiated oxidation of the N-ethyl-perfluorobutanesulfonamide (C 4F 9SO 2–NH–CH 2CH 3; NEtFBSA). We studied in particular the thermodynamic aspects of the possible oxidation reactions so to obtain a first indication on the conceivably preferred pathways and on the structure and stability of the observed products. The reactions of Cl with the model compound CF 3SO 2–NH–CH 2CH 3 produce the three primary radicals CF 3SO 2–N–CH 2CH 3 ( 1), CF 3SO 2–NH–CHCH 3 ( 2), and CF 3SO 2–NH–CH 2CH 2 ( 3). Both 2 and 3 react exoergically with O 2 and eventually form the ketone CF 3SO 2–NH–C(O)–CH 3 and the aldehyde CF 3SO 2–NH–CH 2–C(O)–H, respectively. The addition of O 2 to the N atom of 1 is instead endoergic, but the radical can exoergically react with RO 2 with formation of CF 3SO 2–N(O)–CH 2CH 3, CF 3SO 2–O–N–CH 2CH 3, and/or CF 3SO 2–N–O–CH 2CH 3. These three intermediates may in turn react with HO 2 to produce, at least in principle, the four neutral products CF 3SO 2–N(OH)–CH 2CH 3, CF 3SO 2–N(O)H–CH 2CH 3, CF 3SO 2–O–NH–CH 2CH 3, and CF 3SO 2–NH–O–CH 2CH 3. This explains the proposed formation of a mixture of isomeric products of general formula C 4F 9SO 2N(C 2H 5OH) from the Cl-initiated oxidation of NEtFBSA. CF 3SO 2–N(O)–CH 2CH 3 and CF 3SO 2–O–N–CH 2CH 3 may also dissociate into CH 3CH 2–NO and CF 3SO 2 and/or CF 3. This suggests that the sulfonamide radicals C n F 2 n +1SO 2–N–CH 2CH 3, once oxidized, could be direct precursors of perfluoroalkanecarboxylic acids via C n F 2 n +1SO 2 and C n F 2 n +1O 2. The formation of C n F 2 n +1SO 3–O–N–CH 2CH 3 by reaction of C n F 2 n +1SO 2–N–CH 2CH 3 with O 2, while exoergic, is not supported by the experiments on the Cl-initiated oxidation of NEtFBSA.