Theoretical calculations at the B3LYP level of theory were performed to investigate the Cl-initiated oxidation of the N-ethyl-perfluorobutanesulfonamide (C4F9SO2–NH–CH2CH3; 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 CF3SO2–NH–CH2CH3 produce the three primary radicals CF3SO2–N– CH2CH3 (1), CF3SO2–NH–CHCH3 (2), and CF3SO2–NH–CH2CH2 (3). Both 2 and 3 react exoergically with O2 and eventually form the ketone CF3SO2–NH–C(O)–CH3 and the aldehyde CF3SO2–NH–CH2–C(O)–H, respectively. The addition of O2 to the N atom of 1 is instead endoergic, but the radical can exoergically react with RO2 with formation of CF3SO2–N(O)–CH2CH3, CF3SO2–O–N– CH2CH3, and/or CF3SO2–N–O–CH2CH3. These three intermediates may in turn react with HO2 to produce, at least in principle, the four neutral products CF3SO2–N(OH)–CH2CH3, CF3SO2–N(O)H–CH2CH3, CF3SO2–O–NH–CH2CH3, and CF3SO2–NH–O– CH2CH3. This explains the proposed formation of a mixture of isomeric products of general formula C4F9SO2N(C2H5OH) from the Cl-initiated oxidation of NEtFBSA. CF3SO2–N(O)–CH2CH3 and CF3SO2–O–N–CH2CH3 may also dissociate into CH3CH2–NO and CF3SO2 and/or CF3. This suggests that the sulfonamide radicals CnF2n+1SO2–N–CH2CH3, once oxidized, could be direct precursors of perfluoroalkanecarboxylic acids via CnF2n+1SO2 and CnF2n+1O2. The formation of CnF2n+1SO3–O–N–CH2CH3 by reaction of CnF2n+1SO2–N–CH2CH3 with O2, while exoergic, is not supported by the experiments on the Cl-initiated oxidation of NEtFBSA.

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

ANTONIOTTI, Paola;
2008-01-01

Abstract

Theoretical calculations at the B3LYP level of theory were performed to investigate the Cl-initiated oxidation of the N-ethyl-perfluorobutanesulfonamide (C4F9SO2–NH–CH2CH3; 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 CF3SO2–NH–CH2CH3 produce the three primary radicals CF3SO2–N– CH2CH3 (1), CF3SO2–NH–CHCH3 (2), and CF3SO2–NH–CH2CH2 (3). Both 2 and 3 react exoergically with O2 and eventually form the ketone CF3SO2–NH–C(O)–CH3 and the aldehyde CF3SO2–NH–CH2–C(O)–H, respectively. The addition of O2 to the N atom of 1 is instead endoergic, but the radical can exoergically react with RO2 with formation of CF3SO2–N(O)–CH2CH3, CF3SO2–O–N– CH2CH3, and/or CF3SO2–N–O–CH2CH3. These three intermediates may in turn react with HO2 to produce, at least in principle, the four neutral products CF3SO2–N(OH)–CH2CH3, CF3SO2–N(O)H–CH2CH3, CF3SO2–O–NH–CH2CH3, and CF3SO2–NH–O– CH2CH3. This explains the proposed formation of a mixture of isomeric products of general formula C4F9SO2N(C2H5OH) from the Cl-initiated oxidation of NEtFBSA. CF3SO2–N(O)–CH2CH3 and CF3SO2–O–N–CH2CH3 may also dissociate into CH3CH2–NO and CF3SO2 and/or CF3. This suggests that the sulfonamide radicals CnF2n+1SO2–N–CH2CH3, once oxidized, could be direct precursors of perfluoroalkanecarboxylic acids via CnF2n+1SO2 and CnF2n+1O2. The formation of CnF2n+1SO3–O–N–CH2CH3 by reaction of CnF2n+1SO2–N–CH2CH3 with O2, while exoergic, is not supported by the experiments on the Cl-initiated oxidation of NEtFBSA.
2008
857
57
65
Atmospheric degradation; DFT calculations; N-Ethyl-perfluoroalkanesulfonamides; Structure and stability
Paola Antoniotti; Stefano Borocci; Maria Giordani; Felice Grandinetti
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/57685
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