Rate Constants and Conversion Ratios for Aqueous-Phase Reactions of SO4- with CnF2n+1C(O)O- (n=4-7) at 298 K

Kinetic data for aqueous-phase reactions of sulfate anion radicals (SO4-) with perfluorocarboxylates (CnF2n+1C(O)O-) are needed to evaluate removal and transformation processes of CnF2n+1C(O)O- species in the environment, but rate constants for the reactions of SO4- with CnF2n+1C(O)O- (k(n)) have been reported only for short-chain CnF2n+1C(O)O- species (n = 1-3). Since CnF2n+1C(O)O- reacted with SO4- to form CmF2m+1C(O)O- (m < n), we determined relative rates k(n-1)/k(n) for the reactions of SO4- with CnF2n+1C(O)O- (n = 4-7), along with conversion ratios for conversion of CnF2n+1C(O)O- into Cn-1F2n-1C(O)O- (alpha(n)) and into Cn-2F2n-3C(O)O- (beta(n)) at 298 K. SO4- was photolytically generated from S2O82- by use of sunlamps (lambda approximate to 310 nm). Even if k(n) and k(n-1) change with increasing ionic strength, k(n-1)/k(n) can be determined when k(n-1)/k(n) and alpha(n) remain almost constant during the reaction. The values of k(n)/k(1) for n = 4-7 were nearly equal, and their average was 0.82 +/- 0.04 (2 sigma). Conversion ratios of alpha(n) and beta(n) were mostly independent of n for n = 4-7, and their averages were 0.77 +/- 0.07 (2 sigma) and 0.13 +/- 0.08, respectively. Branching ratios of reactions of a possible intermediate (CnF2n+1O center dot), reaction of CnF2n+1O center dot with H2O, and fission of the C-C bond of CnF2n+1O center dot, seemed to determine alpha(n) and beta(n). (C) 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 735-747, 2009