Reactions of CnFm+ ions with tetrafluoroethene and other perfluorocarbons

Abstract

The gas-phase reactions of CF+, CF2+, CF3+, C2F3+, C2F4+, C3F5+, and C3F7+ with tetrafluoroethylene, c2F4, have been studied using a variable temperature-selected ion flow tube (VT-SIFT) instrument at 300 and 496 K. In addition, reactions of CF3+ with the perfluorocarbons C3F6, 2-C4Fg, and c-C4Fg have been studied at 300 and 496 K. Reaction rate constants and product branching fractions were measured. The reaction of CF+ with C2F4 is fast and produces the ions CF3+, C3F5+, and C2F4+. The ion CF2+ reacts with C2F4 by nondissociative charge transfer at the collisional rate. The reaction of CF3+ with C2F4 proceeds slowly by association, forming C3F7+ which reacts in a secondary reaction with C2F4 to regenerate CF3+. The neutral product of this secondary reaction is inferred to be C4F8; thus, dimerization of C2F4 is catalyzed by CF3+. For the reaction of C2F3+ with C2F4, which is fast, C3F5+ and a minor amount of C2F4+ are produced. The reaction of c2F4+ with c2F4 is slow, has a strong negative temperature dependence, and produces C3F5+ which is itself unreactive with C2F4. While CF3+ does not measurably react with c-C~FB, CF3+ does react rapidly by Ftransfer with both C3F6 and 2424Fg.

Selected Ion Flow Tube Study of the Gas-Phase Reactions of CF+, CF2+, CF3+, and C2F4+ with C2H4, C2H3F, CH2CF2, and C2HF3

“…The data are shown in Table 3, including that for C 2 F 4 because reactions of this molecule have been studied by others. 4,9,11 a The neutral products of these reactions are not detected in the experiment but are proposed as the most likely candidates. b The reaction enthalpy calculated from 298 K enthalpies of formation.…”

The kinetics and product state distributions from gas-phase reactions of small atomic and molecular cations with C2H4, C2H3F, 1,1-C2H2F2, C2HF3and C2F4

“…Results for the reactions of these fluorinated ethenes with four reactant fluorocarbon cations (CF + , CF 2 + , CF 3 + and C 2 F 4 + ) have been published elsewhere, 25 but are shown in Table 1 for completeness. The data for the reaction of these twenty five cations with C 2 H 4 and C 2 F 4 have been taken from a range of papers in the literature, [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] some of which describe earlier results taken with the Birmingham SIFT apparatus. The SIFT technique has been described in detail elsewhere.…”

“…In general, however, these cations react with the fluoroethene molecules via an S N 2 mechanism to form a 3-or 4-carbon noncyclic adduct that may subsequently fragment or re-arrange to form new products. 25 35 Some of these fluorocarbon cation reactions were also studied twenty years ago by Morris et al in a SIFT apparatus, 9 but there are anomalies in the minor products that they report for the reaction of CF 3 + and CF + with C 2 F 4 . The major product of the former reaction is the adduct C 3 F 7 + (Z94%) which must form by an exothermic reaction.…”

“…The importance of steric effects seems clear in some of the reactions of C 2 F 4 , especially the reactions with CO 2 + , N 2 O + , C 2 F 4 + and CF 3 + where a large number of heavy atoms are involved and k exp is significantly less than k c . It should also be noted that all these four reactions show a slight negative temperature dependence, 8,9 suggesting that the Langevin model is failing on the grounds of both reaction efficiency and temperature dependency. When RE o IE, only chemical reactions involving the exchange of atoms and formation of new chemical bonds can occur.…”

“…Examples are the slow reactions C 2 F 4 + + C 2 F 4 and H 3 O + + C 2 H 4 which are both close to thermoneutral in forming the preferred products C 3 F 5 + + CF 3 and C 2 H 5 + + H 2 O, respectively. 6,9 Second, assuming that products can only form from an exothermic reaction and that entropic effects can be ignored, there are several examples of IM reactions where the identity of the accompanying neutral product(s) can unambiguously be deduced. Obviously, as the RE(ion) increases, more possibilities for the neutral products become available.…”