A photoionization study of trifluoromethanol, CF3OH, trifluoromethyl hypofluorite, CF3OF, and trifluoromethyl hypochlorite, CF3OCl

Abstract

CF 3 OH, an important and controversial by-product of atmospheric decomposition of CF 3 CFH 2 ͑HFC-134a͒ and other hydrofluorocarbons, has been examined by photoionization mass spectrometry. The ionization onset is characterized by a broad Franck-Condon distribution, arising primarily from a substantial elongation of the CO bond upon ionization. An upper limit to the adiabatic ionization potential ͑IP͒ of р 13.08 Ϯ 0.05 eV has been established. The appearance potentials ͑APs͒ of the first two fragments have been accurately determined by fitting with appropriate model functions as AP 0 ͑CF 2 OH ϩ /CF 3 OH͒р13.830Ϯ0.005 eV and AP 0 ͑CF 3 ϩ /CF 3 OH͒р13.996Ϯ0.005 eV. While the exact nature of the lowest-energy fragment ͑nominally CF 2 OH ϩ ͒ is not clear, the CF 3 ϩ fragment threshold leads unambiguously to ⌬H f 298 ‫ؠ‬ ͑CF 3 OH͒уϪ217.2Ϯ0.9 kcal/mol and D 298 ͑CF 3-OH͒р115.2Ϯ0.3 kcal/mol. With previously derived ⌬H f 298 ‫ؠ‬ ͑CF 3 O͒ϭϪ151.8 Ϫ1.1 ϩ1.7 kcal/mol, this yields D 298 ͑CF 3 O-H͒ ϭ117.5 Ϫ1.4 ϩ1.9 kcal/mol, very close to, or only slightly weaker than the O-H bond energy in water: D 298 ͑CF 3 O-H͒-D 298 ͑HO-H͒ϭϪ1.8 Ϫ1.4 ϩ1.9 kcal/molϷ0 kcal/mol. Similarly, with the recently redetermined value for ⌬H f ‫ؠ‬ ͑CF 2 O͒, this implies a 298 K reaction enthalpy for the 1,2-elimination of HF from CF 3 OH of 2.8 Ϫ1.1 ϩ1.7 kcal/mol. CF 3 OF and CF 3 OCl have also been examined by photoionization. CF 3 OF produces a very weak parent, with an apparent adiabatic IP͑CF 3 OF͒ р12.710Ϯ0.007 eV. An analysis of the CF 3 ϩ and CF 2 O ϩ fragments from CF 3 OF, when combined with literature data, suggests ⌬H f 298 ‫ؠ‬ ͑CF 3 OF͒ϭϪ176.9 Ϫ1.3 ϩ1.8 kcal/mol. The fitted value for the appearance potential of CF 3 ϩ from CF 3 OCl, AP 0 ͑CF 3 ϩ /CF 3 OCl͒р12.85Ϯ0.01 eV, leads to ⌬H f 298 ‫ؠ‬ ͑CF 3 OCl͒уϪ175.6Ϯ1.0 kcal/mol, D 298 ͑CF 3-OCl͒р88.4Ϯ0.3 kcal/mol, and D 298 ͑CF 3 O-Cl͒р52.8 Ϫ1.5 ϩ2.0 kcal/mol.

Experimental and Computational Investigations of the Reaction of OH with CF3I and the Enthalpy of Formation of HOI

“…The upper bound rests on the CF 3 -I bond strength which Asher et al recently determined to high precision, D 298 (CF 3 -I) ) 227.2 ( 1.3 kJ mol -1 . 30 This is more positive than the value of 223 kJ mol -1 available to Jenkin et al 33 and therefore raises the upper bound to ∆ f H 298 (HOI).…”

Convenient Access to Trifluoromethanol

“…Continuous removal of CF 3 OH by reaction with a suitable reagent shifts the equilibrium in Equation (2) all the way to the right and allows trapping of the CF 3 OH in the form of useful derivatives. We have demonstrated this approach by conversion of the CF 3 OH into either trifluoromethyloxonium MF 6 À (M = Sb or As) salts [see above and Eq. (7)] or ethers,…”

“…In spite of great academic and commercial interest in -OCF 3 substituted compounds, these have been prepared exclusively by relatively cumbersome methods, such as the replacement of the doubly bonded oxygen atom in acyl fluorides by SF 4 or halogen-exchange reactions using HF at elevated temperatures and pressures and long reaction times. [3] A literature survey showed that out of 128 citations found by SciFinder for CF 3 OH, only the original synthesis reports, [2] an unsuccessful attempt to protonate CF 3 OH in HF/ SbF 5 , [4] a measurement of its UV spectrum, [5] and a study of its photoionization [6] involved the actual bulk synthesis or handling of CF 3 OH. Therefore, it was of great interest to find a more convenient access to this interesting compound to make it readily available for general syntheses.…”

Hydrogen bonding and cooperative effects in mixed dimers and trimers of methanol and trifluoromethanol: An ab initio study

“…In addition, it plays an important role in the atmospheric degradation of CF 3 CFH 2 ͑HFC-134a͒ and other hydrofluorocarbons, and is therefore a compound that requires some attention. [24][25][26][27] Our group has recently studied cooperativity effects in cyclic trifluoromethanol trimer at the Hartree-Fock ͑HF͒ level and different basis sets. 23 In contrast to the linear structure of the methanol dimer, we found that the analogous dimer of CF 3 OH involves a secondary hydrogen bond between one of the fluorine atoms of the donor and the hydrogen atom of the acceptor molecule.…”