The photochemistry of hexafluoroacetylacetone in the vapour phase. Occurrence of a novel HF elimination reaction

Abstract

Photolysis of the vapour of hexafluoroacetylacetone HFAA in its enolic form involves decomposition by two independent primary processes, one of which is a novel elimination of H F giving 2,2-difluoro-2,3-dihydro-5trifluoromethylfuran-3-one:The HF is not vibrationally excited. CF2 radicals which, if HFAA is present, undergo an insertion into the enolic OH bond, Photolysis of the cyclic product of reaction ( 5 ) yieldsCF, + CF,C=CHCOCF, -+ CF,C=CHCOCFx I OCF,H I OH The infrared, ultraviolet, nuclear magnetic resonance, and mass spectra of HFAA and of the products of reactions (5) and (6) have been measured. Approximate quantum yields for reactions (1) and ( 5 ) have been obtained. Both + I and +5 depend on pressure and the ratio increases with temperature and decreased wavelength of photolysing light. It is proposed that the ratio 43/45 increases as the vibrational energy of electronically excited HFAA increases.

Dissociative electron attachment to the complexation ligands hexafluoroacetylacetone, trifluoroacetylacetone and acetylacetone; a comparative experimental and theoretical study

“…The transition state for the rotation, which is the rate limiting step, lies energetically below the neutral HFAAc, making this rotation readily available at 0 eV incident electron energy. In analogy to the mechanism proposed by Basset and Whittle, 35 this rotation is proposed as a prerequisite to the loss of HF upon DEA.…”

“…13,38 There we showed that the existence of intramolecular X-H/F-C hydrogen bonds is a prerequisite for the formation of HF. In fact, for the observed HF loss in the photolysis study, Basset and Whittle 35 argued that aer photon absorption, the excited HFAAc undergoes conformational changes through rotation. Hence, bringing the keto-CF 3 group in close vicinity to the enolic hydrogen, thus ensuring the conditions for HF formation and that of the furanone shown in Fig.…”

Laser pyrolysis studies of β-diketonate chemical vapour deposition precursors. Part 1: β-diketones

“…There has been little work reported on the thermal decomposition of 2. There is, however, a substantial of work on CVD related investigations of hfacH over metal and metal oxide surfaces, [42][43][44][45][46][47][48] while the photolysis study by Bassett and Whittle 49 is the only account of the homogeneous decomposition of 2. Photolysis of the predominant enol form of 2 occurred with a novel HF elimination to yield 2,2-difluoro-5-(trifluoromethyl)furan-3(2H)-one (DHTF, 7).…”

“…The mass spectrum of the product eluted at 1.61 min was identical with the mass spectra obtained from the decomposition of a range of oxovanadium(IV) hfac complexes, UO 2 (hfac) 2 , and from UV photolysis of 2. 49,51,52 This compound was identified as 7. The mass spectrum of the compound eluted at 1.65 min was attributed, upon comparison with mass spectral data obtained by Bassett and Whittle, to 8, that is, the product resulting from CF 2 carbene insertion into the O-H bond of a hfacH molecule following UV photolysis.…”

Gas chemical investigation of hafnium and zirconium complexes with hexafluoroacetylacetone using preseparated short-lived radioisotopes

“…• C, decomposition of hfa [62][63][64] (and possibly also of the complexes [48]) sets in, resulting in non-chemically selective aerosol transport. The 3d members of neighboring groups 5 and 6, i.e., Nb and Mo, have been shown to be transported as hfa complexes to a significantly smaller extent, if at all.…”