Methoxycarbonyl trifluoromethyl disulfide, CH3OC(O)SSCF3: synthesis, structure and conformational properties

Abstract

Pure methoxycarbonyl trifluoromethyl disulfide, CH₃OC(O)SSCF₃, has been prepared quantitatively by the reaction of CH₃OC(O)SCl and Hg(SCF₃)₂. The conformational properties of the novel molecule have been studied by vibrational spectroscopy [IR(gas) and Raman(liquid)] and quantum chemical calculations (B3LYP and MP2 methods). The gaseous compound exhibits a conformational equilibrium at room temperature where the most stable form has C₁ symmetry with a synperiplanar (syn) orientation of the CO double bond with respect to the S–S disulfide bond. A second form is observed in the gaseous IR spectra corresponding to a conformer with the carbonyl bond CO in antiperiplanar (anti) position with respect to the S–S single bond. The structure of a single crystal of CH₃OC(O)SSCF₃ has been determined by X-ray diffraction analysis at low temperature using a miniature zone melting procedure. The crystalline solid (triclinic, P, a = 6.4698(5) Å, b = 9.0499(8) Å, c = 12.5700(11) Å, α = 97.219(6)°, β = 93.131(5)°, γ = 96.888(5)° and Z = 4) consists exclusively of molecules with the synperiplanar conformation and the usual gauche orientation around the disulfide bond [ϕ(CS–SC) = 91.06(15)°] is adopted. The geometrical parameters agree with those obtained from quantum chemical calculations.