The product is formed quantitatively if the reactants (on a 2-molar scale, slight excess of SF4) are heated a t 50°C in a closed vessel (200 ml) for 2 hr. The trimethylfluorosilane and the excess of sulfur tetrafluoride can be separated by lowtemperature vacuum-distillation, the pure product (1) remains behind as a clear colorless liquid (b.p. 58 "C/lOO mm, 43 OC/49 mm; vapor pressure = 14 mm at 20 "C). The boiling point (extrapolated to atmospheric pressure) is 111 "C. The compound partly decomposes above 50 O C and becomes yellow. Melting point -34 "C. Molecular weight (Dumas) = 111. The mass spectrum shows typical fragments FSNCN (m/e = 96), SNCN (72), SF2 (70), and SF (51), as well as the molecule ion ( ). The IgF-NMR spectrum includes a singlet at -48.1 ppm (CFC13 as external standard). The IR spectrum, measured for the NaCl and KBr region, shows absorption bands (with tentative assignments) at 2255 (s, VasNC-N 139, 1463 (m), 1337 (vs, vS=N), 844 (vs, vSNCN), 764 (vs, vasSF), 725 (vs, vsSF), 615 (m), and 527 (m). The spectroscopic data are in accordance with the structure assigned and with the data for N-cyaniminosulfur difluoride prepared by a different method [41.