|Molar mass||80.1294 g/mol|
|Appearance||colourless gas or dark red solid|
|Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)|
Disulfur monoxide or sulfur suboxide is an unstable gas being a compound of sulfur and oxygen with formula S2O. It is one of the lower sulfur oxides. It is a colourless gas. It can be formed by reacting thionyl chloride with silver sulfide:
- SOCl2 + Ag2S → 2AgCl + S2O.
This is done under low pressure and high temperature. Another way to form it is via a glow discharge in sulfur dioxide. The arrangement of atoms is SSO in a bent form. The angle formed at the central sulfur atom is 117.88°. The sulfur to sulfur bond length is 188.4pm, and the length of the oxygen bond is 146.5pm. It can form an orange red condensate at liquid nitrogen temperatures. On decomposition at room temperature it forms SO2 and polysulfur oxide.
Disulfur monoxide is also formed in a small amount when sulfur is burnt in insufficient oxygen. It is also formed in part by heating sulfur with cupric oxide.
The gas was first produced by P. W. Schenk in 1933 with a glow discharge though sulfur vapour and sulfur dioxide. He discovered that the gas could survive for hours at single digit pressures of mercury in clean glass, but decomposed when the pressure went up to 30mm of mercury. However he believed that the formula was SO and called it sulfur monoxide. In 1940 K Kondrat'eva and V Kondrat'ev became convinced that the formula was S2O2, disulfur dioxide. However all were wrong until in 1956, David J. Meschi and Rollie J. Myers proved the formula was S2O.
Desulfovibrio desulfuricans is claimed to produce S2O. S2O can be found coming from volcanoes on Io. It can form from 1 to 6% when hot 100 bar S2 and SO2 gas erupts from volcanoes. It is believed that Pele on Io is surrounded by solid S2O.
A self decomposition of S2O can form trithio-ozone S3 and SO2. Also 5,6-di-tert-butyl-2,3,7-trithiabicyclo[2.2.1]hept-5-ene 2-endo-7-endo-dioxide when heated can form S2O. It reacts with diazoalkanes to form dithiirane 1-oxides.
Disulfur monoxide can be a ligand bound to transition metals. These are formed by oxidation with dioxygen for a disulfur ligand complex. Excessive oxygen can yield a dioxygendisulfur ligand, which can be reduced in turn with triphenylphosphine. Examples are: [Ir(dppe)2S2O]+, OsCl(NO)(PPh3)2S2O, NbCl(η-C5H5)2S2O, Mn(CO)2(η-C5Me5)S2O, Re(CO)2(η-C5Me5)S2O, Re(CO)2(η-C5H5)S2O.
More complex nucleations occur with transition metal ligand combinations. The molybdenum compound Mo(CO)2(S2CNEt2)2 reacts with elemental sulfur and air to form a compound Mo2(S2O)2(S2CNEt2)4. Another way to form these complexes is to combine sulfonyliminooxo-λ4-sulfurane (OSNSO2.R) complexes with hydrogen sulfide. Complexes formed in this way are: IrCl(CO)(PPh3)2S2O; Mn(CO)2(η-C5H5)S2O. With hydrosulfide and a base followed by oxygen, OsCl(NO)(PPh3)2S2O can be made.
Disulfur monoxide forms a yellow solution in carbon tetrachloride.
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