Disulfur monoxide or sulfur suboxide is an inorganic compound with formula S2O. It is one of the lower sulfur oxides. It is a colourless gas and condenses to give a pale coloured solid that is unstable at room temperature. It is a bent molecule with an S−S−O angle of 117.88°, S−S bond length of 188.4pm, and S−O bond length of 146.5pm.
sulfur suboxide; Sulfuroxide;
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||80.1294 g/mol|
|Appearance||colourless gas or dark red solid|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Disulfur monoxide was discovered by Peter W. Schenk in 1933. However, only when Myers and Meschi studied it, did the actual composition and shape of the molecule become known.
It can be formed by many methods, including combustion of sulfur vapour in a deficiency of oxygen. It arises by oxidizing sulfur with copper (II) oxide:
- 3 S8 + 12 CuO → 12 CuS + 4 S2O + 4 SO2
Other routes include the reaction of thionyl chloride with silver sulfide:
- SOCl2 + Ag2S → 2 AgCl + S2O
It also arises via thermal decomposition of sulfur dioxide in a glow discharge.
Disulfur monoxide forms a yellow solution in carbon tetrachloride. The solid can be obtained at liquid nitrogen temperatures, often appearing dark colored owing to impurities. On decomposition at room temperature it forms SO2 via the formation of polysulfur oxides.
Disulfur monoxide 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 near 30mm Hg Schenk assigned the formula as SO and called it sulfur monoxide. In 1940 K Kondrat'eva and V Kondrat'ev proposed the formula as S2O2, disulfur dioxide. In 1956, D. J. Meschi and R. J. Myers established the formula as 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.
Condensed solid S2O displays absorption bands at 420 and 530 nm. These are likely to be due to S3 and S4.
The microwave spectrum of S2O has the following rotational parameters: A=41915.44, B=5059.07, and C=4507.19 MHz.
In the ultraviolet S2O has absorption band systems in the ranges 2500 to 3400 Å, and 1900 to 2400 Å. There are bands at 3235 and 3278 Å. The band in the 3150 to 3400 Å range is due to C1A'-X1A'(π*←π) transition.
The bond angle S−S−O is 109°. The harmonic frequency for S−S stretching is 415.2 cm−1.
A self decomposition of S2O can form trisulfur (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 is a ligand bound to transition metals. These are formed by oxidation peroxide oxidation of a disulfur ligands. 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.
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.
Cyclic disulfur monoxide has been made from S2O by irradiating the solid in an inert gas matix with 308 nm ultraviolet light.
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