Chemical elements
  Sulphur
    Isotopes
    Energy
    Extraction
    Refining
    Applications
    Allotropy
    Crystalline
    Amorphous Sulphur
    Colloidal Sulphur
    Physical Properties
    Chemical Properties
    Detection
    Estimation
    Compounds
      Hydrogen Sulphide
      Metal Polysulphides
      Hydrogen Polysulphides
      Hydrogen Pentasulphide
      Hydrogen Trisulphide
      Hydrogen Disulphide
      Sulphur Monofluoride
      Sulphur Tetrafluoride
      Sulphur Hexafluoride
      Sulphur Monochloride
      Sulphur Dichloride
      Sulphur Tetrachloride
      Sulphur Monobromide
      Thionyl Fluoride
      Sulphuryl Fluoride
      Fluorosulphonic Acid
      Thionyl Chloride
      Sulphuryl Chloride
      Sulphur Oxytetrachloride
      Pyrosulphuryl Chloride
      Chlorosulphonic Acid
      Thionyl Bromide
      Sodium Sulphoxylate
      Sulphur Dioxide
      Sulphurous Acid
      Sulphites
      Sulphur Trioxide
      Pyrosulphuric Acid
      Pyrosulphates
      Sulphuric Acid
      Persulphuric Anhydride
      Persulphuric Acid or Perdisulphuric Acid
      Perdisulphates
      Permonosulphuric Acid
      Amidopermonosulphuric Acid
      Thiosulphuric Acid
      Thiosulphates
      Polythionic Acids
      Dithionic Acid
      Trithionic Acid
      Trithionates
      Tetrathionic Acid
      Tetrathionates
      Pentathionic Acid
      Pentathionates
      Wackenroders Solution
      Hexathionic Acid
      Polythionic Acids
      Sulphur Sesquioxide
      Hydrosulphurous Acid
      Hydrosulphites
      Nitrogen Sulphide
      Nitrogen Persulphide
      Nitrogen Pentasulphide
      Sulphammonium
      Hexasulphamide
      Nitrogen Chlorosulphide
      Trithiazyl Chloride
      Thiotrithiazyl Chloride
      Dithiotetrathiazyl Chloride
      Nitrogen Bromosulphide
      Thiotrithiazyl Bromide
      Thiotrithiazyl Iodide
      Thiotrithiazyl Nitrate
      Thiotrithiazyl Hydrogen Sulphate
      Thiotrithiazyl Thiocyanate
      Thionylamide
      Sulphamide
      Imidodisulphamide
      Sulphimide
      Sulphonic Acids
      Amidosulphonic Acid
      Imidosulphonic Acid
      Nitrilosulphonic Acid
      Hydroxylamine-monosulphonic Acid
      Nitrososulphonic Acid
      Hydroxylamine-disulphonic Acid
      Hydroxylamine-isodisulphonic Acid
      Hydroxylamine-trisulphonic Acid
      Dihydroxylamidosulphonic Acid
      Sulphazinic Acid
      Sulphazotinic Acid
      Dehydrosulphazotinic Acid
      Nitrosulphonic Acid
      Nitrosulphonyl Chloride
      Nitrosulphonic Anhydride
      Nitrosulphuric Acid
      Nitrosodisulphonic Acid
      Sulphonitronic Acid
      Sulphates of Hydroxylamine
      Hydroxylamine Dithionate
      Hydrazine Dithionate
      Hydrazine Amidosulphonate
      Carbon Subsulphide
      Carbon Monosulphide
      Carbon Disulphide
      Thioformaldehyde
      Thiocarbonic Acid
      Ammonium thiocarbonate
      Thiolcarbonic Acid
      Xanthic Acid
      Perthiocarbonic Acid
      Sodium perthiocarbonate
      Carbonyl Sulphide
      Thiocarbonyl Chloride
      Thiocarbonyl Tetrachloride or
      Carbon Hexachlorosulphide
      Trichloromethyl Disulphide
      Thiocarbonyl Sulphochloride
      Carbon Bromosulphide
      Amino-derivatives of Thiocarbonic Acid
      Dithiocarbamic Acid
      Thiocarbamide
      Azidodithiocarbonic Acid
      Thiocyanogen
      Cyanogen Monosulphide
      Cyanogen Trisulphide
      Sulphur Thiocyanate
      Disulphur Dithiocyanate
      Thiocyanic Acid
      Thiocyanates
      Dithiocyanic Acid
      Trithiocyanuric Acid
      Perthiocyanic Acid
      Perthiocyanogen
      Sulphates

Carbonyl Sulphide, COS






Carbonyl Sulphide or Carbon Oxysulphide, COS, discovered by Than, is formed synthetically when a mixture of sulphur vapour and carbon monoxide is passed through a hot tube. The action is reversible,

CO + SCOS,

so that the proportion of carbonyl sulphide formed depends upon the temperature and rate of passage of the gaseous mixture. Attempts to synthesise carbonyl sulphide by means of the electric spark seem to give negative results.

Carbonyl sulphide is also formed by the interaction of carbon disulphide and sulphur trioxide, thus:

CS2 + 3SO3 = COS + 4SO2.

When sulphur vapour and air are passed over a red-hot mixture of clay and carbon, and also when sulphur dioxide is passed over red-hot carbon, carbonyl sulphide is formed:

4SO2 + 9C = 6CO + 2COS + CS2.

Some thiocarbonates yield carbonyl sulphide on decomposition, thus:

+ HCl = COS + C2H5OH + KCl.

At 270° C. carbonyl chloride and cadmium sulphide interact according to the equation:

COCl2 + CdS = COS + CdCl2.

An important method of preparing carbonyl sulphide consists in the decomposition of a thiocyanate with moderately concentrated (14N) sulphuric acid, the liberated thiocyanic acid being hydrolysed thus:

HCNS + H2O = COS + NH3.

The carbonyl sulphide is evolved at 20° C. together with hydrocyanic acid, formic acid and carbon disulphide. The gas is purified by passing through concentrated aqueous caustic potash to absorb the acid vapours, and the carbon disulphide is absorbed in a mixture of triethylphosphine, pyridine and nitrobenzene. After drying with sulphuric acid, the gas may be further purified by liquefaction or absorption in toluene.

Carbonyl sulphide may also be obtained by the action of hydrochloric acid on commercial ammonium thiocarbamate, according to the equation:

NH4.CO.S.NH2 + 2HCl = COS + 2NH4Cl.

In this case the gas may be purified by bubbling through 33 per cent, caustic soda solution in order to absorb carbon dioxide and hydrogen sulphide and dried with calcium chloride and phosphorus pentoxide. It is then condensed by means of liquid air, and finally fractionated.


Properties

Pure carbonyl sulphide is a colourless, odourless gas, which is slowly decomposed by water. When dry it is stable, even in sunlight, and if kept over sulphuric acid it undergoes only slight decomposition. Its density at -87° c. is 1.24. It melts at -138.2° C. and boils at -50.2° C. under a pressure of 760 mm.

1 volume of water dissolves 0.54 volumes of COS at 20° C.
1 volume of alcohol dissolves 8.0 volumes of COS at 22° C.
1 volume of toluene dissolves 15.0 volumes of COS at 22° C.

The thermal decomposition of carbonyl sulphide has been investigated. The products of dissociation may be carbon monoxide and sulphur on the one hand, or carbon dioxide and carbon disulphide on the other:
  1. COSCO + S,
  2. 2COSCO2 + CS2.
At 800° C. reaction (2) appears to proceed slowly in either direction, while (1) is very rapid. The fact that the degree of dissociation in (1) is independent of the amounts of carbon dioxide and carbon disulphide present, shows that carbon monoxide and sulphur are primary products of the decomposition of carbonyl sulphide and are not formed secondarily from the carbon dioxide and carbon disulphide. At temperatures below 400° C. decomposition according to equation (1) is not evident, while at 900° C. it reaches a maximum (64 per cent.); reaction (2) reaches a maximum at about 600° C., at which point 43 per cent, of the carbonyl sulphide is decomposed in this way and 16 per cent, according to reaction (1). The carbon monoxide equilibrium depends upon the pressure, whilst the carbon dioxide equilibrium does not. Nearly all the reactions involved in the thermal decomposition of carbonyl sulphide depend greatly on catalytic influences. Quartz is a pronounced catalyst for reaction (2), but has little influence on reaction (1). Carbonyl sulphide is comparatively rapidly decomposed in quartz vessels, but is stable when kept in glass apparatus. The viscosity of gaseous carbonyl sulphide is as follows:

η15 = 1.200×10-4 C.G.S. units,
and
η100 = 1.554×10-4 C.G.S. units;

by extrapolation from Sutherland's formula, η0 = 1.135×10-4 C.G.S. units. The mean area (Å) which the molecule presents in mutual collision is 1.06×10-15 cm2.

The physiological effects of carbonyl sulphide are very similar to those of nitrous oxide.

When the pure gas is passed through a saturated solution of barium hydroxide or copper sulphate, no opalescence or precipitate is produced for at least half a minute; if any carbon dioxide is present, however, the solution becomes milky at once. According to Weeldenburg there is no reaction between carbonyl sulphide and copper sulphate in neutral or acid solution, nor is there any reaction with iodine or ethereal tri-ethylphosphine.

Carbonyl sulphide burns with a blue flame, forming carbon dioxide and sulphur dioxide. With air it forms a mixture which is slightly explosive except when quite dry. The explosive limits lie between 11.9 and 28.5 per cent, of carbonyl sulphide. A white-hot platinum wire completely decomposes the sulphide into carbon monoxide and sulphur.

Water slowly decomposes carbonyl sulphide, forming carbon dioxide and hydrogen sulphide:

COS + H2O = CO2 + H2S.

According to Buchbock the reaction proceeds in two stages, thiol-carbonic acid being an intermediate product:

COS + H2OCO2 + H2S.

Aqueous solutions of the caustic alkalis act only slowly with the oxysulphide to form thiolcarbonates, which, however, soon decompose into carbonate and hydrosulphide:



With alcoholic potash the reaction is more rapid.

Heated mercury, copper, iron and silver remove sulphur from carbonyl sulphide; cuprous chloride reacts according to the equation:

COS + Cu2Cl2 + H2O = Cu2S + 2HCl + CO2;

chlorine forms phosgene, COCl2, together with "sulphur dichloride":

COS + 2Cl2 = COCl2 + SCl2.
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