sulfur dioxide

[′səl·fər dī′äk‚sīd]

(inorganic chemistry)

SO₂ A toxic, irritating, colorless gas soluble in water, alcohol, and ether; boils at -10°C; used as a chemical intermediate, in artificial ice, paper pulping, and ore refining, and as a solvent. Also known as sulfurous acid anhydride.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Sulfur Dioxide

(also sulfurous acid anhydride), SO₂, an oxide of sulfur where the oxidation state is +4. A colorless gas with a characteristic sharp odor, sulfur dioxide is encountered in nature in volcanic gases. It condenses at - 10.5°C to a colorless liquid and solidifies at - 75°C to a crystalline mass. It has a critical temperature of 157.3°C and a critical pressure of 77.8 atmospheres.

Sulfur dioxide dissolves readily in water with the formation of sulfurous acid (H₂ SO₃). Oxygen oxidizes SO₂ at high temperatures in the presence of catalysts. Sulfur dioxide can be oxidized to SO₃ and H₂ SO₄ or reduced to sulfur. It forms salts of sulfurous acid with aqueous alkaline solutions. SO₂ is very stable thermally, dissociating to S and O₂ or to SO and O only at around 2800°C.

In the laboratory, sulfur dioxide is prepared by the action of H₂ SO₄ on hydrosulfites, for example

2NaHSO₃ + H₂ SO₄ = Na₂ SO₄ + 2SO₂ + 2H₂ O

It is also prepared by heating copper filings with concentrated sulfuric acid:

Cu + 2H₂ SO₄ = CuSO₄ + SO₂ + 2H₂ O

SO₂ is used chiefly in the production of sulfuric acid; it is also used in the paper and textile industries and in the sulfation of vegetables and fruits. Sulfur dioxide can be used in refrigeration because it condenses easily and has a high heat of vaporization. As a strong reducing agent in aqueous solutions, SO₂ decolorizes many organic dyes and is used in the bleaching of fabrics and sugar.

Sulfur dioxide is toxic. It can enter the organism through the respiratory passages during the roasting of sulfur ores (in the production of sulfuric acid) at copper-smelting plants and the burning of fuels containing sulfur in forges and boilers at, for example, superphosphate plants and thermal electric power stations. In mild cases, sulfur dioxide poisoning produces a cough, rhinitis, tearing, a dry sensation in the throat, hoarseness, and chest pains. With moderately severe acute poisoning, there is also headache, dizziness, general fatigue, and pain in the epigastric region. Examination will reveal symptoms of chemical burns on the mucous membrane of the respiratory passages. Prolonged exposure to sulfur dioxide may produce chronic poisoning, which manifests itself through atrophic rhinitis and damage of the teeth and is often accompanied by toxic bronchitis with attacks of asphyxia. Damage to the liver and circulatory system and the development of pneumosclerosis are possible.

Preventive measures include the hermetic sealing of production equipment, effective ventilation, the removal of sulfur dioxide from flue and waste gases, and the personal protection of respiratory organs (gas mask). The maximum permissible concentration of sulfur dioxide in the air at production facilities is 1.0 mg/m³. The daily average concentration in populated areas should not exceed 0.15 mg/m³. Every year tens of millions of tons of sulfur dioxide from the industrial combustion of coals and petroleum containing compounds of sulfur are released into the atmosphere. The removal of sulfur dioxide from waste gases is an important scientific and engineering problem.

I. K. MALINA and A. A. KASPAROV

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References in periodicals archive

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