Sulfur dioxide - Sulfur dioxide

SO ₂ (64.07). Sulfurous acid gas is the common name for sulfur dioxide gas. It is naturally found in small amounts in volcanic gases and mineral springs. In industry, it is produced by burning sulfur, hydrogen sulfide, and metal sulfides such as pyrite FeS _2. In the laboratory, sulfur dioxide is produced from commercially available bottled sulfur dioxide, or by decomposing solid sulfite with sulfuric acid or by heating copper with concentrated sulfuric acid. The gas is colorless. It has a pungent odor and is toxic. The liquid is colorless and transparent. The solid is white. Density 1.46 g cm ^-3 (-10 °C, liquid), 2.927 g dm ^-3 (gas). Melting point -75.48 °C, boiling point -10.02 °C. Easily soluble in water, soluble in acetone, ethanol, carbon tetrachloride, benzene, methanol, acetic acid, ether, and chloroform. The gas consists of _two broken-line SO molecules, with S-O 0.14308 nm, ∠OS-O 119.32°, and a dipole moment of 1.59 D.

The reaction rate is slow, and oxidation cannot be achieved efficiently unless a catalyst such as platinum or divanadium pentoxide is used at 400-450 °C. If water is present, oxidation can occur even at room temperature. Sulfur dioxide acts as both an oxidizing agent and a reducing agent. It reacts with hydrogen sulfide to produce sulfur and water. Aqueous solutions of sulfur dioxide have been called aqueous solutions of sulfurous acid, H ₂ SO ₃ , but H ₂ SO ₃ molecules do not exist in aqueous solutions; only hydrated sulfur dioxide molecules exist. Liquid sulfur dioxide dissolves many inorganic and organic compounds as a non-aqueous solvent, and is used in NMR (nuclear magnetic resonance) research and synthesis. It is also used as a solvent for the strongest acid, HSO ₃ F-SbF ₅ (super acid). It is used as a raw material for sulfuric acid production, as a disinfectant, insecticide, flotation, bleaching agent, reducing agent, pesticide, pharmaceutical, antioxidant, etc. Sulfur dioxide is a highly corrosive and toxic substance that can cause conjunctivitis and affect the upper respiratory tract, resulting in symptoms such as coughing, difficulty breathing, and chest pain. The acceptable concentration for occupational health purposes is 5 ppm (= 13 mg _SO2 / ^m3 ). Even a concentration of 1 ppm or less can have a major impact on plants, as photosynthesis is inhibited. Sulfur dioxide is oxidized by oxygen, moisture, and dust in the air to become sulfuric acid, which further increases its danger. It also corrodes various metal surfaces, forming verdigris. The environmental standard for sulfur dioxide in the air is a daily average value of 0.04 ppm or less and an hourly value of 0.1 ppm or less. [CAS 7446-09-5][See other terms]Trace analysis of sulfur dioxide, air pollution

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

SO₂(64.07)．亜硫酸ガス(sulfurous acid gas)は二酸化硫黄の気体の通俗名．天然には，火山ガス，鉱泉中に少量含まれている．工業的には，硫黄，硫化水素，黄鉄鉱FeS₂などの金属硫化物の燃焼によって製造される．実験室では，市販のボンベ入り二酸化硫黄を使用するか，固体亜硫酸塩の硫酸分解，または銅と濃硫酸との熱時反応により発生させる．気体は無色．刺激臭があり有毒．液体は無色透明．固体は白色．密度1.46 g cm^－3(－10 ℃，液体)，2.927 g dm^－3(気体)．融点－75.48 ℃，沸点－10.02 ℃．水に易溶，アセトン，エタノール，四塩化炭素，ベンゼン，メタノール，酢酸，エーテル，クロロホルムに可溶．気体は折れ線形SO₂分子からなり，S-O0.14308 nm．∠O-S-O119.32°．双極子モーメント1.59 D．

の反応速度は遅く，400～450 ℃ で白金または五酸化二バナジウムなどの触媒を用いないと，収率よく酸化されない．水が存在すれば，室温でも酸化される．二酸化硫黄は酸化剤としても還元剤としてもはたらく．硫化水素と反応し，硫黄と水とを生成する．二酸化硫黄の水溶液は亜硫酸H₂SO₃水溶液とよばれてきたが，H₂SO₃分子は水溶液中に存在せず，水和した二酸化硫黄分子が存在するのみである．液体二酸化硫黄は非水溶媒として多くの無機，有機化合物を溶かし，NMR(核磁気共鳴)の研究，合成などに用いられる．もっとも強い酸HSO₃F-SbF₅(super acid)の溶媒としても使われる．硫酸製造の原料，殺菌剤，殺虫剤，浮選，漂白剤，還元剤，農薬，医薬品，酸化防止剤などに用いられる．二酸化硫黄は腐食性の強い有毒物質で，結膜炎を起こしたり，上気道をおかすために，せき，呼吸困難，胸痛などの症状を引き起こす．労働衛生上の許容濃度は5 ppm( ＝ 13 mg SO₂/m³)である．植物では1 ppm 以下でも光合成が阻害されるため，大きな影響が出る．二酸化硫黄は空気中の酸素，水分，じんあいにより酸化されて硫酸になり，さらにその危険度を増す．また，緑青(ろくしょう)のように各種の金属表面を腐食する．大気中の二酸化硫黄の環境基準は，1日平均値が0.04 ppm 以下であり，かつ1時間値が0.1 ppm 以下であること，とされている．[CAS 7446-09-5][別用語参照]二酸化硫黄の微量分析，大気汚染

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