Sulfur Trioxide - Sansankaiou

SO ₃ (80.06). It is produced by reacting sulfur dioxide directly with oxygen using platinum sponge, V ₂ O ₅ , NO, etc. as a catalyst. In its gaseous form, it has ₃ molecules of SO 3, and has a planar triangular structure with S at the center. Interatomic distance S-O0.143 nm. ∠OS-O120°. It is a corrosive gas that reacts violently with water to form sulfuric acid. It reacts with metal oxides, releasing heat, to form sulfates. Three transformations are known in the solid state. (1) Orthorhombic sulfur trioxide (γ-SO ₃ ). It is obtained by condensing the gas at temperatures below −80°C. It is a smoke-emitting, colorless, icy solid. Melting point 16.8°C, boiling point 44.8°C. Density 1.995 g cm ⁻³ (13°C), 1.97 g cm ⁻³ (20°C). It is a molecular crystal consisting of ₉ S ₃ O molecules in a cyclic trimer. (2) Asbestiform sulfur trioxide (β-SO ₃ ), with a silky luster. It is obtained by leaving orthorhombic SO ₃ or liquid SO ₃ in the presence of traces of water at temperatures below 25°C. Its melting point is 32.5°C. It has an infinite spiral structure of tetrahedral SO ₄ Os. (3) The most stable asbestiform sulfur trioxide (α-SO ₃ ). It is obtained by leaving β-SO ₃ in a sealed tube for a long time at temperatures above 32.5°C. Its melting point is 62.2°C. Liquid SO ₃ is a mixture of monomers and trimers, which can be stabilized by the addition of boric acid, and in its pure state it easily polymerizes in the presence of traces of water. It is used as a strong oxidizing agent, sulfonating agent, in the manufacture of ion exchange resins, and in the manufacture of sulfuric acid. It is highly toxic. [CAS 7446-11-9]

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

SO₃(80.06)．二酸化硫黄を白金海綿，V₂O₅，NOなどを触媒として直接酸素と反応させてつくる．気体ではSO₃分子が存在し，Sを中心とする平面三角形型構造．原子間距離S-O0.143 nm．∠O-S-O120°．腐食性気体で，水とはげしく反応して硫酸となる．金属酸化物とは熱を発して反応し硫酸塩となる．固体には三つの変態が知られている．(1)斜方晶系三酸化硫黄(γ-SO₃)．－80 ℃ 以下で気体を凝縮させると得られる．発煙性があり，無色の氷状の固体．融点16.8 ℃，沸点44.8 ℃．密度1.995 g cm^－3(13 ℃)，1.97 g cm^－3(20 ℃)．環状の三量体でS₃O₉分子からなる分子結晶．(2)絹糸光沢のアスベスト状三酸化硫黄(β-SO₃)．25 ℃ 以下で痕跡の水の存在で斜方晶系SO₃または液体SO₃を放置すると得られる．融点32.5 ℃．四面体型のSO₄のOでつながった無限らせん構造である．(3)もっとも安定なアスベスト状三酸化硫黄(α-SO₃)．β-SO₃を封管中で32.5 ℃ 以上に長くおくと得られる．融点62.2 ℃．液体のSO₃は単量体と三量体の混合物で，ホウ酸を添加すると安定化し，純粋な状態では痕跡の水でたやすく重合する．強酸化剤，スルホン化剤，イオン交換樹脂の製造，硫酸製造などに用いられる．猛毒．[CAS 7446-11-9]

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