亜ひ酸

解説三酸化二ヒ素As2O3を水に溶かしたときに存在すると考えられる酸。化学式H3AsO3,HAsO2などであらわされるが，遊離状態では得られていない。弱酸であるが両性を示し，塩基としても働く。酸解離定数Ka＝6×10－6(HAsO2⇄H＋＋AsO2－)，塩基解離定数Kb＝10－14(AsO(OH)⇄AsO＋＋OH－)。中性および微酸性水溶液は安定であるが，アルカリ性水溶液では空気により酸化されてヒ酸となりやすい。株式会社平凡社 世界大百科事典 第２版について 情報

説明Arsenic trioxide, often denoted as As2O3 butmore correctly stated as As4O6, is an inorganic compound mainly used as the precursor for organoarsenic compounds. It can be obtained by the oxidation of arsenic-containing minerals in the air, such as roasting of orpiment. 2As2S3 + 9O2 → As4O6 + 6SO2

使用It is a reductometric standard.

一般的な説明White or transparent, glassy amorphous lumps or crystalline powder. Slightly soluble in water, but dissolves very slowly; more soluble in hot water. Noncombustible. Corrosive to metals in the presence of moisture. Toxic by ingestion.

使用用途三酸化ヒ素は非常に強い毒性を持つため、殺鼠剤、殺虫剤や、農薬として使用されてきた歴史があります。虫歯や白血病治療薬にも用いられてきましたが、副作用として慢性ヒ素中毒やガンにかかることが多く、近年では使用が減少しつつあります。 工業的には金属ヒ素やヒ素化合物を製造する際の原料として用いられる物質です。その他には、触媒、ガラスの脱色、脱硫剤、顔料、染料製造、媒染剤、魚網・皮革の防腐剤、散弾用鉛の硬化剤、半導体製造におけるドーピングや、結晶育成原料などの用途を挙げることができます。

製造方法Arsenic trioxide is obtained by roasting the mineral arsenopyrite, FeAsS, in air at 650 to 700°C. It is also obtained as a by-product during the smelting ofcopper and lead concentrates during the extraction of these metals from their ores that contain arsenic. The latter readily oxidizes to arsenic trioxide which is volatilized. The vapors are then condensed and collected. High purity-grade oxide can be obtained by resublimation of the crude trioxide or by pressure leaching and recrystallization. Arsenic trioxide may also be prepared by hydrolysis of arsenic trichloride, -tribromide or -trifluoride.

純化方法It crystallises in an octahedral form (common form) from H2O or from dilute HCl (1:2), and is then washed, dried and sublimed (193o/760mm). Analytical reagent grade material is suitable for use as an analytical standard after it has been dried at 105o for 1-2hours or has been left in a desiccator for several hours over conc H2SO4. Alternatively: As2O3 (15g) is dissolved by heating in a mixture of H2O (60mL) and HCl (90g, s.g. 1.1), and crystallisation occurs on cooling, accompanied by brilliant flashes of light [Bandrowski Z Phys Chem 17 234 1895]. The amorphous form is a colourless transparent glass (m 200o) which is obtained when the vapour is slowly condensed below the vaporization temperature, and should be kept in a sealed tube because it changes to the octahedral form (m 275o) in the presence of moisture. [Rushton & Daniels J Am Chem Soc 48 384 1926.] A third monoclinic form, is obtained by heating the oxide in a sealed tube at 400o (the vitreous, amorphous form remains at the bottom of the tube) with the monoclinic form subliming onto the intermediate part of the tube at 200o (m 312o), and the octahedral form deposits at the top of the tube. The transition temperature between the last two forms is ~250o. POISONOUS (particularly the vapour, handle in a ventilated fume cupboard). [Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 600 1963.]