ホスホン酸

化学的特性Phosphorous acid is a white crystalline deliquescent solid that can be prepared by the action of water on phosphorus( III) oxide or phosphorus(III) chloride. It is a dibasic acid producing the anions H2PO3- and HPO3 2- in water. The acid and its salts are slow reducing agents. On warming, phosphonic acid decomposes to phosphine and phosphoric(V) acid. Phosphorus acid is used to prepare phosphite salts. It is usually sold as a 20% aqueous solution.

解説ホスホン酸，四面体形の [PHO3]2- を含む二塩基酸。 H3PO3 と書いて，亜リン酸と称していたことがあったが，これは誤称。無色，潮解性結晶，比重 1.65 。還元性が強く，貴金属塩から金属を遊離する。アルカリ塩およびカルシウム塩のほかは水に難溶。なお，ホスホン酸とオルトリン酸とが脱水縮合して生成する酸に相当するものとして次リン酸などが知られている。ブリタニカ国際大百科事典 小項目事典 ブリタニカ

用途塩化ビニル安定剤、有機合成触媒、pH 調整剤、ポリエステルフィルムの表面処理剤、分 析（水銀検出）、還元剤、亜リン酸塩製造（肥料等）.

説明Phosphorous acid, H3PO3, is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is as an intermediate in the preparation of other phosphorous compounds. Because preparation and uses of “phosphorous acid” actually pertain more to the major tautomer, phosphonic acid, it is more often referred to as “phosphorous acid”. Phosphorous acid has the chemical formula H3PO3, which is best expressed as HPO(OH)2 to show its diprotic character. P(OH)3 (IUPAC: phosphorous acid) has CAS number 10294-56-1. It has been shown to be a stable tautomer.

使用Phosphorous acid is used to produce the fertilizer phosphate salt like potassium phosphite, ammonium phosphite and calcium phosphite. It is actively involved in the preparation of phosphites like aminotris(methylenephosphonic acid) (ATMP), 1-hydroxyethane 1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic Acid (PBTC), which find application in water treatment as a scale or corrosive inhibitor. It is also used in chemical reactions as a reducing agent. Its salt, lead phosphite is used as PVC stabilizer. It is also used as a precursor in the preparation of phosphine and as an intermediate in the preparation of other phosphorus compounds.

一般的な説明Phosphorous acid appears as a white or yellow crystalline solid (melting point 70.1°C) or a solution of the solid. Density 1.651 g /cm3 . Contact may severely irritate skin, eyes, and mucous membranes. Toxic by ingestion, inhalation and skin absorption.

使用用途ホスホン酸は還元性が強いため、無電解めっきの還元剤としての使用可能です。やの水溶液から、それぞれ銀やを析出させて、メッキを施せます。 P-アルキルホスホン酸ジアルキルエステル (R-P(=O)(OR')2)は、工業的に重要な中間体です。P-アルキルホスホン酸ジアルキルエステルはホーナー・ワズワース・エモンズ反応 (英: Horner–Wadsworth–Emmons reaction) の基質であり、ホーナー・エモンズ試薬と呼ばれ、アルケンの原料になります。ホーナー・エモンズ試薬は、香料や医薬品の原料として、多方面で使用されています。

製造方法Phosphorus acid can be prepared by the reaction of phosphorus trichloride with water: PCl3 + 3H2O → H3PO4 + 3HClThe reaction is violent. Addition of PCl3 should be extremely cautious and slow. The addition can be carried out safely in the presence of concentrated HCl. Alternatively, a stream of air containing PCl3 vapor is passed into icecold water and solid crystals of H3PO4 form. Alternatively, phosphorus acid can be prepared by adding phosphorus trichloride to anhydrous oxalic acid: PCl3 + 3(COOH）2 → H3PO3 + 3CO + 3CO2 + 3HCl In this reaction, all products except H3PO3 escape as gases leaving the liquid acid. Dissolution of phosphorus sesquioxide in water also forms phosphorus acid. When shaken with ice water, phosphorus acid is the only product . P4O6 + 6H2O → 4H3PO3 However, in hot water part of the phosphorus acid disproportionates to phosphoric acid and phosphorus or phosphine.