|
Hypophosphoric acid is a mineral acid with the formula H4P2O6, with phosphorus in a formal oxidation state of +4. In the solid state it is present as the dihydrate, H4P2O6·2H2O. In hypophosphoric acid the P atoms are identical and joined directly with a P-P bond. There is an isomeric form isohypophosphoric acid which has a different structure with non-identical P atoms, one of which has a directly bonded H atom and an oxidation state of +3, which is joined by a P-O-P bridge to the second P atom which has an oxidation state of +5. ==Preparation and reactions== Hypophosphoric acid can be prepared by the reaction of red phosphorus with sodium chlorite at room temperature.〔Phosphorus: Chemistry, Biochemistry and Technology, Sixth Edition, 2013, D.E.C. Corbridge, CRC Pres, Taylor Francis Group, isbn: 978-1-4398-4088-7〕 :2P + NaClO2 +8H2O → Na2H2P2O6 + 2HCl A mixture of hypophosphoric acid, phosphorous acid (H3PO3) and phosphoric acid (H3PO4) is produced when white phosphorus oxidises in air when partially immersed in water.〔 The tetrasodium salt Na4P2O6·10H2O crystallises at pH 10 and the disodium salt, Na2H2PO6·6H2O at pH 5.2. The disodium salt can be passed through an ion exchange column to form the acid dihydrate, H4P2O6.2H2O.〔 The anhydrous acid can be formed by vacuum dehydration over P4O10 or by the reaction of H2S on lead hypophosphate, Pb2P2O6.〔 Hypophosphoric acid is tetraprotic with dissociation constants pKa1 = 2.2, pKa2 = 2.8, pKa3 = 7.3 and pKa4 = 10.0.〔 On standing the anydrous acid undergoes rearrangement and disproportionation to form a mixture of isohypophosphoric acid, HPO(OH)-O-PO2(OH); pyrophosphoric acid H2P2O7 and pyrophosphorous acid.〔 Hypophosphoric acid is unstable in hot hydrochloric acid, in 4M HCl it hydrolyses to give H3PO3 + H3PO4.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hypophosphoric acid」の詳細全文を読む スポンサード リンク
|