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|Section2= |Section6= |Section7= |Section8= }} Oxalic acid is an organic compound with the formula H2C2O4 (also written as HOOCCOOH). It is a colorless crystalline solid that forms a colorless solution in water. It is classified as a dicarboxylic acid. Its acid strength is much greater than that of acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate (C2O42−), is a chelating agent for metal cations. Typically, oxalic acid occurs as the dihydrate with the formula H2C2O4·2H2O. Excessive ingestion of oxalic acid or prolonged skin contact can be dangerous. ==Preparation== Oxalic acid is mainly manufactured by the oxidation of carbohydrates or glucose using nitric acid or air in the presence of vanadium pentoxide. A variety of precursors can be used including glycolic acid and ethylene glycol.〔Eiichi, Yonemitsu; Tomiya, Isshiki; Tsuyoshi, Suzuki and Yukio, Yashima "Process for the production of oxalic acid", , priority date March 15, 1969〕 A newer method entails oxidative carbonylation of alcohols to give the diesters of oxalic acid: :4 ROH + 4 CO + O2 → 2 (CO2R)2 + 2 H2O These diesters are subsequently hydrolyzed to oxalic acid. Approximately 120,000 tonnes are produced annually.〔Wilhelm Riemenschneider, Minoru Tanifuji "Oxalic acid" in ''Ullmann's Encyclopedia of Industrial Chemistry'', 2002, Wiley-VCH, Weinheim. .〕 Historically oxalic acid was obtained exclusively by using caustics, such as sodium or potassium hydroxide, on sawdust. 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「Oxalic acid」の詳細全文を読む スポンサード リンク
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