Oxalic acid dihydrate

Oxalic acid dihydrate occurs as colorless crystals or a white crystalline powder; it is odorless. It sublimes at 150–160 °C and effloresces in warm, dry air. One gram is soluble in 7 mL of water, 2 mL of boiling water, 2.5 mL of ethanol, 1.8 mL of boiling ethanol, 100 mL of diethyl ether, and 5.5 mL of glycerol; it is insoluble in benzene, chloroform, and petroleum ether. The pH of a 0.1 mol/L solution is 1.3. It has low toxicity; (rabbit, dermal) is 2000 mg/kg.

Oxalic acid dihydrate (OAD) which has very high initial phase transition enthalpy is a promising phase change material (PCM). This compound is low manufacturing cost and wide usage. In OAD, alternating acid and water molecules that act both as hydrogen-bond donors and acceptors. OAD needs a lot of energy to break the hydrogen-bond in the melting process. Therefore, OAD has a very high heat of fusion of 370 J·g-1,which is a very promising PCM in TES for applications such as industrial waste heat recovery or solar energy storage systems[1].

Oxalic acid dihydrate (OAD) crystals are reported to be monoclinic withP21/nspace group. The electron density of OAD has been obtained using X-ray diffraction studies under high resolution.

Crystallise oxalic acid from distilled water. Dry it in a vacuum over H2SO4. The anhydrous acid can be obtained by drying at 100o overnight. [Beilstein 2 IV 1819.]

Oxalic acid dihydrate is a purifying agent in pharmaceutical industry, special in antibiotic medication, such as Oxytetracycline , Chloramphenicol , etc; * Precipitating agent in Rare-earth mineral processing; * Bleaching agent in the textile activities, wood pulp bleaching; * Rust-remover for Metal treatment; * Grinding agent, such as Marble polishing; * Waste water treatment, removing calcium from water.

A diprotic reducing agent used as a buffer.

Oxalic acid occurs in the cell sap of Oxalisand Rumex species of plants as the potassium and calcium salt. It is the metabolicproduct of many molds (Merck 1989). Thereare a large number of applications of thiscompound, including indigo dyeing; calicoprinting; removal of paint, rust, and inkstains; metal polishing; bleaching leather; inpesticide compositions and manufacture ofoxalates. It is also used as an analyticalreagent and as a reducing agent in organicsynthesis.Addition of oxalic acid to chromic acid forthe anodizing of Al alloy has been reported tomodify the morphology and improve the corrosion performance of anodic films (Moutarlier et al. 2004). Also, it is a very effectiveadditive for the ozone treatment of cellulose.It prevents the degradation of cellulose fromozone bleaching.