Oxalic acid dihydrate RC01648

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.]