H2C2O42H2O

H2C2O4·2H2O, commonly written as oxalic acid dihydrate, is the dihydrate form of oxalic acid (ethanedioic acid). Its solid form is a colorless, crystalline substance that is highly soluble in water. The dihydrate arrangement is the form typically encountered in commercial oxalic acid products and laboratory reagents.

Occurrence, preparation, and structure

Oxalic acid occurs naturally in a variety of plants, including leafy greens and rhubarb, and is sometimes present in foods. Industrially, oxalic acid is produced by the oxidation of carbohydrate-rich feedstocks or by crystallization from oxalate-containing solutions. In its solid state, the compound commonly crystallizes with two water molecules in the lattice, giving the dihydrate composition H2C2O4·2H2O.

Acid-base properties and reactions

Oxalic acid is a diprotic acid, capable of donating two protons in aqueous solution to form oxalate species. It readily forms a wide range of oxalate salts with many metal ions. In redox chemistry, oxalic acid can act as a reducing agent under appropriate conditions, and it can reduce certain oxidants such as permanganate in acidic media. Upon heating, oxalic acid dehydrates and decomposes, producing carbon dioxide and carbon monoxide.

Uses and safety

The compound and its salts are used in cleaning and rust-removing formulations, wood bleaching, and as a laboratory reagent for crystallization and preparation of oxalate salts. Oxalic acid is corrosive and toxic if ingested or inhaled; exposure can irritate skin and eyes. In the body, oxalate can combine with calcium to form calcium oxalate, a component of certain kidney stones, highlighting the importance of careful handling and disposal.

See also: Oxalic acid, Oxalate.