Oxalic

Oxalic refers to oxalic acid and the oxalate family of compounds. Oxalic acid is a simple organic dicarboxylic acid with the formula H2C2O4, commonly written HOOC-COOH. It can donate two protons in solution, with dissociation occurring in two steps (pKa values around 1.27 and 4.27). The neutral molecule forms the oxalate dianion, C2O4^2−, which readily combines with metal ions to form oxalate salts.

In nature, oxalates occur widely as secondary metabolites in plants. They can accumulate as calcium oxalate crystals, which serve various defensive roles against herbivory. Dietary sources high in oxalates include leafy greens such as spinach and beet greens, as well as rhubarb leaves and buckwheat. Oxalates are also produced endogenously in small amounts during normal metabolism and are excreted in urine.

Industrially, oxalic acid is produced by oxidation of carbohydrate-rich feedstocks or glyoxal-based methods. It is used as a cleaning and bleaching agent, in rust removal, and for etching or mordanting in certain textile and wood processes. In the laboratory, oxalates serve as chelating agents for removing metal ions, and calcium oxalate forms insoluble deposits.

Safety considerations are important. Concentrated oxalic acid is a corrosive substance that can cause severe irritation and tissue damage if ingested or contacted with skin or eyes. In the human body, excessive oxalate can contribute to kidney stone formation, particularly in susceptible individuals, by combining with calcium to form calcium oxalate crystals. Handling, storage, and use should follow appropriate safety guidelines.