Oxalic acid

The limiting carboxylic dibasic acid with the gross formula C2H2O4 is called, by the systematic nomenclature, ethanedioic acid. This substance is also known under another, more common name - oxalic acid. It was first obtained by the German chemist F. Weller from cyanogen (dinitrile oxalic acid) in 1824. Colorless crystals of acid dissolve in water to form colorless solutions. The molar mass is 90.04 g / mol. In appearance it resembles monoclinic colorless crystals. At a temperature of 20 ° C, 8 g of oxalic acid dissolves in 100 g of water. It dissolves well in acetone, ethyl alcohol and sulfur ether. The density is 1.36 g / cm³. Melts at a temperature of 189.5 ° C, sublimated at 125 ° C, decomposes at 100-130 ° C.

All the chemical properties characteristic of carboxylic acids are possessed by oxalic acid. Its formula: NOOS-COOH. Despite the fact that it refers to carboxylic acids, it is considered to be a strong organic acid (3000 times stronger than acetic acid): C2O4H2 → C2O4H- + H + (pK = 1.27) and further: C2O4H- → C2O42 - + H + (pK = 4.27). Esters and salts of this acid are called oxalates. Oxalate ion C2O42- is a reducing agent. When oxalic acid reacts with a solution of potassium permanganate (KMnO4), the latter is reduced and the solution discolored. It is characterized by a reversible and slowly reacting reaction with alcohols (esterification), resulting in the formation of esters: HOOC-COOH + 2HOR ↔ 2H2O + ROOC-COOR.

In the industry, oxalic acid is obtained by oxidizing chemical compounds. For example, in the presence of a vanadium catalyst (V2O5), a mixture of nitric (HNO3) and sulfuric (H2SO4) acids oxidizes alcohols, carbohydrates and glycols. A method for the oxidation of ethylene and acetylene with nitric acid (HNO3) in the presence of palladium salts Pd (NO3) 2 or PdCl2 is also used. Oxalic acid is obtained from propylene, which is oxidized with liquid nitrogen dioxide (NO2). There is a good prospect for the production of an acid by the interaction of sodium hydroxide (NaOH) with carbon monoxide (CO) through the intermediate stage of formation of sodium formate: NaOH + CO → HCOONa. Then sodium oxalate is formed and hydrogen is liberated: HCOONa + NaOH → NaOOC-COONa + H2 ↑. From sodium oxalate in an acidic medium, oxalic acid is obtained: NaOOC-COONa + 2H + → HOOC-COOH + 2Na +.

The main fields of application of oxalic acid are cleaning or bleaching. Oxalic acid is able to effectively remove rust, so many cleaning products contain this chemical compound. About a quarter of the produced oxalic acid is used as a mordant for dyeing in leather and textile industries. It is also used as a reagent (GOST 22180-76) in analytical chemistry. Ethanedioic acid dihydrate (NOOC-COOH • H2O) according to TU 2431-002-77057039-2006 with a mass fraction of the main substance ≥ 99.3% is used in production processes of organic synthesis, for purification from rust and scaling of metals, for bleaching of sections in microscopy. Beekeepers use a solution of oxalic acid with a mass fraction of 3.2% in sugar syrup to control the parasitic mite. At the completion of marble structures, it processes the surfaces to compact and gloss.

Oxalic acid and oxalates are present in many plants, including black tea, found in animals. The main harm to humans is associated with renal insufficiency, which arises from the interaction of oxalic acid with calcium, resulting in the precipitation of solid calcium oxalate (CaC2O4), the main component of kidney stones. Acid provokes pain in the joints due to the precipitation of such compounds in them. Oxalic acid can be formed in the body as a result of the metabolism of ethylene glycol coming from the environment (for example, anti-icing agent for the treatment of runways and aircraft in airports, as well as other anthropogenic sources). Potential problems with oxalates in the human body can be divided into two. The first - an important macroelement of calcium is associated with oxalic acid and its deficiency in cells of tissues and organs is formed. The second is the formation of kidney stones. The greatest amount of oxalic acid is found in spinach, leaves and stems of rhubarb, sorrel, beetroot, parsley, green onions.