Oxalic acid is a chemical compound that is widespread in nature and used in numerous applications. As the simplest dicarboxylic acid, it is an important substance in industry, household, and medicine. In this blog post, we want to take a closer look at the properties and applications of oxalic acid.

Chemical properties of oxalic acid

Oxalic acid, also called ethanedioic acid, has the chemical formula C₂H₂O₄. It is a colorless, crystalline compound that is well soluble in water. With a melting point of 189°C and a boiling point of 101°C at 13 hPa, oxalic acid belongs to the solids.

As a divalent carboxylic acid, oxalic acid has two carboxyl groups (-COOH) responsible for its reactivity. By releasing hydrogen atoms, oxalate ions (C₂O₄²⁻) can form, which in turn can form salts with metal cations.

Oxalic acid is a relatively strong acid with a pKa value of 1.25 for the first dissociation stage and 4.19 for the second stage. It therefore reacts with bases to form salts, the so-called oxalates.

Occurrence and production of oxalic acid

Oxalic acid naturally occurs in many plants, especially in rhubarb, spinach, chard, and sorrel. It serves as a defense against predators for the plant. Oxalic acid can also be found in fungi, lichens, and some animals.

Industrially, oxalic acid is mainly produced by oxidation of carbohydrates such as glucose or sucrose. The sugar molecules are first converted into carbon monoxide and water, before oxalic acid is formed by further oxidation. Alternatively, oxalic acid can also be obtained from wood or cellulose.

Applications of oxalic acid

The diverse properties of oxalic acid make it a useful material in numerous industries. Here is a selection of the most important application areas:

Cleaning and removal of encrustations

Oxalic acid is an effective cleaning agent, primarily used to remove lime and rust deposits. Therefore, it is widely used in household cleaners, descalers, and rust removers. Oxalic acid is also used in industry to clean metal surfaces.

Chemical Industry

As a starting material for the production of oxalates, esters, and other chemical compounds, oxalic acid plays an important role in the chemical industry. Oxalates are used as reducing agents, complexing agents, or precipitants.

Medical applications

In medicine, oxalic acid is used, for example, to treat gout as it can dissolve uric acid crystals. It is also used in dentistry to remove tartar. Furthermore, oxalic acid is used as an excipient in medications.

Agriculture and horticulture

In agriculture, oxalic acid is used to combat weeds and pests. In horticulture, it is used to clean flower pots and garden tools. Oxalic acid can also be found as an additive in fertilizers.

Further applications

In addition to the mentioned areas of use, oxalic acid is also used in the textile industry, leather processing, photography, as well as in the production of dyes and varnishes.

Safety when using oxalic acid

Although oxalic acid is versatile, caution must be exercised when handling it. In pure form, oxalic acid is toxic and can be harmful to health if swallowed or in contact with skin. Therefore, protective measures such as gloves and good ventilation should be taken.

When handling products containing oxalic acid, it is important to follow dosage recommendations and keep children away from the substance. In case of ingestion or contact with the eyes, medical help should be sought immediately.

Overall, oxalic acid is a useful and versatile chemical, but its use must be carried out with the necessary care. With the right safety measures, oxalic acid can be used safely and effectively in numerous applications.