Oxalic acid is a derivative of Oxalis plants, although it can also be obtained through chemical reactions with other elements. It has uses in food, beekeeping, and as a product for removing rust. It comes in different chemical forms such as dihydrate and sublimated, and in presentations like powder and liquid. Based on its formula, let’s explore all its properties and characteristics.
Oxalic acid
It belongs to the group of ethanedioic acids, being a dicarboxylic acid that consists of two carbon atoms in its molecular composition. The chemical formula of oxalic acid is H₂C₂O₄.
Although it is present in the plant called Oxalis, it is highly corrosive, much more so than other acids used as a treatment for bee parasites.
There are different formulations and compositions with some variations in their chemical structure, which determines their different uses. Let’s take a look at them.
Contents
Types and commercial presentations
- Dihydrated oxalic acid
- Sublimated
- Powder
- Liquid
- Strips
Dihydrated oxalic acid
It is a similar element, except that it contains water. When the term “dihydrated” is added, it means that dihydrated oxalic acid has two water molecules for each one of the main element. In its nomenclature, it should be written as “2H₂O,” while in the trihydrated version, it is “3H₂O.”
Sublimated or with a sublimator
It is widely used in beekeeping as it helps to control varroa mites. Sublimated oxalic acid is a product that can facilitate treatment in some phases of varroosis, requiring a vaporizer or “sublimator” for such use.
The term “sublimated” refers to the change in chemical state, meaning the transition from solid to gas. When purchased in the form of a white powder, it can be converted into gas to vaporize the hive, making it easier to disinfect and eliminate parasites in bees.
Uses of oxalic acid
- Eliminating varroa mites in beekeeping
- Polishing marble
- Rust removal
- Disinfecting and cleaning
- Whitening tanned leather
- Removing iron from textiles
- Metal stripping
- Treating old wood
One of the most well-known uses of oxalic acid is for polishing marble, as well as softening the texture of construction materials used for flooring.
Since it is corrosive and destroys organic tissue, it has antiseptic properties. When applied in low concentrations on surfaces, it can eliminate parasites and clean decay, making it useful for cleaning bathrooms and personal hygiene areas.
In the metallurgical industry, it is applied as a solution to remove metal impurities, descaling, separating inorganic contaminants, and removing rust from ferrous metals. It is also used in aluminum and copper production.
Regarding leather treatment, it works as a substance to whiten and protect tanned leather. It prevents deterioration and rot caused by chromium and tannins in treated hides.
A characteristic related to the textile industry is its use to remove metals from clothing and reduce the alkalinity of detergent, leaving fabrics clean and stain-free. Additionally, it is included in mixtures to enhance prints that require ironing.
In the woodworking and carpentry industry, oxalic acid is used as a cleaner for old wood. It improves the appearance of planks, logs, and old boards, also serving as a degreaser to enhance paint adhesion. It is important to wash the wood after use to prevent deterioration.
Uses of oxalic acid in beekeeping
It is well known and widely applied in beehives as it effectively treats mites that attack these hymenopteran insects. Oxalic acid in beekeeping is used to control varroosis, a disease that reduces the number of colony members by destroying larvae and adult bees.
It is also effective as a repellent for galleriosis or wax moths, although its primary use is to stop the spread of the varroa mite. However, there are some concerns about its use in beekeeping because it can penetrate honey, which is later sold for human consumption.
The concerns arise because it has side effects on health. However, beekeepers who use it argue that natural honey already contains oxalic acid in varying concentrations depending on the type, with higher levels found in honey from almond trees (Prunus dulcis).
Keep in mind that it does not kill varroa mites within the brood. It acts against the phoretic phase, affecting adult bees, making it effective in that case.
To remove rust
To achieve this, mix water with the powder you have purchased. This will trigger a chemical reaction that will remove the corroded parts, leaving the metal looking better, almost like new. To remove rust with oxalic acid, follow these steps:
- Scrub with water and soap to clean the metal.
- Prepare a dilution with 1 liter of water and 100 g of oxalic acid in a plastic bucket or basin.
- Submerge the rusty metal pieces.
- Let it sit for 2 to 3 hours, checking periodically.
- Remove the pieces from the bucket and rinse them under running water. It is important to rinse thoroughly. Scrub if necessary to remove any remaining rust.
- Dry everything well to prevent new oxidation.
Now you know how to use oxalic acid to remove rust from metal. To prevent further corrosion, it is essential to dry the surface properly and apply a layer of oil, petroleum jelly, or grease. Always wear gloves and use the appropriate protection indicated in the safety data sheet.
Relation to acetic acid
Both are used as treatments to eliminate varroa mites in bees, although acetic anhydride and also acetic acid in beekeeping are much more potent. Their effects are about 3000 times more effective, so they must be handled carefully due to their corrosive properties.
Oxalic acid formula and chemical characteristics
It is composed of two carbon atoms and acts as a chelating agent for certain minerals such as iron, magnesium, copper, and zinc, as well as calcium. The chemical formula of oxalic acid is:
- Oxalic acid formula: H₂C₂O₄
- Developed formula: HOOC-COOH
- Other commercial names: ethanedioic acid
- CAS number: 144-62-7(1)
- Density: 1900 kg/m³
- Molar mass: 90.03 g/mol
- Melting point: 374.65 K or 102 °C
- Boiling point: 638.15 K or 365 °C
- pKa: 1.19
It is an organic acid naturally present in food without being added. Although it is not inherently harmful, it is recommended to limit the consumption of products containing it in certain conditions, such as kidney stones and other health issues. Let’s look at which foods contain it.
Foods containing oxalic acid
- Honey
- Spinach
- Rhubarb
- Tea
- Beetroot
- Purslane
- Swiss chard
- Ombú
- Endive
- Cocoa
- Dandelion
- Walnuts
There are many foods that contain oxalic acid, so it is important to check their composition as well as the amount of oxalate—the salt form of oxalic acid—since excessive consumption can be harmful, especially for people prone to developing kidney stones.
Individuals with kidney gravel should avoid consuming these foods, as oxalic acid and its salts are poorly soluble in water and tend to form stones that can block certain bodily ducts and cause discomfort when urinating. The recommendation from the Spanish Ministry of Health and the EU is to consume these foods in moderation in such cases, always in small doses of oxalic acid.
Toxicity
When ingested through food, there is no issue of toxicity or danger. The concerns regarding oxalic acid toxicity are related to its handling as a chemical product, which include:
- Irritation of the respiratory tract due to inhalation, causing severe damage to the throat and nasal passages.
- Burns on the skin and subdermal tissue, penetrating the lower layers upon topical contact.
- Eye damage from splashes or exposure to vapors from sublimated acid.
It is essential to always use the appropriate protective equipment when handling a corrosive chemical compound. The recommended safety measures include wearing gloves, protective goggles, and a mask for strong acids that release vapors. Always follow the safety data sheet that accompanies the product when handling it.
Production
Although it is naturally present in food and vegetables, various laboratory procedures and chemical reactions are currently used to produce oxalic acid.
When heating sodium formate (HCOONa) to 360 °C, sodium oxalate (NaOOC-COONa) begins to form. This reaction releases dihydrogen (H₂). The next step in obtaining it is to add lime slurry to precipitate calcium oxalate. This compound must then be reacted with sulfuric acid (H₂SO₄) to finally produce ethanedioic acid.
Where can it be purchased?
It is available in many specialized stores as well as beekeeping supply shops. You can buy oxalic acid in stores that sell chemical products, as they offer better prices than businesses specializing in wood treatment solutions and drugstores.