Industrial Grade High Purity Oxalic Acid Crystal For Rust Remover

Chemical formula: C₂H₂O₄*2H₂O

CAS: 6153-56-6

Purity: 99.6%

References: Riel Chemical Lab1&2, National public service platform for standards information.

Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula HO−C(=O)−C(=O)−OH, also written as (COOH)2 or (CO2H)2 or H2C2O4. It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water.

Its name is derived from early investigators who isolated oxalic acid from flowering plants of the genus Oxalis, commonly known as wood-sorrels. It occurs naturally in many foods. Excessive ingestion of oxalic acid or prolonged skin contact can be dangerous.

• Molecular weight: 126.07 g/mol
• Appearance: White transparent crystal or powder, industrial products may be slightly yellow due to impurities
• Odor: Tasteless or slightly sour
• Density: 1.65 g/cm³ (20°C)
• Melting point: The dihydrate lost its crystalline water at 101-102°C and was converted to anhydrous oxalic acid (H₂C₂O₄). Anhydrous oxalic acid sublimates at about 189.5°C and decomposes at high temperatures
• Solubility: Water: soluble in cold water (about 10 g/100 mL, 20°C), hot water solubility is higher. Ethanol: slightly soluble (approx. 5.7g /100 mL, 20°C)
• Acid: Binaric acid, acidic stronger than acetic acid (pKa₁=1.25, pKa₂=4.14); It can react with bases, metal oxides, carbonates to form salts (such as sodium oxalate, calcium oxalate)
• Reducibility: Under acidic conditions can be oxidized by strong oxidants (such as potassium permanganate) to produce CO₂ and H₂O
• Complexation: Oxalate (C₂O₄²⁻) forms a soluble complex with metal ions (e.g. Fe³+, Al³+). It is used in metal cleaning or rust removal
• Thermal decomposition: Decomposition when heated above 150°C, producing CO, CO₂ and H₂O

Oxalic acid is produced primarily by oxidizing carbohydrates or glucose with nitric acid or air in the presence of vanadium pentoxide. Another method is to regenerate nitric acid using oxygen, using a variety of precursors, including glycolic acid and glycol. As of 2011, only the Japanese company Mitsubishi has used this process.

A newer method requires oxidative carbonylation of alcohols to obtain dioxalate: 4 ROH + 4 CO + O 2 -> 2 (CO 2 R) 2 + 2 H 2 O. These diesters are then hydrolyzed to oxalic acid. About 120,000 tons are produced annually.

Historically, oxalic acid was prepared by applying a caustic base (such as sodium hydroxide or potassium hydroxide) to sawdust and then acidifying the oxalate with an inorganic acid (such as sulfuric acid). Oxalic acid can also be formed by heating sodium formate in the presence of an alkaline catalyst.

The main uses of oxalic acid include cleaning or bleaching, especially for rust removal (iron complexing agent). Its use in rust remover is due to the fact that it forms a stable water-soluble salt with trivalent iron, namely the iron oxalate ion.

Oxalic acid is an ingredient in some teeth whitening products. About 25% of oxalic acid is used as a mordant in the dyeing process. It is also used in bleach, especially for pulping wood, cork, straw, rattan, feathers, as well as for rust removal and other cleaning, for baking powder, and as a third reagent in silica analysis instruments.

• Concrete/Cement: Oxalic acid can react with calcium compounds in cement, causing the surface to powderize. Long-term use may weaken the structural strength. Applicable scenarios: Only for short-term cleaning of cement stains (such as residues from decoration), thorough rinsing is required.
• Plastic/Rubber: It has relatively low corrosiveness to most plastics (such as PP and PE), but may cause some rubbers to age (such as sealing rings).
• Wood: It will damage the wood fibers, causing color fading or rough surface. It is not recommended for cleaning wooden floors or furniture.

• Residual corrosion: Even if the surface is thoroughly rinsed, oxalic acid may seep into porous materials such as tile gaps and concrete, causing a prolonged and slow reaction. Suggestion: Rinse with clean water several times after use and neutralize with an alkaline solution (such as soapy water).
• Electrochemical corrosion: In a humid environment, oxalic acid may accelerate the electrochemical corrosion of metals (for example, iron nails rust more quickly).

• Electroplating industry: Oxalic acid is used for polishing metals, but a concentration that is too high can cause over-etching of the workpiece (it must be strictly controlled within 5%-10%).
• Textile industry: When used as a mordant, excessive use will reduce the strength of the fibers and it needs to be combined with a pH regulator.
• Post-processing of 3D printing: A few processes clean resin models with oxalic acid, but it may cause cracking (tolerance needs to be tested).

• Disposal: Oxalic acid solution should be neutralized to a pH of 6-9 before being discharged and must not be directly poured into the sewer (in some areas, it is classified as hazardous waste).
• Transportation restrictions: High-concentration oxalic acid (>10%) transportation requires a corrosive label, and some countries require special licenses.