Oxalic Acid CAS 144-62-7: Properties, Applications, Grades and Supplier Guide
Release time: 2026-09-17
Oxalic acid, identified by the Chemical Abstracts Service (CAS) registry number 144-62-7, is a simple dicarboxylic acid with a wide array of industrial and commercial applications. Known for its strong acidity and exceptional chelating properties, this organic compound plays a pivotal role in sectors ranging from textile manufacturing to metal surface treatment. This comprehensive guide details the properties, diverse applications, available grades, and crucial considerations for sourcing oxalic acid.
Table of Contents
Understanding Oxalic Acid (CAS 144-62-7)
At room temperature, oxalic acid typically exists as a colorless, crystalline solid. It is most commonly encountered in its dihydrate form (C2H2O4 · 2H2O), although the anhydrous form (C2H2O4) is also utilized in specific chemical processes. As the simplest dicarboxylic acid, it exhibits acidic strength greater than acetic acid, making it highly effective in various chemical reactions.
Its primary mechanism of action in many applications stems from its ability to bind with metal ions, particularly iron, forming water-soluble complex salts (oxalates). This chelating action is fundamental to its effectiveness as a cleaning and bleaching agent.
Key Physical and Chemical Properties
Understanding the technical specifications of CAS 144-62-7 is essential for its safe and effective application.
| Property | Value (Dihydrate Form) | Value (Anhydrous Form) |
| Chemical Formula | C2H2O4 · 2H2O | C2H2O4 |
| Molar Mass | 126.07 g/mol | 90.03 g/mol |
| Appearance | White crystalline powder | White solid |
| Density | 1.653 g/cm^3 | 1.90 g/cm^3 |
| Melting Point | 101.5 °C (214.7 °F) | 189.5 °C (373.1 °F) (sublimes) |
| Solubility in Water | Highly soluble (~ 143 g/L at 25 °C) | Soluble |
| Acidity ($pK_a$) | pK_{a1} = 1.25, pK_{a2} = 4.14 | N/A |
Primary Industrial Applications
The versatility of oxalic acid drives its demand across multiple industries. Its applications leverage its acidic, reducing, and chelating characteristics.
1. Metal Cleaning and Treatment
One of the most prominent uses of oxalic acid is in metal surface preparation and cleaning. It is highly effective at removing rust, scale, and tarnish from various metals, particularly iron and steel.
- Rust Removal: Oxalic acid reacts with iron(III) oxide (rust) to form the water-soluble ferrioxalate ion ([Fe(C2O4)3]^{3-}). This reaction allows the rust to be easily washed away without significantly attacking the base metal, unlike stronger mineral acids.
- Anodizing Aluminum: In the aluminum anodizing process, oxalic acid is often used in the electrolytic bath. It helps create a hard, durable, and corrosion-resistant oxide layer on the aluminum surface, often imparting a distinct color without the need for additional dyes.
- Metal Polish Formulation: It is a key active ingredient in many commercial metal polishes, facilitating the removal of oxidation and restoring shine.
2. Textile and Leather Industries
The textile industry relies on oxalic acid for several critical processes, primarily leveraging its bleaching and mordanting capabilities.
- Bleaching Agent: It serves as a gentle but effective bleaching agent for wood pulp, cotton, and linen. It is particularly useful for removing iron stains from fabrics during the laundering process.
- Mordant in Dyeing: In dyeing processes, oxalic acid acts as a mordant, helping to fix dyes to the fabric fibers, ensuring colorfastness and vibrant hues.
- Leather Tanning: It is employed in the leather tanning industry to bleach the leather and adjust the pH of the tanning baths, improving the quality and appearance of the final product.
3. Wood Bleaching and Restoration
In woodworking and restoration, oxalic acid is the standard treatment for lightening dark stains in wood, particularly those caused by water damage or the reaction of iron with tannins present in woods like oak and mahogany. It effectively bleaches the wood fibers, restoring a more uniform and natural appearance prior to refinishing.
4. Rare Earth Metal Processing
Oxalic acid is crucial in the extraction and purification of rare earth metals (REMs). It is used as a precipitating agent to separate REMs from other elements in the ore. The addition of oxalic acid to solutions containing rare earth ions results in the precipitation of insoluble rare earth oxalates, which can then be isolated and further processed into pure metals or oxides.
5. Chemical Synthesis
As a fundamental building block, oxalic acid is used in the synthesis of various other chemicals.
- Oxalates: It is the precursor for manufacturing various oxalate salts, such as ammonium oxalate, sodium oxalate, and potassium oxalate, which have specialized applications in photography and laboratory reagents.
- Glyoxylic Acid: It can be reduced to produce glyoxylic acid, a key intermediate in the pharmaceutical and agrochemical industries.
- Polymers: It is utilized in the production of certain polyesters and polyurethanes.
6. Beekeeping (Varroa Mite Control)
A growing agricultural application is in apiculture. Beekeepers utilize oxalic acid treatments to control Varroa destructor mites in honey bee colonies. Applied via vaporization or trickle methods, it provides an effective and relatively low-toxicity means of managing these destructive parasites during broodless periods.
Grades of Oxalic Acid
Oxalic acid is commercially available in several grades, tailored to meet the purity requirements of specific applications. Selecting the correct grade is critical for both performance and cost-effectiveness.
Technical Grade
Technical grade oxalic acid is the most widely used and cost-effective option for bulk industrial applications.
- Purity: Typically ranges from 99.0% to 99.6%.
- Applications: Suitable for rust removal, metal cleaning, wood bleaching, textile processing, and general chemical synthesis where ultra-high purity is not strictly required.
- Characteristics: May contain trace impurities (such as heavy metals, chlorides, or sulfates) that do not interfere with standard industrial processes.
Reagent Grade (Analytical Grade)
Reagent grade, or Analytical Reagent (AR) grade, is manufactured to stringent purity standards for laboratory use.
- Purity: Usually exceeds 99.8%.
- Applications: Essential for analytical chemistry, laboratory research, and quality control procedures where precise measurements and predictable reactions are necessary.
- Characteristics: Impurities are strictly controlled and quantified, often conforming to specifications set by organizations like the American Chemical Society (ACS).
Pharmaceutical Grade
Pharmaceutical grade oxalic acid meets rigorous standards for use in pharmaceutical manufacturing.
- Purity: High purity, conforming to pharmacopeial standards (e.g., USP, EP, BP).
- Applications: Used as an excipient or intermediate in the synthesis of Active Pharmaceutical Ingredients (APIs).
- Characteristics: Subject to strict controls regarding heavy metals, residual solvents, and endotoxins.
Handling and Safety Considerations
While highly useful, oxalic acid is a hazardous substance and must be handled with appropriate care.
- Toxicity: It is toxic if ingested or absorbed through the skin. Ingestion can lead to severe gastrointestinal damage and kidney failure due to the precipitation of calcium oxalate crystals in the renal tubules.
- Corrosivity: As a strong acid, it can cause severe skin burns and eye damage upon contact.
- Inhalation: Inhalation of dust or vapors can irritate the respiratory tract.
- Personal Protective Equipment (PPE): When handling oxalic acid, always wear appropriate PPE, including chemical-resistant gloves, safety goggles, and a lab coat or protective suit. Use in well-ventilated areas or utilize respiratory protection if dust generation is likely.
- Storage: Store in a cool, dry, well-ventilated area, away from incompatible materials such as strong alkalis, oxidizing agents, and silver compounds. Ensure containers are tightly closed and properly labeled.
Supplier Guide: Sourcing Oxalic Acid
Selecting a reliable supplier for CAS 144-62-7 is essential to ensure consistent quality, timely delivery, and regulatory compliance. Consider the following factors when evaluating potential suppliers:
- Quality Assurance and Certifications: Verify that the supplier adheres to robust quality management systems (e.g., ISO 9001). Request Certificates of Analysis (COA) for specific batches to confirm purity and impurity profiles align with your requirements. For specialized applications (e.g., pharmaceutical), ensure the supplier holds relevant industry certifications.
- Production Capacity and Supply Chain Stability: Assess the supplier’s production capacity to ensure they can meet your volume requirements reliably. Investigate their supply chain resilience to mitigate risks of disruption due to raw material shortages or logistical challenges.
- Grade Availability: Confirm that the supplier offers the specific grade (Technical, Reagent, etc.) necessary for your application.
- Packaging Options: Suppliers should offer various packaging options tailored to your handling capabilities, ranging from small laboratory quantities to 25kg bags, bulk bags (FIBCs), or liquid solutions if applicable.
- Technical Support and Regulatory Compliance: A reputable supplier will provide technical assistance and ensure all products comply with relevant local and international regulations (e.g., REACH in Europe, TSCA in the US). They should readily supply Safety Data Sheets (SDS).
- Sustainability Practices: Increasingly, buyers are prioritizing suppliers with transparent and environmentally responsible manufacturing processes and waste management protocols.
By carefully evaluating these criteria, procurement professionals can establish secure and beneficial partnerships with oxalic acid manufacturers and distributors.
FAQs
1. Is it safe to use oxalic acid for removing rust on delicate metal items?
While highly effective for rust removal, oxalic acid can be overly aggressive on certain delicate metals or finishes if not used carefully. For robust metals like iron and structural steel, it is excellent. However, for thin plating, antique finishes, or softer metals, it’s advisable to test the solution on an inconspicuous area first. The concentration of the solution and the duration of exposure should be carefully monitored to prevent etching or damage to the underlying material. Always neutralize the surface with a mild alkaline solution (like baking soda and water) and rinse thoroughly after treatment.
2. What is the difference between oxalic acid dihydrate and anhydrous oxalic acid?
The primary difference lies in the presence of water molecules within the crystal structure. The dihydrate form (C2H2O4 · 2H2O) contains two water molecules for every molecule of the acid, whereas the anhydrous form (C2H2O4) contains no water. The dihydrate is the most common and commercially available form, as it is more stable at room temperature. The anhydrous form is typically only used in specific chemical syntheses where the presence of water would interfere with the reaction. For most general applications like cleaning or bleaching, the dihydrate form is the standard choice.
3. Can I dispose of leftover oxalic acid down the drain?
No, oxalic acid should not be poured directly down the drain without treatment. Because it is a strong acid and toxic to aquatic life, improper disposal can damage plumbing and harm the environment. Small amounts of leftover solution should be carefully neutralized using an alkaline substance, such as sodium bicarbonate (baking soda) or agricultural lime, until the pH is neutral (around pH 7). Once neutralized, the resulting liquid is generally safer to dispose of, but you must always consult and comply with your local municipal waste disposal regulations, as rules can vary significantly by region.