Oxalic Acid, Ethanedioic Acid Dihydrate, Oxalic Acid Dihydrate, 144-62-7, 6153-56-6

OXALIC ACID (CAS 144-62-7)

1. Chemical Identity and Structure

• IUPAC Name: Ethanedioic acid dihydrate

• CA Index Name: Oxalic acid dihydrate

• CAS Numbers: 144-62-7 (anhydrous), 6153-56-6 (dihydrate – common commercial form)

• EC Number: 205-634-3

• RTECS Number: RO2450000

• Molecular Formula: C₂H₂O₄ · 2H₂O

• SMILES: C(=O)(C(=O)O)O

• Crystal System: Monoclinic (dihydrate), space group P21/c

2. Physicochemical Parameters (Dihydrate Form)

3. Spectroscopic Identifiers

• FTIR (KBr, cm⁻¹): 3417 (O–H), 1715 (C=O dimeric), 1250 (C–O), 782 (deformation)

• Raman (cm⁻¹): 1740 (C=O), 890 (C–C)

• ¹H NMR (D₂O): Singlet ~3.4 ppm (exchangeable OH)

• ESI-MS (negative mode): m/z 89 → [M–H]⁻ (anhydrous form)

4. Industrial Production Methods – Detailed Processes

4.1 Classical Nitric Acid Oxidation (Dutch Process)

• Feedstock: Sucrose or glucose (35–40% w/w)

• Oxidant: 60% HNO₃ + V₂O₅ catalyst

• Temperature: 60–70°C

• Reaction: C₆H₁₂O₆ + 6HNO₃ → 3(COOH)₂ + 6NO + 6H₂O

• Yield: 85–90%

• By-products: CO₂, trace HCN

4.2 Oxidative Carbonylation (Monsanto/UBE Process)

• Reaction: 2ROH + 2CO + 0.5O₂ → (COOR)₂ + H₂O

• Catalyst: Pd(II)/Cu(II) or nitrite-based systems

• Reactor: Gas-liquid reactor with distillation column

• Hydrolysis: Diester + H₂O → H₂C₂O₄ + 2ROH (alcohol recycled)

• Yield: >96%

4.3 Sodium Formate Dehydrogenation (Laboratory Scale)

• Reaction: 2HCOONa → Na₂C₂O₄ + H₂ (≥360°C)

• Acidification: Na₂C₂O₄ + H₂SO₄ → H₂C₂O₄ + Na₂SO₄

5. Thermal Decomposition and Phase Behavior

• TGA/DTA Profile:

  • 80–120°C → Loss of crystal water (2 H₂O, endothermic)

  • 160–220°C → CO + CO₂ + H₂O evolution (competes with sublimation)

  • 250°C → Complete decomposition, carbon residue + CO

• Reaction: H₂C₂O₄ → CO + CO₂ + H₂O + C

• Sublimation flux: ~50 mg/h (150°C, 1 atm)

6. Reactivity and Incompatible Chemicals

• Strong oxidizers (KMnO₄, HNO₃, chromates) → vigorous exothermic reaction

• Oxidizing salts (chlorates, bromates) → explosion risk

• Metals (Ag, Cu, Fe) → metal oxalate formation, accelerated corrosion

• Urea, thiourea → explosive compounds above 60°C

• Alkalis → neutralization to oxalate salts (safe when cold)

7. Solubility Behavior and Phase Equilibrium

• Solution viscosity (25°C): 1.2 cP at 10% w/w

• Freezing point depression constant (Kf): 3.88 K·kg/mol (in water)

8. Toxicokinetics and Metabolism

• Absorption: Rapid via oral and inhalation routes (Tmax ~0.5–1 h)

• Distribution: Chelates calcium ions → calcium oxalate crystals

• Metabolism: No enzymatic metabolism in humans; excreted unchanged renally

• Excretion: Renal (~85–90% within 24–48 hours)

• Biological half-life (plasma): 2–3 hours

• Biomarker: Spot urine oxalate/creatinine ratio (>0.1 indicates abnormal)

9. Acute Toxicity Values (OECD Tests)

10. Chronic Toxicity and Carcinogenicity

• NOAEL (oral, rat, 90-day): 50 mg/kg/day

• LOAEL (renal effect): 200 mg/kg/day

• Carcinogenicity classification: IARC Group 3 (not classifiable for humans)

• Teratogenicity: Dose-dependent calcification defects in animal studies (≥100 mg/kg)

• Reproductive toxicity: Testicular effects at high doses (rat)

11. Industrial Hygiene and Exposure Limits

12. Fire and Explosion Data

• Dust explosion class: St1 (Kst ~ 60 bar·m/s)

• Minimum ignition energy (MIE): 40 mJ

• Maximum explosion pressure (Pmax): 6.5 bar

• Extinguishing media: Dry chemical, CO₂, water fog (alcohol-resistant foam)

• Dust cloud ignition temperature: 480°C

• Decomposition gases: CO, CO₂, formic acid vapor

13. Reaction Thermodynamics and Chelate Chemistry

• Metal chelate stability constants (log β, 25°C, ionic strength 0.1):

  • Fe³⁺: log β₁ = 9.4

  • Ca²⁺: log β₁ = 3.0, log β₂ = 4.5

  • Cu²⁺: log β₁ = 6.2

• Complex formation enthalpy (Ca²⁺): ΔH = -18 kJ/mol

• Solubility product (Ksp) of calcium oxalate: 2.32 × 10⁻⁹ (38°C, urine matrix)

14. Industrial Applications – In-Depth Validation

14.1 Rust Removal Formulations

• Optimum concentration: 5–10% w/w oxalic acid + 1% surfactant

• Reaction rate (Fe₂O₃ dissolution): 1.2 mg/cm²/min (25°C)

• Iron complexation capacity: 1 mol H₂C₂O₄ → 0.5 mol Fe³⁺ (pH 2–3)

14.2 Varroa Treatment – Sublimation Protocol

• Suitable device: Electric or gas-powered sublimator (Varrox type)

• Dosage: 1.5–2.0 g per hive (10–15 frames)

• Temperature requirement: 160–180°C (for adequate sublimation)

• Application frequency: 3 times with 4-day intervals during broodless period

• Efficacy: >95% Varroa mortality, bee mortality <1%

14.3 Calcium Determination – Gravimetric Method

• Reagent: 4% ammonium oxalate solution

• pH range: 4–5 (ammonium acetate buffer)

• Digestion time: 4 hours (hot)

• Washing solution: 0.1% ammonium oxalate + 0.1% ammonia

• Muffle furnace: 500°C → weigh as CaO

15. Analytical Methods and Calibration

• HPLC-UV:

  • Column: Aminex HPX-87H (300×7.8 mm)

  • Mobile phase: 5 mM H₂SO₄

  • Flow rate: 0.6 mL/min, detection 210 nm

  • Retention time: 11.2 min

• Ion Chromatography (IC):

  • Column: AS11-HC

  • Eluent: 1–30 mM KOH gradient

  • Sensitivity: 0.1 mg/L

• Titrimetry (permanganate):

  • 1 mol H₂C₂O₄ ≡ 2 mol KMnO₄

  • Endpoint: Pale pink (50°C, H₂SO₄ medium)

• FTIR quantitation: 1715 cm⁻¹ band (KBr pellet method)

16. Shelf Life and Stability Data

• Recommended storage: 15–30°C, <70% RH, original packaging

• Incompatibility indicator: Yellow/brown coloration (iron oxalate formation)

17. Transport and Regulatory Classification

18. Disposal and Environmental Fate

• Biodegradation (water): Rapid (~90% in 2 days, OECD 301D)

• Biochemical oxygen demand (BOD₅): 0.25 g O₂/g (pure)

• Chemical oxygen demand (COD): 0.18 g O₂/g

• Soil adsorption (Koc): 10–20 L/kg (high mobility)

• Fish toxicity (LC₅₀, 96 h):

  • Rainbow trout: 120 mg/L

  • Zebrafish: 160 mg/L

• Disposal method: Neutralization (lime milk) → calcium oxalate sludge → sanitary landfill

19. Quality Specifications (Industrial Grade)

20. Synonyms, Storage Codes, and Reference Standards

• Synonyms: Ethanedioic acid, Aktisal, Aquisal, DeerClean, NSC 132055, NSC 151956

• PubChem CID: 971

• ChemSpider: 946

• MeSH ID: D019815

• Storage codes:

  • D001 (Hazardous waste – corrosive)

  • F003 (Non-flammable)

• Reference standard: NIST SRM 914a (Oxalic acid dihydrate, titrimetric standard)

• Pharmacopeia compliance: USP, Ph.Eur. (no monograph – reagent grade only)