ABSTRACT
CASRN: 144-62-7; DOT: 2449; molecular formula: C2H2O4; FW: 90.04; RTECS: RO2450000; Merck Index: 12, 7043 Physical state, color, and odor: Colorless and odorless rhombic crystals. Hygroscopic. Melting point (°C): 182-189.5 (anhydrous), 101.5 °C (hydrated) (Weast, 1986) Boiling point (°C): Sublimes at 157 (Weast, 1986) Density (g/cm3): 1.895-1.900 at 17 °C (Weast, 1986) 1.653 at 18 °C (Windholz et al., 1983) Diffusivity in water (x 10-5 cm2/sec): 0.97 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant: At 25 °C: pK1 = 1.27, pK2 = 4.27 (Windholz et al., 1983) Henry’s law constant (x 10-10 atm⋅m3/mol): 1.43 at pH 4 (quoted, Gaffney et al., 1987) Ionization potential (eV): 11.20 (Lias et al., 1998) Soil organic carbon/water partition coefficient, log Koc: 0.89 using method of Kenaga and Goring (1980) Octanol/water partition coefficient, log Kow: -0.43, -0.81 (quoted, Verschueren, 1983) Solubility in organics (g/L): Alcohol (40), ether (10), glycerol (181.8) (Windholz et al., 1983) Solubility in water: 120 g/kg at 25 °C (quoted, Saxena and Hildemann, 1996) 95.0 and 1,290 g/L at 15 and 90 °C, respectively (quoted, Verschueren, 1983) Vapor pressure (mmHg): 3 x 10-4 at 30 °C (quoted, Verschueren, 1983)
Biological. Heukelekian and Rand (1955) reported a 5-d BOD value of 0.12 g/g which is 66.7% of the ThOD value of 0.18 g/g. Chemical/Physical. At temperatures greater than 189.5 °C, decomposes to carbon dioxide, carbon monoxide, formic acid, and water (Windholz et al., 1983). Ozonolysis of oxalic acid in distilled water at 25 °C under acidic conditions (pH 6.3) yielded carbon dioxide (Kuo et al., 1977). Absorbs moisture in air forming the dihydrate (Huntress and Mulliken, 1941). Reacts with bases forming water soluble salts. Exposure limits (mg/m3): NIOSH REL: TWA 1, STEL 2, IDLH 500; OSHA PEL: TWA 1; ACGIH TLV: TWA 1, STEL 2 (adopted). Symptoms of exposure: Ingestion may cause vomiting, diarrhea, severe gastrointestinal disorder, renal damage, shock, convulsions, and coma (Patnaik, 1992). Toxicity: Acute oral LD50 in rats 375 mg/kg (quoted, RTECS, 1985). Source: Oxalic acid occurs naturally in many plants including buckwheat leaves (111,000 ppm), lambsquarter (140,000 to 300,000 ppm), black pepper (4,000 to 34,000 ppm), star fruit (50,000 to 95,800 ppm), purslane (1,679 to 16,790 ppm), nance bark (27,300 ppm), rhubarb 4,400 to 13,360 ppm), tea leaves (2,192 to 10,000 ppm), bitter lettuce (10,000 ppm), spinach (6,580 ppm), cacao (1,520 to 5,000 ppm), bananas (22 to 5,240 ppm), ginger (5,000 ppm in rhizome), cashews (3,184 ppm), almonds (4,073 ppm), taro roots (1,334 ppm), tamarind (1,960 ppm), garden sorrel (3,000 ppm), mustard green leaves (1,287 ppm), peppers (257 to 1,171 ppm), sweet potato roots (1,000 ppm), pumpkins, oats (400 ppm), tomatillo (109 to 536 ppm), various cabbage leaves (59 to 350 ppm), and horseradish (Duke, 1992). Oxalic acid was identified as a constituent in a variety of composted organic wastes. Detectable concentrations were reported in all 21 composts extracted with water. Concentrations ranged from 0.60 mmol/kg in a straw + dairy cattle manure to 21.89 mmol/kg in straw + wood bark + dairy cattle manure. The overall average concentration was 9.67 mmol/kg (Baziramakenga and Simard, 1998). Uses: Calico printing and dyeing, analytical and laboratory reagent; bleaching agent; removing ink or rust stains, paint or varnish; stripping agent for permanent press resins; reducing agent; metal polishes; ceramics and pigments; cleaning wood; purifying methanol; cleanser in the metallurgical industry; in paper industry, photography, and process engraving; producing glucose from starch; leather tanning; rubber manufacturing industry; automobile radiator cleanser; purifying agent and intermediate for many compounds; catalyst; rare earth processing.
