ACETALDEHYDE

O CH3 Note: Commercial grades of acetaldehyde (99%) may contain minor amounts of acetic acid (0.1%). CASRN: 75-07-0; DOT: 1089; DOT label: Flammable liquid; molecular formula: C2H4O; FW: 44.05; RTECS: AB1925000; Merck Index: 12, 37 Physical state, color, and odor: Colorless, mobile, fuming, volatile liquid or gas with a penetrating, pungent odor; fruity odor when diluted. Odor threshold concentrations ranged from 1.5 ppbv (Nagata and Takeuchi, 1990) to 0.21 ppmv (Leonardos et al., 1969). Katz and Talbert (1930) reported an experimental detection odor threshold concentration of 120 µg/m3 (67 ppbv). At low concentrations, acetaldehyde imparts a pleasant, fruity, green apple or leafy green-like flavor (van Aardt et al., 2001). Twenty-five panelists were randomly selected for testing milk products and water for determining flavor thresholds. Flavor threshold concentrations determined by a geometric approach were 3,939 ppb for nonfat milk (0.5% milk fat), 4,020 ppb for low-fat milk (2% milk fat), 4,040 ppb for whole milk, 10,048 ppb for chocolate milk, and 167 ppb for spring water (van Aardt et al., 2001). Melting point (°C): -121 (Weast, 1986) -123.5 (Windholz et al., 1983) Boiling point (°C): 20.2 (Suska, 1979) Density (g/cm3): 0.7834 at 18 °C (Weast, 1986) Diffusivity in water (x 10-5 cm2/sec): 1.23 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant, pKa: 14.15 at 0 °C (HSDB, 1989) 13.57 at 25 °C (HSDB, 2005) Flash point (°C): -37.8 (NIOSH, 1997) Lower explosive limit (%): 4.0 (NIOSH, 1994) Upper explosive limit (%): 60 (NIOSH, 1994) Heat of fusion (kcal/mol): 0.775 (quoted, Riddick et al., 1986)

6.25 at 25 °C (headspace-SPME, Bartelt, 1997) 6.60 at 25 °C (headspace-GC, Marin et al., 1999) 6.61 at 25 °C (Buttery et al., 1969) 8.49 at 24.98 °C (headspace-GC, Straver and de Loos, 2005) 2.25 at 10 °C, 6.71 at 25 °C, 8.13 at 30 °C, 10.4 at 35 °C, 15.4 at 45 °C (bubble column-HPLC,

Zhou and Mopper, 1990) 1.81 at 5 °C, 2.54 at 15 °C, 8.77 at 25 °C, 15.24 at 35 °C (bubble column-GC, Betterton and

Hoffmann, 1988) 1.41 at 5 °C, 2.08 at 10 °C, 2.90 at 15 °C, 4.33 at 20 °C, 6.14 at 25 °C (headspace-GC, Ji and

Evans, 2007) 7.69 at 25 °C (Snider and Dawson, 1985; Benkelberg et al., 1995) Ionization potential (eV): 10.21 (Franklin et al., 1969) 10.229 ± 0.007 (Lias, 1998) Soil organic carbon/water partition coefficient, log Koc: Unavailable because experimental methods for estimation of this parameter for aldehydes are lacking in the documented literature. However, its miscibility in water suggests its adsorption to soil will be nominal (Lyman et al., 1982). Octanol/water partition coefficient, log Kow (at 25 °C): 0.36 (generator column-GLC, Tewari et al., 1982) 0.52 (generator column-HPLC, Wasik et al., 1981) Solubility in organics: Miscible with acetone, alcohol, benzene, ether, gasoline, solvent naphtha, toluene, turpentine, and xylene (Hawley, 1981) Solubility in water: Miscible (Palit, 1947) Vapor density: 1.80 g/L at 25 °C, 1.52 (air = 1) Vapor pressure (mmHg): 325 at -0.27 °C, 415 at 5.17 °C, 507 at 9.96 °C, 615 at 14.70 °C, 768 at 20.47 °C (Smith et al.,

1951) 900 at 25 °C (Lide, 1990) Environmental fate: Biological. Heukelekian and Rand (1955) reported a 5-d BOD value of 1.27 g/g that is 69.8% of the ThOD value of 1.82 g/g. Photolytic. Photooxidation of acetaldehyde in nitrogen oxide-free air using radiation between 2900 to 3500 Å yielded hydrogen peroxide, alkyl hydroperoxides, carbon monoxide, and lower molecular weight aldehydes. In the presence of nitrogen oxides, photooxidation products include ozone, hydrogen peroxide, and peroxyacyl nitrates (Kopczynski et al., 1974). Anticipated products from the reaction of acetaldehyde with ozone or OH radicals in the atmosphere are formaldehyde and carbon dioxide (Cupitt, 1980). Reacts with nitrogen dioxide forming peroxyacyl nitrates, formaldehyde, and methyl nitrate (Altshuller, 1983). Irradiation in the presence of chlorine yielded

nitrate, and peroxyacetal nitrate (Cox et al., 1980). The room-temperature photooxidation of acetaldehyde in the presence of oxygen with continuous irradiation (λ >2200 Å) resulted in the following by-products: methanol, carbon monoxide, carbon dioxide, water, formaldehyde, formic acid, acetic acid, CH3OOCH3, and probably CH3C(O)OOH (Johnston and Heicklen, 1964). Acetic acid and carbon dioxide were detected as the main reaction products for the photocatalytic degradation of gas-phase acetaldehyde (100 ppm) at room temperature. The experiment was conducted in a 1-L vessel containing a thin film containing titanium dioxide as the catalyst and UV light (λ = 365 nm) (Ohko et al., 1998). Rate constants reported for the reaction of acetaldehyde and OH radicals in the atmosphere: 9.6 x 10-12 cm3/molecule⋅sec at 300 K (Hendry and Kenley, 1979), 1.5 x 10-11 cm3/molecule⋅sec (Morris et al., 1971), 1.622 x 10-11 cm3/molecule⋅sec (Sabljić and Güsten, 1990), 1.6 x 10-11 cm3/molecule⋅sec (Niki et al., 1978; Baulch et al., 1984); with NO3: 3.02 x 10-15 cm3/molecule⋅sec at 298 K (Atkinson, 1985), 1.40 x 10-15 cm3/molecule⋅sec (Atkinson and Lloyd, 1984), 2.5 x 10-15 cm3/molecule⋅sec (Atkinson, 1985), 2.59 x 10-15, 3.15 x 10-15, and 2.54 x 10-15 cm3/molecule⋅sec at 298, 299, and 300 K, respectively (Atkinson, 1991); with ozone: 3.4 x 10-20 cm3/molecule⋅sec (Stedman and Niki, 1973). Chemical/Physical. Oxidation in air yields acetic acid (Windholz et al., 1983). In the presence of sulfuric, hydrochloric, or phosphoric acids, polymerizes explosively forming trimeric paraldehyde (Huntress and Mulliken, 1941; Patnaik, 1992). In an aqueous solution at 25 °C, acetaldehyde is partially hydrated, i.e., 0.60 expressed as a mole fraction, forming a gem-diol (Bell and McDougall, 1960). Acetaldehyde decomposes at temperatures greater than 400 °C, forming carbon monoxide and methane (Patnaik, 1992). Prolonged exposure to air may result in the formation of explosive peroxides; easily undergoes polymerization (NIOSH, 1997). At an influent concentration of 1,000 mg/L, treatment with GAC resulted in an effluent concentration of 723 mg/L. The adsorbability of the carbon used was 22 mg/g carbon (Guisti et al., 1974). Exposure limits: Potential occupational carcinogen. NIOSH REL: IDLH 2,000 ppm; OSHA PEL: TWA 200 ppm (360 mg/m3); ACGIH TLV: TWA 100 ppm (180 mg/m3), STEL 150 ppm (270 mg/m3). Symptoms of exposure: Conjunctivitis, central nervous system, eye and skin burns, and dermatitis are symptoms of ingestion. Inhalation may cause irritation of the eyes, nose, throat, and mucous membranes. At high concentrations headache, sore throat, and paralysis of respiratory muscles may occur (Windholz et al., 1983; Patnaik, 1992). An irritation concentration of 90.00 mg/m3 in air was reported by Ruth (1986). Toxicity: LC50 (48-h) for red killifish 1,820 mg/L (Yoshioka et al., 1986), hamsters 17,000 ppm/4-h, mice 1,400 ppm/4-h, rats 37 gm/m3/30-min (quoted, RTECS, 1985). LC50 (inhalation) for mice 24 g/m3/4-h (Appelman et al., 1982). LC50 (inhalation) for rats 37 g/m3/30-min (Skog, 1950). Acute oral LD50 for rats 1,930 mg/kg (quoted, RTECS, 1985). LD50 (intravenous) for pregnant mice 1650 mg/kg (O’Shea and Kaufman, 1979). LD50 (subcutaneous) for mice 560 mg/kg and 640 mg/kg for rats (Skog, 1950). Source: Manufactured by oxidizing ethanol with sodium dichromate and sulfuric acid or from acetylene, dilute sulfuric acid, and mercuric oxide catalyst.