ABSTRACT
CASRN: 95-48-7; DOT: 2076; DOT label: Corrosive material, poison; molecular formula: C7H8O; FW: 108.14; RTECS: GO6300000; Merck Index: 12, 2645 Physical state, color, and odor: Colorless solid or liquid with a phenolic odor; darkens on exposure to air. An odor threshold concentration of 0.28 ppbv was reported by Nagata and Takeuchi (1990). Melting point (°C): 30.9 (Weast, 1986) Boiling point (°C): 191.0 (Dean, 1973) Density (g/cm3 at 20 °C): 1.0273 (Weast, 1986) Diffusivity in water (x 10-5 cm2/sec): 0.497 (ceff = 160 µM) at 4.0 °C; 0.926 (ceff = 160 µM) and 0.942 (ceff = 320 µM) at 25.0 °C; 1.608
(ceff = 160 µM) at 50.0 °C (Niesner and Heintz, 2000) Dissociation constant, pKa: 10.19 at 25 °C (Sprengling and Lewis, 1953) 10.33 at 25 °C (quoted, Rosés et al., 2000) Flash point (°C): 82 (NIOSH, 1997) Lower explosive limit (%): 1.4 at 150 °C (NIOSH, 1997) Entropy of fusion (cal/mol⋅K): 10.99 (Poeti et al., 1982) 12.43 (Andon et al., 1967) Heat of fusion (kcal/mol): 3.33 (Poeti et al., 1982) 3.78 (Andon et al., 1967) Henry’s law constant (x 10-6 atm⋅m3/mol): 1.20 at 25 °C (Parsons et al., 1972) 0.22 at 8 °C, 0.31 at 11.3 °C, 0.59 at 16.3 °C, 0.64 at 20.3 °C, 0.95 at 25 °C, 1.15 at 29 °C (column
30.1 at 75.9 °C, 57.6 at 88.7 °C, 85.4 at 98.5 °C (VLE circulation still-UV spectrophotometry,
Dohnal and Fenclová, 1995) 1.57 at 25 °C (thermodynamic method-GC/UV spectrophotometry, Altschuh et al., 1999) 0.34 at 5.25 °C, 0.61 at 10.00 °C, 1.57 at 20.00 °C, 2.33 at 25.00 °C (dynamic equilibrium system-
GC, Feigenbrugel et al., 2004a) Ionization potential (eV): 8.14 (Mallard and Linstrom, 1998) Bioconcentration factor, log BCF: 1.03 (Brachydanio rerio, Devillers et al., 1996) Soil organic carbon/water partition coefficient, log Koc: 1.70 (river sediment), 1.75 (coal wastewater sediment) (Kopinke et al., 1995) 1.34 at pH 5.7 (Brookstone clay loam, Boyd, 1982) Octanol/water partition coefficient, log Kow: 1.93 at pH 7.4 and 37 °C (shake flask, Freese et al., 1979) 2.01 at 35 °C (shake flask-absorption spectrophotometry, Freese et al., 1979) 1.95 (quoted, Leo et al., 1971) 1.99 (Dearden, 1985) 1.96 (generator column-HPLC/GC, Wasik et al., 1981) Solubility in organics: Miscible with ethanol, benzene, ether, glycerol (U.S. EPA, 1985) Solubility in water: 31,000 mg/L at 40 °C, 56,000 mg/L at 100 °C (quoted, Verschueren, 1983) 30.8 g/L at 40 °C (quoted, Howard, 1989) 23 g/L at 8 °C, 26 g/L at 25 °C (quoted, Leuenberger et al., 1985a) 23,000 mg/L at 23 °C (Pinal et al., 1990) 25.2 mM at 25.0 °C (generator column-HPLC/GC, Wasik et al., 1981) 26,800 mg/L at 25 °C (shake flask-HPLC/UV spectrophotometry, Varhaníčková et al., 1995a) 22.0 and 30.8 mL/L at 25 and 60 °C, respectively (shake flask-volumetric, Booth and Everson,
1949) Vapor pressure (mmHg): 0.31 at 25 °C (quoted, Howard, 1989) 0.045 at 8 °C, 0.29 at 25 °C (quoted, Leuenberger et al., 1985a) Environmental fate: Biological. Bacterial degradation of 2-methylphenol may introduce a hydroxyl group producing 3-methylcatechol (Chapman, 1972). In phenol-acclimated activated sludge, metabolites identified include 3-methylcatechol, 4-methylresorcinol, methylhydroquinone, α-ketobutyric acid, dihydroxybenzaldehyde, and trihydroxytoluene (Masunaga et al., 1986). Chloroperoxidase, a fungal enzyme isolated from Caldariomyces fumago, reacted with 2methylphenol forming 2-methyl-4-chlorophenol (38% yield) and 2-methyl-6-chlorophenol (Wannstedt et al., 1990). Heukelekian and Rand (1955) reported a 5-d BOD value of 1.70 g/g which is 67.5% of the ThOD value of 2.72 g/g. In activated sludge inoculum, 95.0% COD removal was achieved. The
Soil. In laboratory microcosm experiments kept under aerobic conditions, half-lives of 5.1 and 1.6 d were reported for 2-methylphenol in an acidic clay soil (<1% organic matter) and slightly basic sandy loam soil (3.25% organic matter) (Loehr and Matthews, 1992). Surface Water. In river water, the half-life of 2-methylphenol was 2 and 4 d at 20 and 4 °C, respectively (Ludzack and Ettinger, 1960). Groundwater. Nielsen et al. (1996) studied the degradation of 2-methylphenol in a shallow, glaciofluvial, unconfined sandy aquifer in Jutland, Denmark. As part of the in situ microcosm study, a cylinder that was open at the bottom and screened at the top was installed through a cased borehole approximately 5 m below grade. Five liters of water was aerated with atmospheric air to ensure aerobic conditions were maintained. Groundwater was analyzed weekly for approximately 3 months to determine 2-methylphenol concentrations with time. The experimentally determined first-order biodegradation rate constant and corresponding half-life were 0.2/d and 3.5 d, respectively. Groundwater contaminated with phenol and other phenols degraded in a methanogenic aquifer to methane and carbon dioxide. These results could not be duplicated in the laboratory utilizing an anaerobic digester (Godsy et al., 1983). Photolytic. Sunlight irradiation of 2-methylphenol and nitrogen oxides in air yielded the following gas-phase products: acetaldehyde, formaldehyde, pyruvic acid, peroxyacetyl nitrate, nitrocresols, and trace levels of nitric acid and methyl nitrate. Particulate phase products were also identified and these include 2-hydroxy-3-nitrotoluene, 2-hydroxy-5-nitrotoluene, 2-hydroxy-3,5dinitrotoluene, and tentatively identified nitrocresol isomers (Grosjean, 1984). Absorbs UV light at a maximum wavelength of 270 nm (Dohnal and Fenclová, 1995). Reported rate constants for the reaction of 2-methylphenol and OH radicals in the atmosphere: 2.0 x 10-13 cm3/molecule⋅sec at 300 K (Hendry and Kenley, 1979), 3.7 x 10-11 cm3/molecule⋅sec at room temperature (Atkinson, 1985); with ozone in the atmosphere: 2.6 x 10-19 cm3/molecule⋅sec at 296 K (Atkinson et al., 1982); with NO3 radicals in the atmosphere: 1 x 10-11 cm3/molecule⋅sec (Atkinson and Lloyd, 1984). Chemical/Physical. Ozonation of an aqueous solution containing 2-methylphenol (200 to 600 mg/L) yielded formic, acetic, propionic, glyoxylic, oxalic, and salicylic acids (Wang, 1990). In a different experiment, however, an aqueous solution containing 2-methylphenol (1 mM) reacted with ozone (11.7 mg/min) forming 2-methylmuconic acid and hydrogen peroxide as end products. The proposed pathway of degradation involved electrophilic aromatic substitution by the first ozone molecule followed by a 1,3-dipolar addition of the second ozone molecule to the cleaved ring (Beltran et al., 1990). In a smog chamber experiment, 2-methylphenol reacted with nitrogen oxides to form nitrocresols, dinitrocresols, and hydroxynitrocresols (McMurry and Grosjean, 1985). Anticipated products from the reaction of 2-methylphenol with ozone or OH radicals in the atmosphere are hydroxynitrotoluenes and ring cleavage compounds (Cupitt, 1980). Kanno et al. (1982) studied the aqueous reaction of 2-methylphenol (o-cresol) and other substituted aromatic hydrocarbons (toluidine, 1-naphthylamine, phenol, m-and p-cresol, pyrocatechol, resorcinol, hydroquinone, and 1-naphthol) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected but was cleaved by chloramine forming cyanogen chloride. The amount of cyanogen chloride formed was increased as the pH was lowered (Kanno et al., 1982). In aqueous solution, 2-methylphenol was degraded by ozone at a reaction rate of 1.4 x 104/M⋅sec at pH range of 1.5 to 2 (Hoigné and Bader, 1983). Exposure limits: NIOSH REL: TWA 2.3 ppm (10 mg/m3), IDLH 250 ppm; OSHA PEL: TWA 5 ppm (22 mg/m3); ACGIH TLV: TWA for all isomers 5 ppm (adopted). Symptoms of exposure: May cause weakness, confusion, depression of central nervous system,
dermatitis. Chronic effects may include gastrointestinal disorders, nervous disorders, tremor, confusion, skin eruptions, oliguria, jaundice, and liver damage (Patnaik, 1992). Toxicity: Acute oral LD50 for rats 121 mg/kg, mice 344 mg/kg (quoted, RTECS, 1985). LD50 (skin) rats 620 mg/kg, rabbits 890 mg/kg (quoted, RTECS, 1985). Source: Detected in distilled water-soluble fractions of 87 octane gasoline (6.61 mg/L), 94 octane gasoline (0.57 mg/L), Gasohol (1.17 mg/L), No. 2 fuel oil (2.64 mg/L), jet fuel A (0.72 mg/L), diesel fuel (1.36 mg/L), and military jet fuel JP-4 (1.51 mg/L) (Potter, 1996). o-Cresol was also detected in 82% of 65 gasoline (regular and premium) samples (62 from Switzerland, 3 from Boston, MA). At 25 °C, concentrations were from 1.1-99 mg/L in gasoline and 70-6,600 µg/L in water-soluble fractions. Average concentrations were 18 mg/L in gasoline and 1.2 mg/L in watersoluble fractions (Schmidt et al., 2002). A high-temperature coal tar contained 2-methylphenol at an average concentration of 0.25 wt % (McNeil, 1983). Occurs naturally in white sandlewood, sour cherries, peppermint leaves (1-10 ppb), tarragon, asparagus shoots, tea leaves, coffee beans, Japanese privet, tomatoes, licorice roots, and African palm oil (Duke, 1992). Schauer et al. (2001) measured organic compound emission rates for volatile organic compounds, gas-phase semi-volatile organic compounds, and particle phase organic compounds from the residential (fireplace) combustion of pine, oak, and eucalyptus. The gas-phase emission rates of 2-methylphenol were 89.6 mg/kg of pine burned, 47.7 mg/kg of oak burned, and 37.8 mg/kg of eucalyptus burned. The particle-phase emission rates were 0.018 mg/kg of oak burned and 0.006 mg/kg of eucalyptus burned. Uses: Disinfectant; phenolic resins; tricresyl phosphate; ore flotation; textile scouring agent; organic intermediate; manufacturing salicylaldehyde, coumarin, and herbicides; surfactant; synthetic food flavors (para isomer only); food antioxidant; dye, perfume, plastics, and resins manufacturing.
