ABSTRACT
CH3 CASRN: 108-38-3; DOT: 1307; DOT label: Flammable liquid; molecular formula: C8H10; FW: 106.17; RTECS: ZE2275000; Merck Index: 12, 10214 Physical state, color, and odor: Clear, colorless, watery liquid with a sweet, aromatic odor. An odor threshold concentration of 48 ppbv was reported by Nagata and Takeuchi (1990). Melting point (°C): -47.9 (Weast, 1986) -47.40 (Martin et al., 1979) Boiling point (°C): 139.30 (Lores et al., 1999) Density (g/cm3): 0.8642 at 20 °C (Weast, 1986) 0.85966 at 25.00 °C (Lores et al., 1999) 0.85550 at 35.00 °C (Goud et al., 1999) Diffusivity in water (x 10-5 cm2/sec): 0.78 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant, pKa: >15 (Christensen et al., 1975) Flash point (°C): 28 (NIOSH, 1997) Lower explosive limit (%): 1.1 (NIOSH, 1997) Upper explosive limit (%): 7.0 (NIOSH, 1997) Entropy of fusion (cal/mol⋅K): 12.28 (Pitzer and Scott, 1941) Heat of fusion (kcal/mol): 2.765 (Pitzer and Scott, 1941) Henry’s law constant (x 10-3 atm⋅m3/mol): 7.35 at 22 °C (dynamic stripping cell-MS, Karl et al., 2003) 7.0 (Pankow and Rosen, 1988)
5.453 at 22 °C (SPME-GC, Saraullo et al., 1997) 4.11, 4.96, 5.98, 7.44, and 8.87 at 10, 15, 20, 25, and 30 °C, respectively (EPICS, Ashworth et al.,
1988) 2.24, 2.15, 2.74, 4.78, and 6.08 at 2.0, 6.0, 10.0, 18.2, and 25.0 °C, respectively; natural seawater:
2.93 and 7.58 at 6.0 and 25.0 °C, respectively (EPICS, Dewulf et al., 1995) 14.80 at 45.00 °C, 17.26.4 at 50.00 °C, 19.90 at 55.00 °C, 23.01.3 at 60.00 °C, 27.46.3 at 70.00 °C
(static headspace-GC, Park et al., 2004) Interfacial tension with water (dyn/cm at 20 °C): 37.89 (Harkins et al., 1920) Ionization potential (eV): 8.58 (Franklin et al., 1969) Soil organic carbon/water partition coefficient, log Koc: 2.22 (Abdul et al., 1987) 2.11, 2.46 (forest soil), 2.20 (agricultural soil) (Seip et al., 1986) Bioconcentration factor, log BCF: 0.78 (clams, Nunes and Benville, 1979) 1.37 (eels, Ogata and Miyake, 1978) 2.40 (Selenastrum capricornutum, Herman et al., 1991) Octanol/water partition coefficient, log Kow: 3.18 (generator column-HPLC/GC, Wasik et al., 1981) 3.20 at 25.0 °C (Tewari et al., 1982) 3.13 at 25.00 °C (generator column-HPLC/GC, Wasik et al., 1981, 1983) 3.22 (shake flask-GC, Jaynes and Vance, 1996) 3.28 (generator column-HPLC, Garst, 1984; RP-HPLC, Garst and Wilson, 1984) 3.68 (estimated from HPLC capacity factors, Eadsforth, 1986) Solubility in organics: Soluble in acetone, ethanol, benzene, and ether (Weast, 1986) Solubility in water: In mg/L: 209 at 0.4 °C, 201 at 5.2 °C, 192 at 14.9 °C, 196 at 21.0 °C, 196 at 25.0 °C, 196 at 25.6 °C, 198 at 30.3 °C, 203 at 34.9 °C, 218 at 39.6 °C (shake flask-UV spectrophotometry, Bohon and Claussen, 1951)
173 mg/L solution at 25 °C (shake flask-UV spectrophotometry, Andrews and Keefer, 1949) 1.51 mM at 25.0 °C (generator column-HPLC, Tewari et al., 1982; generator column-HPLC/GC,
Wasik et al., 1981, 1983) 1.58 mM at 25 °C (headspace analysis, Keeley et al., 1991) 196 mg/kg at 0 °C, 162 mg/kg at 25 °C (shake flask-GC, Polak and Lu, 1973) 146.0 mg/L in distilled water at 25.0 °C, 106.0 mg/L in artificial seawater at 25.0 °C (shake flask-
GC, Sutton and Calder, 1975) 157.0 mg/L at 25 °C (Hermann, 1972) 1.92 mM at 35 °C (Hine et al., 1963) 1.49, 1.52, 1.57, and 1.73 mM at 15, 25, 35, and 45 °C, respectively (Sanemasa et al., 1982) 134.0 mg/kg at 25 °C (shake flask-GLC, Price, 1976) In wt % (°C): 0.031 (127), 0.072 (149), 0.168 (187), 0.648 (239) (Guseva and Parnov, 1963)
al., 1987)
1.94 mmol/kg at 25.0 °C (shake flask-UV spectrophotometry, Vesala, 1974) 1.33 mM at 25.0 °C (Sanemasa et al., 1987) 3.01 x 10-5 at 25 °C (mole fraction, inert gas stripping-GC, Li et al., 1993) 347.9 mg/kg at 67.7 °C, 664.3 mg/kg at 107.3 °C (ampoules-cloud point, Pryor and Jentoft, 1961) Vapor density: 4.34 g/L at 25 °C, 3.66 (air = 1) Vapor pressure (mmHg): 2.2 at 10 °C, 9.1 at 30 °C, 29.3 at 30 °C (Rintelen et al., 1937) 1.71 at 0 °C, 3.35 at 10 °C, 6.25 at 20 °C, 11.1 at 30 °C, 19.0 at 40 °C, 31.3 at 50 °C, 49.7 at 60 °C, 76.6 at 70 °C, 114.6 at 80 °C (cathetometry, Kassel, 1936)
8.3 at 25 °C (quoted, Mackay et al., 1982) 15.2 at 35 °C (Hine et al., 1963) Environmental fate: Biological. Microbial degradation produced 3-methylbenzyl alcohol, 3-methylbenzaldehyde, mtoluic acid, and 3-methylcatechol (quoted, Verschueren, 1983). m-Toluic acid was reported to be the biooxidation product of m-xylene by Nocardia corallina V-49 using n-hexadecane as the substrate (Keck et al., 1989). Reported biodegradation products of the commercial product containing xylene include α-hydroxy-p-toluic acid, p-methylbenzyl alcohol, benzyl alcohol, 4methylcatechol, m-and p-toluic acids (Fishbein, 1985). In anoxic groundwater near Bemidji, MI, m-xylene anaerobically biodegraded to the intermediate m-toluic acid (Cozzarelli et al., 1990). In gasoline-contaminated groundwater, methylbenzylsuccinic acid was identified as the first intermediate during the anaerobic degradation of xylenes (Reusser and Field, 2002). Bridié et al. (1979) reported BOD and COD values of 2.53 and 2.62 g/g using filtered effluent from a biological sanitary waste treatment plant. These values were determined using a standard dilution method at 20 °C and stirred for a period of 5 d. The ThOD for m-xylene is 3.17 g/g. Photolytic. When synthetic air containing gaseous nitrous acid and m-xylene was exposed to artificial sunlight (λ = 300-450 nm) biacetyl, peroxyacetal nitrate, and methyl nitrate were formed (Cox et al., 1980). They reported a rate constant of 1.86 x 10-11 cm3/molecule⋅sec for the reaction of gaseous m-xylene with OH radicals based on a value of 8 x 10-12 cm3/molecule⋅sec for the reaction of ethylene with OH radicals. A n-hexane solution containing m-xylene and spread as a thin film (4 mm) on cold water (10 °C) was irradiated by a mercury medium pressure lamp. In 3 h, 25% of the m-xylene photooxidized into m-methylbenzaldehyde, m-benzyl alcohol, m-benzoic acid, and mmethylacetophenone (Moza and Feicht, 1989). Irradiation of m-xylene isomerizes to p-xylene (Calvert and Pitts, 1966). Glyoxal, methylglyoxal, and biacetyl were produced from the photooxidation of m-xylene by OH radicals in air at 25 °C (Tuazon et al., 1986a). The photooxidation of m-xylene in the presence of nitrogen oxides (NO and NO2) yielded small amounts of formaldehyde and a trace of acetaldehyde (Altshuller et al., 1970). m-Tolualdehyde and nitric acid also were identified as photooxidation products of m-xylene with nitrogen oxides (Altshuller, 1983). The rate constant for the reaction of m-xylene and OH radicals at room temperature was 2.36 x 10-11 cm3/molecule⋅sec (Hansen et al., 1975). A rate constant of 1.41 x 10-8 L/molecule⋅sec was reported for the reaction of m-xylene with OH radicals in the gas phase (Darnall et al., 1976). Similarly, a room temperature rate constant of 2.35 x 10-11 cm3/molecule⋅sec was reported for the vapor-phase reaction of m-xylene with OH radicals (Atkinson, 1985). At 25 °C, a rate constant of 2.22 x 10-11 cm3/molecule⋅sec was reported for the same reaction (Ohta and Ohyama, 1985). Phousongphouang and Arey (2002)
and 740 mmHg containing 5% humidity. Relative to 1,2,3-trimethylbenzene, the rate constants for this reaction were 1.81 and 2.03 x 10-11 cm3/molecule⋅sec. Chemical/Physical. Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of m-tolualdehyde, m-methylbenzyl nitrate, nitro-mxylenes, 2,4-and 2,6-dimethylphenol (Atkinson, 1990). Kanno et al. (1982) studied the aqueous reaction of m-xylene and other aromatic hydrocarbons (benzene, toluene, o-and p-xylene, and naphthalene) 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 increased at lower pHs (Kanno et al., 1982). In the gas phase, m-xylene reacted with nitrate radicals in purified air forming pmethylbenzaldehyde, an aryl nitrate and trace amounts of 2,6-dimethylnitrobenzene, 2,4dimethylnitrobenzene, and 3,5-dimethylnitrobenzene (Chiodini et al., 1993). m-Xylene will not hydrolyze in water because it does not contain a hydrolyzable functional group (Kollig, 1993). Exposure limits: NIOSH REL: 100 ppm (435 mg/m3), STEL 150 ppm (655 mg/m3), IDLH 900 ppm; OSHA PEL: TWA 100 ppm; ACGIH TLV: TWA 100 ppm, STEL 150 ppm (adopted). Symptoms of exposure: May cause irritation of eyes, nose, and throat, headache, dizziness, excitement, drowsiness, nausea, vomiting, abdominal pain, and dermatitis (Patnaik, 1992) Toxicity: EC50 (72-h) for Selenastrum capricornutum 4.9 mg/L (Galassi et al., 1988). LC50 (14-d) for Poecilia reticulata 37.7 mg/L (Könemann, 1981). LC50 (96-h) for Salmo gairdneri 8.4 mg/L, Poecilia reticulata 12.9 mg/L (Galassi et al., 1988). Acute oral LD50 in rats 5 g/kg (quoted, RTECS, 1985). Source: As m+p-xylene, detected in distilled water-soluble fractions of 87 octane gasoline, 94 octane gasoline, and Gasohol at concentrations of 7.00, 20.1, and 14.6 mg/L, respectively (Potter, 1996); in distilled water-soluble fractions of new and used motor oil at concentrations of 0.26 to 0.29 and 302 to 339 µg/L, respectively (Chen et al., 1994). The average volume percent and estimated mole fraction in American Petroleum Institute PS-6 gasoline are 4.072 and 0.04406, respectively (Poulsen et al., 1992). Diesel fuel obtained from a service station in Schlieren, Switzerland contained m/p-xylene at a concentration of 336 mg/L (Schluep et al., 2001). Thomas and Delfino (1991) equilibrated contaminant-free groundwater collected from Gainesville, FL with individual fractions of three individual petroleum products at 24-25 °C for 24 h. The aqueous phase was analyzed for organic compounds via U.S. EPA approved test method 602. Average m+p-xylene concentrations reported in water-soluble fractions of unleaded gasoline, kerosene, and diesel fuel were 8.611, 0.658, and 0.228 mg/L, respectively. When the authors analyzed the aqueous-phase via U.S. EPA approved test method 610, average m+p-xylene concentrations in water-soluble fractions of unleaded gasoline, kerosene, and diesel fuel were lower, i.e., 6.068, 0.360, and 0.222 mg/L, respectively. Based on laboratory analysis of 7 coal tar samples, m+p-xylene concentrations ranged from ND to 6,000 ppm (EPRI, 1990). A high-temperature coal tar contained m-xylene at an average concentration of 0.07 wt % (McNeil, 1983). 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 rate of m-xylene + p-xylene was 60.0 mg/kg of pine burned. Emission rates of both isomers were not measured during the combustion of oak and eucalyptus.
