PENTANE

CH3H3C CASRN: 109-66-0; DOT: 1265; DOT label: Flammable liquid; molecular formula: C5H12; FW: 72.15; RTECS: RZ9450000; Merck Index: 12, 7255 Physical state, color, and odor: Clear, colorless, volatile liquid with an odor resembling gasoline. An odor threshold concentration of 1.4 ppmv was reported by Nagata and Takeuchi (1990). Melting point (°C): -130 (Weast, 1986) Boiling point (°C): 36.1 (Weast, 1986) Density (g/cm3): 0.62624 at 20 °C (Dreisbach, 1959) 0.6290 at 17.2 °C, 0.62139 at 25.00 °C (Curtice et al., 1972) Diffusivity in water (x 10-5 cm2/sec): 0.84 at 20 °C (Witherspoon and Bonoli, 1969) 0.97 at 25 °C (quoted, Hayduk and Laudie, 1974) 0.86 at 25 °C at saturation in heavy water (Price and Söderman, 2000) Dissociation constant, pKa: >14 (Schwarzenbach et al., 1993) Flash point (°C): -49.8 (NIOSH, 1997) -40 (Windholz et al., 1983) Lower explosive limit (%): 1.5 (NIOSH, 1997) Upper explosive limit (%): 7.8 (NIOSH, 1997) Entropy of fusion (cal/mol⋅K): 14.00 (Messerly et al., 1967) 14.02 (Messerly and Kennedy, 1940) 13.96 (Parks and Huffman, 1930) Heat of fusion (kcal/mol): 2.008 (Messerly et al., 1967) 2.011 (Messerly and Kennedy, 1940) 2.002 (Parks and Huffman, 1930)

1.20 at 25 °C (Jönsson et al., 1982) Interfacial tension with water (dyn/cm): 49.0 at 25 °C (Donahue and Bartell, 1952) 50.9 at 22 °C (Goebel and Lunkenheimer, 1997) 48.70 at 25.00 °C (Fu et al., 2000) Ionization potential (eV): 10.28 (Lias, 1998) Soil organic carbon/water partition coefficient, log Koc: Unavailable because experimental methods for estimation of this parameter for aliphatic hydrocarbons are lacking in the documented literature Octanol/water partition coefficient, log Kow: 3.23, 3.39 (Hansch and Leo, 1979) 3.60 at 25 °C (generator column-RPLC, Schantz and Martire, 1987) 3.62 (generator column-HPLC, Tewari et al., 1982; generator column-HPLC/GC, Wasik et al.,

1981) Solubility in organics: In methanol: 620 and 810 g/L at 5 and 10 °C, respectively. Miscible at higher temperatures (Kiser et al., 1961). Solubility in water: In mg/kg: 39.5 at 25 °C, 39.8 at 40.1 °C, 41.8 at 55.7 °C, 69.4 at 99.1 °C. In NaCl solution at 25 °C (salinity, g/kg): 36.8 (1.002), 34.5 (10.000), 27.6 (34.472), 22.6 (50.03), 10.9 (125.10), 5.91 (199.90), 2.64 (279.80), 2.01 (358.70) (shake flask-GLC, Price, 1976)

38.5 mg/kg at 25 °C (shake flask-GC, McAuliffe, 1963, 1966) 65.7 mg/kg at 0 °C, 47.6 mg/kg at 25 °C (shake flask-GC, Polak and Lu, 1973) 39 mg/kg at 25 °C (shake flask-GC, Krzyzanowska and Szeliga, 1978) 360 mg/L at 16 °C (Fischer and Ehrenberg, 1948) 565 µmol/L at 25.0 °C (generator column-HPLC, Tewari et al., 1982; generator column-

HPLC/GC, Wasik et al., 1981) 40.0, 40.4 and 47.6 mg/L at 25 °C (shake flask-fluorescence, Mackay and Shiu, 1981) 0.60 mL/L at 16 °C (shake flask-turbidimetric, Fühner, 1924) 0.11 g/kg at 20 °C and 32 atmHg (gas-liquid equilibrium, Namiot and Beider, 1960) 700 mg/L at 20 °C (shake flask-titration, Korenman and Aref’eva, 1977) In mole fraction (x 105): 1.02, 1.07, 0.98, 1.01, and 1.01 at 4.0, 10.0, 20.0, 25.0, and 30.0 °C,

respectively (shake flask-GC, Nelson and de Ligny, 1968) 1.03 mM at 25 °C and partial pressure of 508 mmHg over water (shake flask-GC, Barone et al.,

1966) 39.0 mg/L at 25 °C (Kryzanowska and Szeliga, 1978) 40.6 mg/L at 25 °C (air-water partitioning-GC, Jönsson et al., 1982) Vapor density: 2.95 g/L at 25 °C, 2.49 (air = 1) Vapor pressure (mmHg): 512.8 at 25 °C (Wilhoit and Zwolinski, 1971)

516.65 at 25.00 °C (GC, Hussam and Carr, 1985) 219.3, 283.7, 424.1, 511.3, and 614.8 at 4.0, 10.0, 20.0, 25.0, and 30.0 °C, respectively (Nelson

and de Ligny, 1968) Environmental fate: Biological. n-Pentane may biodegrade in two ways. The first is the formation of pentyl hydroperoxide, which decomposes to 1-pentanol followed by oxidation to pentanoic acid. The other pathway involves dehydrogenation to 1-pentene, which may react with water giving 1pentanol (Dugan, 1972). Microorganisms can oxidize alkanes under aerobic conditions (Singer and Finnerty, 1984). The most common degradative pathway involves the oxidation of the terminal methyl group forming 1-pentanol. The alcohol may undergo a series of dehydrogenation steps forming an aldehyde (valeraldehyde) then a fatty acid (valeric acid). The fatty acid may then be metabolized by β-oxidation to form the mineralization products, carbon dioxide and water (Singer and Finnerty, 1984). Mycobacterium smegnatis was capable of degrading pentane to 2pentanone (Riser-Roberts, 1992). Photolytic. When synthetic air containing gaseous nitrous acid and pentane was exposed to artificial sunlight (λ = 300-450 nm) methyl nitrate, pentyl nitrate, peroxyacetal nitrate, and peroxypropionyl nitrate formed as products (Cox et al., 1980). The following rate constants were reported for the reaction of pentane and OH radicals in the atmosphere: 3.9 x 10-12 cm3/molecule⋅sec (Hendry and Kenley, 1979); 4.06 x 10-12 cm3/molecule⋅sec (Sabljić and Güsten, 1990); 3.74 x 10-12 cm3/molecule⋅sec at 300 K (Darnall et al., 1978); 3.94 x 10-12 cm3/molecule⋅sec at 297 K (Atkinson, 1990). A photooxidation rate constant of 8.1 x 10-17 cm3/molecule⋅sec was reported for the reaction of pentane and NO3 (Altshuller, 1991). Cox et al. (1980) reported a rate constant of 5.0 x 10-12 cm3/molecule⋅sec for the reaction of gaseous pentane with OH radicals based on a value of 8 x 10-12 cm3/molecule⋅sec for the reaction of ethylene with OH radicals. Chemical/Physical. Complete combustion in air yields carbon dioxide and water. Pentane will not hydrolyze because it does not contain a hydrolyzable functional group. Exposure limits: NIOSH REL: TWA 120 ppm (350 mg/m3), ceiling 610 ppm (1,800 mg/m3), IDLH 1,500 ppm; OSHA PEL: TWA 1,000 ppm (2,950 mg/m3); ACGIH TLV: TWA 600 ppm (adopted). Symptoms of exposure: Inhalation may cause narcosis and irritation of respiratory tract (Patnaik, 1992). Toxicity: LD50 (intravenous) for mice 466 mg/kg (quoted, RTECS, 1985). Source: Schauer et al. (1999) reported pentane in a diesel-powered medium-duty truck exhaust at an emission rate of 1,860 µg/km. A constituent in gasoline. Harley et al. (2000) analyzed the headspace vapors of three grades of unleaded gasoline where ethanol was added to replace methyl tert-butyl ether. The gasoline vapor concentrations of pentane in the headspace were 14.2 wt % for regular grade, 12.6 wt % for midgrade, and 9.3 wt % for premium grade. California Phase II reformulated gasoline contained pentane at a concentration of 27.6 g/kg. Gas-phase tailpipe emission rates from gasoline-powered automobiles with and without catalytic converters were 4.29 and 536 mg/km, respectively (Schauer et al., 2002). Schauer et al. (2001) measured organic compound emission rates for volatile organic

from the residential (fireplace) combustion of pine, oak, and eucalyptus. The gas-phase emission rate of pentane was 4.7 mg/kg of pine burned. Emission rates of pentane were not measured during the combustion of oak and eucalyptus. Uses: Solvent recovery and extraction; blowing agent for plastic foams; low temperature thermometers; natural gas processing plants; production of olefin, hydrogen, ammonia; fuel production; pesticide; manufacture of artificial ice; organic synthesis.