ABSTRACT

Note: According to Chevron Phillips Company’s (2004) Technical Data Sheet, 99.0-99.3 wt % 2methylpropene contains 2-methylpropane (0.1 wt %), 1-butene (0.4 wt %), and n-butane (0.1 wt %). CASRN: 115-11-7; DOT: 1055; DOT label: Flammable gas; molecular formula: C4H8; FW: 56.11; RTECS: UD0890000; Merck Index: 12, 5155 Physical state, color, and odor: Colorless gas with a coal gas-like odor. The odor threshold concentration is 10 ppmv Nagata and Takeuchi (1990). Melting point (°C): -146.8 (McAuliffe, 1966) Boiling point (°C): -6.900 (Windholz et al., 1983) Density (g/cm3): 0.5942 at 20 °C, 0.5879 at 25 °C, 0.5815 at 30 °C (Windholz et al., 1983) Diffusivity in water (x 10-5 cm2/sec): 0.91 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant, pKa: >14 (Schwarzenbach et al., 1993) Flash point (°C): -76 (Hawley, 1981) Lower explosive limit (%): 1.8 (Sax and Lewis, 1987) Upper explosive limit (%): 9.6 (Sax and Lewis, 1987) Heat of fusion (kcal/mol): 1.418 (Dean, 1987) Henry’s law constant (atm⋅m3/mol): 0.20, 0.26, 0.33, and 0.41 at 30, 40, 50, and 60 °C, respectively (Leung et al., 1987; Zhang et al., 2002) Ionization potential (eV): 9.26 (Collin and Lossing, 1959)

oc Estimation of this parameter for aliphatic hydrocarbons are lacking in the documented literature Octanol/water partition coefficient, log Kow: 2.34 (Hansch and Leo, 1985) Solubility in organics (mole fraction): In 1-butanol: 0.131, 0.0695, and 0.0458 at 25, 30, and 70 °C, respectively; chlorobenzene: 0.234, 0.132, and 0.0796 at 25, 30, and 70 °C, respectively; octane: 0.333, 0.184, and 0.119 at 25, 30, and 70 °C, respectively (Hayduk et al., 1988). Solubility in water: 263 mg/kg at 25 °C (shake flask-GC, McAuliffe, 1966) In mmol/L: 4.66 at 30 °C, 3.55 at 40 °C, 2.69 at 50 °C, 1.93 at 60 °C (bubbling reservoir-GC,

Leung et al., 1987) In mmol/L: 4.76 at 30 °C, 2.22 at 50 °C, 1.334 at 70 °C (reactor column-GC, Zhang et al., 2002) Vapor density: 2.29 g/L at 25 °C, 1.94 (air = 1) Vapor pressure (mmHg): 1,976 at 20 °C (quoted, Verschueren, 1983) 2,270 at 25 °C (Wilhoit and Zwolinski, 1971) Environmental fate: Photolytic. Products identified from the photoirradiation of 2-methylpropene with nitrogen dioxide in air are 2-butanone, 2-methylpropanal, acetone, carbon monoxide, carbon dioxide, methanol, methyl nitrate, and nitric acid (Takeuchi et al., 1983). Similarly, products identified from the reaction of 2-methylpropene with ozone included acetone, formaldehyde, methanol, carbon monoxide, carbon dioxide, and methane (Tuazon et al., 1997). The following rate constants were reported for the reaction of 2-methylpropene and OH radicals in the atmosphere: 3.0 x 10-13 cm3/molecule⋅sec at 300 K (Hendry and Kenley, 1979); 5.40 x 10-11 cm3/molecule⋅sec (Atkinson et al., 1979); 5.14 x 10-11 at 298 K (Atkinson, 1990). Reported reaction rate constants for 2-methylpropene and ozone in the atmosphere include 2.3 x 10-19 cm3/molecule⋅sec (Bufalini and Altshuller, 1965); 1.17 x 10-19 cm3/molecule⋅sec at 300 K (Adeniji et al., 1965); 1.21 x 10-17 cm3/molecule⋅sec at 298 K (Atkinson, 1990). Chemical/Physical. Complete combustion in air yields carbon dioxide and water. Incomplete combustion yields carbon monoxide. Symptoms of exposure: An asphyxiant (Patnaik, 1992) Toxicity: LC50 (inhalation) for mice 415 g/m3/2-h, rats 620 g/m3/4-h (quoted, RTECS, 1985). Source: 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 2-methylpropene was 40.1 mg/kg of pine burned. Emission rates of 2-methylbutene were not measured during the combustion of oak and eucalyptus. California Phase II reformulated gasoline contained 2-methylpropene at a concentration of 170 mg/kg. Gas-phase tailpipe emission rates from gasoline-powered automobiles with and without catalytic converters were 15.6 and 427 mg/km, respectively (Schauer et al., 2002).