2-METHYL-1,3-BUTADIENE

CH3 Note: Usually inhibited with 100 ppm 4-tert-butylcatecol to prevent polymerization. CASRN: 78-79-5; DOT: 1218 (inhibited); molecular formula: C5H8; FW: 68.12; RTECS: NT4037000; Merck Index: 12, 5218 Physical state, color, and odor: Colorless, volatile, extremely flammable liquid with an unpleasant odor. An odor threshold concentration of 48 ppbv was reported by Nagata and Takeuchi (1990). Melting point (°C): -146 (Weast, 1986) Boiling point (°C): 34 (Weast, 1986) Density (g/cm3): 0.6810 at 20 °C (Weast, 1986) Diffusivity in water (x 10-5 cm2/sec): 0.88 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant, pKa: >14 (Schwarzenbach et al., 1993) Flash point (°C): -53.9 (Sax and Lewis, 1987) Lower explosive limit (%): 1.5 (NFPA, 1984) Upper explosive limit (%): 8.9 (NFPA, 1984) Heat of fusion (kcal/mol): 1.115 (Dean, 1987) Henry’s law constant (x 10-2 atm⋅m3/mol): 3.45 at 18 °C (dynamic stripping cell-MS, Karl et al., 2003) Ionization potential (eV): 8.845 ± 0.005 (Franklin et al., 1969) 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

ow 1.76 using method of Hansch et al. (1968) Solubility in organics: Miscible with alcohol and ether (Windholz et al., 1983) Solubility in water: 642 mg/kg at 25 °C (shake flask-GC, McAuliffe, 1966) Vapor density: 2.78 g/L at 25 °C, 2.35 (air = 1) Vapor pressure (mmHg): 493 at 20 °C, 700 at 30 °C (quoted, Verschueren, 1983) 550.1 at 25 °C (Wilhoit and Zwolinski, 1971) Environmental fate: Photolytic. Methyl vinyl ketone and methacrolein were reported as major photooxidation products for the reaction of 2-methyl-1,3-butadiene with OH radicals. Formaldehyde, nitrogen dioxide, nitric oxide, and HO2 were reported as minor products (Lloyd et al., 1983). Synthetic air containing gaseous nitrous acid and exposed to artificial sunlight (λ = 300-450 nm) photooxidized 2-methyl-1,3-butadiene into formaldehyde, methyl nitrate, peroxyacetal nitrate, and a compound tentatively identified as methyl vinyl ketone (Cox et al., 1980). The following rate constants were reported for the reaction of 2-methyl-1,3-butadiene with OH radicals in the atmosphere: 9.26 to 9.98 x 10-11 cm3/molecule⋅sec (Atkinson et al., 1985), 5.91 x 10-11 cm3/molecule⋅sec at 298 K (Sabljić and Güsten, 1990), 1.10 x 10-10 cm3/molecule⋅sec (Atkinson et al., 1990), 4.7 x 10-13 cm3/molecule⋅sec at 300 K (Hendry and Kenley, 1979) and 5.94 x 10-13 cm3/molecule⋅sec at 298 K (Atkinson, 1991); with ozone in the gas-phase: 1.65 x 10-17 cm3/molecule⋅sec at 294 K (Adeniji et al., 1981), 5.80 x 10-18 to 1.25 x 10-17 cm3/molecule⋅sec (Atkinson and Carter, 1984), 1.43 x 10-17 cm3/molecule⋅sec at 298 K (Atkinson, 1990); with NO3 in the atmosphere: 1.3 x 10-12 cm3/molecule⋅sec (Benter and Schindler, 1988) and 6.52 x 10-13 cm3/molecule⋅sec at 297 K (Atkinson, 1991). Cox et al. (1980) reported a rate constant of 7.4 x 10-11 cm3/molecule⋅sec for the reaction of benzene with OH radicals based on a value of 8 x 10-12 cm3/molecule⋅sec for the reaction of ethylene with OH radicals. The estimated atmospheric lifetimes for the reaction of 2-methyl-1,3-butadiene with ozone, OH, and NO3 radicals are 28.3, 2.9, and 0.083 h, respectively (Atkinson and Carter, 1984). Chemical/Physical. Slowly oxidizes and polymerizes in air (Huntress and Mulliken, 1941). Toxicity: LC50 (inhalation) for mice 139 g/m3/2-h, rats 180 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-methyl-1,3-butadiene 41.0 mg/kg of pine burned. Emission rates of 2-methyl-1,3butadiene were not measured during the combustion of oak and eucalyptus. Uses: Manufacture of butyl and synthetic rubber; gasoline component; organic synthesis.