2,3-DIMETHYLBUTANE

Note: According to Chevron Phillips Company’s (2004) product literature, 99.0-99.7% 2,3dimethylbutane contains 2,2-dimethylbutane (0.2 wt %) and 2-methylpentane (0.1 wt %) as impurities. CASRN: 79-29-8; DOT: 2457; molecular formula: C6H14; FW: 86.18; RTECS: EJ9350000 Physical state, color, and odor: Colorless liquid with a mild gasoline-like odor. An odor threshold concentration of 4.2 ppmv was reported by Nagata and Takeuchi (1990). Melting point (°C): -128.5 (Weast, 1986) -135 (quoted, Verschueren, 1983) Boiling point (°C): 58.15 (Kirby and Van Winkle, 1970) Density (g/cm3): 0.66164 at 20 °C, 0.65702 at 25 °C (Dreisbach, 1959) Diffusivity in water (x 10-5 cm2/sec): 0.43 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant, pKa: >14 (Schwarzenbach et al., 1993) Flash point (°C): -33 (Aldrich, 1990) Lower explosive limit (%): 1.2 (NFPA, 1984) Upper explosive limit (%): 7.0 (NFPA, 1984) Heat of fusion (kcal/mol): 0.194 (Dean, 1987) Henry’s law constant (atm⋅m3/mol): 1.28 at 25 °C (Mackay and Shiu, 1981) Interfacial tension with water (dyn/cm): 49.8 at 25 °C (quoted, Freitas et al., 1997)

10.24 (Collin and Lossing, 1959) 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: 3.85 (Hansch and Leo, 1979) Solubility in organics: In methanol: 495, 593, 760, and 1,700 g/L at 5, 10, 15, and 20 °C, respectively. Miscible at higher temperatures (Kiser et al., 1961). Solubility in water (mg/kg): 19.1 at 25 °C, 19.2 at 40.1 °C, 23.7 at 55.1 °C, 40.1 at 99.1 °C, 56.8 at 121.3 °C, 97.9 at 137.3 °C,

171.0 at 149.5 °C (shake flask-GLC, Price, 1976) 32.9 at 0 °C, 22.5 at 25 °C (shake flask-GC, Polak and Lu, 1973) Vapor density: 3.52 g/L at 25 °C, 2.98 (air = 1) Vapor pressure (mmHg): 200 at 20 °C (quoted, Verschueren, 1983) 217 at 23.10 °C (Willingham et al., 1945) 234.6 at 25 °C (Wilhoit and Zwolinski, 1971) Environmental fate: Photolytic. Major products reported from the photooxidation of 2,3-dimethylbutane with nitrogen oxides are carbon monoxide and acetone. Minor products included formaldehyde, acetaldehyde and peroxyacyl nitrates (Altshuller, 1983). Synthetic air containing gaseous nitrous acid and exposed to artificial sunlight (λ = 300-450 nm) photooxidized 2,3-dimethylbutane into acetone, hexyl nitrate, peroxyacetal nitrate, and a nitro aromatic compound tentatively identified as a propyl nitrate (Cox et al., 1980). The following rate constants were reported for the reaction of 2,3-dimethylbutane and OH radicals in the atmosphere: 3.1 x 10-12 cm3/molecule⋅sec at 300 K (Hendry and Kenley, 1979); 5.16 x 10-12 cm3/molecule⋅sec (Greiner, 1970); 6.19 x 10-12 cm3/molecule⋅sec (Sabljić and Güsten, 1990); 5.67 x 10-12 cm3/molecule⋅sec at 300 K (Darnall et al., 1978); 6.30 x 10-12 cm3/molecule⋅sec (Atkinson, 1990). Based on a photooxidation rate constant of 6.3 x 10-12 cm3/molecule⋅sec for the reaction of 2,3-dimethylbutane and OH radicals in summer sunlight, the atmospheric lifetime is 22 h (Altshuller, 1991). Photooxidation rate constants of 4.06 x 10-16 and 4.06 x 10-16 cm3/molecule⋅sec were reported for the gas-phase reaction of 2,3-dimethylbutane and NO3 (Atkinson, 1990; Sabljić and Güsten, 1990). Cox et al. (1980) reported a rate constant of 3.8 x 10-12 cm3/molecule⋅sec for the reaction of gaseous 2,3-dimethylbutane 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 vapor. 2,3Dimethylbutane will not hydrolyze because it has no hydrolyzable functional group. Exposure limits: ACGIH TLV: TWA and STEL for all isomers except n-hexane are 500 and 1,000 ppm, respectively (adopted).