ABSTRACT
H3C SH Note: According to Chevron Phillips Company’s (2005) Technical Data Sheet, 99.5-99.8% methyl mercaptan contains methyl ether (≤ 0.1 wt %), dimethyl disulfide (≤ 0.25 wt %), dimethyl sulfide (≤ 0.25 wt %), methanol (≤ 0.1 wt %), and hydrogen sulfide (≤ 0.2 wt %). CASRN: 74-93-1; DOT: 1064; DOT label: Flammable gas; molecular formula: CH4S; FW: 48.10; RTECS: PB4375000; Merck Index: 12, 6023 Physical state, color, and odor: Colorless gas with a garlic-like or rotten cabbage odor. An experimentally determined odor threshold concentration of 2.1 ppbv was reported by Leonardos et al. (1969). A detection odor threshold concentration of 81 µg/m3 (41 ppbv) was determined by Katz and Talbert (1930). Melting point (°C): -123 (Weast, 1986) -121 (Hawley, 1981) Boiling point (°C): 6.2 (Weast, 1986) 5.956 (Wilhoit and Zwolinski, 1971) Density (g/cm3): 0.8665 at 20 °C (Weast, 1986) Diffusivity in water (x 10-5 cm2/sec): 1.25 at 20 °C using method of Hayduk and Laudie (1974) Dissociation constant, pKa: 10.70 at 25 °C (Dean, 1973) Flash point (°C): -17.9 (open cup, NIOSH, 1997) Lower explosive limit (%): 3.9 (NIOSH, 1997) Upper explosive limit (%): 21.8 (NIOSH, 1997) Henry’s law constant (x 10-3 atm⋅m3/mol at 25 °C): 2.56 (Przyjazny et al., 1983) 5.00 (De Bruyn et al., 1994) 3.03 (Hine and Weimar, 1965) Ionization potential (eV): 9.440 ± 0.005 (Franklin et al., 1969)
oc Unavailable because experimental methods for estimation of this parameter for mercaptans are lacking in the documented literature Octanol/water partition coefficient, log Kow: Unavailable because experimental methods for estimation of this parameter for mercaptans are lacking in the documented literature Solubility in organics: Soluble in alcohol, ether (Weast, 1986), and petroleum naphtha (Hawley, 1981) Solubility in water: 23.30 g/L at 20 °C (quoted, Windholz et al., 1983) 0.330 mol/L at 25 °C (Hine and Weimar, 1965) Vapor density: 1.97 g/L at 25 °C, 1.66 (air = 1) Vapor pressure (mmHg): 1,292 at 20 °C (NIOSH, 1997) 1,516 at 25 °C (Wilhoit and Zwolinski, 1971) Environmental fate: Biological. After 20 d, methyl mercaptan started to degrade in anaerobic sediments and sludges producing stoichiometric amounts of methane. Complete degradation was achieved after 20 d. Under anaerobic freshwater conditions, methyl mercaptan were degraded by methanogenic archea (van Leerdam et al., 2006). Photolytic. Sunlight irradiation of a methyl mercaptan-nitrogen oxide mixture in an outdoor chamber yielded formaldehyde, sulfur dioxide, nitric acid, methyl nitrate, methanesulfonic acid, and an inorganic sulfate (Grosjean, 1984a). Chemical/Physical. In the presence of nitric oxide, gaseous methyl mercaptan reacted with OH radicals forming methyl sulfenic acid and methyl thionitrite. The rate constant for this reaction is 2.1 x 10-11 cm3/molecule⋅sec at 20 °C (MacLeod et al., 1984). Forms a crystalline hydrate with water (Patnaik, 1992). Exposure limits: NIOSH REL: 15-min ceiling 0.5 ppm (1 mg/m3), IDLH 150 ppm; OSHA PEL: TWA 10 ppm (20 mg/m3); ACGIH TLV: TWA 0.5 ppm (adopted). Symptoms of exposure: Inhalation of vapors may cause headache, narcosis, nausea, pulmonary irritation, and convulsions (Patnaik, 1992). Exposure of skin to liquid may cause frostbite (NIOSH, 1997). Toxicity: LC50 (inhalation) for mice 6,530 µg/m3/2-h, rats 675 ppm (quoted, RTECS, 1985). Source: Occurs naturally in kohlrabi stems (Brassica oleracea var. gongylodes) and potato plants (Duke, 1992) Uses: Synthesis of methionine; intermediate in the manufacture of pesticides, fungicides, jet fuels, plastics; catalyst; added to natural gas to give odor.
