Product analysis and kinetics of the gas-phase reactions of selected organosilicon compounds with OH radicals using a smog chamber-mass spectrometer system

Kinetics of the gas-phase reactions of OH radicals with alkanes and cycloalkanes

“…21). The relative rate data of Japar et al (1990), Sommerlade et al (1993), Kramp and Paulson (1998) and those of DeMore and Bayes (1999) relative to propane (not used in the evaluation; see above) are in excellent agreement with the recommended rate constant, while that of Edney et al (1986) is 20% lower.…”

“…Rate constants are available from the absolute rate studies of Greiner (1970), Nielsen et al (1986), Bourmada et al (1987), Droege and Tully (1987), Saunders et al (1994) and Donahue et al (1996, and from a number of relative rate studies (Gorse and Volman, 1974;Wu et al, 1976;Atkinson et al, 1982aAtkinson et al, , 1983bTuazon et al, 1983;Edney et al, 1986;Japar et al, 1990;Atkinson and Aschmann, 1992;Sommerlade et al, 1993;DeMore and Bayes, 1999). Most of these rate constants have been measured only at room temperature.…”

Temperature Dependence of the Organic Carbon/Water Partition Ratios (KOC) of Volatile Methylsiloxanes

“…Both were determined using the relative rate method. Atkinson (1991) determined the value of k OH as 1.01 × 10 -12 cm 3 /molecule/s at 24°C, and Sommerlade et al (1993) determined k OH as 1.26 × 10 -12 cm 3 /molecule/s, again at 24°C. There is good agreement between the two determinations.…”

“…A further value (from an unpublished study) of k OH of 3.08 × 10 -12 cm 3 /molecule/s -1 is given in IUCLID (2005), but no further details are given. Sommerlade et al (1993) identified the major products from the reaction of D4 with hydroxyl radicals as heptamethylhydroxycyclotetrasiloxane, along with smaller amounts of heptamethyl(hydroperoxymethyl)cyclotetrasiloxane and 1,2-bis(heptamethylcyclotetrasiloxanyl)ethane, and trace amounts of heptamethyl(hydroxymethyl)cyclotetrasiloxane and bis(heptamethylcyclotetrasiloxanyl)ether. The hydroxyl-substituted products are expected to be more soluble in water than D4, and to have a lower vapour pressure, and so are likely to be removed from the atmosphere by wet and dry deposition (Chandra, 1997).…”

“…The assessment used a simple equilibrium-partitioning model to investigate the relative rates of removal of two representative VMSs (the linear decamethyltetrasiloxane and D4) and their siloxanol degradation products by reaction and atmospheric deposition. The modelling is based on the work of Atkinson (1991) and Sommerlade et al (1993), which demonstrates that siloxanes break down in the atmosphere to form hydroxyl-substituted silanols by reaction with atmospheric hydroxyl radicals. As substitution proceeds the silanols become increasingly water-soluble and less volatile, and so tend to be washed out of the atmosphere by wet deposition.…”