Rate Constants for the Reactions of Hydroxyl Radical with Several Alkanes, Cycloalkanes, and Dimethyl Ether

Abstract

Relative rate experiments were used to measure ratios of rate constants as a function of temperature for the reactions of OH with propane, n-butane, n-pentane, n-hexane, cyclopropane, cyclobutane, cyclopentane, cyclohexane, and dimethyl ether. To assure internal consistency, ratios were measured for seventeen reactant pairs among these reactants. All of the derived rate constants are based on an absolute rate constant of the OH + C2H6 reaction using k(ethane) = 1.0 × 10-11 exp(−1094/T) cm3/molecule s. The rate constants obtained are as follows. propane: 1.29 × 10-11 exp(−730/T), k(298 K) = 1.11 × 10-12. n-butane: 1.68 × 10-11 exp(−584/T), k(298 K) = 2.37 × 10-12. n-pentane: 1.94 × 10-11 exp(−494/T), k(298 K) = 3.70 × 10-12. n-hexane: 2.60 × 10-11 exp(−480/T), k(298 K) = 5.19 ×10-12. cyclopropane: 5.15 × 10-12 exp(−1255/T), k(298 K) = 7.64 × 10-14. cyclobutane: 1.62 × 10-11 exp(−611/T), k(298 K) = 2.08 × 10-12. cyclopentane: 2.57 × 10-11 exp(−498/T), k(298 K) = 4.83 × 10-12. cyclohexane: 3.58 × 10-11 exp(−500/T), k(298 K) = 6.69 × 10-12. dimethyl ether: 1.51 × 10-11 exp(−496/T), k(298 K) = 2.86 × 10-12. These results are compared with previous literature data and are discussed in terms of trends in preexponential factors and activation energies. Also, rate constants and Arrhenius parameters are derived for methylene groups in the alkanes and cycloalkanes. In the low temperature regime, the present data illustrate a persistent discrepancy between absolute and relative rate measurements. The relative data show less curvature at low temperatures, and can be adequately fit with two-parameter Arrhenius expressions.

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

“…The rate constants derived from the relative rate studies of Baker et al (1970) (as re-evaluated by , Hucknall et al (1975), Atkinson et al (1982b), Edney et al (1986), Behnke et al (1987), Finlayson-Pitts et al (1993) and DeMore and Bayes (1999) are in generally excellent agreement with the recommendation, to within 7%, 5%, 2%, 3%, 15%, 4% and 8%, respectively. The rate constants derived from the relative rate measurements of DeMore and Bayes (1999) trend from being 2% higher than the recommendation at 428 K to being 7% lower than the Atmos.…”

“…An Arrhenius plot of the absolute and relative rate data of Talukdar et al (1994), Mellouki et al (1994), Clarke et al (1998), DeMore and Bayes (1999) and Kozlov et al (2003) for temperatures <300 K is shown in Fig. 6.…”

“…The absolute rate constant measurements carried out over the temperature range 231-509 K by Schmidt et al (1985), Droege and Tully (1986b), Abbatt et al (1990), Schiffman et al (1991, Talukdar et al (1994), Donahue et al (1998) and Chuong and Stevens (2002) are in good agreement, with earlier absolute rate measurements of Greiner (1970), Perry et al (1976) and Paraskevopoulos and Nip (1980) at room temperature being ∼10-15% higher than these more recent studies. Figure 7 shows an Arrhenius plot of the absolute rate constants of Droege and Tully (1986b), Abbatt et al (1990), Talukdar et al (1994) and Donahue et al (1998) together with the relative rate data of Baker et al (1970) (as re-evaluated by Baldwin and Walker, 1979), Hucknall et al (1975) and DeMore and Bayes (1999). A least-squares fit of these data (Hucknall et al, 1975;Droege and Tully, 1986b;Abbatt et al, 1990;Talukdar et al, 1994;Donahue et al, 1998;DeMore and Bayes, 1999), using the expression k=AT 2 e −B/T , results in the recommendation of over the temperature range 230-760 K, where the indicated error in the value of B is two least-squares standard deviations, and k(n−butane)= 2.36×10 −12 cm 3 molecule −1 s −1 at 298 K.…”

“…Figure 7 shows an Arrhenius plot of the absolute rate constants of Droege and Tully (1986b), Abbatt et al (1990), Talukdar et al (1994) and Donahue et al (1998) together with the relative rate data of Baker et al (1970) (as re-evaluated by Baldwin and Walker, 1979), Hucknall et al (1975) and DeMore and Bayes (1999). A least-squares fit of these data (Hucknall et al, 1975;Droege and Tully, 1986b;Abbatt et al, 1990;Talukdar et al, 1994;Donahue et al, 1998;DeMore and Bayes, 1999), using the expression k=AT 2 e −B/T , results in the recommendation of over the temperature range 230-760 K, where the indicated error in the value of B is two least-squares standard deviations, and k(n−butane)= 2.36×10 −12 cm 3 molecule −1 s −1 at 298 K.…”

“…However, for the >C 3 alkanes and for the cycloalkanes, rate constants obtained from relative rate studies are an important part of the data-base (and in some cases are the only data available), and the recommendations then use a combination of absolute and relative rate data. As shown in Table 3, for a series of C 3 -C 10 n-alkanes and cyclohexane at room temperature the relative rate studies of Atkinson et al (1982a, b), Benhke et al (1987Benhke et al ( , 1988, and DeMore and Bayes (1999) are in generally excellent agreement, and these relative rate studies severely a Based on the data cited in the table from the studies of Atkinson et al (1982b), Behnke et al (1987Behnke et al ( , 1988 and DeMore and Bayes (1999). There are a number of alkanes for which the OH radical reaction rate constants have been measured relative to those for the reactions of OH radicals with H 2 or CO, often at elevated temperatures.…”