Reactions of OH and Cl with isopropyl formate, isobutyl formate, n-propyl isobutyrate and isopropyl isobutyrate

Abstract

a b s t r a c tThe rate coefficients for the reactions of OH with isopropyl formate, isobutyl formate, n-propyl isobutyrate and isopropyl isobutyrate have been determined using both absolute and relative methods. The relative rate method has been also used to measure the room temperature rate coefficient for the reaction of Cl with the same esters. In addition, a series of runs conducted on the OH-initiated oxidation of isopropyl formate, isobutyl formate and n-propyl isobutyrate showed the formation of acetone from the three reactions. The formation of propanal was also observed for n-propyl isobutyrate.

Gas Phase Kinetics and Mechanistic Insights for the Reactions of Cl atoms with Isopropyl Formate and Isobutyl Formate

“…In the case of reaction R1 , the experimentally measured and computationally calculated rate coefficients at 298 K are k R1–298K Exp = (1.56 ± 0.57) × 10 –11 cm 3 molecule –1 s –1 and k R1–298K Theory = 1.87× 10 –11 cm 3 molecule –1 s –1 respectively which are in excellent agreement with each other within the experimental uncertainties. Both experimentally measured and computationally calculated rate coefficients are in good agreement with previously reported rate coefficients by Pimentel et al [(1.75 ± 0.35) × 10 –11 cm 3 molecule –1 s –1 ] and Zhang et al [(1.40 ± 0.20) × 10 –11 cm 3 molecule –1 s –1 ] within the reported experimental uncertainties (maximum deviation between experimentally measured and reported rate coefficients by Pimentel et al and Zhang et al are found out to be 12% and 11% respectively). Both experimentally measured and computationally calculated temperature dependent rate coefficients have shown a negative temperature dependence due to the formation of stabilized prereactive complexes.…”

“…The typical concentration of Cl atoms in the marine boundary layer (MBL) and in ambient conditions used for the calculation of cumulative lifetime of the test molecules are 1.3 × 10 5 and 1.0 × 10 3 atom cm –3 . , The typical OH radical concentration used in the calculation is 1.0 × 10 6 radical cm –3 . The rate coefficients for the reactions of IPF and IBF with OH radicals at 298 K are (1.87 ± 0.11) × 10 –12 and (3.17 ± 0.20) × 10 –12 cm 3 molecule –1 s –1 respectively . The rate coefficients for the reactions of IPF and IBF with Cl atoms at 298 K and at 1 atm pressure are (1.56 ± 0.47) × 10 –11 and (7.23 ± 1.80) × 10 –12 cm 3 molecule –1 s –1 respectively.…”

“…Although the global average concentration of OH radicals is more than that of Cl atoms (nearly 3 orders of magnitude), Cl atoms undergo a fast oxidation reaction with these esters and hence compete with the OH radical mainly in the midcontinental regions, marine boundary layers (MBL), and urban polluted areas . It can also be degraded in the atmosphere via its reactions with ozone and NO 3 molecules and sunlight-induced photolysis . The Henry’s law constant ( K H ) for IPF and IBF in water are 2.1 × 10 –2 and 2.0 × 10 –2 mol m –3 Pa –1 , respectively.…”

“…They have used ethylene and methanol as reference compounds to measure the rate coefficient for the reaction of IPF with OH radicals and Cl atoms, respectively. Zhang et al reported the rate coefficients for the reaction of IPF and IBF with OH radicals and Cl atoms using both absolute and relative rate techniques. They reported the temperature dependent rate coefficients for the reactions of OH radicals with IPF and IBF as k IPF+OH = (2.76 ± 0.63) × 10 –13 exp [(571 ± 66)/ T] cm 3 molecule –1 s –1 and k IBF+OH = (8.38 ± 1.08) × 10 –13 exp [(398 ± 38)/ T] cm 3 molecule –1 s –1 respectively.…”

“…55,56 The typical OH radical concentration used in the calculation is 1.0 × 10 6 radical cm −3 57. The rate coefficients for the reactions of IPF and IBF with OH radicals at 298 K are (1.87 ± 0.11) × 10 −12 and (3.17 ± 0.20) × 10 −12 cm 3 molecule −1 s −1 respectively 14. The rate coefficients for the reactions of IPF and IBF with Cl atoms at 298 K and at 1 atm pressure are (1.56 ± 0.47) × 10 −11 and (7.23 ± 1.80) × 10 −12 cm 3 molecule −1 s −1 respectively.…”