| 19228051 |
Kaiser EW, Wallington TJ, Hurley MD: Products and mechanism of the reaction of Cl with butanone in N2/O2 diluent at 297-526 K. J Phys Chem A. 2009 Mar 19;113(11):2424-37.
The products, kinetics, and mechanism of the reaction Cl + butanone have been measured by UV irradiation of Cl (2)/butanone/N (2) (O (2)) mixtures using either GC or FTIR analysis. In the absence of O (2), the products are 1-, 3-, and 4-chlorobutanone with yields of 3.1%, 76%, and 22.5%, respectively. As the temperature is increased, the yields of 1- and 4-chlorobutanone increase relative to the 3-chlorobutanone yield. On the basis of these increases, the activation energies for hydrogen abstraction at the 1 and 4 positions are determined to be 1800 (+/-300) and 470 (+300, -150) cal mol (-1) relative to abstraction at the 3 position. In the presence of 400 ppm of O (2) with 700-900 ppm of Cl (2) at 297 K, the yields of 1- and 3-chlorobutanone decrease dramatically from 3.1% to 0.25% and from 76% to 2%, respectively, while the 4-chlorobutanone decreases only slightly from 22.5% to 18.5%. The observed oxygenated species are acetaldehyde (52%), butanedione (11%), and propionyl chloride (2.5%). Increasing the temperature to 400 K (O (2) = 500 ppm) suppresses these oxygenated products and 1- and 3-chlorobutanone again become the primary products, indicating that the O (2) addition reaction to the 1- and 3-butanonyl radicals is becoming reversible. At 500 K and very high O (2) mole fraction (170,000 ppm), a new product channel opens which forms a substantial yield (approximately 20%) of methylvinylketone. Computer modeling of the product yields has been performed to gain an understanding of the overall reaction mechanism in the presence and absence of O (2). The reaction of chlorine atoms with butanone proceeds with a rate constant of 4.0 (+/-0.4) x 10 (-11) cm (3) molecule (-1) s (-1) independent of temperature over the range 297-475 K (E (a) = 0 +/- 200 cal mol (-1)). Rate constant ratios of k (CH (2) C (O) C (2) H (5) + Cl (2))/k (CH (2) C (O) C (2) H (5) + O (2)) = 0.027 +/- 0.008, k (CH (3) C (O) CHCH (3) + Cl (2))/ k (CH (3) C (O) CHCH (3) + O (2)) = 0.0113 +/- 0.0011, and k (CH (3) C (O) CH (2) CH (2) + Cl (2))/k (CH (3) C (O) CH (2) CH (2) + O (2)) = 1.52 +/- 0.32 were determined at 297 K in 800-950 Torr of N (2) diluent. In 700-900 Torr of N (2)/O (2) diluent, the major fate of the alkoxy radicals CH (3) C (O) CH (O) CH (3) and OCH (2) C (O) C (2) H (5) is decomposition to give CH (3) C (O) radicals and CH (3) CHO and HCHO and C (O) C (2) H (5) radicals, respectively. |
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