Products and Mechanism of the Reaction of Cl with Butanone in N2/O2 Diluent at 297−526 K

Abstract

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.