The reactions of atomic chlorine with acrolein, methacrolein and methyl vinyl ketone

An investigation into the reactions between Cl atoms and acrolein (1), meth acrolein (2) and methyl vinyl ketone (3) CH2CHCHO+Cl --> products (1) CH2C(CH3)CHO + Cl --> products (2) CH2CHC(O)CH3 + Cl --> products (3) is presented. Values of the rate constants for the reactions have been dete rmined by an absolute technique for the first time. At a pressure of 1.6 To rr, the rate constants obtained were: and k(1) = 1.1 +/- 0.2, k(2) = 3.3 +/ - 0.6 k(3) = 0.99 +/- 0.20 in units of 10(-10) cm(3) molecule(-1) s(-1). k( 1) was also determined at atmospheric pressure using a relative-rate techni que. The rate constant obtained was (2.2 +/- 0.3) x 10(-10) cm(3) molecule( -1) s(-1); the larger value compared with that for 1.6 Torr is thought to r eflect a true dependence of the reaction rate on pressure. The final produc ts of the reactions performed under an atmosphere of synthetic air were inv estigated using FTIR spectroscopy. The only chlorinated organic species ide ntified as products of the reactions were chloroacetaldehyde in the case of reaction of Cl atoms with acrolein; chloroacetone with methacrolein; and c hloroacetaldehyde with methyl vinyl ketone. Branching ratios for abstractio n (the fraction of reactions occurring by abstraction relative to the sum o f addition and abstraction processes) were found to be 0.22 +/- 0.13 for ac rolein, 0.18 +/- 0.02 for methacrolein and <0.03 for methyl vinyl ketone. T he reaction of Cl atoms with methacrolein proceeds via a mechanism that inv olves the decomposition of the methyl vinyl radical. The decomposition of t his radical in synthetic air, and in the absence of NO, appears to lead to the formation of significantly more CO than previously thought. This observ ation is in agreement with the work of J. J. Orlando, S. E. Paulson and G. S. Tyndall, Geophys. Res. Lett., 1999, 26, 2191 (ref. 1), who studied the d ecomposition of the radical under different conditions.