Rate constants for the reactions of chlorine atoms with a series of unsaturated aldehydes and ketones at 298 K: structure and reactivity

Abstract

The kinetics and mechanisms of chlorine atom reactions with the products of organic oxidations in the atmosphere are of interest for understanding the chemistry of coastal areas. We report here the first kinetics measurements of the reactions of atomic chlorine with 4-chlorocrotonaldehyde and chloromethyl vinyl ketone, recently identified as products of the reaction of chlorine atoms with 1,3-butadiene. The reactions with acrolein, methacrolein, crotonaldehyde, methyl vinyl ketone and crotyl chloride were also studied to probe structure-reactivity relationships. Relative rate studies were carried out at 1 atm and 298 K using two different approaches: long path FTIR for the acrolein, methacrolein, crotonaldehyde and methyl vinyl ketone reactions with acetylene as the reference compound, and a collapsible Teflon reaction chamber with GC-FID detection of the organics using n-butane or n-nonane as the reference compounds for the entire series. The average absolute rate constants (in units of 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹) determined using these techniques are as follows: acrolein (2.5 ± 0.7); methacrolein (2.9 ± 0.8); crotonaldehyde (3.2 ± 0.9); methyl vinyl ketone (2.0 ± 0.5); 4-chlorocrotonaldehyde (1.6 ± 0.4); chloromethyl vinyl ketone (2.0 ± 0.2); crotyl chloride (2.5 ± 0.2). The reported errors are ±2σ and include a reference rate constant error of 20% for acetylene, 10% for n-butane and 3% for n-nonane. These values are in good agreement with previous literature reports for the acrolein, methacrolein and methyl vinyl ketone reactions, while that for crotonaldehyde is 33% larger. The rate constant for acetylene using n-butane as the reference compound was also measured to be (5.23 ± 0.91) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ (2σ), in excellent agreement with the currently recommended value at 1 atm and 298 K. The effect of structure on reactivity of these compounds is discussed and it is shown that these fast reactions will be a major loss process for these compounds in coastal marine areas at dawn.