UC Irvine UC Irvine Previously Published Works Title Rate constants for the reactions of chlorine atoms with a series of unsaturated aldehydes and ketones at 298 K: structure and reactivity Permalink https://escholarship.org/uc/item/4p41x6ph Journal Physical Chemistry Chemical Physics, 4(10) ISSN 14639076 14639084 Authors Wang, Weihong Ezell, Michael J Ezell, Alisa A et al. Publication Date 2002-05-01 DOI 10.1039/b111557j Peer reviewed eScholarship.org Powered by the California Digital Library University of California View Article Online / Journal Homepage / Table of Contents for this issue PCCP Rate constants for the reactions of chlorine atoms with a series of unsaturated aldehydes and ketones at 298 K: structure and reactivity Weihong Wang, Michael J. Ezell, Alisa A. Ezell, Gennady Soskin and Barbara J. Finlayson-Pitts* Department of Chemistry, University of California, Irvine, CA 92697-2025. E-mail: bjfi[email protected]; Fax: 949 824-3168; Tel: 949 824-7670 Received 2nd January 2002, Accepted 31st January 2002 First published as an Advance Article on the web 18th April 2002 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 10À10 cm3 moleculeÀ1 sÀ1) determined using these techniques are as follows: acrolein (2.5 Æ 0.7); methacrolein (2.9 Æ 0.8); crotonaldehyde (3.2 Æ 0.9); methyl vinyl ketone (2.0 Æ 0.5); 4- chlorocrotonaldehyde (1.6 Æ 0.4); chloromethyl vinyl ketone (2.0 Æ 0.2); crotyl chloride (2.5 Æ 0.2). The reported errors are Æ2s 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 Æ 0.91)  10À11 cm3 moleculeÀ1 sÀ1 (2s), 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. from this laboratory have shown that isoprene28,29 and 1,3- Published on 18 April 2002. Downloaded by University of California - Irvine 06/02/2015 23:57:42. Introduction butadiene30,31 react with chlorine atoms to form unique, chlor- Atomic chlorine is generated in the marine boundary layer ine-containing aldehydes and ketones. Because these are from reactions of sea salt particles.1–6 In addition, chlorine formed only through chlorine atom chemistry, they can be used atom chemistry has been observed in the Arctic at polar sun- as ‘‘markers’’ for chlorine atoms in the lower atmosphere. For rise7–13 and may have occurred in the plumes from the burning example, 4-chlorocrotonaldehyde (CCA) is formed in both the of oil wells in Kuwait due to the presence of brine.14–21 Mole- presence and absence of NO, while chloromethyl vinyl ketone 31 cular chlorine, Cl2 , a precursor to atomic chlorine has been (CMVK) is formed only in the absence of NO: measured in marine air masses at concentrations up to 150 ppt (parts per trillion).22 Non-HCl inorganic gaseous chlorine compounds, hypothesized to be mainly Cl2 ranging from 13 to 127 ppt were measured indirectly using mist chambers at coastal sites.23,24 Photolyzable chlorine compounds25–27 have also been identified in the Arctic during surface ozone deple- tion in the spring. Such photolytically labile chlorine com- pounds will be photolyzed at sunrise and generate chlorine atoms. The rate constants for chlorine atom reactions with organic compounds reactions are about one to two orders of magni- tude faster than the corresponding OH reactions. In the early morning hours when OH concentration is small (105 cmÀ3) and the atomic Cl concentration may be of the order23 of 104 to 105 cmÀ3, chlorine atoms could be the most important oxidant in the marine boundary layer. However, direct mea- surements of chlorine atom concentrations are not available. A potential approach is to measure unique chlorine-containing compounds formed from Cl-organic reactions. Recent studies 1824 Phys. Chem. Chem. Phys., 2002, 4, 1824–1831 DOI: 10.1039/b111557j This journal is # The Owner Societies 2002 View Article Online lene was used as the reference compound in one set of experi- ments and n-butane or n-nonane in another, the relative rate constant for acetylene compared to n-butane was also mea- sured to ensure there were no systematic errors due to the use of different reference compounds. Experimental Rate constants were measured at room temperature (298 Æ 3) K and 1 atm in air or N2 using the relative rate technique with two different approaches: (1) a borosilicate glass chamber with 1 long path FTIR detection, and (2) Teflon reaction chambers with GC-FID detection. In both cases, a mixture of the analyte and a reference compound, for which the rate constant for reaction with Cl atoms is known, was introduced into the reac- tion chamber. Relative rates were carried out in air or N2 to check for potential interference from OH chemistry. Molecular chlorine was added to generate chlorine atoms and was photo- In order to use such compounds to quantify the concentra- lyzed using a set of blacklamps surrounding the reaction cham- tion of chlorine atoms in air, their rates of removal must be bers. These lamps emit radiation in the 300–450 nm range with known. Loss of these products occurs by reaction with OH, a maximum intensity at 360 nm, providing a good overlap with the Cl absorption spectrum. Photolysis was typically car- O3 ,NO3 and chlorine atoms, as well as by photolysis. Loss 2 through Cl reactions could be the most important process in ried out in increments of 1 to 5 min, depending on the com- the early morning hours when CCA and CMVK are generated. pound and reaction conditions. The lamps were turned off to We report here relative rate studies at room temperature and stop the reaction during sampling. Total photolysis times were 1 atm pressure for the reactions of chlorine atoms with 4-chlor- 6 to 30 min. The loss of the organic and reference compound ocrotonaldehyde (CCA) and chloromethyl vinyl ketone with reaction time were measured either by FTIR or by GC- (CMVK). To further understand the structural features that FID as described in more detail below. control reactivity of unsaturated aldehydes and ketones, the The organic and the reference compound react simulta- org reactions with acrolein (ACR), methacrolein (MACR), croto- neously with the chlorine atoms, with rate constants k and ref naldehyde (CA), and methyl vinyl ketone (MVK) were also k , respectively: studied using the same techniques: korg organic þ Cl ! products ð1Þ kref reference þ Cl ! products ð2Þ As described in detail elsewhere,6 the simultaneous decay of the organic and the reference compound from their initial con- centrations at time t ¼ 0, [org]o and [ref]o , to [org]t and [ref]t at time t is given by eqn. (I): org ref lnf½org0=½orgtg¼ðk =k Þlnf½ref0=½reftgðIÞ Thus, a plot of {ln [org] /[org] } versus {ln [ref] /[ref] } Published on 18 April 2002. Downloaded by University of California - Irvine 06/02/2015 23:57:42. o t o t should be linear through the origin with a slope equal to the ratio of rate constants korg/kref. A major advantage of the rela- tive rate approach is that accurate measurements of absolute concentrations of the organic and reference compounds are not required. Chemicals The chemicals used were as follows: n-butane (Matheson, Kinetics studies of the reactions of chlorine atoms with 99.5%); acetylene (Air Products, Industrial Grade); n-nonane ACR, MACR, CA and MVK have been reported (Aldrich, 99+%); acrolein (Arcos, 97%); methacrolein recently,32–35 but there are no reports of the rate constants (Aldrich, 95%); methyl vinyl ketone (Aldrich, 99%); crotonal- for the CCA or CMVK reactions. Our combined data set per- dehyde (Aldrich, 99+%, predominantly trans-); crotyl chloride mits probing structure-reactivity relationships for this series of (Aldrich, 95%, predominantly trans-); N2 (Oxygen Service unsaturated aldehydes and ketones. In addition, ACR is the Company, Ultrahigh Purity, >99.999%); air (Oxygen Service major product from the OH-butadiene reaction, MACR and Company, Ultrahigh Purity). The gases were used as received. MVK from the OH-isoprene reaction, and MVK from the Acrolein, methacrolein, methyl vinyl ketone and crotonalde- Cl-isoprene reaction. Their rate constants with Cl atoms will hyde were subjected to several freeze–pump–thaw cycles prior contribute to a better understanding of isoprene and 1,3-buta- to vaporizing a measured pressure into 5 L bulbs; N2 was then diene chemistry in coastal regions.