Chlorination Chemistry I: Rate Coefficients, Reaction Mechanisms, and Spectra of the Chlorine and Bromine Adducts of Propargyl Halides

Published

September 16, 1999

Author(s)

D B. Atkinson, Jeffrey W. Hudgens

Abstract

Cavity ring-down spectroscopy (CRDS), end-product analysis, and ab initio calculations have determined the reaction rate coefficients, mechanisms and thermochemistry relevant to the addition of halogen atoms to propargyl chloride and propargyl bromide. Halogen atoms were produced by laser photolysis and halogen addition reaction products were probed at a variable delay by CRDS using a second laser pulse. We report the continuum spectra of C₃H₃Cl₂, C₃H₃ClBr, and C₃H₃Br₂ between 238 and 252 nm and the absorption cross-sections, ς ₂₄₀(C₃H₃Cl₂) = 4.20 + 1.05 x 10^-17 cm²-molec^-1 and ς₂₄₂(C₃H₃Br₂) = 1.04 + 0.31 x 10^-17 cm²-molec^-1. When a chlorine atom adds to the acetylenic carbon of propargyl chloride, the incipient radical regenerates a chlorine atom and produces chloroallene. Chlorine atom addition at the center carbon of propargyl chloride forms the 2,3-dichloro-1-propene-2-yl radical, which we monitor with CRDS. By fitting the observed data to complex reaction schemes, the 295K rate coefficients for formation of 2,3-dihalo-1-propene-2-yl radicals were found to be k(Cl+C₃H₃Cl, 665 Pa)= 1.2+0.2x10^-10 cm³molec^-1s^-1 and k(Br+C₃H₃Br, 625 Pa)= 2+1 x 10^-12 cm³molec^-1s^-1. Self-reaction rate coefficients of the adducts at 295K were found to be k(C₃H₃Cl₂+C₃H₃Cl₂)= 3.4+0.9x10^-11 cm³molec^-1s^-1 and k(C₃H₃Br₂+C₃H₃Br₂)= 1.7 + 1.1 x 10^-11 cm³molec^-1s^-1. The listed uncertainties are twice the standard deviation of individual determinations and the rate coefficients include the uncertainty of the appropriate absorption cross-section.

Citation

Journal of Physical Chemistry A

Volume

103

Pub Type

Journals

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Keywords

ab initio calculation, bromine reaction, C₃H₃ + C₃H₃Cl₂ reaction, cavity ring-down spectra, chlorine reaction, Cl + C₃H₃Cl₁ reaction, electronic spectrum, reaction mechanism, reaction rate coefficient

Citation

Atkinson, D. and Hudgens, J. (1999), Chlorination Chemistry I: Rate Coefficients, Reaction Mechanisms, and Spectra of the Chlorine and Bromine Adducts of Propargyl Halides, Journal of Physical Chemistry A, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=831544 (Accessed July 17, 2024)