Kinetics and products of propargyl (C3H3) radical self-reactions and propargyl-methyl cross-combination reactions

Abstract

Propargyl (HCCCH2) and methyl radicals were produced through the 193-nm excimer laser photolysis of mixtures of C3H3Cl/He and CH3N2CH3/He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self-reactions and propargyl-methyl cross-combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C6H6 isomers with 1,5-hexadiyne(CHCCH2CH2CCH, about 60%); 1,2-hexadiene-5yne (CH2CCCH2CCH, about 25%); and a third isomer of C6H6 (∼15%), which has not yet been, with certainty, identified as being the major products. The rate constant determination in the propargyl-methyl mixed radical system yielded a value of (4.0 ± 0.4) × 10−11 cm3 molecule−1 s−1 for propargyl radical combination reactions and a rate constant of (1.5 ± 0.3) × 10−10 cm3 molecule−1 s−1 for propargyl-methyl cross-combination reactions. The products of the methyl-propargyl cross-combination reactions were two isomers of C4H6, 1-butyne (about 60%) and 1,2-butadiene (about 40%). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 118–124, 2000