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ChemInform Abstract (kinetics, mechanism).

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The radicals were generated from the respective halide RX by the reaction Na + RX → R + NaX in a low‐pressure flow reactor fed by a multi‐slit diffusion burner. Test results are reported for the system Na/CH3I giving k(Na + CH3I) = 6.0 · 10−3 and k(CH3 + CH3) = 2.8·1013 cm3 mol−1 s−1. The main part deals with the production of C2H in the system Na/C2HBr and its consecutive reactions with C2HBr and added C2H2 and C4H2. The rate constant k(Na + C2HBr) was found to be 2.9 · 1013 cm3 mol−1 s−1. The bimolecular rate constants of C2H with the compounds above have been determined to 1.0·1014, 2.3 · 1013 and 4.0·1013 cm3 mol−1 s−1, respectively, at a temperature of 603 K. – The main products in this reaction system are polyynes with a minor formation of ethyne and very little hydrogenated polyynes. The formation of an aromatic compound (ethynylbenzene) is negligibly small, a fact which is discussed in its relation to aromates in hydrocarbon flames. The primary reaction Na + C2HBr and its products are discussed as well as the unimolecular decomposition and stabilization of energized adducts formed by C2H.