Disproportionation/combination ratio for H +sec-C4H9

Abstract

The reactions of hydrogen atoms with large excesses of various butene isomers have been investigated at a temperature of 290 ± 3 K, over a pressure range 4–16 Torr (predominantly argon) in a conventional flow-discharge system with gas-chromatographic analysis of the infinite-time reaction products. Two series of experiments were carried out. In the first, each of but-1-ene, (Z)-but-2-ene and (E)-but-2-ene was separately reacted with hydrogen atoms the only measurements made being the ratio of the yields of the other two butenes which are produced. The products of the three possible disproportionation reactions of H +sec-C₄H₉ are in the proportions but-1-ene : (E)-but-2-ene: (Z)-but-2-ene = 43.0 : 40.8 : 16.3.

In a second series of experiments, (Z)-but-2-ene and (E)-but-2-ene reacted separately with hydrogen atoms with a full analysis of products being made. Values are derived for the disproportionation/combination ratio for H +sec-C₄H₉(0.66 ± 0.08) and for the upper limit to the ratio of the rate constant for unimolecular decomposition to that for bimolecular stabilisation (< 1.2 × 10^–7 mol cm^–3) for excited C₄H₁₀ produced by addition of H to sec-C₄H₉. The basic analysis procedure used is validated by showing that the flow rate of hydrogen atoms necessary to generate the observed products is, within experimental error, equal to the measured flow rate of hydrogen atoms.