Acetylene dissociation propyne

The pyrolysis of pyrrole produces a variety of products hydrogen cyanide, propyne, allene, acetylene, c/ -crotonitrile, and allyl cyanide, among them. Lifshitz et al. hypothesized that pyrrole undergoes 1,2-bond (N—C) cleavage, then an internal H-atom transfer, to yield a radical intermediate that can isomerize to either c/ -crotonitrile or allyl cyanide, or dissociate to HCN and propyne.Bacskay et al. completed quantum chemical comparisons of the isoelectronic pyrrolyl and cyclopentadienyl radicals they hypothesized that pyrrolyl radical is formed via C—H bond scission in the intermediate pyrrolenine (2/f-pyrrole) rather than directly via N—H bond cleavage (Fig. 14). Mackie et al. explained a similar finding, postulating that it was the formation of pyrrolenine that dictated the rate at which pyrrole pyrolysis occurred. 

Reaction (44a) is analogous to the 02-reaction of the vinyl radical leading to HCO and HCHO as reported by Gutman and co-workers [118,119], Evidence for the occurrence of reaction (44b) was based on the observation of a-dicarbonyl products in the absence of NO. Schmidt et al. [120] have recently observed the regeneration of HO from the HO + C2H2 reaction by means of a laser fluorescence technique. The branching ratios for the two unimolecular dissociation channels typified by reactions (44a) and (44b) were estimated to be 0.4 0.1 and 0.7 + 0.3 (acetylene), 0.12 + 0.02 and 0.53 0.03 (propyne), and 0.12 + 0.87 0.07 (2-butyne), respectively. In any case, the formation of acidic products as well as the a-dicarbonyl products from these reactions is of potential importance in the atmosphere. 

No conclusion could be reached from the global quenching of the signal after adsorption of methanol, but propyne can discriminate oxide ions of low coordination. Indeed, PL results indicate that Che- and Che2 ions are involved in propyne dissociation. On the basis of PL and IR (semiquantitative evaluation of the number of molecules dissociated per square meter) characterizing dissociative adsorption of propyne and in line with theoretical results showing that acetylene does not dissociate on CLc 2 (Nicholas et al., 1998), it is inferred that Mg3C—O and Mg —03c ion pairs are involved in propyne dissociation (Chizallet et al., 2006). 

The proton transfer reaction between H3O+ and acetylene (C2H2) is substantially endothermic and therefore cannot occur [32,33]. However, propyne (C3H4), which has a proton affinity greater than H2O, undergoes fast non-dissociative proton reaction with H3O+. 

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