In our recent paper [1] (CSP), we concluded that a radical-chain mechanism of acetylene pyrolysis must be appreciable and possibly dominant and argued that impurities, for example acetone, may contribute significantly to chain initiation. To support our conclusions, a model including acetone chemistry was developed but it did not invoke vinylidene reactions or other non-chain processes despite reasonable arguments [2] in support of such steps. Nevertheless, we also recognized, and stated in the paper that the vinylidene mechanism could not be disproven and may in fact play a role.
This analysis apparently prompted Duran, Amorebieta, and Colussi [3] (DAC1) to perform additive experiments. They pyrolyzed acetone/acetylene mixtures at ratios of about 0.2 to 2, selected a decomposition rate expression and determined associated rate constants. Colussi [4] extrapolated this rate expression down to concentration ratios of 0.001 and concluded that the impurity effect can be neglected since it can account for only 2 to 14% of the decomposed acetylene at 910K. In contrast to the suggestion of Colussi, we do not consider these results to be in conflict with our conclusions.
First of all, the uncertainty in extrapolating a rate expression derived from experiments with 0010-2180/91/S3.50