Radical processes in the pyrolysis of acetylene

Abstract

The literature on the pyrolysis of acetylene below 1000 K is reviewed and it is shown that the reaction is a radical chain polymerization initiated by H atoms. The induction period is examined and shown to arise from a rapid autocatalysis produced by the very first product, vinyl acetylene. Data from studies of acetylene polymerization induced by vinyl acetylene and styrene are examined and shown to be in good qualitative agreement with the radical chain process presented. Measured and where needed, estimated rate constants are given to produce numerical estimates of chain length, rates of polymerization, induction period, and rates of initiation. It is further shown that all the products of the polymerization are capable of efficiently initiating chains in the system. An examination of the possible kinetics of vinylidene shows that it does not play any role in acetylene chemistry.

Pyrolysis of methane in the presence of hydrogen

“…Their results showed that only additions of vinylic l-C4H; and 1-C4H; radicals to ethyne were fast enough to account for the highest observed rates of benzene formation. Benzene and phenyl were formed "directly" by chemically-activated channels, These reactants and elementary reactions have also been proposed by Benson [41], Hall et al [42] and…”

Cycloaromatization of Open and Masked 1,3-Hexadien-5-ynes − Mechanistic and Synthetic Aspects

“…Ϫ in acetylene pyrolyses, [61] and Ϫ in combustion processes, especially in fuel-rich flames and the corresponding hot waste gases. [15,54,62,63] Additionally, hexadienynes of this type have been synthesized and used as precursors for the thermal generation of 1,2,4-cyclohexatriene derivatives by the Hopf cyclization (see Section 4) and high-temperature syntheses of specially designed PAHs by FP and FVP techniques (see Sections 5Ϫ7).…”

IR laser-induced carbothermal reduction of silicon monoxide

“…The prevailing ethyne and butadiyne (identified through their respective diagnostic bands at 730 and 627 cm À1 ) formed on the irradiation in benzene are typical products of pyrolysis [33,34] and carbonization [32] of benzene and confirm that benzene is decomposed to transient C 2 and C 4 fragments. The prevailing butadiyne (and minor C 3 H 6 and C 4 H 4 products) formed on the irradiation in ethyne were previously observed in conventional pyrolysis [32,35,36] and carbonization [37] of ethyne. Carbon monoxide being observed in all experiments indicates a reaction of carbonaceous fragments with silicon monoxide, which should resemble the known carbothermal reduction of silica [38].…”