Über die Darstellung von freiem Methyl

Paneth, Fritz; Hofeditz, Wilhelm

doi:10.1002/cber.19290620537

Cited by 151 publications

(117 citation statements)

References 21 publications

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“…For example, Paneth and Hofeditz (16) found no positive evidence, so that if any radicals participate in the reaction, they may have unusual properties. On the other hand, Minkoff, Kewitt, and Rutledge have confirmed the findings of Burnham and Pease (4) and of Frank-Kamenetzky (7), who observed that nitric oxide can almost completely inhibit the polymerization, and that after the nitric oxide has been used up, the reaction proceeds a t the normal rate.…”

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confidence: 99%

Excited States of Acetylene and Their Role in Pyrolysis

Minkoff¹

1958

Can. J. Chem.

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Previous theories of acetylene pyrolysis are reviewed in the light of recent work by Minkoff, Newitt, and Rutledge. I t is shown that the relatively large rates observed a t the beginning of the induction period do not agree with mechanisms involving the intervention of comparatively stable dimers. The required kinetic form is obtained, however, if a triplet diradical is produced on the surface in a bimolecular process, followed by gas phase polymerization, with some chain ending on the surface. The detailed mechanism closely resembles Flory's scheme for liquid phase vinyl polymerization. The shape of the radical is discussed, and it is suggested that the trans-configuration leads to polymerization, while the cis facilitates dehydrogenation.There has recently been some interest in the reactions of atoms or molecules in excited states (12,14), and particularly of unsaturated molecules in triplet states. The purpose of this communication is to examine the role played by acetylene, and its polymers, in triplet states, during the pyrolysis of acetylene a t temperatures below 500" C., particularly in view of the failure of mechanisms based on ground state molecules and radicals (21). In fact, there has been considerable controversy not only over the proposed mechanisms, but also over the experimental results. As a consequence of some recent work a t temperatures below 525" C. (15), it has been possible to select those results which are most likely to be free of unexpected complications, and to propose a simple mechanism to account for most of the observations. REVIEW O F PREVIOUS WORKThe maill difficulties indicated in the literature are threefold; the first are coi~cerned -/ , -with the nature of the products, the second with the effect of surfaces, and the third is related to the effect of nitric oxide and the role of radicals. These will be considered in turn.Confusion has often arisen regarding the products, since it is frequently stated, for example, that benzene is the main product of pyrolyzing acetylene. The latter result is only obtained under special conditions; the main reaction a t low temperatures (i.e. below 500" C.) is polymerization to polycyclic and substituted aromatic coinpounds (see Ref.15 for detailed references). Above 7-800" C., this is almost entirely superseded b y decomposition to carbon and hydrogen (2). Products in the intervening region vary continuously from hydrogen and methane down to lower aromatics, including benzene, depending mainly on the temperature, but also on other factors. In particular iVIinkoff, Newitt, and Rutledge have show11 that even a t low temperatures, polymerization call be replaced by decomposition to carbon and hydrogen when halogen compounds or some metals are added to acetylene.The elucidation of the mechanism has also been hindered by the differing reports of the effect of packing the reaction vessel with glass or other supposedly inert materials. Schlapfer and Bruniler (19), and Frank-Kamenetsky (7), found the rate to be unaffected by increasing the su...

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confidence: 99%

Excited States of Acetylene and Their Role in Pyrolysis

Minkoff¹

1958

Can. J. Chem.

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“…Obviously, CH 3 ⋅ radicals are comparably stable [48] and formed in large quantities compared to all other radical species in the reaction network. Indeed, the numerical simulations of the meth [24] show that CH 3 ⋅ radicals downstream the gauze have a higher concentration than HO 2 and OH.…”

Section: Discussionmentioning

confidence: 99%

In-situ investigation of gas phase radical chemistry in the catalytic partial oxidation of methane on Pt

et al. 2009

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The catalytic partial oxidation of methane on platinum was studied in situ under atmospheric pressure and temperatures between 1000 and 1300 °C. By combining radical measurements using a molecular beam mass spectrometer and threshold ionization with GC, GC-MS and temperature profile measurements it was demonstrated that a homogeneous reaction pathway is opened at temperatures above 1100 °C, in parallel to heterogeneous reactions which start already at 600 °C. Before ignition of gas phase chemistry, only CO, H 2 , CO 2 and H 2 O are formed at the catalyst surface. Upon ignition of gas chemistry, CH 3 ⋅ radicals, C2 coupling products and traces of C3 and C4 hydrocarbons are observed. Because the formation of CH 3 ⋅ radicals correlates with the formation of C2 products it can be concluded that C2 products are formed by coupling of methyl radicals in the gas phase followed by dehydrogenation reactions. This formation pathway was predicted by numerical simulations and this work presents an experimental confirmation under high temperature atmospheric pressure conditions.

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“…The heat source was then moved upstream. A new lead deposit formed, growing progressively denser, while the old deposit became progressively thinner (17). The tetramethyl lead was breaking up into lead and a reactive species that could remove a cold lead deposit.…”

Section: Photodissociationmentioning

confidence: 99%

Some Pleasures in Chemical Physics

Bersohn

2003

Annu. Rev. Phys. Chem.

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Über die Darstellung von freiem Methyl

Cited by 151 publications

References 21 publications

Excited States of Acetylene and Their Role in Pyrolysis

Excited States of Acetylene and Their Role in Pyrolysis

In-situ investigation of gas phase radical chemistry in the catalytic partial oxidation of methane on Pt

Some Pleasures in Chemical Physics

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