Acetylene ions, decomposition

Ab initio methods, 147-49 Acetate ion, decomposition, 135 Acetylene, interaction with palladium, tunneling spectroscopy, 435,437f Acid-dealuminated Y zeolites catalytical properties, 183 sorption, 175-78 Acid sites, on zeolites, 254 acidification effects, 266 Acoustic ringing, in NMR, elimination, 386 Active sites, nature, 104 Activity measurements, Co-Mo catalysts, 74 Adsorbed molecules,... 

From a study of metastable ion decompositions of [C2(H, D)sS] + ions, the average isotope effect, i, for acetylene loss was reported as 1.6 [137]. Isotope effects on metastable ion decompositions of (C3H7S)+ ions have proved difficult to study, because of hydrogen randomisation and facile isomerisation of ion structures. Nevertheless, the metastable ion abundances for H2S and HDS loss from [CH3(CD3)C = SH]+ have been shown to be in the ratio 2.2 1 [136]. 

From a study of metastable ion decompositions of [C2(H, D)5S] ions, the average isotope effect, i, for acetylene loss was reported as... 

With 2-methyl- and 2,4-dimethylthiazole, the methyl thiirenium ion (m/e 72) is obtained, which can easily lose a hydrogen radical to give the ml ell ion (confirmed by the metastable peak). This latter can rearrange by ring expansion to give the thietenyl cation whose structure was confirmed in certain spectra by the presence of a metastable peak corresponding to the decomposition of the m/e 71 ion to give the thioformyl cation m/e 45, probably by elimination of acetylene. 

Formation of cuprene is either by a free-radical chain reaction or by clustering around the parent ion (cluster size 20) followed by neutralization, which is not a chain process. The M /N value for decomposition of acetylene is about 20, giving the corresponding G value as 70-80, which is very large. The G value of benzene production is 5, whereas the G of conversion of monomers into the polymer is 60. 

We note finally that in view of the apparent fragmentation of parent species, it seems somewhat surprising that the low temperature ethylene desorption peak is not accompanied by a partial decline in the intensity of the C2H2 ion. In fact, the intensity of this ion appears to increase slightly in this region. We suggest that this is due to the formation of additional acetylenic complexes by decomposition of adsorbed ethylene upon heating. 

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The reaction may be taken a step further using a mixture of acetylene and carbon monoxide. The products are particularly sensitive to reactant concentration, solvent, and available moisture, and can be visualized as the growth of an organic chain, bonded to a nickel atom, by the successive insertion of CO or acetylene molecules, which is interrupted at various points by the uptake of a proton or hydroxyl ion or by decomposition of the intermediate. This may be followed by rearrangement, or further reaction with molecules of solvent. 

Among the 9 million tons of carbon black which are produced globally per year, only a small fraction of very specific, high-purity conductive carbon blacks can be used as conductive additive in lithium-ion batteries. A traditional conductive carbon is acetylene black, a special form of a thermal black produced by the thermal decomposition of hydrocarbon feedstock.74-75 The particularity of acetylene black to other thermal carbon black production is that the starting hydrocarbon, acetylene, exothermally decomposes above 800°C.75-77 Once the reaction is started, the acetylene decomposition autogenously provides the energy required for the cracking of acetylene to carbon followed by the synthesis of the carbon black ... 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

Vinylidenes have been transferred from a variety of precursors to olefins to produce methylenecyclopropanes . Because of ready intramolecular hydrogen shifts to give terminal acetylenes, the addition of vinylidene to olefins is rather limited to 2,2-disubstituted species. The methodologies so far developed include (1) gem-dibromides, 7, with MeLi, (2) vinyl halides " or vinyl triflates, 8 " with r-BuOK, (3) the fluoride ion promoted decomposition of vinylsilanes, 92 2,243 4 thermolysis of mercuric derivatives, 10, at 250 (5) decomposition of vinylazo compounds, 11, at 25 (6) the alkaline... 

Various forms of radiation have been used to produce ions in sufficient quantitites to yield neutral products for subsequent analysis. In principle, it should be possible to use intense beams of UV below ionization threshold for this purpose. To date, however, efforts to collect neutrals from resonant multiphoton ionization (REMPI) have not succeeded. In one experiment, 1 mbar of gaseous -propyl phenyl ether was irradiated at room temperature with a 0.1 W beam of 266 nm ultraviolet (from an 800 Hz laser that gives 8 n pulses) concurrent with a 0.5 W beam at 532 nm. The beams were intense enough not only to ionize the ether in the mass spectrometer, but also to excite it so that it expels propene. After several hours of irradiation < 10% of the starting material remained. Production of carbon monoxide and acetylene (decomposition products of the phenoxy group) could be detected by infrared absorption spectroscopy, but the yield of neutral propene (as measured by NMR spectroscopy) was infinitesimal. 

On the basis of previous discussion, the only additional source of ethylene in the radiolysis is the decomposition of excited neutral ethyl chloride molecules. If the ion-molecule contribution to this product is subtracted from the total yield reported in Table III, an ethylene-acetylene yield of G = 4.24 may be attributed to excited neutral decomposition. If we now assume that the photolysis experiments provide a direct measure of the neutral excited molecule decomposition to be expected in the radiolysis, this ethylene yield may be used as a basis for normalization to estimate the contributions from this source to the other products using the relative photolysis distributions from Table IV. In this way, the contributions from excited neutral decomposition reported in Table V were derived. 

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