Secondary reactions acetylene

Explosive reactions can occur between oxygen and a wide range of chemicals including organic compounds (such as acetone, acetylene, secondary alcohols, hydrocarbons), alkali and alkaline earth metals, ammonia, biological specimens previously anaesthetized with ether, hydrogen and foam rubber. 

These reactions yield acetylene and hydrogen. However, it is evident that these processes result in the following secondary reactions... 

Reduced isoindoles are formed when acetylenes are cooligomerized with N-phenyl- or N-methylmaleimide but the synthetic value of these processes is limited by competing secondary reactions of product cycloaddition (Scheme 51) and oxidation.87... 

Regarding the first problem, the most elemental treatment consists of focusing on a few points on the gas-phase potential energy hypersurface, namely, the reactants, transition state structures and products. As an example, we will mention the work [35,36] that was done on the Meyer-Schuster reaction, an acid catalyzed rearrangement of a-acetylenic secondary and tertiary alcohols to a.p-unsaturatcd carbonyl compounds, in which the solvent plays an active role. This reaction comprises four steps. In the first, a rapid protonation takes place at the hydroxyl group. The second, which is the rate limiting step, is an apparent 1, 3-shift of the protonated hydroxyl group from carbon Ci to carbon C3. The third step is presumably a rapid allenol deprotonation, followed by a keto-enol equilibrium that leads to the final product. 

The production of thiophen when acetylene interacts with sulphur vapour has already been mentioned (p. 258). That this product is not the result of a secondary reaction between acetylene and carbon disulphide follows from the fact that thiophen is only produced in quantity from these two reactants at a considerably higher temperature than that required when sulphur is used. Acetylene saturated -with carbon disulphide vapour and passed through an electrically heated tube containing broken porous pot, yields a condensate which at the optimum temperature of 700° C. contains about 10 per cent, by volume of thiophen and 10 per cent, of hydrocarbons.1... 

In spite of the above, there are some aspects that are not clear at present such as the influence of the preparation method on the SMSI state, and the effect of SMSI phenomena on secondary reactions such as coking. In a previous work we examined partial aspects of the catalytic performance of Ni0-Al203-Ti02 mixed oxides, prepared by the sol-gel route, in the hydrogenation of acetylene and phenylacetylene (13). 

As has been stated in the case of ethylene, the catalytic oxidation of unsaturated hydrocarbons is complicated by the fact that such substances are somewhat sensitive to the action of hydrolyzing agents. The presence, therefore, of even small amounts of water in the oxidizing gases makes it difficult to determine the exact mechanism of the process, i.e., whether the primary reaction consists of oxidation, hydration, or simultaneous oxidation and hydration. The same situation is met with again in the catalytic oxidation of acetylene and is further complicated by the fact that the primary products of hydrolysis and oxidation tend to undergo a variety of different secondary reactions. 

A variety of propargylamines can be prepared by three-component Mannich condensation of acetylenes, aldehydes, and secondary amines (Scheme 7.19) [66, 67). These reactions were performed using CuCl to activate the acetylene component. Reaction times varied from 3-36 h. Silver iodide has recently been used to catalyze the reaction [68]. 

Both turbulent burners and premix burners have been used for atomic fluorescence. The premix burner is usually round in shape (a modification of the Meker-type burner), since this provides better geometry for fluorescence than does a slot burner. For an optimum detection limit, the premix burner is also shielded that is, an inert gas such as argon or nitrogen is directed in a sheath around the flame. This elongates the interconal zone and lifts the secondary reaction zone above the burner, separating it from the lower part of the interconal zone where the excitation beam passes. The result is less background emission and less noise, particularly in hydrocarbon flames like air-acetylene or nitrous oxide-acetylene. The premix burner, especially when shielded, appears to offer increased sensitivity over the turbulent burner. 

Base lb also catalyzes the deacetylation of protected alcohols under mild conditions in quantitative yields [138]. The reaction with propargyl alcohol is very selective because the reactive acetylene functionality is not affected. In contrast, DIBAL-H is known to react with acetylenes. Secondary and tertiary alcohol acetates also were deacetylated in excellent yields and it is interesting that the latter alcohols do so without undergoing side reactions such as elimination. 

The dinitrogen oxide-acetylene flame can be used for those elements which cannot be determined successfully with an air-acetylene flame. The temperature of the N20-acetylene flame is only a little lower than that of the air-acetylene flame. In addition, the air-acetylene flame is safer because of its smaller burning velocity (Table 5). A slightly rich N2O-acetylene flame consists of about 2 to 4 mm high blue-white primary reaction zone, above that about 5 to 50 mm high red reduction zone, and on the top a blue-violet secondary reaction zone where the fuel gas oxidizes. The dissociation of the sample takes place in the red reduction zone. 

High temperature Plasma (1380°F-1650°F) 900-1100 (1650°F-2010°F) >1650 Secondary reactions additional hydrogen Acetylene carbon black... 

In favourable cases, the Lewis acid catalysed addition of mono-alkyl acetylenes to olefins also gave useful yields of cyclobutenes. The yields were highest with the most highly alkylated oleflnic reactants. Bicyclo[2,2,0]hexenes were formed in a secondary reaction. The use of dialkyl acetylenes in this reaction did not give any [2+ 2] addition products. 

Secondary reactions of ethylene, acetylene and propylene As ethylene accumulates. It will begin to disappear In tne dehydro-genatlon and methylatlon sequences reactions (6, 7 and 2, and 8,... 

As the yields of these initial products decrease with increased residence times, cyclic compounds such as cyclopentene, cyclopen tadiene, cyclohexene and benzene are produced. In the case of propylene (, 7 ), the reaction proceeds 2-4 times faster than that of ethylene and ethylene, methane, butadiene, butenes, acetylene, and methylcyclopentene are the main products during the initial step cyclopentadiene, cyclopentene, benzene, toluene and polycyclic compounds higher than or equal to naphthalene are products of secondary reactions. A remarkable fact for the thermal reaction of propylene is that the yields of five membered ring compounds are larger than those in the case of ethylene. 

The thermal decomposition of propylene involves a series of primary and secondary reactions leading to a complex mixture of products. Studies showed that the distribution of pyrolysis products varies considerably with the pyrolysis conditions and the type of reactor used. There is agreement among the studies on propylene pyrolysis that the three major products of pyrolysis are methane, ethylene, and hydrogen. However, there is disagreement on the types and amounts of minor or secondary product species. Ethane, butenes, acetylene, methylacetylene, allene, and heavier aromatic components are reported in different studies, Laidler and Wojciechowski (1960), Kallend, et al. (1967), Amano and Uchiyama (1963), Sakakibara (1964), Sims, et al. (1971), Kunugi, et al. (1970), Mellouttee, et al. (1969), conducted at different conversion and temperature levels. Carbon was also reported as a product in the early work of Hurd and Eilers (1943) and in the more recent work of Sims, et al. (1971). 

Yield curves of a few products of secondary reactions (e.g acetylene, higher aromatics) follow an S shape, well approximated with the tangent hyperbolic function, already mentioned In connection with the conversion curves ... 

The acrylic acid ester initially formed in the reaction of acetylene, carbon monoxide and water/alcohol mixtures reacts to give succinic add diester [205,226,388 -400] in a secondary reaction if cobalt catalysts are used. 

In developing a systematic scheme of polymer identification, pyrolysis conditions must be such that all polymers degrade rapidly. However, at temperatures above 1000 °C the pyrograms will also be less suitable for identification, since secondary reactions become predominant, leading to increasing amounts of simple molecules such as carbon dioxide, acetylene, ethylene or benzene which gives less characteristic patterns than those observed for monomers or primary degradation products. Pyrolysis temperatures between 500 and 800 C (optimum 610 °C) for 10 seconds are recommended. 

In the first method a secondary acetylenic bromide is warmed in THF with an equivalent amount of copper(I) cyanide. We found that a small amount of anhydrous lithium bromide is necessary to effect solubilization of the copper cyanide. Primary acetylenic bromides, RCECCH Br, under these conditions afford mainly the acetylenic nitriles, RCsCCHjCsN (see Chapter VIII). The aqueous procedure for the allenic nitriles is more attractive, in our opinion, because only a catalytic amount of copper cyanide is required the reaction of the acetylenic bromide with the KClV.CuCN complex is faster than the reaction with KCN. Excellent yields of allenic nitriles can be obtained if the potassium cyanide is added at a moderate rate during the reaction. Excess of KCN has to be avoided, as it causes resinifi-cation of the allenic nitrile. In the case of propargyl bromide 1,1-substitution may also occur, but the propargyl cyanide immediately isomerizes under the influence of the potassium cyanide. 

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