Methylacetylene-allene mixture

Chemical Designations - Synonyms Allene-methylacetylene mixture MAPP gas Methylacetylene-allene mixture Propadiene-methylacetylene mixture Chemical Formula. CH3C=CH+CH2=C=CHj Ohservahle Characteristics - Physical State (as shipped) Liquefied compressed gas Color. Colorless Odor Offensive, like acetylene. 

Alkylbenzenesulfonic Acid, Sodium Salt Allene-Methylacetylene Mixture... 

Methylacetylene also is used in welding torches. Methylacetylene does not decompose as easily as acetylene, and it burns better in air (as opposed to pure oxygen). Methylacetylene is well suited for household soldering and brazing that requires higher temperatures than propane torches can reach. The industrial synthesis of methylacetylene gives a mixture with its isomer, propadiene (allene). This mixture is sold commercially under the name MAPP gas (MethylAcetylene-T roPadiene). 

The US fire code covers installation and use of gaseous oxygen-fuel gas systems for welding and cutting, for the thermodynamically unstable fuels acetylene, MAPP (methylacetylene-allene-propene-propane mixtures), and the stable hydrocarbons propane or butane. 

Both methylacetylene and allene, in the ratio 1.6 1, were found by Terao and Shida130 in the gas phase photolysis of ketene-acetylene mixture. The product ratio was independent of pressure and wavelength of photolysis. Again, cyclopropene was not a product. ... 

Although many routes to allene are described in the literature, most preparations give a mixture of aUene and methylacetylene. 

Preparation. Most routes to allene give difficultly separable mixtures of allene and methylacetylene, but material free from methylacetylene can be prepared by dechlorination of 2,3-dichloropropene with zinc dust. ... 

The most convenient synthesis of 1,3-dimethylbicyclo[1.1.0]butane (4) employs the following two-step process.2 Hydrogen bromide is added to allene and/or methylacetylene to give a mixture of cis- and /rans-l,3-dibromo-l,3-dimethyl-cyclobutanes (3). This mixture is stirred with a suspension of 2% lithium amalgam in dioxane for 48 hours at room temperature (4) is obtained in 85% yield. 

Anhydride manufactured by acetic acid pyrolysis sometimes contains ketene polymers, eg, acetylacetone, diketene, dehydro acetic acid, and particulate carbon, or soot, is occasionally encountered. Polymers of allene, or its equilibrium mixture, methylacetylene—allene, are reactive and refractory impurities, which if exposed to air, slowly autoxidize to dangerous peroxidic compounds. 

Sodium triethylhydroborate reacts with propyne (methylacetylene) with hydrogen evolution even at room temperature.4 In place of pure propyne, a hydrocarbon mixture containing ca. 30% propyne and ca. 30% allene can also be used.4 Only the propyne reacts. 

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). 

For small-scale and consumer welding applications, many hardware stores sell cylinders of MAAP gas, which is a mixture of prop)me (methylacetylene) and 1,2-propadiene (allene), with other hydrocarbons. How would you prepare the methylacetylene/allene mixture from propene in the laboratory ... 

The reaction of ketoximes with simplest homolog of acetylene, methylacetylene, its isomer (allene), and their mixtures has been studied [284], The reaction proceeds in the systems MOH/DMSO (M=K, Cs) or KOBu-t/DMSO both at atmospheric and elevated pressure to furnish 5-methyl- and 4-methylpyrroles (Scheme 1.109). 

SCHEME 1.111 Vinylation of 2,4- and 2,5-dimethylpyrroles with methylacetylene-allene mixture in superbase media. 

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