Reactivities acetylene

Because of its high chemical reactivity, acetylene has found wide use in synthesis of vinyl chloride, vinyl acetate, acrylonitrile, vinyl ethers, vinyl acetylene, trichloro- and tetrachloro-ethylene etc., in oxyacetylene cutting and welding, and as a fuel for atomic absorption instruments. 

The original rnanufacturing route to vinyl chloride (VC) didn t involve ethylene dichloride (EDC) but was the reaction of acetylene with hydrochloric acid. This process was commercialized in the 1940s, but like most acetylene-based chemistry in the United States, it gave way to ethylene in the 1950s and 1960s. The highly reactive acetylene molecule was more sensitive, hazardous,... 

Repetition of the reaction with DEAD as the dipolarophile furnished the desired cycloadduct 55 in 48% yield, but with 25% yield of the enamide 56 also being isolated. This was rationalized by invoking decomposition of the ylide precursor 57 to the (trimethylsilylmethyl)silyl amine 58, which undergoes subsequent addition to the highly reactive acetylene (Scheme 3.14). 

Apparatus .for reactive acetylenes (RCsCOCH, RCH=CHCnCH, Aryl-CsCH, Hetero-aryl-OCH, RSCsCH, RSCH=CHC=CH) fig. 1. 500 ml for other acetylenes a reflux condenser instead of the thermometer in fig. 1. 

After addition of 2 g of Cu(OAc)2, the solution of R 2NCH2OH (half the amount of that prepared in exp. 1.1 is used) is brought 10 70 C, then the reactive acetylenic compound (0.55 mol) is added over - 20 min. while keeping the temperature between 70 and 80 C. Tie conversion is terminated by heating the mixture (brown suspension) for an additional half hour at 90"G after which it is cooled to room temperature. 

This multigeneration strategy for the synthesis of pyrimidines combines efficiently a novel cyclocondensation reaction using the highly reactive acetylenic ketones 153215,218 to build the pyrimidine skeleton, with a multicomponent reaction, and a multidirectional cleavage procedure. The Ugi four component reaction is especially useful in the context of building peptidomimetic-derived combinatorial libraries as it affords directly dipeptide analogues of type 159. 

As stated in the preceding section, the intermediacy of cycloheptyne has been proved unequivocally by trapping reactions and kinetic studies. However, the isolation of the parent cycloheptyne - could not be achieved, presumably owing to rapid addition reactions to the highly reactive acetylenic bond even in diluted solutions - - - ... 

Since thiol additions may be initiated readily by radicals this is always a complication to process (1). In the absence of controlled reaction conditions, the resulting regio and/or syn-anti selectivity as well as the reactivity could differ from what one expects from nucleophilic attack. For example, the usually reactive acetylene-dicarboxylic ester reacts more slowly with FjCcSH than does PhC=CR (R = H or... 

Oligomers and polymers with reactive acetylenic groups 84UK518. Polyheteroarylenes 84MI2 83UK812 81UK2250. 

In summary, it appears that Reissert salts undergo 1,3-dipoIar addition reactions with reactive acetylenic 1,3-dipolarophiles to give compounds of type 24 and undergo complex condensation-rearrangement reactions with olefinic dienophiles to give products of the type 25. 

Figure 7. Radiation treatment of HDPE with and without reactive acetylene monomer. (Reprinted from Ref. 7, copyright 1978, and Ref. 16, copyright 1977.)...

Incompatibilities and Reactivities Acetylene, ammonia, chlorine dioxide, azides, calcium (amalgam formation), sodium carbide, lithium, rubidium, copper ... 

Incompatibilities and Reactivities Acetylene, ammonia, hydrogen peroxide,... 

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. 

Other types of hydrocarbons are formed during the petroleum refining process. Important among these are olefins and acetylenes. Olefins are unsaturated hydrocarbons with at least one double bond in the molecular structure, which may be in either an open chain or ring configuration olefins are highly reactive. Acetylenes are also unsaturated and contain at least one triple bond in the molecule. 

In the Pauson-Khand reaction one acetylene, one olefin and cobaltcarbonyl (as a carbon monoxide source) are used and cyclopentenone is obtained by a [2 + 2 -t-1 ] cyclization addition [56-61]. As shown in Scheme 17.5, the Pauson-Khand reaction is, at first, two -electrons of the reactive acetylene bond to two cobalt atoms (Figure 17.6), then the olefin coordinates to one cobalt atom and then inserts into the cobalt-carbon bond. Further, one carbonyl inserts into the new cobalt-carbon bond, and cyclopentenone is obtained by elimination of Co2(CO)6 [56]. 

Principally the described ester synthesis can be achieved with the same metal carbonyl catalysts as used in the hydrocarboxylation. Recently the catalyst systems Pd/HCl, PdClg [446] and Pd/HI [447] have been reported to be very effective. These catalysts are suitable for converting the less reactive acetylene carboxylic acid esters. In analogy to cobalt catalysts, Pd causes a double hydrocarboxylation of the alkynes ... 

Diene syntheses. Dicyanoacetylene is a highly reactive acetylenic dienophile.— E Slightly more than 2 moles of furan and dicyanoacetylene added to tetrahydrofuran, and stored 3 days at room temp. 1,4,5,8-diepoxy - 4a,8a - dicyano -1,4,4a,5,8,8a - hexa-hydronaphthalene. Y 96%.— This ring system is formed with unusual ease. 

Startg. m. passed at 620°/0.01-0.05 mm through a quartz tube p-dimethyl-aminophenylacetylene. Y 85%. - Even reactive acetylenes with sensitive substituents can be prepared by this method. F. e. s. C. Wentrup and W. Reichen, Helv. 59, 2615 (1976). 

Bohlmann, F., and E. Bresinsky, Polyacetylenic Compounds. 120. Conversion of Reactive Acetylene Compounds with Sulfur Compounds. Chem. Ber. 100,107 (1967). 

An important use of transition metal complexation has been in the stabilization of reactive molecules including cyclobutadiene, trimethylene-methane, o-xylylene, carbenes, carbynes, and others. In many cases, release of the ligand by chemical means has proven possible, making the complexed precursors valuable as shelf-stable sources of the reactive species for structural study or synthetic deployment. There also has been considerable interest in analogous complexes of benzyne, other strained cycloalkynes, and highly reactive acetylenes. 

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