Acetylene 49. Also

Synthesis The CO2H group spells trouble. We would certainly have to use an ester, but the a-bromoester is too reactive to use with an acetylene. Also there is a danger that the double bond in A will move into conjugation. We can get round all these problems with an epoxide and then oxidise at the end ... 

Acetylene also plays an important role as intermediate in soot formation in flames, because the reverse of reaction (la) forms singlet methylene,... 

The reaction of C(3P) with acetylene also exhibits chemical branching, with competing exit channels ... 

Acetylene, C2H2, and ethylene, C2H4, are both used as fuels. They combine with oxygen gas to produce carbon dioxide and water in an exothermic reaction. Acetylene also reacts with hydrogen to produce ethylene, as shown. 

Figure 4 in Scheme 2.3-4 demonstrates that when using a triphenylphosphane-modified Ni-catalyst, butadiene reacts with 2-butyne to form a 2 1-adduct whereas with methyl 2-butynoate, a 1 2 co-oligomer is obtained. Butadiene and phenyl-acetylene also form 1 2 products As we may have shown, a change from X- to C- or Z-type substituents in the co-substrates alters the ratio from 2 1 to 1 2 in a synthon coupling reaction. 

Alkynes have also been shown to form the [2 + 2] cycloaddition product. Acetylene (H—C=C—H), the simplest alkyne, forms an interesting adsorption case, because the specific adsorption geometries of acetylene on Si(100)-2 x 1 have been debated [11,201,207,210,224-236]. Acetylene was first found experimentally to form a [2 + 2] C=C cycloaddition product that exhibits a cyclobutene-like surface structure on Si(100)-2 x 1 [210,227]. Later STM measurements revealed that at least two different surface products were present [228,231,233], and identified a product that is oriented perpendicularly to the dimer row. From these images, it was argued that in addition to an intradimer [2 + 2] C=C cycloaddition geometry, acetylene also forms a surface adduct that bridges two dimers along a row. Several theoretical... 

Label scrambling in propene occurs through the framework-bound alkoxyl intermediate 23, which is seen at 89 ppm in studies of propene-2-l3C on HZSM-5 (45). Analogous alkoxyl species have been reported on acidic zeolites from the reactions of certain alcohols and acetylene. In the latter case, structure 24 was proposed as the product obtained by heating acetylene on HZSM-5 (126). Evidence for this assignment included the formation of acetaldehyde as a hydrolysis product. Acetylene also reacts... 

The purity of the gas is tested by explosion analysis (J. C. S., 84, 555) the ratio, contraction on explosion to absorption by baryta water after explosion, should lie between 0-73 and 0-77 (theoretical 0,75). Great care must be taken that this preparation is carried out in the absence of flame, and that neither the apparatus nor the collected gas is exposed to direct sunlight, which decomposes acetylene. Also the cupric chloride solution employed for washing should be kept acid if it becomes alkaline the explosive copper aeetylide is precipitated. Should this occur the solution is mixed with much water and poured away. 

The vinyl ether of the oxime 55, 2-methyl-l-vinyloxy-3-butanone oxime (58) with excess acetylene also gives the pyrrole 57, however, none of the pyrrole 56 is formed in this case (Scheme 29). Upon distillation, pyrrole 57 polymerizes readily, which is one reason for its low yield. 

Acetylene also is manufactured by thermal or arc cracking of hydrocarbons and by a process utilizing the partial combustion of methane with oxygen. The acetylene produced from calcium carbide is basically pure, with only water and air as impurities. 

Related displacements with acetylenes9 and electrophilic olefins6 have been reported to give complexes formulated as [Pd [ P (C 6H 6) 3 2 (olefin or acetylene) ]. Also, oxidative additions of alkyl and aryl halides have been shown to occur giving palladium ) complexes, [Pd[P(C6H5)3 2(R)Cl].10... 

It has been shown that acetylene when submitted to a high frequency electric discharge yields some diacetylene 75. The action of ultra-violet radiation of wavelength 2,378-2,100 A on acetylene also produced diacetylene, and Cherton considered that the primary step must be the photodissociation of acetylene to C2H and H. At sufficient pressure the absorption spectrum of acetylene shows a continuous absorption in this region superimposed in the band structure. This gives an upper limit of 121 kcal to D(HC C-H). 

In the acetylene inhibition technique, acetylene is added to a water sample, which inhibits the reduction of N2O to N2 (Sorensen, 1978). The accumulation of N2O is then measured using gas chromatography and an electron capture detector and the denitrification rate is taken to be equal to the total N2O flux. One potential problem is incomplete inhibition of N2O reduction to N2, particularly in the presence of hydrogen sulfide, a compound commonly found under anaerobic conditions. Another potential problem with the technique is that acetylene also inhibits nitrification, a process that often supplies the NOs and N02 substrates for denitrification. To inhibit nitrification is to inhibit denitrification if it is at aU substrate limited (Hynes and Knowles, 1978). 

Acetylene also reacts with Fe3(CO),.> to yield a red complex melting at 140°C and an orange complex melting at 62°C, both of which have the com[)osition (C2H.2)3Fe.>(CO)6 (47, 599). The red complex has the structure (102) involving a Tr-cyclopentadicnyl bond (411), whereas the orange... 

With shorter wavelength radiation acetylene also produces carbon and molecular hydrogen (equation 5) in a different primary process. ... 

Zelikoff and Aschenbrand found that the gaseous products included benzene, diacetylene, hydrogen, ethylene and vinylacetylene. These authors photolysed C2H2 at pressures from 2 to 75 torr at 1849 A. The quantum yield of benzene formation increases markedly with pressure. Although the quantum yield for the disappearance of acetylene also increases with pressure it remains very much larger than the quantum yield of the sum of the products. The quantum yields of di-... 

While caoutchouc was first obtained by polymerizing isoprene it has been found that other hydrocarbons containing the buta i-ydi-ene group will likewise yield caoutchouc. Such hydrocarbons have been obtained from several sources, e.g., turpentiney petroleuniy coaly acetylene. Also compounds related to succinic acid, e.g., pyrotartaric acid (methyl succinic acid) are possible of transformation into isoprene. Levulinic acid, which is aceto propionic acid, CHa—CO—CH2—CH2—COOH, yields a cyclic sulphur compound, methyl-thiophen (p. 853), which, like methyl pyrrolidine, yields isoprene. Ethyl alcohol by conversion into acetone and then by aldol condensation with ethane yields 2-methyl buta 2-ene, CHa—C = CH—CHa which may be transformed... 

Substituted acetylenes also react under similar conditions to form the corresponding alkylhydroquinones. Of particular interest is that a mixture of methyl acetylene and dimethyl acetylene yields trimethylhydroquinone, which is an important precursor of vitamin E (eq (5)) [25]. 

The hydroboration of acetylenes also involves cis addition, leading to stereodefined vinylic organoboranes ... 

In accord with this model, groups larger than methyl generally provide lower asymmetric induction. In the case of acetylenic ketones, the acetylene also occupies the equatorial position. Thus, the reagent does not appear to discriminate by purely steric factors. In fact, it is proposed that there is an unfavorable h/tt interaction between the axial oxygen of the 1, l -bi-2-naphthalenol moiety and an unsaturated system if it is in the axial position. One exception to this generalization is in the reduction of 4-cyclopentene-l,3-dione in which the alkene portion presumably occupies the axial position. In this case there is said to be a favorable n/tr interaction. 

Acetylenes also react with alkylidene complexes to afford a new carbene derivative formed by inserting the triple bond into the alkylidene-metal bond . A metallacyclo-butene is the intermediate species ... 

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