Ethyne 1 - -, preparation

Ethyne can be used as a starting material for the preparation of many industrially important organic compounds. Currently, it is more cost-effective to prepare these compounds from petroleum. However, as petroleum supplies dwindle in the future, ethyne prepared from coal via calcium carbide will become more economically attractive as a source of these compounds. 

Prepared from ethyne and ammonia or by dehydration of ethanamide. Widely used for dissolving inorganic and organic compounds, especially when a non-aqueous polar solvent of high dielectric constant is required, e.g. for ionic reactions. 

HOCH2CH2CH2CH2OH. B.p. 228"C. Prepared ethyne plus methanal, hydrogenated to butanediol. Used in production of y-buty-rolactone and 2-pyrrolidone. Widely used in polyurethane products, butylenes See butenes. 

HOCH2C = CCH2OH. White solid, m.p. 58 C, b.p. 238- C prepared by the high pressure reaction between ethyne and methanol and also from BrMgCCMgBr and methanal. Used in electroplating (Ni), as a corrosion inhibitor, and in paint and varnish removal. 

COT is prepared by the polymerization of ethyne at moderate temperature and pressure in the presence of nickel salts. The molecule is non-planar and behaves as a typical cyclic olefin, having no aromatic properties. It may be catalytically hydrogenated to cyclo-octene, but with Zn and dil. sulphuric acid gives 1,3,6-cyclooclairiene. It reacts with maleic anhydride to give an adduct, m.p. 166 C, derived from the isomeric structure bicyclo-4,2,0-octa-2,4,7-triene(I) ... 

C. It occurs in natural gas. May prepared by reduction of ethene or ethyne by hydrogen under pressure in the presence of a nickel catalyst, or by the electrolysis of a solution of potassium elhanoate. It has the general properties of the paraffins. Used in low-temperature refrigeration plant. 

The three isomeric icosahedral carboranes (76-78) are unique both in their ease of preparation and their great stability in air, and consequently their chemistry has been the most fully studied. The 1,2-isomer in particular is available on the multikilogram scale. It is best prepared in bulk by the direct reaction of ethyne with decaborane in the presence of a Lewis base, preferably Et2S ... 

Pure CaC2 is a colourless solid, mp 2300°C. It can be prepared on the laboratory scale by passing ethyne into a solution of Ca in liquid NH3, followed by decomposition of the complex so formed, under reduced pressure at 325° ... 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

Dihydro-2f/-pyran-2-one has been prepared by reductive cycliza-tion of 5-hydroxy-2-pentynoic acid [2-Pentynoic acid, 5-hydroxy-], which is obtained in two steps from acetylene [Ethyne] and ethylene oxide [Oxirane] 3 and by the reaction of dihydropyran [277-Pyran, 3,4-dihydro-] with singlet oxygen [Oxygen, singlet].4,5 2ff-Pyran-2-one has been prepared by pyrolysis of heavy metal salts of coumalic acid [2//-Pyran-5-carboxylic acid, 2-oxo-],8 by pyrolysis of a-pyrone-6-carboxylic acid [211 - Pyran-6-carboxyl ic acid, 2-oxo-] over copper,7 and by pyrolysis of coumalic acid over copper (66-70% yield).8... 

Diphenylmethyl vinyl ether has also been prepared from benzhydrol and acetylene (ethyne) under high-pressure conditions.3 In the described method, which is an adaptation of the procedure ofWeinstock and Boekelheide,4 improved yields of the alkene are obtained by using more convenient experimental conditions. 

The same arsenal of preparative methods has been applied successfully for the corresponding dinuclear derivatives of ethyne HC CH and dialkynes HC C-X-C CH, where X can be virtually any spacer unit.50-52,54 55 57 61 62 71 76-83 As mentioned in the introduction to this chapter, ethyne is readily converted into polymeric explosive AuC=CAu and its complexes (L)AuC=CAu(L), of which the families with L = R3P84 and L = RNC are particularly large (Chapter 7). With the unit X in (L)AuC=CXC=CAu(L) being an alkylidene spacer, flexible complexes are obtained, while with alkenylidene, alkynylidene, or arylidene units,57 rigid molecules (L)AuC=CXC=GA11(L) are generated. Specific examples are presented below in the context with the structural patterns of extended systems. 

Tri-fi m-butylazadiboriridine, 187, was observed to react with ethyne in a manner sensitive to the ratio of the reactants. When the reactants were combined in a 1 1 ratio, the heterocyclopentene, 188, resulted. Under normal conditions, 188 did not react further with excess 187 at the G=C bond. On the other hand, [l,2,5]azabiborolo[3,4-f][l,2,5]azadiborole 76, the product of a double diborylation of ethyne, was prepared by reaction of 187 and ethyne in a 2 1 ratio in the presence of a catalytic amount of Bp3-OEt2 (Equation 18) <2001ZEA1815>. 

As reported previously, preparation and handling of highly purified [Go2(GO)8] required tiresome and careful operations because it ignites spontaneously upon contact with air. Some modified ways to use stable cobalt precursors appeared in the literature. Early attempts of Billington to use ethyne-[Go2(GO)6] and recent examples using 17 and 18 are representative examples in this category (Figure 2). ... 

Ethynes are industrially used as a starting material for polymers, e.g. vinyl flooring, plastic piping. Teflon and acrylics. Polymers are large molecules, which are prepared hy linking many small monomers. Polyvinyl chloride, also commonly known as PVC, is a polymer produced from the polymerization of vinyl chloride. 

The preparation of ethynylpurines was achieved through the use of protected acetylenes. Hocek and co-workers coupled halopurines with trimethysilylacetylene to introduced the masked ethyne function, which was efficiently released on treatment with fluorides or base (8.26.).35 The same compounds were also prepared by Hayashi and Kotschy, who used 2-methyl-3-butyn-2-ol as acetylene source and a strong base to remove the protecting group from the acetyl moiety.36... 

Grassian and Pimentel (210) prepared such surface groups by thermal decomposition of cis- and frans -dichloroethenes at temperatures >200 K or by their photolysis at 110 K on Pt(lll). An ethyne type B spectrum was obtained, as had also been obtained from the direct low-temperature adsorption of ethyne on this surface (Section II.B.l). 

Trichloroethene ( Tri-Clene , bp 87°) is a widely used dry-cleaning solvent. It can be prepared from either ethene or ethyne ... 

Suggest possible reactions by which the following compounds could be prepared from ethyne and any other necessary compounds ... 

Cyclooctatetraene can be prepared readily by polymerization of ethyne in the presence of nickel cyanide ... 

Under Friedel-Crafts-type conditions, many electrophilic displacements of the silyl moiety occur, so l-phenylsulfonyl-2-TMS-ethyne (49) can be prepared from 12 with benzenesulfonyl chloride in presence of catalytic amounts of aluminum chlo-... 

The principle of dick chemistrf presented by Hawker et al. (see Section 2.3.5) offers an efficient and versatile method of functionalisation. For example, it utilises [3+2]-cycloaddition of azide-functionalised reagents with ethyne end groups of a dendrimer precursor to prepare dendrimers with triazole-functionalised end groups. The mild reaction conditions, almost quantitative reaction, and not least the tolerance towards numerous functional groups permit the use of widely differing molecular frameworks (e.g. poly(benzyl ether), POPAM dendrimer structures or hyperbranched polyesters) and different functionalised azides... 

Ethyne, CH = CH commonly known as acetylenes in the first number of this series and is prepared in the laboratory by the action of water on calcium carbide (CaC2)... 

Binary compounds with less electronegative elements include hydrides, nitrides, sulphides and phosphides. They are decomposed by water and can provide convenient routes for the preparation of non-metal hydrides. The anions may be polyatomic or polymerised, as with CaC2, which contains C22- and reacts with water to give acetylene (ethyne) C2H2. 

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