Reactions of Acetylene

Acetylenes have a special place in transition metal chemistry because of their high reactivity and the large variety of products which they afford. The field of palladium-catalyzed reactions of acetylenes has made considerable progress in the past 3 years, mainly due to the efforts of Maitlis and co-workers. Also much interesting work has been carried out on Pt(II) catalysis of acetylenes. This work has recently been reviewed 36). 

Probably the first well-characterized reaction of acetylenes is the reaction of diphenylacetylene with palladium(II) chloride to give a crystalline compound (i31). It was later shown to be a 7r-allyl complex which could be converted to a tetraphenyl cyclobutadienyl complex by acid  

In aptotic solvents, hexaphenyl benzene and the tetraphenyl cyclobutadiene palladium(II) chloride are obtained directly. The brilliant work of Maitlis and his co-workers has clarified the pathways for this reaction. 

One fact that this route must explain is the formation of structure (XVII) from cyclization of CDgC CCHg. This was explained by the 

The formation of the cwdo-ir-allyl structure (XIX), can be explained by trans attack of alcohol followed by a thermally allowed conrotatory cyclization step (X = OR) 183)  

Acetylenic Grignard reagents are formed when ethylmagnesium bromide reacts with acetylene or alkyl or aryl-acetylenes  

They then yield acetylenic ketones when treated with acid anhydrides  

3- Octyn-2-one 483 Ethyl chloride in twice its quantity of ether is converted into ethyl-magnesium chloride by reaction with the metal. The solution is then stirred in an atmosphere of nitrogen while the calculated amount of an alkylacetylene is introduced. The mixture is 

Ziegenbein, (a) Athinylierung und Alkinylierung, Verlag Chemie, Weinheim BergstraBe, 1963, (b) p. 9. 

Hexinylmagnesium chloride solution (0.25 mole), prepared as above, is cooled to — 30° and stirred vigorously while acetic anhydride (0.5 mole) in ether is added at a rate such that the temperature does not exceed —25° (2.5 h). The mixture is stirred for a further 2 h at —30°, then for 2 h at —5° (ice-salt bath), the product is decomposed by ice-water, and the ethereal layer is fractionated. This affords some 1-hexyne (8 g) and the product, 3-octyn-2-one (18 g, 98% calculated on hexyne consumed), b.p. 76-77°/15 mm. 

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They are colourless liquids with characteristic odours, and are prepared by the condensation of ketones with alkyl orthoformates in the presence of alcohols, or by the reaction of acetylenes with alcohols in presence of HgO and BF3. In some cases trichloroethanoic acid is used as the catalyst. They lose alcohol when heated and form vinyl ethers. Exchange of alcohol groups occurs when the ketals of the lower alcohols are boiled with alcohols of greater molecular weight. See acetals. 

Monosodium acetylide may also be prepared by the reaction of acetylene with sodium In liquid ammonia ... 

Acrylic Acid, Acrylates, and Acrylonitrile. Acryhc acid [79-10-7], and acrylates were once prepared by reaction of acetylene and... 

Butynediol. Butynediol, 2-butyne-l,4-diol, [110-65-6] was first synthesized in 1906 by reaction of acetylene bis(magnesium bromide) with paraformaldehyde (43). It is available commercially as a crystalline soHd or a 35% aqueous solution manufactured by ethynylation of formaldehyde. Physical properties are Hsted in Table 2. 

Vlayl fluoride [75-02-5] (VF) (fluoroethene) is a colorless gas at ambient conditions. It was first prepared by reaction of l,l-difluoro-2-bromoethane [359-07-9] with ziac (1). Most approaches to vinyl fluoride synthesis have employed reactions of acetylene [74-86-2] with hydrogen fluoride (HF) either directly (2—5) or utilizing catalysts (3,6—10). Other routes have iavolved ethylene [74-85-1] and HF (11), pyrolysis of 1,1-difluoroethane [624-72-6] (12,13) and fluorochloroethanes (14—18), reaction of 1,1-difluoroethane with acetylene (19,20), and halogen exchange of vinyl chloride [75-01-4] with HF (21—23). Physical properties of vinyl fluoride are given ia Table 1. 

Acetyhdes of the alkaU and alkaline-earth metals are formed by reaction of acetylene with the metal amide in anhydrous Hquid ammonia. 

Acetylene Grignard reagents, which are useful for further synthesis, are formed by the reaction of acetylene with an alkyhnagnesium bromide. 

CycIoa.ddltlons. Cyclobutene adducts are formed from the reaction of acetylenic derivatives and maleic anhydride through a 2 + 2 cycloaddition (48). The reaction is photochemicaHy cataly2ed (see Photochemical technology). 

Acetylene has a low solubiHty in Hquid oxygen. Excessive concentrations can lead to separation of soHd acetylene and produce accumulations that, once initiated, can decompose violently, detonating other oxidizable materials. Acetylene is monitored routinely when individual hydrocarbons are determined by gas chromatography, but one of the wet classical methods may be more convenient. These use the unique reaction of acetylene with Ilosvay s reagent (monovalent copper solution). The resulting brick-red copper acetyHde may be estimated colorimetricaHy or volumetricaHy with good sensitivity (30). 

Reactions of acetylene and iron carbonyls can yield benzene derivatives, quinones, cyclopentadienes, and a variety of heterocycHc compounds. The cyclization reaction is useful for preparing substituted benzenes. The reaction of / fZ-butylacetylene in the presence of Co2(CO)g as the catalyst yields l,2,4-tri-/ f2 butylbenzene (142). The reaction of Fe(CO) and diphenylacetylene yields no less than seven different species. A cyclobutadiene derivative [31811 -56-0] is the most important (143—145). 

Isoxazole-3-carbaldehyde has been obtained as a minor product from the reaction of acetylene with a mixture of nitric oxide and nitrogen dioxide (61JOC2976). Although 3-aryl-4-formylisoxazoles have been synthesized in good yields from the reaction of benzonitrile Af-oxides with 3-(dimethylamino)-2-propen-l-one (71S433), the parent member of the series, isoxazole-4-carbaldehyde, has never been reported. It may possibly be obtained by the addition of fulminic acid to 3-(dimethylamino)-2-propen-l-one. 

Vinyl acetate was originally prepared industrially by the reaction of acetylene with acetic acid or by oxidation of ethylene. 

One class of materials with some inherent PSA properties includes polyvinyl-ethers. Vinyl ether monomers are industrially derived from the reaction of acetylene with alcohols [117]. The most common alcohols used are methanol, ethanol or isobutanol. A generic structure of the vinyl ether is shown below ... 

Dj Ethynylation Reaction of acetylene with formaldehyde over a CaCf-supported catalyst. 

Reaction of acetylene with electropositive metals in liquid ammonia. 

The ease with which thiophenes are formed in the reaction of acetylenic epoxides " and of polyacetylenes with hydrogen sulfide is of great interest in connection with the biosynthesis of the naturally occurring thiophenes (cf. Section VIH,A) and also of preparative importance. 2-Methyl-l,2-oxido-5-hexene-3-yne (56) in water containing barium hydroxide reacts with HzS at 50°C to give 4-... 

III. Reactions of Acetylenic Acids and Esters with Individual Nitrogen ... 

The first representative of the acetylenic derivatives, 3(5)-ethynylpyrazole, was obtained by condensation of diacetylene with diazomethane by Kuhn and Henkel (41LA279) and later by other authors (69IZV2546), and by reaction of acetylene with diazopropyne (62AG252 68LA113) (Scheme 2). 

Another application of catalyst 8 is to the reaction of acetylenic aldehydes [10c] (Scheme 1.18, Table 1.6). Two acetylenic dienophiles have been reacted with cyclo-pentadiene or cyclohexadiene to give bicyclo[2.2.1]heptadiene or bicyclo[2.2.2]octa-diene derivatives in high optical purity. A theoretical study suggests that this reaction proceeds via an exo transition state. 

Yamamoto et al. have developed a catalytic enantioselective carbo-Diels-Alder reaction of acetylenic aldehydes 7 with dienes catalyzed by chiral boron complexes (Fig. 8.10) [23]. This carbo-Diels-Alder reaction proceeds with up to 95% ee and high yield of 8 using the BLA catalyst. The reaction was also investigated from a theoretical point of view using ab-initio calculations at a RHF/6-31G basis set. 

Fig. 8.10 The catalytic enantioselective carbo-Diels-Alder reaction of acetylenic aldehydes 7 with cyclopentadiene 2 catalyzed by chiral...

The most convenient method for the preparation of sodium acetylide appears to be by reaction of acetylene with sodium methylsulfinyl carbanion (dimsylsodium). The anion is readily generated by treatment of DMSO with sodium hydride, and the direct introduction of acetylene leads to the reagent. As above, the acetylide may then be employed in the ethynylation reaction. 

Butadiene could also be obtained by the reaction of acetylene and formaldehyde in the vapor phase over a copper acetylide catalyst. The produced 1,4-butynediol is hydrogenated to 1,4-butanediol. Dehydration of 1,4-butanediol yields butadiene. 

A three-step process developed hy Snamprogetti is based on the reaction of acetylene and acetone in liquid ammonia in the presence of an alkali metal hydroxide. The product, methylhutynol, is then hydrogenated to methylhutenol followed hy dehydration at 250-300°C over an acidic heterogeneous catalyst. 

Vinyl acetate was originally produced hy the reaction of acetylene and acetic acid in the presence of mercury(II) acetate. Currently, it is produced hy the catalytic oxidation of ethylene with oxygen, with acetic acid as a reactant and palladium as the catalyst ... 

The major oxidation reactions of acetylene black in an alkaline electrolyte (30 wt% KOH + 2 wt% LiOH) are strongly dependent on the potential (vs. Hg/HgO) and temperature [30] ... 

Germanium carbide, GeC, produced by the reaction of acetylene and germane.1 1... 

Beta SiC powder from the decomposition of methyl-trichlorosilane (MTS) in the presence of hydrogen in an argon plasma. Also from the gaseous thermal decomposition of tetramethylsilane, Si(CH3)4, in a flowthrough reactor between 850 and 1500°CP 1 and by the reaction of acetylene and silane. 

The dinuclear rhenium disulfido complex with n,rj -S2 ligands (ReCp )2(/U-S2)2 (Cp =7j -C5Me4Et) (type IIa2 complex in Fig. 2) undergoes an insertion reaction of acetylene and ethylene into the S-S bond according to Scheme 57. 

Scheme 12 Orbital phase environment in the EHels-Alder reactions of acetylenic aldehydes exo-selectivity...

Vinyl cations also have been invoked as intermediates in the addition of carbonium ions generated in strong acid to acetylene (50-53). Sasaki et al (50) observed 1-adamantyl methyl ketone, 25, as the sole product in the reaction of acetylene with 1-bromoadamantane in concentrated H2SO4 at 5°. Bott (51), on the other hand, reported a mixture consisting of 75% 1-adamantylacetaldehyde,... 

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