Alkynes ethyne

In contrast to diphenylacetylene, the activated alkyne, ethyne dicarboxylic methyl ester, coordinates to OsHCl(CO)(P Pr3)2 tram to the hydride. Then rearrangement to the cw-isomer takes place, followed by insertion to yield the... 

Have you ever seen a construction worker using an oxyacetylene torch (See Figure 14.6.) A brilliant white light comes from the torch as it cuts through steel. The intense heat that is associated with this flame comes from the combustion of ethyne, a very common alkyne. Ethyne is also known as acetylene. 

Dehydrogenation of alkanes such as ethane (1.38) relates them to alkenessuch as ethene (ethylene, 1.39). The same functional group may be obtained by dehydration of ethanol (1.40). Further dehydrogenation of ethene would generate an alkyne, ethyne (acetylene, 1.41). In terms of oxidation level, the alkene is related to the alcohol and the alkyne is related to the ketone. 

As was true for alkanes and alkenes vide supra), alkynes are attacked by oxygen. Indeed, one of the earliest uses of the parent or simplest alkyne, ethyne (acetylene, HC=CH), was to bum it in air for purposes of illumination. As an illuminant, when... 

In addition to lUPAC nomenclature, chemists use common names for many alkynes. Ethyne (H—C=C—H) is called acetylene, while larger alkynes have common names that identify the alkyl groups attached to the parent acetylene ... 

Alkynes Ethyne is the fuel used in oxyacetylene torches. Oxyacetylene torches can reach temperatures of over 3000°C. 

Alkynes are nonpolar and exhibit the same trends in boiling points and physical states as other hydrocarbons. The smallest alkyne, ethyne, is a gas. The combustion of ethyne when it is mixed with pure oxygen produces the intense heat of welding torches, as shown in Figure 2.11. As mentioned, the common name of ethyne is acetylene, so these welding torches are commonly called oxyacetylene torches. 

Outline a retrosynthetic pathway that leads from muscalure , the sex attractant pheromone of the conunon housefly back to the simplest alkyne, ethyne (acetylene). Then show the synthesis. You may use any inorganic compounds, or solvents, you need and alkyl halides of any length necessary. 

In an alkyne, a triple bond forms when two carbon atoms share three pairs of valence electrons. In the simplest alkyne, ethyne (C2H2), the two carbon atoms of the triple bond are each attached to one hydrogen atom, which gives a triple bond a linear geometry. Ethyne, commonly called acetylene, is used in welding where it reacts with oxygen to produce flames with temperatures above 3300 °C. 

In naming alkynes the usual lUPAC rules for hydrocarbons are followed and the suffix ane is replaced by yne Both acetylene and ethyne are acceptable lUPAC names for HC=CH The position of the triple bond along the chain is specified by number m a manner analogous to alkene nomenclature... 

Another analogous series of unsaturated hydrocarbons that contain just one multiple bond, but, instead of being a double bond, it is a triple bond is the alkynes. The names of all the compounds end in -yne. The only compound m this series that is at all common happens to be an extremely hazardous material. It is a highly unstable (to heat, shock, and pressure), highly flammable gas that is the first compound in the series. This two-carbon unsaturated hydrocarbon with a triple bond between its two carbon atoms is called ethyne, and indeed this is its proper name. It is, however, known by its common name, acetylene. 

A convenient route to three-carbon carboranes is the hydroboration of an alkyne with a preformed dicarbaborane. For example, reaction of ethyne (or propyne) with arachno-4,5-C2B7Hi3 (70) in hexane at 120°C gives a mixture of tri- and tetra-carbaboranes, e.g. (71), (72), (73), (74) in modest yield. Access to other... 

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 ... 

Now consider the alkynes, hydrocarbons with carbon-carbon triple bonds. The Lewis structure of the linear molecule ethyne (acetylene) is H—O C- H. To describe the bonding in a linear molecule, we need a hybridization scheme that produces two equivalent orbitals at 180° from each other this is sp hybridization. Each C atom has one electron in each of its two sp hybrid orbitals and one electron in each of its two perpendicular unhybridized 2p-orbitals (43). The electrons in the sp hybrid orbitals on the two carbon atoms pair and form a carbon—carbon tr-bond. The electrons in the remaining sp hybrid orbitals pair with hydrogen Ls-elec-trons to form two carbon—hydrogen o-bonds. The electrons in the two perpendicular sets of 2/z-orbitals pair with a side-by-side overlap, forming two ir-honds at 90° to each other. As in the N2 molecule, the electron density in the o-bonds forms a cylinder about the C—C bond axis. The resulting bonding pattern is shown in Fig. 3.23. 

The alkynes are hydrocarbons that have at least one carbon-carbon triple bond. The simplest is ethyne, FIO CH, which is commonly called acetylene (20). Alkynes are named like the alkenes but with the suffix -yne. 

The bidentate formate ligand of OsH(K2-02CH)(CO)(P,Pr3)2 is converted into a monodentate group by carbonylation. Thus, the reaction of this compound with carbon monoxide gives 0sH K1-0C(0)H (C0)2(P Pr3)2. Similarly, the addition of a stoichiometric amount of trimethylphosphite yields 0sH k -0C(0)H (C0) P(OMe)3 (P Pr3)2, and the addition of a stoichiometric amount of ethyne di-carboxylic methyl ester leads to 0sH K1-0C(0)H (C0)(r 2-Me02CC=CC02Me) (P Pr3)2, which in solution partially dissociates the alkyne. As is shown in... 

In the direct synthesis of aryl terminal alkynes via Pd-catalyzed cross-coupling of aryl halides with ethynylmetals, formation of diarylethynes is one of the potential side reactions. Indeed, the Kumada coupling of 2-iodo-5-methylthiophene (29) with ethynylmagnesium chloride gave the desired 2-ethynyl-5-methylthiophene (30) in only 35% yield, along with 24% of bis(5-methyl-2-thienyl)ethyne (31) [29], The high propensity for H-Mg exchange reaction to occur was blamed for the diarylethyne formation. 

DihydroindolesA novel synthesis of fused dihydroindoles involves [2 + 2 + 2]cycloaddition of alkynes with the 2,3-double bond of N-alkynoylated pyrroles. The reaction of 1 with bis(trimethylsilyl)ethyne results in two diaster-... 

The dissociative route has been explored in two independent DFT studies [25, 27] using ethyne as the alkyne model. The investigation by Gleichmann, Dotz, and Hess (GDH) [25] shows that the dissociation reaction... 

In an interesting catalysed conversion of trichloroethene by secondary amines into aminoacetamides, the initial steps are thought to involve the p-elimination of HC1 to produce dichloroethyne (Scheme 9.1), which reacts with the secondary amine under the wet conditions to produce the amide [35] the reaction does not work with N-alkylanilines. Such a mechanism is realistic, as it is well known [36] that trichloroethene is converted into the inflammable and explosive dichloroethyne by bases, and quaternary ammonium salts catalyse the formation of the alkyne when trichloroethene is reacted with oxiranes [37]. Chloroethynes have also been obtained by the catalysed reaction of terminal ethynes with carbon tetrachloride under basic conditions [38]. 

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