Alkynes Acetylenes

Terminal alkenes containing hydrogen linked to the triple bond undergo oxidative coupling to diacetylenes by cupric salts [5 S, 357] or by oxygen in the presence of cuprous salts [59, 66] (equation 139). Copper salts are solubilized by complexing with tertiary amines, most frequently pyridine [59, 357] and tetramethylethylenediamine [66]. The coupling can also be carried out with cuprous salts of acetylenes [5 S]. 

The oxidative coupling of long-chain terminal diacetylenes carried out in very dilute solutions gives macrocyclic diacetylenes and polyacetylenes 

Dialkylalkynes are oxidized to acyloins or their alkyl ethers by thallium trinitrate in aqueous or aqueous-alcoholic solutions, respectively 4I3. Only symmetrical alkynes give acceptable yields (70-90%) (equation 141). 

Alkylarylacetylenes undergo oxidative rearrangement to esters of al-kylarylacetic acid (equation 142) under similar conditions [413], 

Diarylacetylenes are converted in 55-90% yields into a-diketones by refluxing for 2-7 h with thallium trinitrate in glyme solutions containing perchloric acid [413. Other oxidants capable of achieving the same oxidation are ozone [84], selenium dioxide [509], zinc dichromate [660], molybdenum peroxo complex with HMPA [534], potassium permanganate in buffered solutions [848, 856, 864,1117], zinc permanganate [898], osmium tetroxide with potassium chlorate [717], ruthenium tetroxide and sodium hypochlorite or periodate [938], dimethyl sulfoxide and iV-bromosuccin-imide [997], and iodosobenzene in the presence of a ruthenium catalyst [787] (equation 143). 

Alkyncs can be prepared through the use of two basic procedures. Before these procedures are presented, it should be noted (hat the smallest ring in which an acetylene linkage is stable at room temperature for an extended period of time is cyclooctyne. 

The halogens may be vicinal (on adjacent carbon atoms) or geminal (on the same carbon atom). If there is a choice of more than one product being formed, the more highly substituted alkyne will be formed in greater abundance. 

Reaction of sodium acctylidcs with primary alkyl halides. (Excellent method for the addition of carbon atoms to molecules). 

Note For this reaction to proceed, there must be a H on an acetylenic carbon. 

Using any monosubstituted cyclic molecule, any monosubsti-tuted acyclic organic molecule containing no more than four carbons and any inorganic reagent, prepare the following  

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Hydrocarbons, compounds of carbon and hydrogen, are stmcturally classified as aromatic and aliphatic the latter includes alkanes (paraffins), alkenes (olefins), alkynes (acetylenes), and cycloparaffins. An example of a low molecular weight paraffin is methane [74-82-8], of an olefin, ethylene [74-85-1], of a cycloparaffin, cyclopentane [287-92-3], and of an aromatic, benzene [71-43-2]. Cmde petroleum oils [8002-05-9], which span a range of molecular weights of these compounds, excluding the very reactive olefins, have been classified according to their content as paraffinic, cycloparaffinic (naphthenic), or aromatic. The hydrocarbon class of terpenes is not discussed here. Terpenes, such as turpentine [8006-64-2] are found widely distributed in plants, and consist of repeating isoprene [78-79-5] units (see Isoprene Terpenoids). 

Reactions of alkynes with electrophiles are generally similar to those of alkenes. Because the HOMO of alkynes (acetylenes) is also of n type, it is not surprising that there IS a good deal of similarity between alkenes and alkynes in their reactivity toward electrophilic reagents. The fundamental questions about additions to alkynes include the following. How reactive are alkynes in comparison with alkenes What is the stereochemistry of additions to alkynes And what is the regiochemistry of additions to alkynes The important role of halonium ions and mercurinium ions in addition reactions of alkenes raises the question of whether similar species can be involved with alkynes, where the ring would have to include a double bond ... 

Initially alkynes were polymerised by trial and error with the use of Ziegler type recipes and the mechanism for these reactions may well be an insertion type mechanism. Undefined metathesis catalysts of ETM complexes were known to give poly-acetylene in their reaction with alkynes (acetylene) [45] and metallacycles were proposed as intermediates. Since the introduction of well-defined catalysts far better results have been obtained. The mechanism for this reaction is shown in Figure 16.24 [46], The conductive polymers obtained are soluble materials that can be treated and deposited as solutions on a surface. 

Alkanes n-butene, isopentane, isooctane Cydoalkanes t dohezane, methylcyclopentane Olefins (sometimes called alkenes ) ethylene, propylene, butene Cydoolefins ( clohezene Alkynes acetylene Aromatics toluene, i ene CHLORINATED HYDROCARBONS ALDEHYDES, RCHO formaldehyde, acetaldehyde KETONES, RCX R " acetone, methylethylketone NITRIC OXIDE, NO ... 

N-Substituted amides derived from 2-chloro- or4-chloronicotinic acid react with CH-acidic nitriles in the presence of base to yield amino derivatives of [l,6]naphthytid-5(6//)-ones and [2,7]naphthyrid-l(2//)-ones <1997JHC397>. 3-(l-Alkylamino)pyridines react with electron-deficient alkynes (acetylene dicatboxylates) in the presence of acid to give l,2-dihydro[2,7]naphthyridine-3,4-dicarboxylates in up to 72% yield compounds unsubstituted at C-1 were readily oxidized with potassium permanganate to naphthyridine-l-ones <2005TL3953>. 

The two stretching vibrations in alkynes (acetylenes) involve C=C and C—H stretching. Absorption due to C—H bending is characteristic of acetylene and monosubstituted alkynes. The spectrum of Figure 3.12 is that of a typical terminal alkyne. 

Alkyne ( Acetylene Series). A group of unsaturated aliphatic hydrocarbons of the general formula C, contg triple bonds. 

The literature of the vibrational spectra of adsorbed alkynes (acetylene and alkyl-substituted acetylenes) is very much in favor of single-crystal studies, with fewer reported investigations of adsorption on oxide-supported metal catalysts. Fewer studies still have been made of the particulate metals under the more advantageous experimental conditions for spectral interpretation, namely, at low temperatures and on alumina as the support. (The latter has a wide transmittance range down to ca. 1100 cm-1.) A similar number of different single-crystal metal surfaces have been studied for ethyne as for ethene adsorption. We shall review in more detail the low-temperature work which usually leads to HCCH nondissociatively adsorbed surface structures. Only salient features will be discussed for higher temperature ethyne adsorption that often leads to dissociative chemisorption. Many of the latter species are those already identified in Part I from the decomposition of adsorbed ethene. 

High temperature, pressure, and catalyst are required to achieve addition of ammonia to alkynes. Acetylene and ammonia yield a complex mixture of heterocyclic nitrogen bases.311,312 Ethylideneimines, thought to form through the intermediate enamines, are the products of the reaction of acetylene with primary alkylamines in the presence of catalysts.313... 

Acetylene is by far the most important commercial alkyne. Acetylene is an important industrial feedstock, but its largest use is as the fuel for the oxyacetylene welding torch. Acetylene is a colorless, foul-smelling gas that burns in air with a yellow, sooty flame. When the flame is supplied with pure oxygen, however, the color turns to light blue, and the flame temperature increases dramatically. A comparison of the heat of combustion for acetylene with those of ethene and ethane shows why this gas makes an excellent fuel for a high-temperature flame. 

Alkynes (acetylenes, RCsCR) may be prepared by the elimination of a hydrogen halide from alkenyl halides under vigorous conditions. This is exemplified by the preparation of phenylacetylene from cinnamic acid via the dibromide and (o-bromostyrene (Scheme 3.26). The contrast between the conditions required for the bromodecarboxylation and for the second elimination to form the alkyne reveals the difference in reactivity between an alkyl and an alkenyl halide. Alternative modes of elimination, such as allene formation or rearrangement reactions, restrict the use of this procedure. 

When the results are examined, many of the individual species are present at relatively low concentrations. It thus makes sense to group some compounds together by molecular type, for example, adding all the dienes together and adding all the alkynes (acetylenes) together. 

Saturated (alkanes, paraflSns, CnHjn + j) (2) Unsaturated (a) Alkenes (olefins, CnHjn) (b) Alkynes (acetylenes, CnHjn-a). As their molecular formulas indicate, the unsaturated differ from the saturated by containing less hydrogen. 

The alkylation of j p-carbon can, in principle, involve the alkyne (acetylene) either as the nucleophile or the electrophile. In practice by far the most important process involves the alkyne as nucleophile since the acidity of the alkyne proton (pK = 25) allows the ready formation of alkynide ions. These are excellent nucleophiles and they readily undergo acylation and alkylation with appropriate electrophiles. The recent introduction of palladium-catalyzed reactions, usually involving copper(I) salts but also other cations, has greatly increased the use made of arylation and vinylation reactions. In this chapter only the alkylation of the alkynide ion will be discussed acylation, vinylation and arylation reactions are discussed elsewhere. The alkylation of alkynide anions is a reaction of considerable synthetic use and has been extensively reviewed. ... 

This is a general reaction for alkynes (acetylene, phenylacetylene, diphenylacetylene, cyclodecyne, etc.) that occurs at RT, producing 75% yields of products. The two cobalt atoms and two carbons form a tetrahedron. Analogous iron complexes are prepared in low yield by reaction of diphenylacetylene with Fe3(CO)i2 . Similar molybdenum complexes are prepared by addition of alkynes to molybdenum multiple bonds ... 

Simple alkenes are named by following the name of the corresponding alkyl group with ene, as in ethylene and propylene. Alkynes can be named as derivatives of the simplest alkyne, acetylene. Vinyl is the prefix designation for a two carbon alkene and allyl for a three carbon alkene. 

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