Acetylenes activity

Nonempirical quantum-chemical calculations of acetylide molecules support the ready displacement of alkali metal cations to the bridge position (87IZV2777 88IZV1335, 88IZV1339). This naturally leads to the conclusion that the polarization and deformation of the ir-electronic shell of acetylene must depend on the atomic number of the cation attached to the acetylene anion. However, the acetylene activation in the reaction with ketoximes via acetylides suggests nucleophile attack at a carbanionlike complex, which is of course a week point of the hypothesis. Nevertheless, the electrophilic assistance from the alkali metal cation (Na+) to the... 

Scheme 5. Acetylene activation by Jt-complex formation between Cu and the triple bond, postulated by Bohlmann et al.[10f).

As already mentioned, there have been few mechanistic examinations of the copper-catalyzed Cadiot-Chodkiewicz heterocoupling reaction. Kinetic studies with the less reactive chloroalkynes [11a] have led to the assumption, shown in Scheme 7, that coupling between alkynes and haloalkynes proceeds through initial formation of copper(I) acetylides, probably formed by an acetylenic activation process similar to that described above for oxidative homocouplings. Subsequently, two reaction pathways may be reasonable ... 

Scheme 9 Acetylene activation via jr-complexation with copper(I) and proposed mechanism for the formation of diacetylene bond via cuprated alkyne dimers...

Finally a carbene compound with a U=C bond is Cp3U=CHPMe3.61 Various alkyl and hydrido Cp species can catalyze oligomerization of terminal acetylenes, activate C-H bonds, hydrogenate alkenes, and so on.62... 

Acetophenone, A/-methyloxazolidine derivative, lithiation, 56, 261 Acetyl hypofluorite fluorination of uracil by, 59, 3 fluorination using, 60, 7 reaction with pyridines, 58, 280, 289 Acetylacetone, hexafluoro-, reaction with ethylenediamine, 56, 3 Acetylene cyclic dimer, trimer. tetramer, dissociation energies, 56, 343 Acetylenes, activated reactions with 3-diazo-azoles, 59, 70... 

Figure 5.6. Synthesis of graft copolymers containing poly acetylene. Active catalysts for acetylene polymerization are generated on the polymer backbone, and the polyacetylene grows from the backbone.

Cycloaddition reactions of alkynes aided by transition metals were reviewed Various trimerization processes of acetylenic compounds have been reported. Titanium chloride catalyses the trimerization of acetylenic compounds, by way of intermediate complexes that can be isolated and characterized. This is shown in Table 2 for TiCU and 2-butyne. Acetylenes activated by ether groups in the propargyl position undergo trimerization catalysed by NiBri/Mg. Acetylenes without activation also undergo the same reaction, but with lower yields. Iron 7i-complexes can catalyse stepwise polymerization of alkynes ... 

Trimethylsilane reacts with 1 to give a mixture of the cis- and trans-hydrido trimethylsilyl complexes. This reaction is of particular interest because trimethylsilane represents the only case in which we can be certain that there is no form of precoordination before attack to give the hydrido species. In all other cases—arenes, acetylenes, activated methyl groups, and others—there is some conceivable mode of coordination prior to the attack on the C-H bond... 

Haloprogin is an iodinated acetylene active against dermatophytes (54). Haloprogin is only used for topical applications (Table 40.1). The mechanism of haloprogin is not clear, but it appears to lead to nonspecific metabolic disruption. It has been demonstrated to interfere Afith DNA biosynthesis and cell respiration. 

Scheme 2.20 Formation of tris-molybdenum dithiolene through acetylene activation and its degradation to a thiophene derivative.

In reactions with nucleophilic reagents diacetylene behaves as acetylene activated with acceptor group that is common to conjugated polyynes. Therefore, the nucleophilic addition of amines, alcohols, and thiols occurs to its terminal position and leads to the formation of the corresponding l-heteroalk-l-en-3-ynes readily involved in diverse cyclization reactions. 

The special value of the TIPS group lies in its easy removal (TBAF/25 °C/2 h) to make the acetylene available for further substitution. Furthermore, the present availability of the TIPS-protected acetylene triflone should make possible a further exploration of the addition and cycloaddition reactions of the acetylene activated by the strong electron-withdrawing power of the triflone group. 

Acetylenes activated by perfluoroalkyl and dialkyl phosphonate groups also show high reactivity as dienophiles (Scheme 4.6) [436]. 

Olefins are uncommon in crude oils due to the high chemical activity of these compounds which causes them to become saturated with hydrogen. Similarly, acetylene is virtually absent from crude oil, which tends to contain a large proportion of the saturated hydrocarbons, such as the alkanes. 

The Diels-Alder Reaction consists in the direct combination of a compound containing a conjugated diene system u ith a reagent which possesses a double or triple bond activated bj suitable adjacent groups. Examples of such reagents are maleic anhydride, p-benzoquinone, acraldehyde and acetylene dicarboxylic esters. Combination always occurs at the 1,4 positions of the diene system ... 

Compounds containing a double or triple bond, usually activated by additional unsaturation (carbonyl, cyano, nitro, phenyl, etc.) In the ap position, add to the I 4-positions of a conjugated (buta-1 3-diene) system with the formation of a ax-membered ring. The ethylenic or acetylenic compound is known as the dieTwphile and the second reactant as the diene the product is the adduct. The addition is generally termed the Diels-Alder reaction or the diene synthesis. The product in the case of an ethylenic dienophile is a cyctohexene and in that of an acetylenic dienophile is a cyctohexa-1 4-diene. The active unsaturated portion of the dienophile, or that of the diene, or those in both, may be involved in rings the adduct is then polycyclic. 

The high acidity of superacids makes them extremely effective pro-tonating agents and catalysts. They also can activate a wide variety of extremely weakly basic compounds (nucleophiles) that previously could not be considered reactive in any practical way. Superacids such as fluoroantimonic or magic acid are capable of protonating not only TT-donor systems (aromatics, olefins, and acetylenes) but also what are called (T-donors, such as saturated hydrocarbons, including methane (CH4), the simplest parent saturated hydrocarbon. 

Although we have been able to see on inspection which vibrational fundamentals of water and acetylene are infrared active, in general this is not the case. It is also not the case for vibrational overtone and combination tone transitions. To be able to obtain selection mles for all infrared vibrational transitions in any polyatomic molecule we must resort to symmetry arguments. 

The vibrations of acetylene provide an example of the so-called mutual exclusion mle. The mle states that, for a molecule with a centre of inversion, the fundamentals which are active in the Raman spectmm (g vibrations) are inactive in the infrared spectmm whereas those active in the infrared spectmm u vibrations) are inactive in the Raman spectmm that is, the two spectra are mutually exclusive. Flowever, there are some vibrations which are forbidden in both spectra, such as the torsional vibration of ethylene shown in Figure 6.23 in the >2 point group (Table A.32 in Appendix A) is the species of neither a translation nor a component of the polarizability. 

Addition of HCN to unsaturated compounds is often the easiest and most economical method of making organonitnles. An early synthesis of acrylonitrile involved the addition of HCN to acetylene. The addition of HCN to aldehydes and ketones is readily accompHshed with simple base catalysis, as is the addition of HCN to activated olefins (Michael addition). However, the addition of HCN to unactivated olefins and the regioselective addition to dienes is best accompHshed with a transition-metal catalyst, as illustrated by DuPont s adiponitrile process (6—9). 

The reactors were thick-waked stainless steel towers packed with a catalyst containing copper and bismuth oxides on a skiceous carrier. This was activated by formaldehyde and acetylene to give the copper acetyUde complex that functioned as the tme catalyst. Acetylene and an aqueous solution of formaldehyde were passed together through one or more reactors at about 90—100°C and an acetylene partial pressure of about 500—600 kPa (5—6 atm) with recycling as required. Yields of butynediol were over 90%, in addition to 4—5% propargyl alcohol. 

The concentration of is determined by measurement of the specific P-activity. Usually, the carbon from the sample is converted into a gas, eg, carbon dioxide, methane, or acetylene, and introduced into a gas-proportional counter. Alternatively, Hquid-scintiHation counting is used after a benzene synthesis. The limit of the technique, ca 50,000 yr, is determined largely by the signal to background ratio and counting statistics. 

The two synthetic steroidal estrogens which have attained the greatest degree of therapeutic use are ethinyl estradiol [57-63-6] (EE) (5) and its 3-methyl ether, mestranol [72-33-3]((5). In contrast to the naturally occurring estrone derivatives, these acetylenic analogues are orally active and are the main estrogenic components of combination oral contraceptives (see Contraceptives) and certain estrogen replacement products. 

Acetylene can be deterrnined volumetricaHy by absorption in Aiming sulfuric acid (or more conveniently in sulfuric acid activated with silver sulfate) or by reaction with silver nitrate in solution and titration of the nitric acid formed ... 

Simple olefins do not usually add well to ketenes except to ketoketenes and halogenated ketenes. Mild Lewis acids as well as bases often increase the rate of the cyclo addition. The cycloaddition of ketenes to acetylenes yields cyclobutenones. The cycloaddition of ketenes to aldehydes and ketones yields oxetanones. The reaction can also be base-cataly2ed if the reactant contains electron-poor carbonyl bonds. Optically active bases lead to chiral lactones (41—43). The dimerization of the ketene itself is the main competing reaction. This process precludes the parent compound ketene from many [2 + 2] cyclo additions. Intramolecular cycloaddition reactions of ketenes are known and have been reviewed (7). 

For fixed-bed reactors containing rapidly deactivating catalysts, the scheduled changes ia operating variables to accommodate activity loss can have a marked effect on mn length. This is exemplified by acetylene hydrochiorination to produce vinyl chloride ia tubular fixed-bed reactors. Steel reactors,... 

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