Chemical propyne

Allene Radical Cations. The bimolecular reactivity of the radical reactions of allene and propyne has been a longstanding matter of interest. Myher and Harrison179 studied the ion/molecule reactions of ionized C3H4 with the respective neutral precursor in a medium-pressure chemical ionization source. CsH7+ ions were found to be amongst... 

With the aid of 13C NMR, 6Li NMR and XH HOESY (heteronuclear Overhauser effect spectroscopy) NMR of a-lithiomethoxyallene (106) and l-lithio-l-ethoxy-3-J-butylallene (107) as well as by ab initio model calculations on monomeric and dimeric a-lithiohy-droxyallene, Schleyer and coworkers64 proved that 106 and 107 are dimeric in THF (106 forms a tetramer in diethyl ether) with a nonclassical 1,3-bridged structure. The 13C NMR spectrum of allenyllithium in THF is also in agreement with the allenic-type structure the chemical shift of C2 (196.4 ppm) resembles that of neutral allene (212.6 ppm), rather than C2 of propyne (82.4 ppm). 

The kinetics and mechanism of pyrrole pyrolysis were investigated by ab initio quantum-chemical calculations. It was revealed that pyrrole undergoes tautomerization to form 2H- and 37/-pyrroles prior to any thermal decomposition. It has been shown that the major product, HCN, arises from a hydrogen migration in pyrrole to form a cyclic carbene with the NH bond intact. Ring scission of the carbene leads to an allenic imine of HCN and propyne which is the lowest energy pathway. The 277-pyrrole... 

FIGURE 11. Infrared absorption in the aUenic region for propyne (left) and for propyne + 4 -butylUthium in hexane, as a function of time and temperature after addition. Reprinted with permission from Reference 102. Copyright 1969 American Chemical Society... 

The pyrolysis of pyrrole produces a variety of products hydrogen cyanide, propyne, allene, acetylene, c/ -crotonitrile, and allyl cyanide, among them. Lifshitz et al. hypothesized that pyrrole undergoes 1,2-bond (N—C) cleavage, then an internal H-atom transfer, to yield a radical intermediate that can isomerize to either c/ -crotonitrile or allyl cyanide, or dissociate to HCN and propyne.Bacskay et al. completed quantum chemical comparisons of the isoelectronic pyrrolyl and cyclopentadienyl radicals they hypothesized that pyrrolyl radical is formed via C—H bond scission in the intermediate pyrrolenine (2/f-pyrrole) rather than directly via N—H bond cleavage (Fig. 14). Mackie et al. explained a similar finding, postulating that it was the formation of pyrrolenine that dictated the rate at which pyrrole pyrolysis occurred. 

Method A. To an alumina (Harshaw Chemical Co. 80 mesh alumina, slightly basic type used for chromatography is dried at 160°-170°C for 5 days before use) column (1.7 x 11 cm) is added a solution of 0.77 gm of l-(p-bi-phenyl)-3-phenyl-l-propyne in n-pentane. After 45 min the product is eluted with -pentane and concentrated at room temperature using a nitrogen atmosphere (with a water aspirator) to afford 0.53 gm (69%), m.p. 84.8°-86.4°C. 

Fig. 5. Infrared spectra of ethyne adsorbed on several metals (A) Rh/Si02 (B) Co/Si02 (C) Cu/SiOj (D) infrared spectrum of propyne (methylacetylene) adsorbed on Pt/Si02. [(A) from Ref. 91 (B) reprinted with permission from Ref. 96. Copyright 1974 American Chemical Society (C) from Ref. 68 (D) from Refs. 77 and 111 ...

The same process can be carried out to determine the oxidation levels of carbon atoms in several common functional types. It is clear that by using these procedures we can assign oxidation levels to carbon atoms in a wide variety of compounds. It is also clear that knowing the oxidation level is insufficient to assign the functional group present. For example, the alkane neopentane, the alkene isobutylene, the alkyne propyne, the alcohol isopropanol, and formaldehyde all have a carbon with an oxidation level of 0 yet all belong to completely different functional classes and have different physical and chemical characteristics. 

Work in groups to research the chemical formulas for and build models of the following molecules methane, propyne, pentene, butane, ethyne (acetylene). The chemical formulas are methane, CH4 propyne, C3H4 pentene, C5H10 butane, C4H10 ethyne, C2H2. 

M. Langsam, M. Anand and E.J. Karwacki, Substituted Propyne Polymers I. Chemical Surface Modification of Poly [ 1 -(trimethylsilyl)propyne] for Gas Separation Membranes, Gas Sep. Purif. 2, 162 (1988). 

The chemical properties and uses of propargyl alcohol has three potentially reactive sites (1) a primary hydroxyl group (i.e., CH2OH), (2) a triple bond (-C=C-), and (3) an acetylenic hydrogen (-C=CH) that makes the alcohol an extremely versatile chemical intermediate. The hydroxyl group can be esterified with acid chlorides, anhydrides, or carboxylic acids, and it reacts with aldehydes or vinyl ethers in the presence of an acid catalyst to form acetals. At low temperatures, oxidation with chromic acid gives propynal or propynoic acid ... 

Conversion of a terminal alkyne to its alkynylsilane prevents loss of the relatively acidic terminal hydrogen (pKa of ethyne c. 25) during later synthetic steps. For example, the terminal hydrogen of propyne was masked whilst its propargylic anion was used in a synthesis of Cecropia juvenile hormone, a chemical which plays ail important role in insect development (Figure Si5.2). 

The polymer of methyl methacrylate (MMA) is known as Perspex. It is a clear transparent glasslike material with high hardness, resistance to fracture, and chemical stability. The conventional route, as shown by reaction 4.10, involves the reaction between acetone and hydrocyanic acid, followed by sequential hydrolysis, dehydration, and esterification. This process generates large quantities of solid wastes. An alternative route based on a homogeneous palladium catalyst has recently been developed by Shell. In this process a palladium complex catalyzes the reaction between propyne (methyl acetylene), methanol, and carbon monoxide. This is shown by reaction 4.11. The desired product is formed with a regioselectivity that could be as high as 99.95%. 

The importance of 1,3-dipolar cycloadditions (1,3-DC) in the realm of heterocyclic synthesis is widely documented and recent results concerning the intramolecular version of this methodology, including reactions with nitrile oxides and nitrones for access to isoxazole derivatives, have been reviewed <07T12247>. A quantum chemical study of the Lewis acid effect on the cycloaddition of benzonitrile oxide to propyne has been reported evidencing a small influence on the outcome of the reaction <07T5251>. 

Alkynes are potentially useful as building blocks in the synthesis of numerous organic compounds, and the use of disubstituted alkynes permits the formation of ortho-disubstituted derivatives. However, the commercial development of alkyne chemistry has been hampered by the high cost of most acetylenes. Indeed, only acetylene and propyne can be regarded as low-cost chemicals. Perhaps recent progress in the synthesis of alkynes (206-209) will lead to further large-scale developments. 

Phenyl-2-propyn-l-ol was purchased from Lancaster Synthesis Ltd. and used as received. 1-Propanethiol was purchased from Aldrich Chemical Company, Inc., and used as received. 

Although propyne can be made available from naphtha crackers as chemical feedstock (in amounts varying between 0.2 and 1.0% on total intake of hydrocarbon feedstock), until recently there existed no prospect of a feasible propyne carbonylation process to provide a route to MMA via the reaction represented in eq. (2) - i.e., a reaction similar to eq. (1) ... 

MAPP gas from Dow Chemical Company, Midland, Mich. Gas chromatography showed 8.1% propene, 20.2% propane, 28.9% propyne, 29.7% allene, 1.3% cyclopropane, 2% isobutane, and 9.7 % of 1-butene and isobutene. 

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