Hydrocarbons ethynyl

CONDENSATIONS WITH SODAMIDE IN LIQUID AMMONIA Acetylenic compounds are conveniently prepared with the aid of Uquid ammcx as a solvent. The preparation of a simple acetylenic hydrocarbon ( -butylacetylene or 1-hexyne) and also of phenylacetylene is described. Experimental details are also given for two acetylenic carbinols, viz., 1-ethynyl-eyciohoxanul and 4-pentyn-l-ol. It will be noted that the scale is somewhat laige smaller quantities can readily be prepared by obvious modifications of the directions. 

Stabilized lithium acetyhde is not pyrophoric or shock-sensitive as are the transition-metal acetyhdes. Among its uses are ethynylation of halogenated hydrocarbons to give long-chain acetylenes (132) and ethynylation of ketosteroids and other ketones in the pharmaceutical field to yield the respective ethynyl alcohols (133) (see Acetylene-derived chemicals). 

A number of hydrocarbon radicals having multiple bonds at the radical centre have also been trapped in inert matrices and studied by IR spectroscopy. Thus, ethynyl radical was obtained by vacuum UV photolysis (9) of matrix-isolated acetylene (Shepherd and Graham, 1987) as well as when acetylene and argon atoms excited in a microwave discharge were codeposited at 12 K (Jacox and Olson, 1987). An appearance of diacetylene bands was observed when the matrices were warmed up, while the absorptions of the radical C2H disappeared. Detailed isotopic studies of D-and C-labelled ethynyl radicals showed a surprisingly low frequency of the C=C bond stretching vibration at 1846 cm instead of c.2100cm for a true C=C triple bond (the band at 2104 cm was attributed to the... 

Of course, the additional substituents need not be of the same type. Beginning with vinylallene (2) again and adding an ethynyl group, the four combinations 24— 27 arise (Scheme 5.2). Again, the last hydrocarbon is an interesting substrate for cyclization reactions (see Section 5.5). 

At higher temperatures, 29 (360-500 °C, R = H) undergoes a formal 1,3-ethynyl shift yielding the cross-conjugated enyne 2-ethynyl-l,3-butadiene (344). Deuteriumlabeling studies indicate that species such as 343 or hydrocarbons derived therefrom could be intermediates in the process [143],... 

A1 Planar polyaromatic hydrocarbons (PAHs) Benzo[ ] pyrene 1-Ethynyl pyrene TCDD, PAHs Many PAHs... 

R = vinyl or ethynyl) predominates (c/. Vol. 1, p. 36 Vol. 2, p. 35). Base treatment of a 2-alkoxypyridinium tosylate of nerol gives expected e.g. limonene 82%) cyclic hydrocarbons whereas the corresponding geraniol salt yields similar amounts of cyclic and acyclic hydrocarbons. SnCU-catalysed cyclization of the N-benzylimine derived from R-(+)-citronellal yields the expected menthylamines after catalytic hydrogenation. ... 

Acetylene is the simplest unsaturated hydrocarbons and as such an understanding of its photochemistry is important. The reactions of ethynyl radicals (C H) are important in combustion as well as in the photochemistry of Jupiter and Titan atmospheres, although, unfortunately, C2H radical has apparently only very weak and complex absorption spectra in the visible and ultraviolet region and no LIF has been found. 

Beginning with diethynylbenzene derivatives, it is obvious that the para-isomer 45 could lead to rod-like hydrocarbons, whereas the meta- (46) and the ortho-isomers (47), respectively, could provide angular and circular structures. Of course, an increase in the number of ethynyl groups results in an increased number of coupling possibilities. 1,3,5-Triethynylbenzene (48), for example, is of interest since it can be used for the construction of bicyclic hydrocarbons - it constitutes a blown-up version of a bridgehead. Clearly, hexa-ethynylbenzene (49) [32] can function as a tile for the preparation of novel forms of... 

Treatment of some a-ethynyl acetates with a mixture of nitrosyl fluoride and nitrosonium tetrafluoroborate affords bis[(acetoxyalkyl)carbonyl]furoxans the presence of the a-acetoxy group appears to be essential (81JOC312). Monosubstituted furoxans have been obtained by nitrosation of unsaturated hydrocarbons thus the reaction of nitrous acid with p -hydroxycin-namic acid affords 3-(p-hydroxyphenyl)furoxan, its structure being confirmed by X-ray crystallography (80LA1557). 

FIGURE 11.10 Products formed in the reactions of ethynyl and cyano radicals with unsaturated hydrocarbon molecules under single collision conditions. The reaction of ethynyl radicals with benzene is currently being studied in our laboratory. 

It should be stressed that in case of the ethynyl-acetylene reaction, a molecular hydrogen loss channel synthesizing the 1,3-butadienyl radical is open as well. Since the reactions of cyano and ethynyl radicals have no entrance barrier, are exoergic, and aU transition states involved are lower than the energy of the separated reactants, these reaction classes are extremely important to form nitriles and complex unsaturated hydrocarbons in low-temperature environments. On the other hand, the corresponding phenyl radical reactions are—due to the presence of an entrance barrier—closed in those environments. However, the elevated temperature in combustion systems helps to overcome these barriers, thus making phenyl radical reactions important pathways to form aromatic molecules in combustion flames. 

A mixture of reactive intermediates, including l,l-dimethyl-3,3-bis(trimethylsilyl)-Tsilaallene and dimethylsilylene, along with l,l-dimethyl-2,3-bis(trimethylsilyl)-l-silacyclopropene 86 were formed and detected from the direct irradiation of [(trimethylsilyl)ethynyl]pentamethyldisilane in hydrocarbon solution (Equation 21). These species were detected and identified using laser flash photolysis. They were trapped as their methanol adducts in steady-state irradiation experiments. Steady-state irradiation in the presence of methanol affords MeOH-addition products which are consistent with the formation of the silaallene, silacyclopropene, and silylene along with bis(trimethylsilyl) acetylene as the major product <1997JA466>. 

Fang J, Tanaka K, Kita H, and Okamoto K. Pervaporation properties of ethynyl-containing copolyimide membranes to aromatic/non-aromatic hydrocarbon mixtures. Polymer 1999 40 3051-3059. 

There is one known example in which a monodehydrobromination reaction leads to the formation of an alkynylcyclopropane. When 4-bromo-l,l-dimethylspiropentane (1) was treated with excess potassium tert-butoxide in dimethyl sulfoxide at 25 °C, a mixture of hydrocarbons was obtained from which 2-ethynyl-l,l-dimethylcyclopropane (4) was isolated in 30% yield. 

Petrov and Mironov267 have reviewed recent investigations of organo-silicon, -germanium, and -tin compounds, especially those containing unsaturated hydrocarbon groups such as vinyl and ethynyl, including their preparation and reactions. 

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