The Butynes

Extending the alkyl substituent from methyl to ethyl makes little difference to the characteristics of the hydrogenation the only new feature introduced with 

1- butyne is the possibility of Z- and E-2-butenes being formed in addition to the expected 1-butene in fact this constitutes the sole or major product in most cases. On Pd/Al203, ° and Pd/BaS04 in ethanol solution, it is 98%, and with other palladium catalysts (including a number of rare-earth intermetallics ) the 

Once again the most informative technique for elaborating the mechanism is the use of deuterium as an isotopic tracer. On 0.03% Pd/Al203 the 1-butene was 72% 1-butene-1,2- 2 and no molecules contained more than three deuterium atoms thus only the terminal hydrogen could have exchanged. A small amount of 1-butyne-l-di was observed, and this may have been the precursor to l-butene-rfs. In another study, l-butene-rf2 was 70-80% of the product, the rest having been formed by a different route . The amounts of the 2-butenes formed 

The hydrogenation of 2-butyne presents an even simpler picture. On the base metals (Fe, Co, Ni, and palladium the total selectivity was 

The cleanliness of the reactions of propyne, butynes and higher alkynes on certain metals, especially palladium and copper, and of ethyne on silver and 

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The difference in activity of the E and Z olefins against HRV-14 was explained by examining the relatively low energy virus-bound conformations. The result of an overlay of WIN-54954 (based on x-ray crystallography data), minimize E- and Z-olefinic structures and the butyne analogue, suggested that the E isomer showed a reasonable fit while the Z isomer did not. Furthermore, when the Z isomer was inserted into the HRV-14 pocket, unfavorable interactions occurred. 

Of further significance is the fact that no 1,3-pentadiene is formed This behavior is similar to that of the butynes, where also no 1,3-butadiene was observed. Furthermore, this is in complete accordance with the proposed mechanism of the potassium 3-aminopropylamide-mediated isomerization of internal alkynes to terminal alkynes by repetitive alkyne-allene-alkyne isomerizations [24]. 

The physical properties of alkynes (Table 9-2) are similar to those of alkanes and alkenes of similar molecular weights. Alkynes are relatively nonpolar and nearly insoluble in water. They are quite soluble in most organic solvents, including acetone, ether, methylene chloride, chloroform, and alcohols. Many alkynes have characteristic, mildly offensive odors. Ethyne, propyne, and the butynes are gases at room temperature, just... 

In the presence of a suitable catalyst, hydrogen adds to an alkyne, reducing it to an alkane. For example, when either of the butyne isomers reacts with hydrogen and a platinum catalyst, the product is n-butane. Platinum, palladium, and nickel catalysts are commonly used in this reduction. 

The interaction of aUcynes with iridium hydride complexes can lead to a number of different alkyne complexes. Reaction between two equivalents of 2-butyne and [IrH4(PPhMe2)3] produces one equivalent of butene and the butyne complex [Ir(MeC=CMe)(PPhMe2)3]+ (35) with a structure that differs from the expected square planar. Reaction between the same iridium complex and dimethylacetylenedicarboxylate produces a bis-aUcyne complex (36). ... 

A mixture of red phosphorus (12.4 g, 0.40 mol), hexafluorobut-2-ync (2 32.0 g, 0.20 mol), and I2 (2.5 g. 0.01 mol) was heated at 200 C for 8h under autogenous pressure. The mixture was then heated for a short time at 00 C under open vacuum (10 Torr) to remove volatile oils. The solid residue was then shaken with Hg and sublimed at 100 C (10 Torr) to give a volatile solid yield 22.4 g. Recrystallization (HOAc) followed by another sublimation under the same conditions gave triene 8 yield 16.2g (43%. based on the butyne 2) mp 118-119 C (subl.). 

Treatment of a solution of 1 in toluene with the butyne derivative at -30°C affords the polycyclic silaheterocycle VII in high yield. For the above reaction we propose the following pathway (see Scheme 4) First a nucleophilic attack of 1 to one of the alkyne carbon atoms takes place under formation of the dipolar intermediate 9, which is stabilized by migration of a fluorine atom from a CFs group to the silicon atom. The resulting cumulene 10 is not stable under the reaction conditions and reacts instantly with one of the Cp ligands in a [2+2] cycloaddition to form the final product VII... 

The important intermediate ds-butene diol (10) can be made by hydrogenation of the corresponding acetylene (11). The butyne diol (11) is made commercially by a catalytic process using the strategy we have developed here. ... 

Persoonol dimethyl ether, the 3(Z)-alkene from Persoona elliptica has been synthesised (ref. 37) from 3,5-dimethoxybenzyl bromide by way of 4-(3,5-dimethoxyphenyl)but-1-yne which was alkylated with n-heptyl 4-toluenesulphonate followed by final reduction of the all ne product as shown in the scheme This method of preparation of the butyne was probably obligatory because of the inapplicability of the alkylation technique with 2-(3,5-dimethoxyphenyl)ethyl bromide due to its facile dehydrobromination. 

In summary, indirect "adsorption measurements" indicate some surprizing results. First a rather large effect of small changes in acid concentration is observed for the butyne-diol. It would be rather difficult to explain this in terms of adsorption theory because the adsorption isotherm in 4N hydrochloric acid crosses the one obtained in 6N hydrochloric acid. 

The butyne is much less reactive towards tetrakis(trifluoromethyl)diarsine however, a 1 1 adduct is slowly formed on ultraviolet irradiation (188). Tetramethyidiarsine and 3,3,3-trifluoropropyne afford different products... 

CC02Et>HCsCPh>MeCsCC02Me>PhCsCPh, In solid volatile [Cu(MeCsCMe) (CF3COCHCOCF3)] (19) the butyne ligand is parallel to the CF3COCHCOCF3 plane thermolysis of (19) provides Cu. 

The Diels-Alder adduct formed by treating furan with hexafluorobut-2-yne has been subjected to a retro-Diels-Alder reaction acetylene is eliminated and the reaction provides a route to 3,4-bis(trifluoromethyl)furan. The corresponding cycloadduct (154) formed from l,l-dimethyl-2,5-diphenyl-sllacyclopentadiene and the butyne was decomposed in an attempt to generate dimethylsilylene by a symmetry-allowed cheletropic fragmentation (Scheme 50) 836 evidence for silylene formation could be obtained unless the decomposition was effected photochemically or in refluxing cumene, under which conditions the addition of tolan enabled dimethylsilylene to be trapped... 

In contrast, tetraphenyldiazocyclopentadiene and l,2-diphenyl-3,4-benzo-diazocyclopentadiene react with the butyne under identical conditions to give only benzpyrazoles, e.g. (167). ... 

Free-radical initiation of the polymerization of pcrfluorobut-2-yne is difficult, and the solid polymer has previously been obtainable only by y-ray initiation or by a fluoride-initiated anionic pathway. - " A new technique now disclosed involves the use of trifluoromethyl hypofluorite, which at sub-ambient temperatures catalyses the conversion of the butyne to a polymer which is quite stable at 450 "C. Mass spectrometric analyses of the oligomers obtained by the anionic pathway, containing up to twelve butyne units, are consistent with an all-fra s conjugated polyolefin structure H—[CfCFs) C(CFa)]B—F. This result is wholly consistent with trapping experiments in which the incipient vinyl anions are intercepted by, for example, penta-fluoropyridine to give /ranj-olefins and /ranj,fra j-dienes. - ... 

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