Octene, from octyne

Davis 69) found no considerable variation in the o-xylene versus ethylbenzene ratio as a function of hydrogen pressure. He also observed that the relative amount of o-xylene from n-octane increased (a) with decreasing Pt loading of the catalyst (70) b) with increasing tin addition 69, 7J) (c) with the poisoning of the catalyst with thiophene (77) and d) if octenes or octynes... 

The interaction of alkyne complexes with protic acids has been the most thoroughly studied of electrophilic reactions. When these reactions proceed to organic products, alkenes are formed, often stereospecifically. Schwartz and co-workers have studied the reactions of Cp2MH(alkyne) complexes of the early transition metals, Ta (Labinger et al, 1974) and Nb (Labinger and Schwartz, 1975). These complexes gave cis alkenes exclusively in nearly quantitative yield when treated with strong acids, as exemplified by the formation of cis-2-octene from the tantalum-octyne complex. Since the... 

The study of Tables I and II has revealed the fact that isomerization of a normal paraffin to an isoparaffin produces certain specific and characteristic changes in the physical constants as the methyl group is moved from point to point along the chain. In a paper presented before the Refining Division of the American Petroleum Institute in November 1942, attention was called by this author to alternation in the melting points of the n-octenes and n-octynes as the point of unsaturation is moved from position 1 to 2 to 3 to 4 (5). Now that the cis-trans pairs have been separated and more highly purified, the alternation remains characteristic of both forms, although the data on the cis forms are not fully verified. 

This catalyst (1) is a selective catalyst for hydrogenation of 4-octyne to cw-4-octene (90% yield). If the product is left in contact with 1, it isomerizes to the trans-isomer. Since monoalkenes are hydrogenated slowly with this catalyst, cyclo-octene can be obtained from either 1,3- or 1,5-cyclooctadiene. Of more interest, benzene can be hydrogenated to cyclohexane (83% yield). One drawback is that the catalyst loses about 90% of its activity after one cycle. 

The base-induced dehydrohalogenation of vinyl halides and allyl halides often gives low yields of allenes because of the competing reaction to alkynes alkynes can either be formed by direct elimination from vinyl halides or by isomerization of the allene first formed to the isomeric alkyne. Since it has been established that anti elimination of hydrogen halide from vinyl halides to yield alkynes is much faster than syn elimination, the proper choice of the starting material is often important for a successful allene synthesis. When ( )-4-bromo-4-octene was treated with NaOMe, the sole product was 3,4-octadiene, whereas the conesponding Z-educt yielded 4-octyne (Scheme 66). ... 

Halogenation of vinylboranes generates vinyl halides. Both cis and trans halides are available by modification of the reaction conditions. When trans-alkenyl boronic acid (73, derived from 1-octyne) was treated with iodine and sodium hydroxide, trans-1-iodo-l-octene (74) was formed in 90%. When the boronic acid was treated with iodine and then with base, the (Z)-alkenyl iodide (75) was produced.Vinylboranes derived from internal alkynes lead to cis-trans mixtures with both of these procedures. Boronic acids derived from alkynes and catecholborane give the (Z)-bromide on addition of bromine followed by sodium hydroxide. ... 

The sp -hybridi2ed C—H bonds in saturated hydrocarbons such as octane (Figure 2.10a) absorb infrared radiation in the 2850—3000 cnr region. The sp -hybridized C—H bonds in alkenes such as 1-octene absorb energy at 3080 cnr . This peak appears separately from the absorptions associated with the sp -hybridized C—H bonds in this molecule (Figure 2.10b). The isomeric cyclooctane would not have the 3080 cm" absorption. An sp-hybridized C—H bond in a molecule such as 1-octyne (Figure 2.10c) absorbs infrared radiation at 3320 cm". An isomeric bicyclic hydrocarbon with no multiple carbon-carbon bonds, and hence no sp - or sp-hybridized carbon atoms, would have absorptions only in the 2850-3000 cm" region. 

Terminal acetylenes can be alkylated to give chain-lengthened internal acetylenes in good yield, either by the rapid addition of trialkylalanes in the presence of nickel(ii) catalysts or by electrochemical addition of organoboranes. Hydroalumination may be used in a convenient conversion of terminal olefins into the corresponding acetylenes. An improved procedure for the synthesis of cyclo-octyne from cyclo-octene by a bromination-dehydrobromination sequence has been reported. ... 

What can we do if we want the tra s-alkene rather than the ds-isomer from alkyne reduction This can be accomplished using a dissolving metal reduction. When an alkali metal such as sodium is added to liquid ammonia, it is ionized to give solvated electrons (these are blue, but that s a story for the physical chemists...). One electron is added to the alkyne to give a radical anion (Figure 11.94). Because electrons repel each other, the orbitals containing the lone pair and the odd electron are on opposite sides of the triple bond. The lone pair is protonated by the solvent then a further electron and proton are added to complete the process. Thus, 4-octyne is cleanly reduced to fraKS-4-octene. 

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