1,3-Butadiene with butyne

The basic catalyst in the isomerization of 1,2-butadienes to butynes acts by removing an alkenic proton from the hydrocarbon. Two different anions can be formed, each of which is stabilized by electron delocalization involving the adjacent multiple bond. Either anion can react with the solvent by proton transfer to form the starting material or an alkyne. At equilibrium the most... 

Butadiene and butyne, in a 2-to-l ratio, react with both the naked-nickel and nickel-ligand catalyst to form 4,5-dimethyl-cb,m,tram-1,4,7-cyclodecatriene (DMCDeT) (94). The yield with naked-nickel, however, never exceeds 25% and will not be discussed further. 

Fig. 3. Volume contraction in the co-oligomerization of butadiene with 2-butyne (nickel-ligand catalyst) (94) I = P(C6H5)3, II = P(OC6H5)3.

In this series, the HC oxidation and CO oxidation become more and more difficult with increasing unsaturation degree of the HC. The inhibiting effect of butyne is far more important than that of 1,3-butadiene. With butadiene, CO conversion starts at about 150°C, and reaches 50 % at 278°C, whereas with butyne it only starts very slowly at 250°C, and increases abruptly above 310°C. 

In the presence of butane, the NO reduction profile can be decomposed into two curves corresponding to the oxidation respectively of CO and of butane. With butene, butadiene and butyne it is not possible to separate the contribution of CO and HC in the reduction of NO. 

The overall effect of this scheme would then result in a rapid forward proton transfer to 2-butyne to form 2 and an approximately equal reverse rate to give butadiene, rather than 2-butyne, for a pseudoequilibrium constant close to unity, as observed. The fact that the proposed reaction scheme mimics equilibijum behavior so closely for both 2-butyne and 1,2-butadi e is a result of a completely fortuitous coincidence of the proton affinity of 1,3-butadiene and the apparent proton affinity limit for protonation of 2-butyne and 1,2-butadiene with rearrangement to the allylic cation. Remarkably, 1-butyne, 1,1-dimethylallene, 3-methyl-1-butyne, and 2-pentyne all show a very similar pattern of behavior in proton-transfer experiments, with apparent heats of formation 25-50 kJ mol" too low for the vinyl cation products shown in Table 2 and 59-71 kJ mol" too high for the corresponding allylic ion products. Thus, the PA of 1-butyne is near to that of butadiene and the ultimate reaction product is apparently 1-methylallyl cation 2, as with 2-butyne and by the same sort of reversible proton exchanges within the ion-neutral reaction complexes. 

A [4+2] cycloaddition of butadiene with 2-butyne or diphenylacetylene catalyzed by either (dicyclooctatetraene)iron(O) [Fe(cot)2], a combination of iron(III) chloride and isopropylmagnesium chloride, or tris(acetylacetonato)iron and triethylaluminum provides... 

The labile hydroxyl group is easily replaced by treatment with thionyl chloride, phosphorous chlorides, or even aqueous hydrogen haUdes. At low temperatures aqueous hydrochloric (186) or hydrobromic (187) acids give good yields of 3-halo-3-methyl-l-butynes. At higher temperatures these rearrange, first to l-halo-3-methyl-1,2-butadienes, then to the corresponding 1,3-butadienes (188,189). 

This review covers the personal view of the authors deduced from the literature starting in the middle of the Nineties with special emphasis on the very last years former examples of structure-sensitive reactions up to this date comprise, for example, the Pd-catalyzed hydrogenation of butyne, butadiene, isoprene [11], aromatic nitro compounds [12], and of acetylene to ethylene [13], In contrast, benzene hydrogenation over Pt catalysts is considered to be structure insensitive [14] the same holds true for acetonitrile hydrogenation over Fe/MgO [15], CO hydrogenation over Pd [16], and benzene hydrogenation over Ni [17]. For earlier reviews on this field we refer to Coq [18], Che and Bennett [9], Bond [7], as well as Ponec and Bond [20]. 

Indium can effectively mediate the coupling of l,4-dibromo-2-butyne with aldehydes in a 1 1 ratio to give l,3-butadien-2-yl-methanols in aqueous media (Eq. 8.83).211 When a 1 2 ratio was used, the reaction... 

These reactions are found to be promoted by electron-donating substituents in the diene, and by electron-withdrawing substituents in the alkene, the dienophile. Reactions are normally poor with simple, unsubstituted alkenes thus butadiene (63) reacts with ethene only at 200° under pressure, and even then to the extent of but 18 %, compared with 100% yield with maleic anhydride (79) in benzene at 15°. Other common dienophiles include cyclohexadiene-l,4-dione (p-benzoquinone, 83), propenal (acrolein, 84), tetracyanoethene (85), benzyne (86, cf. p. 175), and also suitably substituted alkynes, e.g. diethyl butyne-l,4-dioate ( acetylenedicarboxylic ester , 87) ... 

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 reaction between deuterium and 1-butyne, 2-butyne, 1,2-butadiene, and 1,3-butadiene, respectively, was conducted in a flow system at near ambient temperatures. The catalyst (0.03 wt % palladium on alumina) was prepared by impregnating hard alumina pellets with palladium chloride so that the metal was probably confined to an outer shell of each particle. 

Ketones containing triple bonds in the a,)3-positions are reduced to the corresponding unsaturated alcohols with sodium cyanoborohydride or tetra-butylammonium cyanoborohydride in 64-89% yields [780]. Thus 4-phenyl-3-butyn-2-one gave 4-phenyl-3-butyn-2-ol [780]. If the same ketone was converted to its p-toluenesulfonylhydrazone and this was reduced with bis benzyloxy)borane, 1-phenyl-1,2-butadiene was obtained in 21% yield [786]. 

Figure 4 in Scheme 2.3-4 demonstrates that when using a triphenylphosphane-modified Ni-catalyst, butadiene reacts with 2-butyne to form a 2 1-adduct whereas with methyl 2-butynoate, a 1 2 co-oligomer is obtained. Butadiene and phenyl-acetylene also form 1 2 products As we may have shown, a change from X- to C- or Z-type substituents in the co-substrates alters the ratio from 2 1 to 1 2 in a synthon coupling reaction. 

To a large bottle are added 470.0 gm (5.6 moles) of 2-methyl-3-butyne-2-ol, 1000 ml of 48 % technical grade hydrobromic acid, 200.0 gm (2.04 moles) of ammonium bromide, and 70.0 gm (0.71 mole) of cuprous chloride. The bottle is sealed, shaken at room temperature for 4J hr, opened, and the organic layer is separated. The organic layer is washed twice with sodium bicarbonate solution, once with a saturated sodium bisulfite solution, dried over calcium chloride, and fractionally distilled through a glass-helix-packed column to afford 500 gm (61 %) of almost pure product (ir 1956 cm-1 allene), b.p. 34°C (18 mm), d5 1.5163. The ir showed that the product contained a trace of l-bromo-3-methyl-1,3-butadiene (1580 and 1620 cm-1). 

Exercise 13-13 The rearrangement of 1,2-butadiene to 2-butyne shown above uses ethoxide ion as a basic catalyst. When one mole of 1,2-butadiene is treated with one mole of sodium amide in liquid ammonia, and water is added, the product is 1-butyne. Show the steps involved and explain why the product is different when an equivalent amount of a very strong base is used. (You may wish to review Section 11-8.)... 

In Section 10-5 we showed that ethyne is much less reactive toward chlorine than is ethene. The same is true for hydrogen chloride. Flowever, when hydrogen chloride adds to 3-butenyne, it adds to the triple bond instead of the double bond, thereby forming 2-chloro-1,3-butadiene instead of 3-chloro-1-butyne. With reference to the discussion in Section 13-2, explain why the order of reactivity of the double and triple bonds of 3-butenyne toward electrophilic reagents may be different from that of ethene and ethyne ... 

Reaction of PhZnCl with 3-acetoxy-3-methyl-1-butyne (116) gives l-phenyl-3-methyl-1,2-butadiene (119) in high yield [28-30]. The reaction can be explained by transmetallation of the allenylpalladium intermediate 117 with PhZnCl to generate the allenyl(phenyl)palladium intermediate 118, followed by reductive elimination to afford 119. 

Excess of butadiene is necessary in order to minimize the formation of co-oligomers containing more than one molecule of butyne [see Eq. (52)], and the reaction must be interrupted when all the alkyne is consumed to prevent further reaction of DMCDeT with butadiene to give higher oligomers. 

Boitiaux et al. (61) have examined the influence of palladium sulfuration on the hydrogenation and isomerization of 1-butene, 1,3-butadiene, and 1-butyne. The tested catalysts have been sulfided with thiophene to obtain an atomic ratio (sulfur per surface palladium) varying between 0 and 0.5. The thiophene in heptane solution is put in contact with the reduced palladium catalyst at 50°C, under 2 MPa hydrogen pressure. The butane evolution is followed during the sulfiding step (see above) and a control of total sulfur adsorption is performed by the analysis of the heptane after the sulfiding step and through X-ray fluorescence after the reaction step. 

For 1,3-butadiene hydrogenation, the toxicity of sulfur is 3 (Fig. 13). which is lower than the toxicity for olefin hydrogenation. The hydrogenation of 1-butyne has also been studied for various ratios of sulfur over palladium. As was already published (86), the 1-butyne hydrogenation rate increases with time. The same effect has been observed on sulfided palladium. The turnover number is consequently presented for 1-butyne hydrogenation versus the sulfur content for various 1-butyne conversions (see Fig. 14). During the first minutes of reaction (0-25% conversion), the toxicity of sulfur appears close to 1 the rates are proportional to the free surface. However, at higher conversion, the rate becomes independent from the sulfur ratio. The toxicity is zero. 

The different toxicities found for 1-butene, 1,3-butadiene, and l-butyne hydrogenation can be explained by assuming that the energetic adsorption of unsaturated hydrocarbons destabilizes the metal-sulfur bond producing a real desulfurization with l-butyne. The destabilization exists also with the butadiene, as has been shown on platinum (71). 

Higher-order zinc cyanocuprates react in a similar manner with propargyl chlorides and bromides46. Allenes are the result (S 2 substitution), except in the case of l,4-dihalo-2-butynes, which undergo two successive S 2 substitutions to afford 2,3-disubstituted butadienes (equations 33 and 34)47. 

Indium-promoted reaction of l,4-dibromo-2-butyne with carbonyl compounds gives 1,3-butadiene derivatives via the allenic indium intermediates (Scheme 56).220 Similar indium-mediated l,3-butadien-2-ylation reactions of optically pure azetidine-2,3-diones have been investigated in aqueous media, offering a convenient asymmetric entry to the 3-substituted 3-hydroxy-/ -lactam moiety (Equation (40)). The diastereoselectivity of the addition reaction is controlled by the bulky chiral auxiliary at Q4 221 222... 

Butadiene and HC1 (4 of Table 5) yield a mixture of trans and cis chloro-2-butene together with considerable amounts of 2-butyne which, in turn, adds HC1 much more slowly than the parent isomer. The orientation is that predicted following equation (11) and indicates the intermediacy of a vinyl cation. 

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