Butadienes general discussion

Acylamidoxime-butadiene-acrylonitrile terpolymers, SAW detection of simulant vapors, 309-319 Additivity, spectroscopic response, general discussion, 274 Adsorption of water, effect on TPD spectra of oxygen on Pd-doped tin(IV) oxide, 75,78f... 

Copolymerization of butadiene and styrene in hexane with a number of initiators, such as lithium morpholinide, lithium dialkylamide, lithium piperidinide, etc., has also been examined. In general, the microstructure and styrene content of the polymers are dependent on the type of initiator and the polymerization conditions. Detailed results including a postulated mechanism for these polymerizations are discussed. 

The mechanism of coordination polymerization of 1,3-butadiene and, in general, that of conjugated dienes follows the same pathway discussed for alkene polymerization that is, monomer insertion into the transition metal-carbon bond of the growing polymer chain occurs. One important difference, however, was recognized very early.47,378,379 In the polymerization of dienes the growing chain end is tt-allyl complexed to the transition metal ... 

The light hydrocarbons produce only minor amounts of by-products, while naphtha and heavier feeds produce substantial quantities of propylene, butadiene, and aromatics. Thus, while in the United States these products are obtained generally from other routes at present, in Europe and Japan ethylene production serves as a major source of these chemicals. As discussed in greater detail later, by-product outlet considerations can play an important role in feedstock selection, and by-product realizations can have a major effect on the ethylene production economics. 

Owing to uncertainties in the analysis methods, only general trends seem to warrant discussion. With butadiene, the 1,2/1,4 ratio increases in the series Li to Cs. In tetrahydrofuran the polymer is even more rich in 1,2 structures and varies little with the alkali metal or its compounds. With isoprene, only lithium and its compounds give a highly cis-1,4 polymer in hydrocarbons. Increasing amounts of the 3,4 structure occur with the other alkali metals. The amount of 1,4 polymer and its internal distribution is in doubt. In ethers the 3,4 polymer is the major constituent with all initiators. The N. M. R. data suggest the microstructure... 

The general character of alkene polymerization by radical and ionic mechanisms was discussed briefly in Section 10-8. The same principles apply to the polymerization of alkadienes, with the added feature that there are additional ways of linking the monomer units. The polymer chain may grow by either 1,2 or 1,4 addition to the monomer. With 1,3-butadiene, for example,... 

However, newer adhesives systems having moderate temperature resistance have been developed with improved toughness without sacrificing other properties. When cured, these structural adhesives have discrete elastomeric particles embedded in the matrix. The most common toughened hybrids using this concept are acrylic and epoxy systems. The elastomer is generally a vinyl- or carboxyl-terminated acrylonitrile butadiene copolymer. These adhesive formulations are discussed in detail in Chaps. 8 and 12. 

In contrast to the great number of calculations concerning the all-carbon Diels-Alder reaction [39], there are only a few theoretical studies on the hetero Diels-Alder reaction [41,42,45 - 53 ]. The general mechanism of the Diels-Alder reaction is still in discussion however, in most cases a concerted reaction is assumed,but there is also evidence for a two-step path. The ab initio calculations carried out for the butadiene/ethene system by Houk, Ortega, Bernardi und Gajewski gave a symmetrical transition structure only using the semiempirical AM1/CI method (half electron approximation) an unsymmetrical diradicaloid intermediate was found [40]. 

Thiophene is obtained in 6% yield by passing butadiene into molten sulfur at 320-420°. The reaction is general and affords somewhat higher yields (31 40%) of methylated thiophenes from homologs of butadiene. The free-radical nature of the reaction has been discussed. Dibenzo-thiophene is conveniently prepared by heating biphenyl and melted sulfur with aluminum chloride at 120°. The yield is 47%... 

The most outstanding example for the applieation of homogeneously catalyzed hydrocyanation is the DuPont adiponitrile process. About 75 % of the world s demand for adiponitrile is covered by hydrocyanation of butadiene in the presence of nickel(O) phosphite species. This process is discussed for the addition of HCN to dienes as an example, because in this case a well-founded set of data is available. Though it was Taylor and Swift who referred to hydrocyanation of butadiene for the first time [45], it was to Drinkard s credit that this principle was fully exploited for the development of the DuPont adiponitrile process [18]. The overall process is described as the addition of two equivalents of HCN to butadiene in the presence of a tetrakisphosphite-nickel(O) catalyst and a Lewis acid promoter. A phosphine-containing ligand system for the catalyst is not suitable, since addition of HCN to the tetrakisphosphine-nickel complex results in the formation of hydrogen and the non-aetive dicyano complex [67], In general the reaction can... 

Site selectivity is that selectivity shown by a reagent towards one site (or more) of a polyfunctional molecule, when several sites are, in principle, available. The preference for electrophilic attack at the ortho and para positions of X-substituted benzenes is just one of many examples discussed in Chapter 3. In cycloadditions, site selectivity always involves a pair of sites thus, butadiene reacts faster with the quinone (308) at C-2 and C-3 than at C-5 and C-6,256 and Diels-Alder reactions of anthracene (309) generally take place257 across the... 

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