Ethylene reaction with 1,3-butadiene

Figure 5.13. Cycloaddition products at the silicon dimer of the Si(100)-2 x 1 surface, (a) shows the [2 + 2] cycloaddition product formed in the reaction with ethylene, and (b) shows the [4 + 2], or Diels-Alder, cycloaddition product formed in the reaction with 1,3-butadiene.

In order to answer the question first posed in Chapter 1 and repeated above, we begin by ignoring the substituents and counting only those parts of the conjugated system directly involved in the reaction. (We shall return to the crucial role of the substituents later in the chapter.) Thus the Diels-Alder reaction is simplified to that of butadiene reacting with ethylene the former component has four rc-electrons and the latter two, and these are the only electrons directly involved, as we can see from the curly arrows. Such a reaction is called a [4 + 2] cycloaddition. We now examine the signs of the coefficients of the frontier orbitals on the atoms which are to become bonded (Fig. 4-1). We are not yet concerned with the magnitude of the coefficients of the frontier orbitals, and therefore in this section all orbitals are drawn the same size, so as not to... 

The required terminal olefins used as substrates for the hydroformylation, such as 1-pentene or 1-octene, are available in large scales and can be derived either from Sasol s Fischer-Tropsch process or from the shell higher olefins process (SHOP), respectively [43, 44]. Alternatively, trimerization or tetramerization of ethylene affords 1-hexene [45] or 1-octene [46]. Dimerization of butadiene in methanol in the presence of a Pd catalyst (telomerization) is another industrially used access for the manufacture of 1-octene [46]. 1-Octene can also be produced on a large scale from 1-heptene via hydroformylation, subsequent hydrogenation, and dehydration (Scheme 6.2) [44]. This three-step homologation route is also valuable for the production of those higher olefins that bear an odd number of C atoms. (X-Olefins can also be derived from internal olefins by cross-metathesis reaction with ethylene [47]. 

Acryhc stmctural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acryhc adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated stmctural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, N,1S7-dimethyl- -toluidine, and saccharin, can be apphed to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

The dienoplules for reaction with butadiene can be alkenes, allenes, and alkynes. Simple alkenes like ethylene are poor dienoplules resulting in sluggish reactions. Substituted olefins, X—C=C—X, are more reactive when X and/or X are C=C, Ar, COOR, COOH, COH, COR, COCl, CN,... 

As part of his elegant and comprehensive examination ot the competition between [2+2] and [2+4] reactions of fluorinated ethylenes, Bartlett found that trifluoroethylene s [2+4] reaction with butadiene competed somewhat with its [2+2] cycloaddirion [66] (equation 62). 

In a definitive study of butadiene s reaction with l,l-dichloro-2,2-difluoio-ethylene, Bartlett concluded that [2+4] adducts of acyclic dienes with fluorinated ethylenes are formed through a mixture of concerted and nonconcerted, diradical pathways [67] The degree of observed [2+4] cycloaddition of fluorinated ethylenes IS related to the relative amounts of transoid and cisoid conformers of the diene, with very considerable (i.e., 30%) Diels-Alder adduct being observed in competition with [2+2] reaction, for example, in the reaction of 1,1 -dichloro-2,2-difluoro-ethylene with cyclopentadiene [9, 68]... 

In contrast with exo (top) facial selectivity in the additions to norbomene 80 [41], Diels-Alder reaction between isodicyclopentadiene 79 takes place from the bottom [40] (see Scheme 32). To solve this problem, Honk and Brown calculated the transition state of the parent Diels-Alder reaction of butadiene with ethylene [47], They pointed ont that of particular note for isodicyclopentadiene selectivity issue is the 14.9° out-of-plane bending of the hydrogens at C2 and C3 of butadiene. The bending is derived from Cl and C4 pyramidalization and rotation inwardly to achieve overlap of p-orbitals on these carbons with the ethylene termini. To keep the tr-bonding between C1-C2 and C3-C4, the p-orbitals at C2 and C3 rotate inwardly on the side of the diene nearest to ethylene. This is necessarily accompanied by C2 and C3 hydrogen movanent toward the attacking dienophile. They proposed that when norbomene is fused at C2 and C3, the tendency of endo bending of the norbomene framework will be manifested in the preference for bottom attack in Diels-Alder reactions (Schane 38). 

Another catalytic application emanating from the Hieber base reaction was developed by Reppe and Vetter [108]. They showed that 1-propanol 126 could be generated by treatment of ethylene 125 with catalytic amounts of Fe(CO)5 78 under CO-pressure and basic reaction conditions (Scheme 33). Thereby, trimethylamine and V-alkylated amino acid derivatives mrned out to be optimal bases for this reaction. Like ethylene 125, propylene could be transferred mainly to 1-butanol diolefins like butadiene only reacted to monoalcohols. By employing these reaction conditions to olefins in the presence of ammonia, primary or secondary amines, mono-, di-, and trialkylamines were obtained whose alkyl chains were elongated with one carbon atom, compared to the olefins. 

On orbital symmetry grounds, the addition of ethylene to ethylene with ring closure (cycloaddition) should be thermally forbidden. If one compares this reaction with the reaction of trimethylene with approaching ethylene and butadiene (Fig.4), it is readily seen that, the A level being below the S level in trimethylene, the behaviour with respect to cycloaddition to olefins is reversed, that is, trimethylene is essentially an anti-ethylene structure. This principle can be generalized for instance (16) ... 

Pd2+ salts are useful reagents for oxidation reactions of olefins. Formation of acetaldehyde from ethylene is the typical example. Another reaction is the formation of vinyl acetate by the reaction of ethylene with acetic acid (16, 17). The reaction of acetic acid with butadiene in the presence of PdCl2 and disodium hydrogen phosphate to give butadienyl acetate was briefly reported by Stem and Spector (110). However, 1-acetoxy-2-butene (49) and 3-acetoxy-l-butene (50) were obtained by Ishii and co-workers (111) by simple 1,2- and 1,4-additions using PdCl2/CuCl2 in acetic acid-water (9 1). 

The second pathway is represented by Eqs. (8)—(11). These reactions involve reduction of the Nin halide to a Ni° complex in a manner similar to the generation of Wilke s bare nickel (37, 38) which can form a C8 bis-77-alkyl nickel (17) in the presence of butadiene [Eq. (9)]. It is reasonable to assume that in the presence of excess alkyaluminum chloride, an exchange reaction [Eq. (10)] can take place between the Cl" on the aluminum and one of the chelating 7r-allyls to form a mono-77-allylic species 18. Complex 18 is functionally the same as 16 under the catalytic reaction condition and should be able to undergo additional reaction with a coordinated ethylene to begin a catalytic cycle similar to Scheme 4 of the Rh system. The result is the formation of a 1,4-diene derivative similar to 13 and the generation of a nickel hydride which then interacts with a butadiene to form the ever-important 7r-crotyl complex [Eq. (11)]. 

C Primary kinetic isotope effects for the concerted reaction of butadiene with ethylene, for the stepwise reaction of butadiene with ethylene and for the concerted reaction of butadiene with acrolein, have also been calculated207. The experimental values of 1.0438 and 1.0474 found recently196 in the reaction of 2,3-dimethylbutadiene with [1-14C]- and [2-14C]-l-nitro-2-phenylethylene, respectively, similar at both reacting termini, are in accord with the calculated value of 1.046 for knc/ki4c (373.15 K) in a synchronous concerted reaction of butadiene with ethylene. The 14C KIE values predicted for the asynchronous acrolein reaction are 1.015 and 1.045 for the T and 2 isotopomer, respectively207. 

The reaction of 1-butene with 0 , followed by the thermal decomposition of surface intermediates, leads to the formation of butadiene as the main product. Thus, 1-butene appears to be more similar to alkanes than to ethylene or propylene in its reaction with 0 . 

The new recycling concept was apphed to several C - C bond-forming reactions, for example, to the telomerization of butadiene with ethylene glycol or carbon dioxide, to the isomerizing hydroformylation of frans-4-octene and to the hydroamino-methylation of 1-octene with morpholine. 

The telomerization of butadiene with ethylene glycol was chosen as an example for a reaction of a polar and a non-polar substrate to a semipolar product (Scheme 1). 

One difficulty in the determination of an appropriate solvent system for the telomerization of butadiene with ethylene glycol is the change of polarity in the reaction mixture during the reaction. 

Catalysis experiments were performed to investigate the telomerization of butadiene with ethylene glycol in selected TMS systems (e.g. si toluene DMF 1 5 4 or sl 2-octanol DMSO 1.35 3 5.2). With Pd/TPPTS as the catalyst a maximum yield of only 10% of the desired products could be achieved. With Pd/TPPMS the yield increased up to 43% in the TMS system si toluene isopropyl alcohol, but additional water had to be added to obtain a phase split after the reaction. The catalyst leaching is very high and 29% of the palladium used is lost to the product phase. 

Table 1 Telomerization of butadiene with ethylene glycol in TMS systems. Reaction conditions 0.06 mol % Pd(acac)2 based on ethylene glycol, Pd/P =1 3 butadiene/ethylene glycol = 2.5 1, si = ethylene glycol water 2 1, 80 °C 4 h 1200 rpm...

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