Vinylcyclohexene cyclodimerization, butadiene

Production of ethylbenzene from butadiene has been iavestigated by many researchers. It consists of two steps cyclodimerization of 1,3-butadiene to 4-vinylcyclohexene and dehydrogenation of the vinylcyclohexene to ethylbenzene. 

The use of zeolites is particularly advantageous for self-Diels-Alder reactions of gaseous dienes because it reduces the polymerization of the reactant. An example is the cyclodimerization of 1,3-butadiene to 4-vinylcyclohexene [20a] carried out at 250 °C with satisfactory conversion when non-acidic zeolites, such as large-pore zeolites Na-ZSM-20, Na- S and Na-Y, are used. 

The Cu+/zeolite-catalyzed cyclodimerization of 1,3-butadiene at 100°C and 7 atm was found to give 4-vinylcyclohexene [Eq. (13.12)] with high (>99%) selectivity. Subsequent oxidative dehydrogenation over an oxide catalyst in the presence of steam gives styrene. The overall process developed by Dow Chemical113 offers an alternative to usual styrene processes based on ethylation of benzene (see Section 5.5.2). 

The first work in this area appeared in the form of two patents assigned to Union Carbide in 1969/1970 (172,173). These patents described methods of preparation of monovalent copper-containing zeolites which were claimed to be active and selective catalysts for the cyclodimerization of butadiene to 4-vinylcyclohexene (VCH), i.e.,... 

Similar types of cyclodimerizations were also pointed out with vinyl pyridines and vinyl quinoleines [213]. Lastly, selective cyclodimerization reactions of 1,3-diolefins catalyzed by electrogenerated Fe(NO)2 —from athodic reduction of FeCl3 in the presence of NO—allowed the conversion of butadienes into vinylcyclohexenes in good yields [214] (Scheme 40). 

The first step of the process involves the cyclodimerization of butadiene to 4-vinylcyclohexene. The reaction is exothermic and can be catalyzed by either a copper-containing zeolite catalyst or an iron dinitrosyl chloride catalyst complex. Although both vapor-phase and liquid-phase processes have been studied, it appears that liquid-phase reactions are preferred because they achieve higher butadiene conversion levels. The second step is oxidative dehydrogenation of the 4-vinylcyclohexene to produce styrene. Dow has led the research effort in this area and has... 

As well as [2 + 2], [4 + 4] and [4 + 4 + 4] products, the cyclodimerization of conjugated dienes also yields [4 + 2] cycloadducts47Thus, butadiene gives 4-vinyleyelohexene, ci.v-1,2-divinyl-cyclobutane and 1,5-cyclooctadiene. The influence of the catalyst and reaction conditions on the product distribution has been carefully investigated50- 53. Efforts towards asymmetric induction have concentrated on the stereoselective synthesis of 4-vinylcyclohexene as the sole chiral product. 

Additional experiments were also carried out with complex 133 which results from the substitution of the COD ligand in 73 by a 1,4-diaza-l,3-diene (DAD) [48], The catalytic activity of 133 in the cyclodimerization of 1,3-butadiene was compared to that of its carbon counterpart the [Fe(r/6-toluene)(DAD)] complex. In this case, the toluene complex proved to be 10 times more efficient and yielded better TON than the phosphinine-based complex for the formation of COD (1,5-cyclooctadiene) and VCH (vinylcyclohexene). This lack of activity was ascribed to the stronger affinity of phosphinine ligands towards Fe(0) thus limiting the generation of the 12 VE [Fe(DAD)] complex which is the genuine catalytic active species (Scheme 27). 

Cyclodimerization of 1,3-butadiene via arene metal-mediation has received relatively little attention. To date, the only example of such a dimerization has been described by Zenneck and co-workers [46]. This group has shown that (r -arene)(r[ -diazadiene)iron complexes catalyze 1,3-butadiene dimerization to afford a mixture of 3-vinylcyclohexene and 1,5-cyclooctadiene. The initial observations showed a strong dependence of [4-1-4]/[4-1-2] product ratio on the nature of the arene coordinated to the metal center. These early results offer good opportunities for the further improving on the chemoselectivity of this cyclization. 

Zeolites are clays with rather large internal pore structures which have the property of concentrating nonpolar organic compounds within their cavities. Measurements of gaseous hydrocarbon equilibria have shown enhancements of several orders of magnitude within zeolite pores relative to the vapor phase. Cyclodimerization of butadiene to 4-vinylcyclohexene (Equation 7.5) at 250°C was catalyzed by large-pore zeolites in the sodium form (Dessau, 1986). Zeolites in the Cu(I) form also promoted Diels-Alder addition of furan and other dienes with electron-deficient dienophiles such as methyl vinyl ketone (Equation 7.6). Dichloro-methane was the solvent in these reactions, which usually were carried out at 0°C or lower (Ipaktschi, 1986). 

A similar Ni(0) species is derived from (cyclooctadiene) nickel and a phosphinated polystyrene.The catalyst has little intrinsic activity in butadiene cyclodimerization to cyclooctadiene and vinylcyclohexene, but this was enhanced to a level of about 60-100 g-product/g-Ni/hr by the addition of AlEt2(OEt). Cyclododecatriene was not produced, indicating coordination of a phosphine to the nickel throughout the process. 

The thermal polymerization of butadiene yields, according to Ziegler et al., a mixture of vinylcyclohexene with at most 15% of cyclooctadiene (95, 96). In 1954 Reed (97) discovered the catalytic cyclodimerization of butadiene to cycloocta-1,5-diene with Reppe catalysts, with a 30-40% conversion at 120-130° C. Wilke et al. recently synthesized a very efficient class of catalyst. If nickel-acetylacetonate is treated with metal alkyls (especially aluminum alkyls) in the presence of electron-donating compounds (mainly cycloolefins), new tt complexes of nickel are obtained which catalyze the cyclo-oligomerization of butadiene (98, 99). Using cycloocta-1,5-diene as the olefinic component, the well-crystallized, faintly yellow bis(cycloocta-... 

An intermediate isolated from the dimerization of butadiene in the presence of nickel complexes, thought to be (56), has been shown to be the cyclic compound (57) it is quite possible that (56) is a transient precursor of (57). This reassignment of structure may somewhat affect the arguments, based on reactivities of (58) and what was thought to be (56), for a mechanism involving formation of linear polymers followed by cyclization, rather than of concerted cyclo-oligomerization, for cyclopolymerization - at least in the present case of the cyclodimerization of butadiene to divinylcyclobutane (59) and vinylcyclohexene (60). The... 

The cyclodimerization of butadiene forming a mixture of cycloocta-1,5-diene and vinylcyclohexene can be catalyzed by a (l,4-diaza-l,3-diene)iron complex in the presence of a Grignard reagent (Scheme 4-308). ... 

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