Hydrogenation of 1,3-butadiene

Rhodium- and cobalt-catalyzed hydrogenation of butadiene and 1-hexene [47, 48] and the Ru-catalyzed hydrogenation of aromatic compounds [49] and acrylonitrile-butadiene copolymers [50] have also been reported to be successful in ionic liquids. 

Cold hydrogenation may also be used for the selective hydrogenation of butadiene and for the selective hydrogenation of methyl acetylene and pro-padiene in propylene feedstocks (K22). 

Most organopentacyanides are stable towards [Co(CN)jH], with the exception of allyl complexes which react to liberate propylene derivatives (105). This is one of the steps in the homogeneous hydrogenation of butadienes catalyzed by cobalt cyanide complexes (see Section VII,A). 

The subsequent hydrogenation of butadiene to but-l-ene and but-2-ene is kineti-cally insignificant, and these hydrocarbons have no influence on the rate of the first step. H2S, however, does influence the rate. Briefly, the reaction proceeds over a site where a sulfur atom in the catalyst is missing (see Chapter 9 for details). A high pressure of H2S simply reduces the number of these vacancies and therefore adversely affects the rate. 

As a final example of catalytic hydrogenation activity with polymer-stabilized colloids, the studies of Cohen et al. should be mentioned [53]. Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films. The organometallic repeat-units contained in the polymer were reduced by exposing the films to hydrogen at 100 °C, leading to the formation of nearly monodisperse Pd nanoclusters that were active in the gas phase hydrogenation of butadiene. 

The immobilization of Pd(acac)2 as hydrogenation catalyst in the ionic liquids [BMIM][BF4] and [BMIM][PF6] was reported by Dupont et al. in 2000 [70]. These authors compared the biphasic hydrogenation of butadiene with the homogeneous system with all reactants being dissolved in CH2C12, with the reaction in neat butadiene and with a heterogeneous system using Pd on carbon as catalyst. 

Hydrogenation of butadiene with K3Co(CN)5, which is known to hydrogenate selectively conjugated dienes [75], was possible with 100% conversion and selectivity and a TOF up to 72 h-1 in the ionic liquid [BMIM][BF4], but the catalyst was deactivated after the first run and the inactive complex (BMIM)3Co(CN)5 was formed [69]. 

The hydrogenation of butadiene is structure-sensitive on Pd and Rh but lacks particle-size dependence in the case of platinum. The strong complexation of the diene to atoms of low coordination number is a possible explanation for this phenomenon where it occurs37,38. 

Mo, W) decreases with the increase in basic strength of the framework oxygen of the host zeolite [32]. The M(CO)3(Oz)3 (Oz = zeolite framework oxygen) species generated by the thermal treatment are active in the stereoselective hydrogenation of butadiene to cis-2-butene [33, 34]. 

Researchers performed the biphasic hydrogenation of cyclohexene with Rh(cod)2 BF4 (cod = cycloocta-1,5-diene) in ILs. They observed roughly equal reaction rates, reported as turnover frequencies of ca. 50 h in either [bmim][BF4] or [bmim][PF6]. The presumption here was that the [bmim][BF4] was free from chloride. In a separate report, the same group showed that RuCl2(Ph3P)3 in [bmim][BF4] was an effective catalyst for the biphasic hydrogenation of olefins, with turnover frequencies up to 540 h Similarly, (bmim)3-Co(CN)5 dissolved in [bmim][BF4] catalyzed the hydrogenation of butadiene to but-l-ene, with 100% selectivity at complete conversion. 

No organometallic products from the reaction of palladium or platinum vapors with butadiene have yet been reported. However, the platinum-butadiene condensate is a catalyst for the hydrogenation of butadiene, the product being mainly butane (104). 

Equation 14 actually represents the result of several consecutive reactions involving additions of CoH to nitrobenzene and intermediates such as nitroso-benzene to form complexes subject to further interaction with CoH to yield reduction products in a manner similar to that postulated for the hydrogenation of butadiene (see Equations 1 and 3). Equation 15 defines the role of alkali whereby reduction products are released and the hydroxo complex so formed is able to undergo the reverse aging process as discussed in other examples. Equation 16 is similar to that shown for benzoquinone (Equation 11) and indicates a possible interaction of the substrate with nonhydrogenated cyanocobaltate(II). 

Scheme 15. Hydrogenation of butadiene on (a) 3MH2-site and (b) 3MH-site.

The 7r-electrons in 3-methylallyl carbanion are distributed with more electron density on the a carbon atom than on the y carbon, but the formation of 1-butene from ris-2-butene indicates the kinetic feasibility of the attack of a proton on the y carbon of 3-methylallyl carbanion. Accordingly, the hypothesis that the hydrogenation of butadiene through a 7t-allylic carbanion would prefer a priori the 1,4-addition has no scientific basis (57). 

The idea of this work was the realization of a not easily selective hydrogenation under conditions relevant to the surface science, in order to get a better understanding of the mechanism. Such an approach already led to interesting conclusions concerning the hydrogenations of butadiene and isoprene (ref. 2). 

The hydrogenation of trans-l-phenyl-1,3-butadiene has been discussed49 in terms of the mechanism originally proposed,45 and 773-allyl species were invoked. NMR studies on the hydrogenation of butadiene have shown that Tj -but-2-enyl and r 3-l-methylallyl complexes are present in the reaction mixture. With isoprene, an q1 -methylbut-2-enyl complex was observed.50 By using a two-phase system and a phase-transfer catalyst, the turnover numbers attainable with conjugated dienes can be increased to about 30.51... 

Scheme 4.11 Hydrogenation of butadiene with CpFe(CO)2CI (Cp = cyclopentadienyl).

Fig. 2.24 Results from a library of Pd-a-AI203 catalysts and inert materials in the partial hydrogenation of butadiene.

Pradier et al. (81) do not confirm the results obtained in the hydrogenation of butadiene on Pt(l 10) when they consider the (100) face. The activity decrease is no longer proportional to the sulfur coverage. They consider that the sulfur action changes with the crystallographic face the sulfur would adsorb on the diene sites over the (100) face, but on the hydrogen activation sites, over the (110) face. Moreover, the complexity of the sulfur action is not only seen by changing the substrate or the catalyst. It is... 

Examination of the reaction products indicated that the primary products of reaction were probably butadiene and H2S. The rates of hydrogenation of butadiene and butene were found to be consistent with the amounts appearing in the reaction products (provided, in the case of cobalt molybdate catalyst, that H2S was present to simulate reaction conditions). The results support the view that C-S bond cleavage is the first step in thiophene desulfurization, rather than hydrogenation of the ring. 

BASF/ABB Lummus Global Butadiene-free C4 hydrocarbons, mixed Mixed C4 hydrocarbons Selective hydrogenation of butadiene from mixed C4s stream product—butadiene-free C4 stream 6 2001... 

CDTECH Isobutylene Raffinate 1 Selective hydrogenation of butadiene and hydroisomerization of butene-1 to butene-2 via catalytic distilation to recover isobutylene 1 1994... 

Tables 3.10, 3.11 and 3.12 provide economic data on techniques for the selective hydrogenation of butadiene contained in a C4 cut, on the processes for the separation and manufacture of isobutene, and on those relative to the production of n-butenes.

In more recent work on hydrogenation of butadiene polymers and copolymers, the attempt was made to explain the dependence on hydrogen pressure with sole rate control by olefin addition to H2RhClPh2 (X3) and quasi-equilibrium rhodium distribution over the complexes with and without hydrogen [59] instead of kinetic significance of the step Xq + H2 — X3. This gives a rate equation for double-bond disappearance of the form... 

Dehydrogenation and hydrogenation of cyclohexene Hydrogenation of butadiene Dehydrogenation of isopropyl alcohol... 

A mechanism, somewhat diflFerent from that for the hydrogenation of butadiene, has been proposed (77) for the hydrogenation of cinnamate —i,e,... 

Table VI. Products of Homogeneous and Heterogeneous Hydrogenations of Butadiene...

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