Palladium butadiene hydrogenation

Nonconjugated dienes, namely, allenes and isolated dienes, react preferentially on the terminal double bond.10 Hydrogenation of 1,2-butadiene over palladium yields 1-butene and d.s-2-butene as the main products with moderate discrimination of the two double bonds.68 Deuteration experiments indicated that the dominant syn addition to either the 1,2- or the 2,3-olefinic bond occurs. Different vinyl and Jt-allyl intermediates were invoked to interpret the results.69 70... 

The monohydrogenation of conjugated dienes can occur by either 1,2 or 1,4 addition. 1-Butene (53%) and trans-2-butene (42%) are the main products in the hydrogenation of 1,3-butadiene on palladium with only a small amount of cis-2-butene.68 Deuterium distribution reveals that the trans isomer is produced by 1,4 addition. 

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. 

Boitiaux et al. and Verna (61, 62) confirmed this variation of selectivity in the butadiene hydrogenation for the parallel reactions (1,2 and 1,4 addition) on presulfided palladium. Figure 16 shows the 2-butene/1-butene and the fraus-butene/c/s-butene ratios versus the sulfurization extent of the surface palladium. The sulfur decreases the trans/cis ratio and favors the 1,4 addition. 

Butadiene hydrogenation is structure-sensitive and thus regarded as particle size-dependent (530-53 ). When the total number of Pd surface atoms on the nanoparticles is used for rate normalization, a size-dependent rate is indeed observed (stars and dashed line in Fig. 58b the data show the number of butadiene molecules reacted per Pd surface atom per second within 1 h). Apparently, this TOF increases linearly with particle size, indicating that larger palladium particles are more active than smaller ones, in agreement with what is commonly reported for this reaction (see References (530,537) and references cited therein). 

Surface structure and catalytic reactivity of palladium overlayers for 1,3-butadiene hydrogenation... 

What is clear from all these results, is that structural parameters and catalytic activity are intimately related. Starting from one metal, palladium in this case, we have shown that, by alloying with or deposition on other metals, it was possible to generate a lot of distinct local structures where surface Pd could exhibit largely modified chemical reactivity. Some particular systems can show large amplifications of activity for the 1,3-butadiene hydrogenation reaction... 

It is not intended that the literature concerning the hydrogenation of alkenylalkynes and dialkynes shall be reviewed in detail. However, the hydrogenation of molecules as unsaturated as these provides further examples of the operation of the thermodynamic factor which are of interest. The palladium-, platinum-, and nickel-catalyzed hydrogenations of vinylacetylene (H2C=CH—C=CH) provides 1,3-butadiene as the major initial product butenes and butane are also produced (57). The product distributions are constant in liquid phase reactions until the parent hydrocarbon has been removed, showing that vinylacetylene is more strongly adsorbed than 1,3-butadiene and the butenes. The relative yields of butenes and butane resemble those obtained in 1,3-butadiene hydrogenation over these metals (see Section III, F, 6). 

Third, n-allyl complexes are formed by palladium and cobalt analogous complexes of nickel and platinum are less stable, while ruthenium, rhodium, and iridium are not yet known to form them. In catalytic reactions the deuteration of cyclic paraffins over palladium has provided definite evidence for the existence of rr-bonded multiply unsaturated intermediates, while 7r-allylic species probably participate in the hydrogenation of 1,3-butadiene over palladium and cobalt, and of 1,2-cyclo-decadiene and 1,2-cyclononadiene over palladium. Here negative evidence is valuable platinum, for example does not form 7T-allylic complexes readily and the hydrogenation of 1,3-butadiene using platinum does not require the postulate that 7r-allylic intermediates are involved. Since both fields here are fairly well studied it is unlikely that this use of negative evidence will lead to contradiction in the light of future work. 

In a related process, 1,4-dichlorobutene was produced by direct vapor-phase chlorination of butadiene at 160—250°C. The 1,4-dichlorobutenes reacted with aqueous sodium cyanide in the presence of copper catalysts to produce the isomeric 1,4-dicyanobutenes yields were as high as 95% (58). The by-product NaCl could be recovered for reconversion to Na and CI2 via electrolysis. Adiponitrile was produced by the hydrogenation of the dicyanobutenes over a palladium catalyst in either the vapor phase or the Hquid phase (59,60). The yield in either case was 95% or better. This process is no longer practiced by DuPont in favor of the more economically attractive process described below. 

Another alternative method to produce sebacic acid iavolves a four-step process. First, butadiene [106-99-0] is oxycarbonylated to methyl pentadienoate which is then dimerized, usiag a palladium catalyst, to give a triply unsaturated dimethyl sebacate iatermediate. This unsaturated iatermediate is hydrogenated to dimethyl sebacate which can be hydrolyzed to sebacic acid. Small amounts of branched chain isomers are removed through solvent crystallizations giving sebacic acid purities of greater than 98% (66). 

Troublesome amounts of C and Q acetylenes are also produced in cracking. In the butadiene and isoprene recovery processes, the acetylenes in the feed are either hydrogenated, polymerized, or extracted and burned. Acetylene hydrogenation catalyst types include palladium on alumina, and some non-noble metals. 

Some companies are successfully integrating chemo- and biocatalytic transformations in multi-step syntheses. An elegant example is the Lonza nicotinamide process mentioned earlier (.see Fig. 2.34). The raw material, 2-methylpentane-1,5-diamine, is produced by hydrogenation of 2-methylglutaronitrile, a byproduct of the manufacture of nylon-6,6 intermediates by hydrocyanation of butadiene. The process involves a zeolite-catalysed cyciization in the vapour phase, followed by palladium-catalysed dehydrogenation, vapour-pha.se ammoxidation with NH3/O2 over an oxide catalyst, and, finally, enzymatic hydrolysis of a nitrile to an amide. 

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. 

Nagamoto, H. and H. Inoue. 1986. The hydrogenation of 1,3-butadiene over a palladium membrane. Bull. Chem. Soc. Japan 59 3935-3939. 

The adipic acid process we have developed involves butadiene oxidative carbonylation in the presence of methanol, a l, l-dimethoxycyclohexane dehydration agent, and a palladium(ll)/ copper(ll) redox catalyst system (Equation 1.). The reaction sequence includes an oxycarbonylation, hydrogenation and hydrolysis step(17-19). The net result is utilization of butadiene, the elements of synthesis gas, l, -dimethoxycyclohexane and air to give adipic acid, cyclohexanone and methanol. 

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