Palladium isoprene hydrogenation

Platinum catalysts have given product distributions that were not consistent with the mechanism that seems to apply to palladium." " Isoprene hydrogenation has also been performed on Pt(lll) at 423 K, 5tot was very low (37%). Raney nickel has also been used." ... 

Isoprene Hydrogenation on Palladium Black Influence of Diethylsulfide... 

In the isoprene hydrogenation results of Table XII, the ratio of the 1,4 addition/1,2 addition decreases on palladium with sulfur addition. Such a result is not at all in accordance with other studies dealing with nickel... 

The initial selectivity will be independent on the pressure of B. Moreover, if the ratio k K4 CB/ ki is small enough, the selectivity remains essentially equal to unity up to high conversions, decreasing thereafter. The character of selectivity beyond the point of high conversions will be pressure dependent, so that at higher pressures (concentrations) of B, the selectivity towards C will be lower. Such dependencies have been observed for isoprene hydrogenation over a palladium catalyst (Figure 4.26). 

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. 

Hydrocarbons. The reaction of isoprene with toluene, ethylbenzene, or isopropylbenzene is catalyzed by sodium or potassium (72). The reactions are carried out at 125°C in a pressure autoclave by adding the isoprene slowly to the alkylarene in which the alkali metal is dispersed along with a trace quantity of 0-chlorotoluene which is used as a chain initiator. The products are chiefly monopentenylated in the side chain, and no information can be obtained on whether the addition is 1,4- or 1,2- since under these conditions the double bond migrates. The alkene products subsequently are reduced to alkanes by hydrogenation using 5% palladium on charcoal as catalyst. 

TABLE 3.10 The Products (%) in Half-Hydrogenation of Isoprene over Platinum, Palladium, and Raney Ni"... 

These reactors were employed for coupling of isopentcnes dehydrogenation into isoprene with toluene hydrodemethylation. Hydrogen evolved during the first reaction in one compartment dissolved in palladium alloy plates and penetrated through them to the other compartment, where the second reaction took place. 

Palladium-catalysed reaction of trans-j8-farnesene, formed by catalytic tri-merization of isoprene, resulted in regioselective head-to-head coupling to a dimer which yielded squalene on hydrogenation. A detailed n.m.r. study of functionalized squalane derivatives and model compounds suggests the presence of precoiled conformations. ... 

TABLE 8.12. Hydrogenation of Isoprene (2-Methyl-l,2-Butadiene) Product Selectivities Obtained with Palladium Catalysts, and Matching Calculations ... 

The analysis has been extended to cover many of the published product se-lectivities found when hydrogenating isoprene on palladium catalysts." When... 

These eomplexes have been deeomposed in aleoholie media by sodium aeetate and by hydrogen gas. 1-Methoxymethyl-2-methyl-tt-allyl palladium ehloride l, derived from isoprene, methanol and sodium ehloropalladite, was dissolved in methanol and deeomposed with sodium aeetate at reflux. 

Palladium-catalyzed reaction of isoprene with thiophenol in the presence of CO gave, depending on the solvent, either a thiocarbonylation product (16a) or a product in which a 1,4-addition of sulfur and a hydrogen had occurred (16b) [31]. The reaction was optimized for the formation of the thiocarbonylation product (in CH2CI2) to give 1,4-addition products in good yields. 

Hydrogenation of CPD and DCPD with noble metal catalysts tends to produce a mixture of dihydro and tetrahydro derivatives. If only the dihydro derivatives are to be produced, selective hydrogenation catalysts must be used. Hydrogenation catalysts designed for the conversions of conjugated diolefins like 1,3-butadiene or isoprene to the olefins have been used for this service. These catalysts are mostly palladium metal modified with one or more promoters (33). 

A detailed study of the hydrogenation of valylene (2-methyl-but-l-ene-3-yne) and isoprene has shown that palladium catalysts poisoned with lead can give highly chemoselective reductions. ... 

T.-B. Lin, T.-C. Chou, 1994, Selective hydrogenation of isoprene on eggshell and uniform palladium profile catalysts, Apphed Catalysis A General, 108,7-19. 

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