Palladium catalyst poisoning

The nature of the unsaturated hydrocarbon has a very important role in the sulfur action Berenblyum et al. (83) have reactivated a palladium catalyst, poisoned with thiols, through the interaction with phenylacethyl-ene the presence of acetylenics together with low levels of sulfur even activate the nickel sites activity for acetylene hydrogenation (84, 85). 

The Intermediate In this synthesis of disparlure, (Z)-2-tridecenol, Is obtained by hydrogenation of 2-trldecynol In the presence of a palladium catalyst poisoned with barium sulfate and quinoline. Oxidation of (Z)-2-tridecenol with tert-butyl hydroperoxlde/tItanium tetralsopropoxlde/D (-)-diethyl tartrate gives (2R, 3S)-epoxytrldecanol In enantiomeric excess reported to be as much as 98 percent after recrystalllzatlon. 

Similar deactivation is observed with bismuth and copper salts. A palladium catalyst poisoned with quinoline-sulfur and support on barium sulfate is used in the Rosenmund-Saytzeff reaction (p. 67). 

Other partially poisoned catalysts have long been used in the laboratory. Supported palladium catalysts, poisoned with lead (Lindlar catalysts), sulfur, or quinoline, are used for the hydrogenation of acetylenic compounds to cis-olefins. Another... 

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. Mallat, S. Szabd and 3. Petrd, Palladium catalysts poisoned by metal ions, Acta Chim. Hung., 119 (1985) 127-133. 

It has been stated that thiourea (about 20 per cent, of the weight of the palladium - barium sulphate) may also be used as a catalyst poison. 

Hydrogenolysis of the acetylene-cumulenes 19 can be achieved by means of a partially poisoned palladium catalyst to yield the regular [22]porphyrin(2.2,2.2) 20 with cisjrans.cis,-trans configuration of the two-carbon bridges. 

The similar phenomenon of poisoning in situ of a palladium catalyst by hydrogen which was in this case the product of a reaction was observed by Brill and Watson (37). The reaction studied was the decomposition of formic acid... 

A similar reaction was studied by Kowaka Jfi) who investigated the catalytic activity of palladium and its alloys with silver in the hydrogenation of ethylene. The author alluded to the poisoning effect of hydrogen pretreatment of the palladium catalyst. 

Quite recently Yasumori el al. (43) have reported the results of their studies on the effect that adsorbed acetylene had on the reaction of ethylene hydrogenation on a palladium catalyst. The catalyst was in the form of foil, and the reaction was carried out at 0°C with a hydrogen pressure of 10 mm Hg. The velocity of the reaction studied was high and no poisoning effect was observed, though under the conditions of the experiment the hydride formation could not be excluded. The obstacles for this reaction to proceed could be particularly great, especially where the catalyst is a metal present in a massive form (as foil, wire etc.). The internal strains... 

The deleterious effects of catalyst poisoning when carrying out asymmetric hydrogenations at low catalyst loading caimot be overemphasised. In order to eliminate the possibility that the substrate synthesis introduced inhibitory impurities, an alternative synthetic protocol was examined (Scheme 7.4). The use of a brominating agent and an expensive palladium catalysed step in the initial route could limit the development of this as an economically favourable process and this was further motivation to examine alternative routes to the hydrogenation substrate. 

The disulfide intermediate was also hydrogenolyzed very efficiently at about 2-3 times the rate of the thiocyanate in selected solvents such as tetrahydrofuran at a lower temperature and pressure, as illustrated in Table 15.2. Of course, in the disulfide hydrogenolysis, no hydrogen cyanide was available as a coproduct to poison the palladium catalyst. 

Hydrogenation reduction of acid chloride to aldehyde using BaS04-poisoned palladium catalyst. Without poison, the resulting aldehyde may be further reduced to alcohol. 

Example 22 removal of allyl group attached to a phosphorus centre with Pd, Pt and Rh complexes is a well established procedure [51] but is inconvenient for synthesis of therapeutic compounds on a large scale. During the deprotection step the palladium catalyst is susceptible to poisoning especially with P-S compounds resulting in loss of catalytic efficiency. Furthermore traces of organometallic compounds remain in the product after deprotection. In the paper of Manoharan et al. other methods of deprotection of allyl... 

Alkynes may also be hydrogenated, initially to alkenes, and then further to alkanes. By suitable modification of the catalyst, it has proved possible to stop the reaction at the intermediate alkene. Typically, platinum or palladium catalysts partially deactivated (poisoned) with lead salts are fonnd to be suitable for reduction of alkynes to alkenes. Again, syn addition is observed. 

It has been found that the rhodium catalyst is not nearly as sensitive to poisoning as platinum or palladium catalyst. The metal inlet tube to the reaction bottle was merely rinsed with acetone, followed by ethanol, and the rubber stopper was soaked in 30-40% sodium hydroxide solution overnight. 

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