Acetylene palladium catalyst

The presence of other functional groups ia an acetylenic molecule frequendy does not affect partial hydrogenation because many groups such as olefins are less strongly adsorbed on the catalytic site. Supported palladium catalysts deactivated with lead (such as the Liadlar catalyst), sulfur, or quinoline have been used for hydrogenation of acetylenic compound to (predominantiy) cis-olefins. 

The depropanizer overhead, Cj and lighter feed is compressed to about 300 psi and then passed over a fixed bed of acetylene removal catalyst, generally palladium on alumina. Because of the very large amount of hydrogen contained in this stream, the operating conditions are critical to selectively hydrogenate the acetylene without degrading the valuable ethylene to ethane. 

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. 

Palladium catalyst foe partial ee DUCTION OF ACETYLENES, 46, 89 Palladium on charcoal, catalyst for reductive methylation of ethyl p-mtrophenylacetate, 47, 69 in reduction of l butyl azidoacetate to glycine J-butyl ester 4B, 47 Palladium oxide as catalyst for reduction of sodium 2 nitrobenzene sulfinate, 47, S... 

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 increase of selectivity in consecutive reactions in favor of the intermediate product may be sometimes extraordinarily high. Thus, for example, in the already cited hydrogenation of acetylene on a platinum and a palladium catalyst (45, 46) or in the hydrogenation or deuteration of 2-butynes on a palladium catalyst (57, 58), high selectivities in favor of reaction intermediates (alkenes) are obtained, even though their hydrogenation is in itself faster than the hydrogenation of alkynes. 

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... 

In 2003, the microwave-assisted coupUng of aryl hahdes with acetylenes using a palladium catalyst were carried out employing a modified Smith Process vial [49]. These vessels, equipped with a polypropylene frit and screw cap at the bottom, and sealed with an aluminum crimp cap fitted with a silicon septum at the top (Fig. 8), faciUtated the processing of approximately 1 g of solid support. Notably, they are compatible with stirring of the reaction mixture and monitoring of the temperature and pressure. 

Haloalkynes (R—C=C—X) react with ArSnBu3 and Cul to give R—C= C—Ar. Acetylene reacts with two equivalents of iodobenzene, in the presence of a palladium catalyst and Cul, to give 1,2-diphenylethyne. 1-Trialkylsilyl alkynes react with 1-haloalkynes, in the presence of a CuCl catalyst, to give diynes and with aryl triflates to give 1-aryl alkynes. Alkynes couple with alkyl halides in the presence of Sml2/Sm. Alkynes react with hypervalent iodine compounds " and with reactive alkanes such as adamantane in the presence of AIBN. ... 

Similar reactions have been carried out on acetylene. Aldehydes add to alkynes in the presence of a rhodium catalyst to give conjugated ketones. In a cyclic version of the addition of aldehydes, 4-pentenal was converted to cyclopen-tanone with a rhodium-complex catalyst. In the presence of a palladium catalyst, a tosylamide group added to an alkene unit to generate A-tosylpyrrolidine derivatives. ... 

There are relatively few examples of C-C bond formation on solid surfaces under UHV conditions. There are virtually no examples of catalytic C-C bond formation under such conditions. Perhaps the closest precedent for the present studies on reduced Ti02 can be found in the studies of Lambert et al. on single crystal Pd surfaces. Early UHV studies demonstrated that acetylene could be trimerized to benzene on the Pd(lll) surface in both TPD and modulated molecular beam experiments [9,10]. Subsequent studies by the same group and others [11,12] demonstrated that this reaction could be catalyzed at atmospheric pressure both by palladium single crystals and supported palladium catalysts. While it is not clear that catalysis was achieved in UHV, these and subsequent studies have provided valuable insights into the mechanism of this reaction as catalyzed by metals, including spectroscopic evidence for the hypothesized metallacyclopentadiene intermediates [10,13,14]. 

Besides palladium catalysts, nickel was also found to be an effective catalyst for the Sonogashira reaction in aqueous media. Recently, Beletskaya et al. reported a Ni(PPh3)2Cl2/CuI-catalyzed Sonogashira coupling reaction of terminal acetylenes with aryl iodides in aqueous dioxane in high yields (Eq. 4.19).39... 

Several syntheses of furans are based upon the use of acetylenes to form carbon-carbon linkages. Of two that employ palladium catalysts,7172 one is outlined in Scheme 11,71 A simpler approach is to treat a 1,3-diketone with... 

A new type of asymmetric hydrosilylation which produces axially chiral allenylsilanes has been reported by use of a palladium catalyst coordinated with the bisPPFOMe ligand 51b.64 The hydrosilylation of l-buten-3-ynes substituted with bulky groups such as tert-butyl at the acetylene terminus took place in a 1,4-fashion to give allenyl(trichloro)-silanes with high selectivity. The highest enantioselectivity (90% ee) was observed in the reaction of 5,5-dimethyl-T hexen-3-yne with trichlorosilane catalyzed by the bisPPFOMe-palladium complex (Scheme 13). 

Primary propargylic formates decarboxylate in the presence of Pd(acac)2 and Bu3P at room temperature to give mainly allenic products (Eq. 9.115) [91]. Initial formation of a propargylic palladium complex, which rearranges to the more stable allenylpalladium species, accounts for this transformation. Under similar conditions, a terminal allenyl formate afforded a 99 1 mixture of allene and acetylene product (Eq. 9.116) [91]. However, a mixture of enyne elimination products was formed when a secondary propargylic carbonate was treated with a palladium catalyst (Eq. 9.117). 

The utility of a palladium catalyst in the synthesis of substituted aryl acetylenes is well established.(7,8,9,10) The end-capping agent I was produced by using a standard catalyst system, dichlorobls(triphenylphosphlne)palladlum (II)/copper (I) iodide/triphenylphosphlne mixture, which has been employed in previously developed ethynylation procedures.(10) The copper (I) iodide is believed to act as a cocatalyst, reducing the palladium (II) complex to the active palladium (0) catalyst. The scheme is shown in Figure 3 (diethylamine is the solvent).(11)... 

In support of the concept that acetylenes form tt complexes with a single surface atom of the catalyst, McQuillin el al. (39) have cited the parellelism between the effect of substances such as amines and phosphines as inhibitors for the hydrogenation of butynediols to butenediols on a palladium catalyst with the ability of these same substances to form complexes with metals of the class to which palladium belongs (40). 

Palladium catalysts are more often modified for special selectivities than platinum catalysts. Palladium prepared by reduction of palladium chloride with sodium borohydride Procedure 4, p. 205) is suitable for the reduction of unsaturated aldehydes to saturated aldehydes [i7]. Palladimn on barium sulfate deactivated with sulfur compounds, most frequently the so-called quinoline-5 obtained by boiling quinoline with sulfur [34], is suitable for the Rosenmund reduction [i5] (p. 144). Palladium on calcium carbonate deactivated by lead acetate Lindlar s catalyst) is used for partial hydrogenation of acetylenes to cw-alkenes [36] (p. 44). 

Acetylenic oximes undergo in a similar manner conversion to 3,5-disubstituted isoxazoles. Thus, oximes 195 in the system K2C03/Me0H at room temperature afforded isoxazoles 196 in excellent yields (equation 85). a, S-Unsaturated ketoximes 197 can be also easily transformed to the corresponding 5-arylisoxazoles 198 (yield up to 95%) by treatment with iodine and potassium iodide. The presence of isoxazoline was detected in the reaction mixture (equation 86) . a, S-Unsaturated ketoximes in the presence of palladium catalyst afforded isoxazolines . 

Addition of acetylene to acetone results in the formation of 2-methyl-3-butyn-2-ol, which is hydrogenated to 2-methyl-3-buten-2-ol in the presence of a palladium catalyst. This product is converted into its acetoacetate derivative with diketene [38] or with ethyl acetoacetate [39]. The acetoacetate undergoes rearrangement when heated (Carroll reaction) to give 6-methyl-5-hepten-2-one ... 

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