Hydrogenation, of acetylene

Ethylene. During Wodd War 11 the Germans manufactured more than 60,000 t/yr of ethylene [74-85-1], by hydrogenation of acetylene,... 

Hydrogenation. Acetylene can be hydrogenated to ethylene and ethane. The reduction of acetylene occurs in an ammoniacal solution of chromous chloride (20) or in a solution of chromous salts in H2SO4 (20). The selective catalytic hydrogenation of acetylene to ethylene, which proceeds... 

Hydrogenation of Acetylenes. Complete hydrogenation of acetylenes to the corresponding alkanes, which maybe requited to remove acetylenic species from a mixture, or as a part of a multistep synthesis, may be accompHshed using <5 wt % palladium or platinum on alumina in a nonreactive solvent under very mild conditions, ie, <100°C, <1 MPa (10 atm). Platinum is preferred in those cases where it is desired to avoid isomeri2ation of the intermediate olefin. Silver on alumina also can be used in this appHcation as can unsupported platinum metal. 

Since both complete hydrogenation of acetylene or any hydrogenation of the ethylene results in the production of a less valuable product such as ethane, conditions must be chosen carefiiUy and a catalyst must be used that is both sufficiently active for acetylene hydrogenation and extremely selective to avoid ethylene hydrogenation. Since hydrogenation of acetylenic bonds proceeds stepwise and since acetylene is more strongly adsorbed on the catalytic... 

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. 

Hydrogenation of acetylenes to olefins, 134 Hydrogenation of dienes, 124 Hydrogenation of dienones, 130 Hydrogenation of enones, 130... 

Highly stereospecific hydrogenations of acetylenes to cis olefins have been achieved also with nickel (P 2) catalysts in the presence of ethylenediamine as prorrtoter (37 8 55 58,72). The catalyst is prepared by reduction of nickel acetate in ethanol with sodium borohydridefi ). Despite successes (44), the use of nickel is relatively infrequent (51). 

Amines (7a,12a), especially pyridine (75), have also been used as solvents in the hydrogenation of acetylenes. Hydrogenation of 3 over 5% Pd-on-BaS04 in pyridine gave df-cis-jasmanate (4) quantitatively (40). The authors comment that this combination for reduction of acetylenes was superior to the Lindlar catalyst in all cases examined. (See also Refs. 12 and 24 for similar conclusions.)... 

Hydrogenation of acetylenic carbinols is sometimes accompanied by isomerization to the ketone. In the case of 13, the isomerization to 15 was most pronounced when hydrogenations proceeded very slowly as when impure 13 was used (39). 

Fig. 2. Pressure fall —AP (Torr) against time t (arbitrary units) in hydrogenation of acetylene on Pt/AhOa catalyst at 110°C and Pst/Pctnt 2. In the initial slow period of the reaction the main product is ethylene, and after the acceleration, further hydrogenation of ethylene to ethane predominates. From G. C. Bond and P. B. Wells, J. CaM. 4, 211 (1965).

Concerning consecutive reactions, a typical example is the hydrogenation of alkynes through alkenes to alkanes. Alkenes are more reactive alkynes, however, are much more strongly adsorbed, particularly on some group VIII noble metal catalysts. This situation is illustrated in Fig. 2 for a platinum catalyst, which was taken from the studies by Bond and Wells (45, 46) on hydrogenation of acetylene. The figure shows the decrease of... 

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. 

The process is characterized by high yield (nearly complete hydrogenation of acetylenes) and high selectivity (only a small loss of butadiene by hydrogenation). The process does not lead to polymerization, which might otherwise cause catalyst deactivation, and only infrequent regeneration of catalyst is necessary. 

S. Tracey, A. Palermo, J.P.H. Vazquez, and R.M. Lambert, In Situ Electrochemical Promotion by Sodium of the Selective Hydrogenation of Acetylene over Platinum, J. Catal. 179, 231-240 (1998). 

The much more stable MIL-lOO(Cr) lattice can also be impregnated with Pd(acac)2 via incipient wetness impregnation the loaded catalyst is active for the hydrogenation of styrene and the hydrogenation of acetylene and acetylene-ethene mixtures to ethane [58]. MIL-lOl(Cr) has been loaded with Pd using a complex multistep procedure involving an addition of ethylene diamine on the open Cr sites of the framework. The Pd-loaded MIL-lOl(Cr) is an active heterogeneous Heck catalyst for the reaction of acrylic acid with iodobenzene [73]. 

Hydrogenation of acetylene into ethylene gave rise to an accident (this reaction is no longer carried out on an industrial level). The temperature was fixed at 400°C by mistake. The ethylene reached a temperature of 950°C because of the exothermicity of the reaction. Its decomposition caused the installation to detonate and led to a fire which took four days to put out. It was assumed that the degradation had led to the formation of methane and hydrogen given the pressure that was reached. 

Palladium is good for hydrogenations of most unsaturations except benzenes. It is frequently used by synthetic organic chemists for hydrogenolyzing off protecting groups. It is especially useful for the half-hydrogenation of acetylenes. 

The points for Ag and Pd-Ag alloys lie on the same straight line, a compensation effect, but the pure Pd point lies above the Pd-Ag line. In fact, the point for pure Pd lies on the line for Pd-Rh alloys, whereas the other pure metal in this series, i.e., rhodium is anomalous, falling well below the Pd-Rh line. Examination of the many compensation effect plots given in Bond s Catalysis by Metals (155) shows that often one or other of the pure metals in a series of catalysts consisting of two metals and their alloys falls off the plot. Examples include CO oxidation and formic acid decomposition over Pd-Au catalysts, parahydrogen conversion (Pt-Cu) and the hydrogenation of acetylene (Cu-Ni, Co-Ni), ethylene (Pt-Cu), and benzene (Cu-Ni). In some cases, where alloy catalysts containing only a small addition of the second component have been studied, then such catalysts are also found to be anomalous, like the pure metal which they approximate in composition. 

Partial hydrogenation of acetylenic compounds bearing a functional group such as a double bond has also been studied in relation to the preparation of important vitamins and fragrances. For example, selective hydrogenation of the triple bond of acetylenic alcohols and the double bond of olefin alcohols (linalol, isophytol) was performed with Pd colloids, as well as with bimetallic nanoparticles Pd/Au, Pd/Pt or Pd/Zn stabilized by a block copolymer (polystyrene-poly-4-vinylpyridine) (Scheme 9.8). The best activity (TOF 49.2 s 1) and selectivity (>99.5%) were obtained in toluene with Pd/Pt bimetallic catalyst due to the influence of the modifying metal [87, 88]. 

Scheme 12.8 Hydrogenation of acetylene dicarboxylic acid dimethylester to the corresponding maleate [8 a].

It has been proposed (Shankar, PhD Thesis, Monash University, Australia, 1976) that the gas phase catalytic hydrogenation of acetylene occurs by... 

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