Hydrogenation of acetylene and ethylene

Adsorbed hydrogen atoms which are the intermediates of reaction 8 can be used for the hydrogenation of ethylene and acetylene. The light driven reaction occurs according to the following scheme ... 

For the hydrogenation of ethylene and acetylene with chloroplatinic acid and stannous chloride as catalyst, a number of steps have been outlined which are characteristic of the mechanism 305). These steps are (1) competitive formation of a rr-ethyleneplatinum and a hydroplatinum complex (2) formation of the hydro-rr-ethyleneplatinum complex (3) rearrangement by insertion to form an ethylplatinum complex and (4) attack of the protonic hydrogen on the metal-carbon bond to form ethane and the catalyst. The reduction of acetylene to ethane proceeds via the intermediate formation of ethylene. 

Platinum. Rate laws have been determined for homogeneous hydrogenation of ethylene and acetylene in the presence of platinum(n)-tin(ii) catalysts. This kinetic evidence and ancillary results from deuterium tracer experiments suggest a mechanism in which the molecular hydrogen is split heterolytically to give a Pt—H bond plus H+ ethylene or acetylene then... 

The indirect cyclisation of bromoacetals via cobaloxime(I) complexes was first reported in 1985 [67], At that time the reactions were conducted in a divided cell in the presence of a base (40yo aqeous NaOH) and about 50% of chloropyridine cobaloximeflll) as catalyst precursor. It was recently found that the amount of catalyst can be reduced to 5% (turnover of ca. 50) and that the base is no longer necessary when the reactions are conducted in an undivided cell in the presence of a zinc anode [68, 69]. The method has now been applied with cobaloxime or Co[C2(DOXDOH)p ] to a variety of ethylenic and acetylenic compounds to prepare fused bicyclic derivatives (Table 7, entry 1). The cyclic product can be either saturated or unsaturated depending on the amount of catalyst used, the cathode potential, and the presence of a hydrogen donor, e.g., RSH (Table 7, entry 2). The electrochemical method was found with some model reactions to be more selective and more efficient than the chemical route using Zn as reductant [70]. 

Addition of hydrogen to compounds with multiple bonds, such as the formation of ethane from ethylene or acetylene. Rideal1 found 137° C. to be the optimum temperature for the hydrogenation of ethylene, and considers the mechanism of the process to be explicable on the hypothesis of Langmuir 2 that the reaction proceeds in a unimolecular film on the surface of the nickel catalyst. 

Adsorption of ethylene and acetylene on platinum in the presence of hydrogen was investigated using elastic recoil detection analysis (ERDA). Below 200 K no change was observed for acetylene, while at room temperature C2H3 radicals were formed The geometry of acetylene adsorbed on the Ni (100) face was determined by LEED (low energy electron diffraction) intensity analysis. ... 

Another approach to understanding the yields of ethylene and acetylene has been suggested by Back et al. (1963). The degree of saturation of the products (CjHg, O2H4 and C2H2) formed is assumed to be proportional primarily to the amount of hydrogen available at the insertion site (no distinction is made whether by carbon atoms or by... 

The effect of hyperconjugative interactions can be evaluated from the difference between the heats of hydrogenation of ethylene and 1-butene that provides an estimate for stabilization of ethylene (in kcal/mol) by an ethyl substituent (2.4G3 2.2G3- (MP2) 2.7 experimental). Likewise, the hyperconjugative stabilization of acetylene by an ethyl group (4.9G3 4.8G3(MP2) 4.7 expt) is the difference between the heat of hydrogenation of acetylene and 1-butyne. Equivalently, the hyperconjugative stabilization can also be described by isodesmic reactions in Figure 6.130 that produces data consistent with the above evaluation ... 

A snag was that these companies now had to dispose of hydrogen chloride. The most elegant solution was to react this with acetylene in a separate stage, to give what became known as the Balanced Process. This scheme became a driving force for naphtha cracking to mixtures of ethylene and acetylene, as exemplified by the Wulff process. 

Neurock and co-workers used ab initio calculations to determine the influence of both Ag and Au on Pd for the hydrogenation reaction of ethylene and 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... 

By-products from EDC pyrolysis typically include acetjiene, ethylene, methyl chloride, ethyl chloride, 1,3-butadiene, vinylacetylene, benzene, chloroprene, vinyUdene chloride, 1,1-dichloroethane, chloroform, carbon tetrachloride, 1,1,1-trichloroethane [71-55-6] and other chlorinated hydrocarbons (78). Most of these impurities remain with the unconverted EDC, and are subsequendy removed in EDC purification as light and heavy ends. The lightest compounds, ethylene and acetylene, are taken off with the HCl and end up in the oxychlorination reactor feed. The acetylene can be selectively hydrogenated to ethylene. The compounds that have boiling points near that of vinyl chloride, ie, methyl chloride and 1,3-butadiene, will codistiU with the vinyl chloride product. Chlorine or carbon tetrachloride addition to the pyrolysis reactor feed has been used to suppress methyl chloride formation, whereas 1,3-butadiene, which interferes with PVC polymerization, can be removed by treatment with chlorine or HCl, or by selective hydrogenation. 

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