1-Butene, hydrogenation over

Following a variation of the well-known Horiuti-Polanyi mechanism, we consider the following steps as possible for the system -butane- -butenes-hydrogen over chromia alumina catalyst ... 

The first step is the liquid phase addition of acetic acid to butadiene. The acetoxylation reaction occurs at approximately 80°C and 27 atmospheres over a Pd-Te catalyst system. The reaction favors the 1,4-addition product (l,4-diacetoxy-2-butene). Hydrogenation of diacetoxybutene at 80°C and 60 atmospheres over a Ni/Zn catalyst yields 1,4-diacetoxybu-tane. The latter compound is hydrolyzed to 1,4-butanediol and acetic acid ... 

From the results of other authors should be mentioned the observation of a similar effect, e.g. in the oxidation of olefins on nickel oxide (118), where the retardation of the reaction of 1-butene by cis-2-butene was greater than the effect of 1-butene on the reaction of m-2-butene the ratio of the adsorption coefficients Kcia h/Kwas 1.45. In a study on hydrogenation over C03O4 it was reported (109) that the reactivities of ethylene and propylene were nearly the same (1.17 in favor of propylene), when measured separately, whereas the ratio of adsorption coefficients was 8.4 in favor of ethylene. This led in the competitive arrangement to preferential hydrogenation of ethylene. A similar phenomenon occurs in the catalytic reduction of nitric oxide and sulfur dioxide by carbon monoxide (120a). 

Fig. 16. Butene-1 hydrogenation over Cu-Ni alloy films, annealed in hydrogen at 530°C (117).

Proposed Mechanism for Butadiene Reduction. The above results are compatible with the reaction sequence illustrated below. In the absence of a hydrogen atmosphere, CoH, formed via the aging reaction of cyanocobaltate(II), reacts reversibly with butadiene to yield Co(C4H7) which reacts further with CoH and/ or undergoes hydrolysis to yield butenes. The over-all result is oxidation of cyano-cobaltate(II) to cyanocobaltate(III) with concomitant reduction of butadiene to butenes. 

One of the earliest studies of n-butene hydrogenation was that reported by Twigg [121] who observed that, for the reaction of l butene with hydrogen over a nickel wire between 76 and 126°C, both hydrogenation and double-bond migration occurred. Hydrogenation and double-bond migration followed the same kinetic rate law, namely... 

Activation energies for butene hydrogenation and isomerisation over a nickel wire catalyst [122]... 

The hydrogenation of buta-1 2-diene appears to have received relatively little attention. Over palladium—alumina at room temperature, the products of the gas phase hydrogenation were c/s-but-2-ene, 52% but-l-ene, 40% frans-but-2-ene, 7% and n-butane, 1% [189]. Some isomerisation of the buta-1 2-diene to but-2-yne (10%) together with traces of but-l-yne and buta-1 3-diene was also observed. A similar butene distribution (namely, cis-but-2-ene 52%, but-l-ene 45% and frans-but-2-ene 3%) was observed in the liquid phase hydrogenation over palladium [186]. 

Petrov and co-workers polymerized acetylene with simultaneous hydrogenation over nickel or nickel plus zinc chloride and obtained saturated and olefinic products. The ratio of products boiling in the gasoline range to heavier products depended upon the catalyst as well as the pressure. The liquid obtained from nickel consisted of a gasoline obtained in 50 % yield in the runs under atmospheric pressure, and in 70 % yield under 20 atm. pressure. The rest comprised diesel fuel hydrocarbons (292). The structure of the liquid hydrocarbons formed was unaffected by the presence of phosphoric acid or zinc in the catalyst. The gas contained up to 80% butenes, depending upon the conditions. This work of Petrov on the synthesis of hydrocarbons is apparently being continued at the present time. 

The importance of H2S adsorption from the point of view of the over-all reaction is shown by its effect on butene hydrogenation and on thiophene conversion (Figure 2). These indicate that H2S adsorption competes for sites which are essential to the reaction. Since its effect on thiophene adsorption was to cut peak delay by only 10 to 30%, it may be that H2S competes for hydrogen adsorption... 

For the compound numbers, see Scheme 3.16. No butane and butenes were observed for the hydrogenations over the catalysts other than Adams platinum. 

The normal butenes were pyrolyzed in the presence of steam in a nonisothermal flow reactor at 730°-980°C and contact times between 0.04 and 0.15 sec to obtain conversion covering the range between 3% and 99%. Isomerization reactions accompanied the decomposition of these olefins however, the decomposition was the dominant reaction under these conditions. Pyrolysis of 1-butene is faster than that of either cis- or trans-2-butene. Methane, propylene, and butadiene are initial as well as major products from the pyrolysis of the n-butenes. Hydrogen is an initial product only from the 2-butenes. Ethylene appears to be an initial product only from 1-butene it becomes the most prominent product at high conversions. Over the range of conditions of potential practical interest, the experimental rate expressions for the disappearance of the respective butene isomers, have been derived. 

Figure 31 Competitive hydrogenation of 1-heptene (O) and 3,3-dimethyl-l-butene (A) over Ti02/Pt catalyst at 100°C...

Fig. 11. The exchange of cts-2-butene and the deuterium content of the isomerized butenes as a function of percentage hydrogenation, over palladium-alumina at 18° (31).

Fig. 19. The isomerization of 1-butene during its hydrogenation over rhodium-alumina at 166 (31). The dotted lines show the equilibrium concentrations expected at this temperature.

It is not intended that the literature concerning the hydrogenation of alkenylalkynes and dialkynes shall be reviewed in detail. However, the hydrogenation of molecules as unsaturated as these provides further examples of the operation of the thermodynamic factor which are of interest. The palladium-, platinum-, and nickel-catalyzed hydrogenations of vinylacetylene (H2C=CH—C=CH) provides 1,3-butadiene as the major initial product butenes and butane are also produced (57). The product distributions are constant in liquid phase reactions until the parent hydrocarbon has been removed, showing that vinylacetylene is more strongly adsorbed than 1,3-butadiene and the butenes. The relative yields of butenes and butane resemble those obtained in 1,3-butadiene hydrogenation over these metals (see Section III, F, 6). 

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