Hydrogenation of 1-hexene

Crabtree described the use of dibenzo[a,e]cyclooctatetraene, a potent selective poison of homogeneous hydrogenation catalysts, as a tool to distinguish between homogeneous and heterogeneous catalysis in the hydrogenation of hexene with a range of catalysts [24]. 

This makes it easy to predict that solutions of HRh(PPh3)4 are more active catalysts than solutions of HRh(CO) (PPh3)3, either because the concentration of coordinatively unsaturated complexes increases or because the rate constant of the oxidative addition of hydrogen increases. A kinetic investigation of the hydrogenation of hexene catalyzed by solutions of hydridotetrakis( triphenylphosphine) rhodium (I) is reported here. 

Palladium, rhodium and ruthenium complexes of the Schiff base salen are synthesized in the supercages of zeolite Y. The existence of intracrystalline transition metal-salen complexes is verified by a detailed physicochemical characterization. The catalytic properties of the prepared host/guest inclusion compounds are explored in the hydrogenation of hexene-(l) or an equimolar mixture of hexene-(l) and 2,4,4-trimethylpentene-(l). 

Figure 3. Hydrogenation of hexene-(l) over RusalenY-zeolites with one, two or four RuSalen complexes per unit cell. Reaction conditions T = 70 °C, W/F(,e e g.(i)=7 g h/mol, Phexene-(l) = 7 kPa.

VIII. Processes in the Hydrogenation of Hexenes and in Isotopic Exchange... 

Case Study II Heterogeneously Catalyzed Hydrogenation of Hexene... 

In the presence of dilute sodium or potassium hydroxide, //-butyraldehyde undergoes the aldol reaction to form 2-ethyl-3-hydroxyhexanal [496-03-7] which, on continued heating, is converted iato 2-ethyl-2-hexenal [26266-68-2]. Hydrogenation of the latter gives 2-ethyl-1-hexanol/7 (94-7%., aptincipal plastici2er alcohol. 

What two stereoisomeric alkanes are formed in the catalytic ] hydrogenation of ( )-3-methyl-2-hexene What are the relative amounts of each J... 

Hydrogenation of 2,5-diacetoxy-2,5-dimethyl-3-hexyne 10 over 0% palladium-on-carbon is exceptionally complex. Seven different products are formed together with acetic acid. All are hydrogenolysis products arising from the initially formed 2,5-diacetoxy-2,5-dimethyl-3-hexene 11. One of these, 2,5-dimethyl-2-acetoxy-4-hexene 12 forms in as much as 4S yield. 

Rhodium- and cobalt-catalyzed hydrogenation of butadiene and 1-hexene [47, 48] and the Ru-catalyzed hydrogenation of aromatic compounds [49] and acrylonitrile-butadiene copolymers [50] have also been reported to be successful in ionic liquids. 

Complex 5 was more active than the well-known precious-metal catalysts (palladium on activated carbon Pd/C, the Wilkinson catalyst RhCl(PPh3)3, and Crabtree s catalyst [lr(cod)(PCy3)py]PFg) and the analogous Ai-coordinated Fe complexes 6-8 [29] for the hydrogenation of 1-hexene (Table 2). In mechanistic studies, the NMR data revealed that 5 was converted into the dihydrogen complex 9 via the monodinitrogen complex under hydrogen atmosphere (Scheme 4). 

Table 2 Comparison of iron complexes with transition precious-metal catalysts for the hydrogenation of 1-hexene...

Hydrogenations involving consecutive reactions are common in the organic process industry and even in the hydrogenation of fats. In the fine chemicals industry we have examples of acetylenic (triple) bonds to be selectively converted to olefinic (double) bonds. Lange et al. (1998) have shown, for the comversion of the model substance 2-hexyne into cis-2-hexene, how catalytically active microporous thin-film membranes can accomplish 100% selectivity. This unusual selectivity is attributed to avoidance of backmixing. 

A series of anchored Wilkinson s catalysts were prepared by reacting the homogeneous Wilkinson catalyst with several alumina/heteropoly acid support materials. These catalysts were used to promote the hydrogenation of 1-hexene. The results were compared with those obtained using the homogeneous Wilkinson and a l%Rh/Al203 catalyst with respect to catalyst activity and stabihty as well as the reaction selectivity as measured by the amount of double bond isomerization observed. The effect which the nature of the heteropoly acid exerted on the reaction was also examined. 

Figure 20.2. Reciprocal temperature-rate plot for the determination of the energy of activation for the hydrogenation of 1-hexene over Wilk/STA.

Figure 20.3. Effect of hydrogen pressure on the initial rates of hydrogenation of 1-hexenes over Wilk/STA...

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