1-Hexene isomerisation

P-24 - Zirconium containing Al-MCM-41- synthesis, characterisation and catalytic performance in 1-hexene isomerisation... 

Let us employ the example of 1-hexene isomerisation. The reaction mixture is formed by a total of 17 isomeric hexenes. Clearly the matrix of constitution coefficients will consist of 17 equal rows (6 12). The rank of this matrix will be H = 1 16 linearly independent reactions are possible, i.e. skeleton isomerisation, doublebond shift along the chain and cis-trans conversion. Basing the calculation on 1 mole of 1-hexene, the set (5.121) will be reduced to a single equation of the type... 

A series of zeolite-Y hosts containing different proton concentrations has been used for MTO encapsulation [80], and the resulting materials were studied for 1-hexene metathesis. The MTO molecule was activated by intra-zeolite protons, and simultaneously blocks their isomerisation activity. The ability to tune intra-zeolite acidity and the doping levels of the intact MTO precatalyst permits control over selectivity in the metathesis reaction. 

Table 21.3 Reaction products from isomerisation and degradation of (Z)-3-hexenal...

A patented process for the production of green notes applying bakers yeast for in situ reduction of enzymatically produced aldehydes [67, 68] has been called into question regarding the effective production of (Z)-3-hexenol. According to Gatfield s report [69] the isomerisation of (Z)-3-hexenol to (E)-2-hexenal is a very fast process. The latter undergoes facile conversion to hexanol. Beside this, baker s yeast can add activated acetaldehyde to ( )-2-hexenal, forming 4-octen-2,3-diol. 

Adsorption of hex-l-ene, a mixture of cis- and frans-hex-2-ene, and c/s-hex-3-ene on nickel—silica results in identical infrared spectra [83]. Addition of hydrogen results in an intensification of the spectrum suggesting that the initial spectrum results from dissociatively adsorbed species, a conclusion substantiated by the observation that the gas in equilibrium with the surface during the initial adsorption contains isomerised hexenes. Evacuation of the hydrogen causes a decrease in intensity and the reappearance of the initial spectrum. 

If 1-butene or 1-hexene is chosen instead of propylene as the monomer polymerising with the Me2C(MeCp)(Flu)ZrCl2-based catalyst, the polymers obtained become enriched in m diads. This has been suggested to testify to the preference of site isomerisation prior to the coordination of the next monomer molecule with increasing size of the polymerising a-olefin [121]. 

One problem of 2,co-polymerisation is that the molecular weight of the product, poly[2,co-(a-olefin)], is always very low (Mw k6x 103), whereas the molecular weight distribution is small (Mw/Mn ss 1.6). It is possible, however, to increase the molecular weight of the polymer, e.g. the molecular weight of poly[2,6-(l-hexene)], to Mw 90 x 103 by increasing the reaction pressure to 1400 MPa. The reason for this is the possible kinetic pressure effect in the case of 1-hexene in which the insertion but not the isomerisation is the rate determining step for 2,co-polymerisation [183]. 

Ligand Hex-l-ene % Isomerised hexenes % 2-ethyl- pentanal % 2-methyl- pentanal % Heptanal % Conversion % Selectivity to aldehydes % n i ratio... 

When properly optimized, the metal function of the catalysts essentially maintains hexane-hexene equilibrium. The reaction energy scheme deduced" for hexene protonation and isomerisation is shown in figure 2. 

Extension of the linear carbon chain to five or six atoms opens up additional possible reaction paths. Higher 1,3-alkadienes are expected to behave in a similar fashion to 1,3-butadiene, except the two double bonds may differ in reactivity under the influence of the alkyl substituent, and their reduction naturally affords distinguishable products. Thus for example 1,3-hexadiene can give 1- and 3-hexenes by respectively 3,4- and 1,2-addition as well as 2-hexenes by 1,4-addition or isomerisation. A new feature in the higher 1,3- alkadienes is the existence of geometrical isomerism Z- and -l,3-pentadienes have been examined separately. ... 

Using a mesostmctnred alnminosiUcate of the MCM-41 type with the same composition but varying the pore size from 2.3 to 9.3 mn, Tanchoux et al measnred the adsorption energetics and the catalytic isomerisation of 1-hexene. The authors could demonstrate that the geometry-dependent contributions dominated catalytic behaviour over all other factors. 

CpRu( feCN) T)2-P(Oallyl)3 ]PF5. Allylic alcohols are isomerised to ketones under photochemical conditions using Fc3(CX))i2> In comparison, [Ru(H20)5p transforms hexene into 2- and 34iexene as (E) isomers under mild thermal conditions (35 Hartree-Fock... 

Diisocyano-Rh dimers photocatalytically decompose water [13] and diisocyano complexes catalyze hydrogenation and isomerisation of alkenes and alkynes (although they are far less active than the Wilkinsons catalyst [14]). Alkene hydrogenation is a probe reaction for such reaction centres, especially since the hydrogenation of alk-l-enes over Wilkinson s catalyst [hydrido-carbonyl tris(triphenylphosphine).Rh ] in benzene is quite selective (i.e. was 45 times faster than the cis-aIk-2-ene [15]). Surprisingly, the active centres in such catalysts are still not entirely understood, despite extensive analysis [16]. Rh complexed with 4,4 -diisocyanobiphenyl and 1,4-diisocyanobenzene is active in hydrogenation and isomerization of 1-hexene [14], while Rh complexed with aliphatic amines is active in catalysis of hydrogenation of alkenes and cycloalkenes [16]. 

In hydrozirconation with Schwartz s reagent, Cp2ZrHCl, addition to al-kenes leads to the anti-Markovnikov alkyl (Eq. 14.40). Remarkably, 1-, 2-, and 3-hexene all give the same n-hexyl product. The reason must be that the initially formed alkyls -eliminate. This moves the C=C bond along the chain in an alkene isomerisation reaction (Section 9.1), until the least hindered and thermodynamically most stable n-hexyl complex is formed (Eq. 14.41) ... 

Saim and Subramanian addressed the effect of supercritical CO2 as solvent media in the homogeneous chemical equilibria of different reacting systems, including the isomerisation of hexane and 1-hexene and the oxidation of 2-methylpropane. The Peng-Robinson equation of state was used to calculate the critical loci of CO2 with each hydrocarbon the information was used to avoid the two-phase region in the computation of conversion for each system studied. 

Our CNDO/S calculations on E-and Z-3-hexen--l,5-di3mes show that the Z-isomer should absorb at a longer wavelength than the E-isomer, which means that cis-trans isomerisation should have a similar effect in the absorption properties of the enyne-and the polyene systems, as well. The prediction and the observation are consistent in the case of 1,4-diphenylbutenynes. Both isomer may have a stable fully conjugated planar conformation, since no repulsion is expected between the phenyl group and the triple bond in these compounds. 

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