Hexenes from propylene dimerization

A square-planar nickel hydride complex is suggested as the catalytic species [589]. In the first step, the nickel hydride catalyst adds across the double bond of propylene to give two intermediates, namely, a propyl nickel and isopropyl nickel complex. Both of these intermediates can react further with propylene by insertion of the double bond into the nickel-carbon bond, resulting in formation of four more intermediates. ( -Elimination of nickel hydride from these intermediates produces the possible products of propylene dimerization, namely, 4-methyl-1-pen-tene, cis- and trans-4-methyl-2-pentene, 2,3-dimethyl-l-butene, n-hexene, 2-hexene, and 2-methyl-l-pentene. Terminal unbranched olefins are rapidly isomerized under the influence of catalyst by a process of repeated nickel hydride addition and elimination to the internal olefins. Therefore, under ordinary reaction conditions the yield of 4-methyl-l-pentene is low. 

Ethylene for polymerization to the most widely used polymer can be made by the dehydration of ethanol from fermentation (12.1).6 The ethanol used need not be anhydrous. Dehydration of 20% aqueous ethanol over HZSM-5 zeolite gave 76-83% ethylene, 2% ethane, 6.6% propylene, 2% propane, 4% butenes, and 3% /3-butane.7 Presumably, the paraffins could be dehydrogenated catalyti-cally after separation from the olefins.8 Ethylene can be dimerized to 1-butene with a nickel catalyst.9 It can be trimerized to 1-hexene with a chromium catalyst with 95% selectivity at 70% conversion.10 Ethylene is often copolymerized with 1-hexene to produce linear low-density polyethylene. Brookhart and co-workers have developed iron, cobalt, nickel, and palladium dimine catalysts that produce similar branched polyethylene from ethylene alone.11 Mixed higher olefins can be made by reaction of ethylene with triethylaluminum or by the Shell higher olefins process, which employs a nickel phosphine catalyst. 

Table 4 also summarizes the calculated activation barriers of all the typical reactions (in Scheme 17) during the induction period over catalyst models similar to 4g, 4g-l, and 4g-2 except that both Si atoms within each model were fully fluorinated. Fluorination of the silica support for the F-modified Phillips catalyst showed negligible influence on ethylene dimerization to 1-butene and metathesis to propylene [160], However, the energy barrier was increased significantly in reaction 5 of Scheme 17, in which 1-hexene was formed from the chromacycloheptane species through a one-step intramolecular hydrogen shift. Fluorination showed a positive effect on ring expansion in reaction 4 of Scheme 17. 

This trend toward new nses of low-cost feeds for adding value to surfactants is continuing. Recently, BASF reported specific C13 detergent alcohols from hydroformylation of a C 2 olefin derived from dimerization of 3-hexene, a by-product of butane metathesis to propylene. - " Since 3-hexene appears to have no direct market value compared to ethylene, expectations are that the cost of the alcohol will be competitive with the ethylene-based alcohols. 

In the dimerization of propylene with a 1 45 16 Ni Al P mole ratio for the Ni(acac)2-Et2Al2Cl3-PPh3 system, raising the reaction temperature from —50 to 40°C decreases the yield of 2-methylpentenes [599]. The yield of 2,3-dimethyl-hutenes increases, and the yield of hexenes remain constant. An increase in the P/Ni ratio from 0 to 8 at Al/Ni ratio of 45 is associated with a decrease of hexenes and an increase of 2,3-dimethylbutenes. 

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