Ethylene dimerizations/codimerizations

Propjiene (qv) [115-07-1] is the predominant 0x0 process olefin feedstock. Ethylene (qv) [74-85-1J, as well as a wide variety of terminal, internal, and mixed olefin streams, are also hydroformylated commercially. Branched-chain olefins include octenes, nonenes, and dodecenes from fractionation of oligomers of C —C olefins as well as octenes from dimerization and codimerization of isobutylene and 1- and 2-butenes (see Butylenes). 

The rate equation for the dimerization of ethylene (5) can be used to describe the codimerization in the presence of large excesses of butadiene. The rate of the addition reaction as measured by the disappearance of ethylene is represented in Eq. (5). It is first order in ethylene, proton, chloride, and rhodium. 

In the codimerization reaction, both reactants are present in large excess compared to the catalyst concentration. The selectivity toward a 1 1 codimerization to form 1,4-hexadiene, instead of a random oligomerization, represents a rather unique reaction, especially in view of the fact that the same catalyst also dimerizes ethylene to butene (3) at about the same rate as the codimerization. The explanation forwarded by Cramer (4, 7) is based on the overwhelmingly favored stability of the tt-... 

The nickel catalyst under the condition for the 1 1 codimerization is not known to dimerize or polymerize ethylene, although a similar catalyst system has been known to dimerize propylene (26, 27) via a w-allyl intermediate. 

Figure 7.6 Industrial use of (from the top) propylene dimerization, butadiene dimerization, butadiene trimer-ization, and butadiene plus ethylene codimerization. In EPDM rubber, the terminal double bond of 1,4-hexadiene takes part in polymer formation. The internal double bond is used during curing.

Olehns with four to eight carbon atoms can be obtained by dimerization and codimerization of ethylene, propylene and butenes. 

Under similar conditions, methylenecyclopropane reacted with norbornene to yield a mixture of cycloadduct (2, 78%) and dimer (7, 21%). With norbornadiene and a nickel catalyst only the [2-1-2] cycloadduct was formed. " The codimerization of 2-phenylmethylenecyclo-propane and ethylene in the presence of a triisopropylphosphane modified palladium(O) catalyst... 

The 1,4-hexadiene is made by codimerization of ethylene and butadiene, with a RhCls/EtOH catalyst (Eq. 12.16). The catalyst is about 80% selective for the rnms-i,4-hexadiene, a remarkable figure considering all the different dimers Chat could have been formed. The catalyst is believed to be a rhodium hydride formed by reduction of the RhCls with the ethanol solvent (Section 3.2). This must react with the butadiene to give mostly the ann -methylallyl (crotyl) intennediate, which selectively inserts an ethylene at the unsubstituted end. The ds/trans ratio of the product Hobably depends on the ratio of the two isomers of the crotyl... 

See Table VIII. Titanium based catalysts dimerize ethylene to 1-butene and codimerize ethylene and 1-butene into mixed hexenes (probably for steric reasons titanium is unable to homodimerize 1-butene or other... 

The trans isomer of 1,4-hexadiene is one of the required monomers for EPDM rubber. Although iron-, cobalt-, and nickel-based Ziegler-type catalysts can codimerize butadiene and ethylene, the selectivity to the desired trans isomer is low. A soluble rhodium complex can, however, catalyze the dimerization with high selectivity to the trans isomer. 

Ans (a) Dimerization of butadiene followed by selective hydrogenation followed by ROMP see reaction 7.2.3 (b) and (c) trimerization of butadiene followed by several other steps see reactions 7.2.4 and 7.2.5 (d) codimerization of butadiene and ethylene to trans-Ud-hexadiene, followed by copolymerization of ethylene, propylene, and 1,4-hexadiene. They are aU specialty polymers. 

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