Dimerization of Ethylene and Propylene

As we saw in the Chapter 6, the ability of nickel to catalyze the dimerization of ethylene, the so-called nickel effect, was first discovered by Ziegler. Although there are many reports on the uses of other metals, nickel is the metal industrially used for the dimerization of both ethylene and propylene. 

As shown by reactions 7.2.1.1 and 7.2.1.2, selective dimerization of ethylene may take place either by the Cossee mechanism or by the metallacycle mechanism. With the Ni catalysts, the Cossee mechanism operates. The experimental evidence for this is discussed later. 

Complexes 7.4 and 7.5 are intermediates derived from 7.2 by inserting the second propylene molecule in an anti-Markovnikov and 

Markovnikov manner, respectively. Similarly, 7.6 and 7.7 are intermediates from 7.3 by the insertion of the second propylene molecule. These four nickel-alkyl intermediates by /3-eliminations give the products. 

The following points may be noted. First, in 7.5 and 7.7 other /3-carbons are also available and eliminations from those will produce isomers of alkenes, which are not shown. Second, 7.1 can catalyze the isomerization of the products into the other isomers of -hexenes, methyl pentenes, and dimethyl butenes by the chain walk type of mechanism discussed earlier. 

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A one-carbon insertion reaction similar to that proposed above could also be used to account for the observed dimerization of ethylene and propylene by palladium(II) systems (28, 56). A possible route for this reaction is given in Reaction 17. 

After insertion of ethylene occurs, presumably subsequent to coordination to Ni, a (CgFjjNi-CHz-CHz-capped norbornene polymer intermediate is formed. Free rotation about the -CH2-CH2- bond of this intermediate offers two /Miydro-gens that can be readily eliminated to form a neutral NiHfCgFs) species and a vinyl-terminated polynorbornene chain. A similar hydride intermediate has been proposed by Klabunde for the dimerization of ethylene and propylene [61]. 

After treatment of the complexes with OAC active gel-immobilized catalysts are formed. The catalytic activity of the obtained catalysts was studied in the reactions of dimerization of ethylene and propylene. 

Another report from the Klabunde laboratory shows the catalytic dimerization of ethylene and propylene in the presence of arene nickel complexes [32]. 

Certain low-valent early transition metal complexes catalyze the dimerization of ethylene and propylene selectively to 1-butene and 2,3-dimethyl-l-butene. The regioselec-tivity of this dimerization of propene signals a different mechanism than the insertion and elimination mechanism presented in the previous section. The formation of 1-butene occurs selectively because of the absence of a persistent metal hydride complex that isomerizes this olefin to the more stable 2-butene. 

Of prime importance for utilizing the new catalyst was the observation that the products of propylene dimerization with phosphine-modified catalyst system, XVI, are strongly influenced by the nature of the phosphine PR3 (24, 25). To understand the phosphine effect, it is necessary to examine the dimerization of ethylene and of propylene in some detail. The dimerization of ethylene formally involves the addition of the C-H bond of one olefin molecule across the double bond of a second one ... 

Ethylene and propylene episulfides polymerize in THE at 0-70°C in the presence of sodium naphthalene, and (importantly) the polymer contains no naphthalene residues. The reaction involves one-electron transfer followed by dimerization of the resulting radical to give a dithiolate ion. This ion then polymerizes an episulfide by anionic mechanism (Boileau et al. 1967 Scheme 7.14). 

EP is abbreviation, EPM means ethylene and propylene only, EPDM means ethylene, propylene, and dimer Most, about 85%, of EP is EPDM 55% Ethylene, 40% propylene, 5% dimer for cross-linking... 

A number of new processes exploiting metathesis have been developed by Phillips. A novel way to manufacture lubricating oils has been demonstrated.145 The basic reaction is self-metathesis of 1-octene or 1-decene to produce Ci4-C28 internal alkenes. The branched hydrocarbons formed after dimerization and hydrogenation may be utilized as lubricating oils. Metathetical cleavage of isobutylene with propylene or 2-butenes to isoamylenes has a potential in isoprene manufacture.136,146 High isoamylene yields can be achieved by further metathesis of C6+ byproducts with ethylene and propylene. Dehydrogenation to isoprene is already practiced in the transformation of isoamylenes of FCC C5 olefin cuts. 

ReCl5 has been found to act as a Friedel-Crafts catalyst for the alkylation of benzene with ethylene. Ethylbenzene, x-butylbenzene and hexaethylbenzene were formed.612 When propylene was used in place of ethylene, cumene and di-, tri- and tetra-isopropylbenzenes were obtained.613 Ethylbenzene and anisole were also alkylated with ethylene. A carbonium ion mechanism was proposed, in some cases with dimerization of ethylene preceding alkylation. 

Steam cracking of various petroleum fractions is gaining widespread use for the production of olefins. These olefins are produced essentially for use as feed stock for numerous petrochemical processes, but the by-product butylenes and propylenes are sometimes used as feed stock for aviation and motor alkylation units. Ethylene is the most important of the olefins produced from this type of cracking, and propylene is second in importance. These two olefins are normally charged to either alkylation or polymerization units for the production of petrochemicals or petrochemical intermediates. Polyethylene and propylene dimers, trimers, tetramers, and penta-mers are some of the more important polymers produced, while ethybenzene, dodecylbenzene, cumene, diisopropylbenzene, and alkylated... 

The latest industrial application of metathesis was developed by Phillips who started up a plant in late 1985 at Cbannelview, Texas, on the L ondell Petrochemical Complex with a production capacity of 135,000 t/year of propylene from ethylene. This facility carries out the disproportionation of ethylene and 2-butenes, in the vapor phase, around 300 to 350°C, at about 0.5.10 Pa absolute, with a VHSV of 50 to 200 and a once-througb conversion of about 15 per cent 2-butenes are themselves obtained by the dimerization of ethylene in a homogeneous phase, which may be followed by a hydroisomerization step to convert the 1-butene formed (see Sections 13.3.2. A and B). IFP is also developing a liquid phase process in this area. 

Even as a toluene emulsion, these complexes show catalytic activity towards ethylene and propylene which is several orders higher than that of TT-allylnickel halides. Paralleling the increase in catalytic activity, the selectivity of this catalyst is also increased—i.e., the products are mainly ethylene or propylene dimers. The most active catalytic systems for dimerizing ethylene and propylene are obtained by replacing toluene with halogenated hydrocarbons such as chlorobenzene since in these more polar solvents, the complexes XIII are soluble. 

The dimerization reaction has been carried out under two different conditions. In laboratory experiments, the reaction is conveniently carried out under 1 or less than 1 atmosphere and at a temperature of —20° to — 10°C. These relatively low temperatures are necessary to obtain a sufficient concentration of ethylene or propylene in the catalyst solution. The dimerization catalyst for laboratory experiments is usually prepared by mixing, for example, chlorobenzene solutions of a 7r-allylnickel halide and an aluminum halide (or alkylhalide) in molar ratio of at least 1 1. The phosphine-modified catalyst is obtained by simply adding 1 mole of a phosphine per mole of nickel to the solution of the catalyst. When ethylene or propylene is introduced into the catalyst solution, reaction starts immediately, as evidenced by a sudden rise in temperature. Dimerization is exothermic to the extent of about 28 kcal./mole propylene dimer. Hence, the mixture must be stirred and cooled intensively during the reaction. Under these conditions (Table V), reaction rates of about 6 kg. 

Allhtnigh the rate of reaction of olefins with nitrosyl chloride decreases with ilecreiising number of alkyl substituents, crystalline nitroso chlorides (dimeric) have been obtained even from ethylene and propylene. ... 

Propene and higher a-olefins also may be dimerized or oligomerized by these catalysts. Generally, reactivity is much lower than that of ethylene and decreases in the order ethylene propylene > 1-butene > 1-hexene > 1-octene > 1-decene. Also the selectivity is lower and mainly branched dimers or oligomers are formed. ... 

The dimerization of ethylene to form a mixture of butene isomers is not particularly useful in the field of commodity chemicals at this time because this mixture of butenes is usually cheaper than ethylene. Selective dimerization of ethylene to 1-butene using a titanium catalyst is practiced, but this chemistry occurs through metallacycles and is described in the next section. The dimerization of propylene by migratory insertion chemistry typically produces the mixture of isomeric olefins shown in Equation 22.32. Four skeletal isomers of the intermediate metal alkyl can arise from the two different directions of M-H insertion, followed by two different inodes of M-R insertion. The dimerization of ethylene is particularly fast when catalyzed by the combination of NiBr(-r) -C3H5)(PCy3) and EtAlCl this dimerization in chlorobenzene at 25 °C occurs witii turnover frequencies up to 60,000 per second. The more selective dimerization of propene to 2,3-dimethylbutene is conducted on an industrial scale with titanium catalysts, again via metallac clic intermediates described in the next section. 

Organoaluminum compounds are used as polymerization catalysts of butene, isoprene and butadiene besides ethylene and propylene, dimerization catalysts of linear higher a-olefins, linear higher-a-alcohols and olefins, productions of organo-metallic compounds such as organotin compounds and organolead compounds, productions of high purity alumina and aluminum thin film. 

In addition to ethylene and propylene oxide, a variety of other cyclic ethers have also been copolymerized with MA. Monomers such as cyclohexene oxide,piperylene dimer mono and diepoxide, epichlorohydrin, " " 3,3,3-trichloropropylene oxide, " tetrahydrofuran, " " and ethylene carbonate or ethylene sulfite " have received attention. Condensation reactions between allyl glycidyl ether and MA are reported to be highly useful for preparing plastics with remarkable hardness, high heat distortion, and brilliant clarity.The cyclohexene oxide copolymerizations were second order in MA, with an activation energy of 13.8 kcal/mol. For the epichlorohydrin system the rate was dependent on the temperature and proportional to the catalyst concentration, with an activation energy of 14.5 kcal/mol. 

In the beginning of 90th, Tan and Davis [136] investigated the coreaction of ethylene and methanol over silicalite S-115 by the isotopic tracer method ( "C labeled or unlabeled methanol and unlabeled or labeled ethylene) and concluded that ethylene was converted by adding a Cj specie derived from methanol. However, the relative "C in the hydrocarbon products revealed that the alkylation of alkenes is more rapid than the formation of Cj" and alkenes from methanol oidy. For the conversion of ethylene only (in the absence of MeOH), the dimerization to form butenes was the dominant reaction. Adding a flow of water in an amount equimolar to ethylene significantly decreased the conversion of ethylene. The addition of methanol to the feed stream, in an amount equal to that of ethylene, increased the total conversion and altered the product distribution so that propylene is formed in about twice the amount of butenes. The labels on the C3-C5 number products were similar to that of ethylene. The authors concluded therefore that the C3-C5 products were formed by the successive addition of an unlabeled Cj species derived from methanol to labeled ethylene. The data clearly show that the formation of ethylene from methanol is a slow reaction compared to the addition of the Cj species to the products. Thus, the formation of ethylene is an important issue only for the reaction initiation. In those processes, where a small amount of alkenes are added to the methanol feed, the formation of ethylene directly from methanol represents a small part of the hydrocarbons produced from methanol. 

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