Dimerization of Propylene

One of the industrially important dimerization reactions that involves the use of homogeneous catalysts is the dimerization of propylene. Dimerization of propylene produces mixtures of the isomers of methyl pentenes, hexenes, and 2,3-dimethyl butene and is practiced by the Institut Francis du Petrole (IFP), Sumitomo, and British Petroleum (BP). The methyl pentenes and hexenes are used as gasoline additives. Dimethylbutene is used in the fragrance and the agrochemical industries. 

Dimerization of butadiene is used for the selective formation of 1,5-cyclo-octadiene (1,5-COD), which on selective hydrogenation gives cyclooctene. By ring-opened metathesis polymerization of cyclooctene a specialty polymer is obtained (see Section 7.6.1). Hulls sells this polymer as Vestenamer . 

Butadiene could also be trimerized to give cyclododecatriene. The trimer is again used by Hulls to manufacture nylon 12 and Vestamid . The codimerization of butadiene and ethylene is used by DuPont to manufacture 1,4-hexadiene, one of the monomers of EPDM (ethylene, propylene, diene, monomers) rubber. The role of the diene monomer in EPDM rubber is to provide with two double bonds of different reactivities. The more reactive, terminal double bond takes part in the polymerization with ethylene and propylene. The less reactive internal one is used later on for cross-linking. These important catalytic reactions are shown in Fig. 7.6. 

The dimerization of propylene carried out by IFP is called the DIMEROSOL process and involves the use of nickel catalysts. This is shown in Fig. 7.7. Complexes 7.20 and 7.21 are the anti-Markovnikov and Markovnikov insertion products into the Ni-H bond. Structures 7.23(A) and (B) are intermediates derived from 7.21 by inserting the second propylene molecule in a Markovnikov and anti-Markovnikov manner, respectively. Similarly 7.22(A) and (B) are intermediates from 7.20 by the insertion of the second propylene molecule. These lour nickel-alkyl intermediates by /3-elimination give six alkenes. Under the process conditions these alkenes may undergo further isomerization. 

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A mixture of (C H ) , TiCl, and AlCl is useful for polymerizing C —olefins (85). The dimerization of propylene is accompHshed by using catalysts such as Ni(PR2)4 (86). Alkylphosphines such as / fZ-butylphosphine [2501-94-2] have been proposed as a substitute for high purity phosphine in the production of the semiconductor gallium phosphide (87). 

The product is a mixmre of dimers, trimers, tetramers, and pentamers having an average RON (Research Octane Number) = 95. Table 3-14 shows the analysis of feed and products from dimerization of propylene. ... 

Typical feed and products from the dimerization of propylene ... 

Another approach for producing isoprene is the dimerization of propylene to 2-methyl-1-pentene. The reaction occurs at 200°C and about 200 atmospheres in the presence of a tripropyl aluminum catalyst combined with nickel or platinum. 

Dimer. A molecule formed by the union of two identical molecules. Hexene (CgHn) is the dimer of propylene (C3H6). 

Dimerization of propylene is also used to produce isoprene. Several steps are involved. Initially, dimerization of propylene to 2-methyl-1-pentene occurs. Then isomerization to 2-methyl-2-pentene is effected. Finally, the 2-methyl-2-pentene is pyrolyzed to isoprene and methane. Another multistep synthesis starts with acetylene and acetone. Perhaps the most attractive route involves formaldehyde and isobutylene (equation 17.42). 

Methyl- 1-pentene belongs to the class of the hexenes. It can be produced by the catalytic dimerization of propylene (1,2). The dimerization of propene with a high selectivity to 4-methyl-l-pent-ene can be achieved in the presence of a catalyst, which is obtained by dispersing metallic sodium and metallic potassium on a molded article comprising an anhydrous inorganic potassium compound and elemental carbon (3). 

Double-bond isomerization was once used in the multistep synthesis of isoprene developed by Goodyear.266-268 2-Methyl-1-pentene produced by the dimerization of propylene was isomerized to 2-methyl-2-pentene over a silica-alumina catalyst at 100°C. The product was cracked to isoprene and methane. Because of the lower cost of isoprene isolated from naphtha or gas oil-cracking streams, synthetic isoprene processes presently are not practiced commercially. 

Dimerization of propylene leads to the formation of isomeric methylpentenes in the presence of alkali metals.34 The product distribution strongly depends on the metal used. 4-Methyl-1-pentene is formed with high selectivity in the presence of potassium and cesium. Because of extensive isomerization, an equilibrium mixture of the isomers with 4-methyl-2-pentene and 2-methyl-2-pentene as the main products was isolated in a reaction catalyzed with sodium. 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

A new, selective catalyst was reported for the dimerization of propylene to 2,3-dimethylbutenes that are valuable intermediates in the manufacture of specialty chemicals.44 The catalyst is composed of nickel naphthenate, Et3Al, a phosphine, a diene, and chlorinated phenol. Either 2,3-dimethyl-1-butene or 2,3-dimethyl-2-butene can be selectively produced by controlling the catalyst composition. 

Dimerization of propylene and butenes is also accomplished commercially to produce valuable motor gasoline components. IFP s Dimersol G process86-88... 

Mcthyl-1 -Pcntcnc is produced commercially by dimerization of propylene in the presence of potassium-based catalysis at 150-16O°C and 10 MPa. 

That this latter reaction has become the basis of a very large isoprene production is not to be credited to my institute but to the cooperation between the two American companies, Goodyear Tire Rubber Co. and Scientific Design Co. These two firms added to our dimerization of propylene the rearrangement of the 2-methyl-l-pentene into 2-methyl-2-pentene and then cracked this product to give isoprene and methane (10). 

Isoprene (melting point -146°C, boiling point 34°C, density 0.6810) may be produced by the dehydrogenation of iso-pentane in the same plant used for the production of butadiene. However, the presence of 1,3-pentadiene (for which there is very little market) requires a purification step. One method produces isoprene from propylene. Thus, dimerization of propylene to 2-methyl-1-pentene is followed by isomerization of the 2-methyl-1-pentene to 2-methyl-2-pentene, which upon pyrolysis gives isoprene and methane. 

Z. Su et al., Chiral self-recognition Direct spectroscopic detection of the homochiral and heterochiral dimers of propylene oxide in the gas phase. J. Am. Chem. Soc. 128, 17126-17131 (2006)... 

As might be expected, the selectivity to heptenes is not particularly high due to competitive reactions such as self-dimerization of propylene and butene. 

Organometallic compounds like Ce(COT)2, Ce2(COT)3 have been used in polymerization of ethylene. Dimerization of propylene is catalyzed by a mixture of rare earth acetyl... 

The IFP Dimersol Process for Dimerization of Propylene into Isohexenes... 

Branched a-alkenes, most notably propylene, can insert in either a Markovnikov (secondary or 2,1) fashion or anti-Markovnikov (primary or 1,2) fashion (equation 5). Depending on the regioorientation of the next inserting monomer, this can lead to head-to-taU sequences (the most frequent in polypropylene), head-to-head or tail-to-tail. An illustration of the possible structures is shown in the catalytic dimerization of propylene by nickel catalysts (Figure 1). n-Hexenes, methylpentenes, and 2,3-dimethylbutene can be formed by the nickel hydride catalyst... 

Similar results have been reported (35) for the reaction of propylene under these conditions. Dimerization of propylene was observed, and... 

We also studied the dimerization of propylene in the presence of gel-immobilized nickel complexes. It is known that in the dimerization of propylene with homogeneous nickel complexes a mixture of dimers containing 4-methyl-1-pentene, 4-methyl-2-pentene, 2-methy-2-lpentene, 2,3-dimethyl-2-butene, hexene and other compounds is formed, and the content of 4-methyl-1-pentene does not exceed 8% mass [11]. It is also known that 4-methyl-1-pentene has more practical application as its polymer is widely used in electric power engineering, electronics, medicine, etc. 

Table 2. Effect of Tertiary Phosphine Ligands on the Dimerization of Propylene - ...

The cationic nickel complex [ /3-allylNi(PR3)]+, already described by Wilke etal. [21], as an efficient catalyst precursor for alkene dimerization when dissolved in chlorinated organic solvents. It proved to be very active in acidic chloroaluminate ionic liquids. In spite of the strong potential Lewis acidity of the medium, a similar phosphine effect is observed. Biphasic regioselective dimerization of propylene into 2,3-dimethylbutenes can then be achieved in chloroaluminates. However, there is a competition for the phosphine between the soft nickel complex and the hard aluminum chloride coming from the dissociation of polynuclear chloroaluminate anions. Aromatic hydrocarbons, when added to the system, can act as competitive bases thus preventing the de-coordination of phosphine ligand from the nickel complex [22 b]. Performed in a continuous way, in IFP pilot plant facilities, dimerization of propene and/or butenes with this biphasic system (Difasol process) compares... 

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