Propylene isoprene synthesis

Propylene Dimer. The synthesis of isoprene from propjiene (109,110) is a three-step process. The propjiene is dimeri2ed to 2-methyl-1-pentene, which is then isomeri2ed to 2-methyl-2-pentene in the vapor phase over siUca alumina catalyst. The last step is the pyrolysis of 2-methyi-2-pentene in a cracking furnace in the presence of (NH 2 (111,112). Isoprene is recovered from the resulting mixture by conventional distillation. 

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). 

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. 

The rhodium-catalyzed addition of ethylene to 1,3-butadiene to yield 1,4-hexadiene (5a, 151) proceeds via a similar mechanism (151) with the exception that, upon formation of the alkylrhodium(III) species, the hexadiene synthesis proceeds without further change in the oxidation state of the metal. In these reactions with butadiene the coordinated alkyl groups are either chelate or 7r-allyl structures which appear to stabilize Rh(III) (151). The addition of propylene to butadiene and isoprene to produce [Pg.297]

Various metal complex systems of Ziegler type are widely applied within industry for the production of high-density polyethylene, isotactic polypropylene, 1,4-c/s-and 1,4- rans-polymers of isoprene and 1,2-poly butadiene, and many other types of copolymers, such as ones based on ethylene and propylene, which could not be produced earlier based on traditional methods of synthesis. 

The process may easily be transformed for the synthesis of other elastomers and copolymers with a double bond in the backbone of the monomer unit. Therefore, the range of elastomers is extensive isoprene, butadiene, butadiene-styrene rubbers, ethylene-propylene terpolymer, and so on. 

The preparation and introduction of catalytic complex components to the polymeriser, using a tubular turbulent prereactor, enables the synthesis of copolymers (styrene-propylene (SSP) and styrene-ethylene-propylene (SSEPT)) which demonstrate high stability and durability. According to the laboratory results, obtained from the commercial production of ethylene and propylene copolymerisation, during separation of the active site formation and initiation of isoprene polymerisation on a Ti-Al catalytic system, an increase in copolymer yield and its molecular weight, as well as a decrease in catalyst rate were observed. 

Copolymers.—Both Monomers Vinyl. Ethylene-propylene copolymers have attracted the greatest attention,befitting their industrial importance. A variety of techniques has been used to assign the rather complex C spectra observed, including the synthesis of model oligomers and model polymers e.g. by hydrogenation of isoprene ). Propylene may add by either primary or secondary insertion, and a terpolymerization model has therefore been used to quantify the sequence distribution. Alternatively, Randall has proposed an analysis in terms of —CHa— or —CH(CHs)— units, rather than monomer residues. 

Baas, C. J., De synthesis van isopren uit propen. Delft, 1963 (Netherlands). Feldblyum, V. Sh., and Farverov, M. 1., Synthesis of isoprene from propylene. Kinetics of propylene dimerization, Neftekhimia, 5, 493, 1965 (Russian). 

Starting with a functionaUzation of a,(o-dihydroxy-terminated poly(ethylene oxide) or poly(propylene oxide) by HDl 18, followed by a reaction with a,(0-diamino-terminated copolymer of butadiene and acrylonitrile, a triblock macroactivator was synthesized the anionic polymerization of CL at 140 °C in the presence of this copolymer gave an A-B-C-B-A copolymer [61]. A similar macroactivator for block copolymer synthesis was prepared by a stepwise anionic polymerization of isoprene (with dilithium a-methylstyrene tetramer) and oxirane [62]. 

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