Isoprene process, Goodyear

The pyrolysis of propylene dimers to isoprene was investigated as part of the cortimercialization of the Goodyear Isoprene Process (ls2 3)> A significant amount of experimentation has been done to characterize some of the many reaction variables that affect the formation of isoprene during pyrolysis of various methyl pentenes. 

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. 

Until the mid-1970s metal-catalyzed propylene dimerization had practical significance in isoprene manufacture. Goodyear developed a process to dimerize propylene in the presence of tri-n-propylaluminum to yield 2-methyl-1-pentene.16,95,96 This was then isomerized to 2-methyl-2-pentene followed by cracking into isoprene and methane. This and other synthetic pocesses, however, are no longer practiced since they are not competitive with isoprene manufactured by cracking of naphtha or gas oil. 

In the presence of triethylalununum, the Goodyear-Scientific Design process produces 2-methvl l-oentene with a selectivity of 99 molar per cent The reaction takes place around 200 at 20.10 Pa. 2-metbyl 1-pentcnc is the starting material for the synthesis of isoprene, in which it is hrst isomerized to 2-methyl 2-pentenes, and then cracked to produce isoprene. 

When isoprene and similar hydrocarbons polymerize only a part of the double bonds present are involved in the union of the several molecules the rubber formed as a result is unsaturated. It shows the reactions characteristic of the derivatives of ethylene. Owing to this unsaturation it will add sulphur. This process, which is called vulcanization, was discovered by Goodyear in 1839. Vulcanization is usually effected by heating the mixture of rubber and sulphur at about 140°. Sheet rubber can be vulcanized in the cold by dipping it into a dilute solution of sulphur monochloride in a volatile solvent, such as carbon disulphide or benzene. 

An important example of cross-linking is the vulcanization of natural rubber, a process discovered by Charles Goodyear in 1839. Natural rubber is formed from a liquid resin derived from the inner bark of the Hevea brasiliensis tree. Chemically, it is a polymer of isoprene, CsHg (A Figure 12.41). Because rotation about the carbon-carbon double bond does not readily occur, the orientation of the groups boimd to the carbons is rigid. In natural rubber, the chain extensions are on the same side of the double bond, as shown in Figure 12.41(a). 

An important example of cross-linking is the vulcanization of natural rubber, a process discovered by CTiarles (Goodyear in 1839. Natural rubber is formed from a liquid resin derived from the inner bark of the Hevea brasiliensis tree. Chemically, it is a polymer of isoprene, CsHg. 

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