2:4: 4-Trimethyl-l-pentene

The two dimers of (CH3)2C=CH2 are formed by the mechanism shown in Figure 6.16. In step 1 protonation of the double bond generates a small amount of tert-butyl cation in equilibrium with the alkene. The car bocation is an electrophile and attacks a second molecule of 2-methylpropene in step 2, forming a new carbon-carbon bond and generating a carbocation. This new carbocation loses a proton in step 3 to form a mixture of 2,4,4-trimethyl-l-pentene and 2,4,4-trimethyl-2-pentene. 

Terminal olefins appear to be reactive only if they are not allylic in nature (e.g., styrene and 2,4,4-trimethyl-l-pentene). Allylbenzene (3-phenyl-l-pro-pene) is inert toward nitrosyl chloride, whereas propenylbenzene (1-phenyl-l-propene) reacts. The preparations are usually carried out at low temperatures. When molecular weights of the products are determined at 5°C, they correspond to dimeric structures. At the melting point of naphthalene, the products are predominantly monomeric. This observation is reasonably general for nitroso compounds [69]. 

MCjAl does not t-butylate 2,4,4-trimethyl-l-pentene below —65°, however, produces neopentane indicating very rapid methylation of the tBu by the MeaAlCl . Evidently at low temperatures methylation (termination) of t-Bu is more facile than t-butylation (initiation) of Cg olefin. Olefin conversions increase from —65° to —40° but decrease again at —30°. The ascending branch at lower temperatures is conceivably due to an increased rate of t-butylation. Indeed, product analysis (Table 3) shows that at temperatures higher than —65°, the yields of first generation products (Cj j and C13) increase. At —65° or below mostly neopentane is obtained. The descending branch from —40° to —30° is difficult to explain. 

In a 5-1. three-necked flask fitted with a mechanical stirrer, a thermometer, and a dropping funnel equipped with a calcium chloride drying tube are placed 112.2 g, (1.00 mole) of freshly distilled 2,4,4-trimethyl-l-pentene (Note 1) and 11. of methylene chloride (Note 2). The flask is immersed in an ice-salt bath, and the stirred solution is cooled to 0-5°. A solution of 158 g. (1.02 moles) (Note 3) of freshly distilled chromyl chloride (Note 4) in 200 ml. of methylene chloride (Note 5) is added dropwise with stirring from the dropping funnel while the temperature is maintained at 0-5° (Note ( ). I hc reaction mixture is stirred for 15 minuti s, and 184 g. of I0 05% ti chnical... 

Step 3 Loss of a proton from this carbocation can produce either 2,4,4-trimethyl-l-pentene or 2,4,4-trimethyl-2-pentene ... 

The 2,4,4-trimethyl-l-pentene is not wasted because a dual catalyst can be used to ensure that it is converted into 2,4,4-trimethyl-2-pentene as this gets used up by ethenolysis. With a 1 3 catalyst mixture of a W03/Si02 metathesis catalyst and a MgO isomerization catalyst (at 370 °C and 30 bar ethene pressure), an average of 65-70 % conversion of the diisobutene can be achieved with approximately 85 % selectivity for neohexene. The coproduct isobutene can be recycled to an isobutene dimerization reactor. Neohexene is used to make the class of synthetic... 

Trimethyl-l-pentene 2,3,4-Trimethyl-2-pentene 2,4,4-Trimethyl-2-pentene 2,3,4-Trimethylphenol 2.3.5-Trimethylphenol... 

Experimentally, 2,4,4-trimethyl-l-pentene was dissolved in methyl chloride containing A1(CH3)3 at — 78° C. Reaction was initiated by the introduction of tm-butyl chloride as coinitiator. After 30 min of agitation, the polymerization was terminated by the introduction of methanol and the reaction products were separated and characterized. 

The heats of hydrogenation of 2,4,4-trimethyl-l-pentene and of 2,4,4-trimethyl-2-pentene are -25.5kcal/mol and -26.8 kcal/mol, respectively. Which isomer is more stable Is the result consistent with the common generalization that the more stable alkene isomer is the one with the greater number of alkyl substituents on the carbon-carbon double bond If not, explain why the generalization does not offer the correct prediction in the case of these two compounds. 

To produce p-tert-octylphenol, phenol and diisobutylene (a mixture of 2,4,4-trimethyl-l-pentene and 2,4,4-trimethyl-2-pentene) are fed through a bed of ion-exchange resin in the ratio 1.5 1 the resin is maintained at a temperature of 100 to 105 °C by internal cooling tubes. The alkylation is restricted to 95% diisobutylene conversion, to avoid the formation of undesirable by-products. The reaction mixture, which is separated into its constituents by vacuum distillation, consists of 93 to 96% p-tert-octylphenol the concentration of o-tert-octylphenol is between 2 and 3%. 

In addition to carbocation stability and monomer nucleophilicity, steric factors are also important. For example 1,1-diphenylethylene, a very reactive monomer can only be dimerized, because of the formation of a sterically buried carbenium ion (27). Other monomers that cannot be polymerized to high polymers because of steric congestion in the transition state are 2,4,4-trimethyl-l-pentene, 1,2-diphenylethylene (stilbene), 3-methylindene, and 2-methylenenorbomane. 

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