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ChemicalBook CAS DataBase List 3-METHYLHEXANE
589-34-4

3-METHYLHEXANE synthesis

11synthesis methods
-

Yield:-

Reaction Conditions:

indium (III) iodide at 180; for 0.5 h;

Steps:

23
In order to demonstrate that InI3 catalyzed alkane homologation can be used to homologate C6 alkanes other than 2,3-dimethylbutane, a reaction was performed using 2-methylpentane as the starting alkane. The reaction was performed using 6.2 mmol of MeOH, 6.2 mmol of 2-methylpentane, 4.13 mmol of InI3 and 0.367 mmol of adamantane. A similar procedure to that described above for 2,3-dimethylbutane was used and the reaction was heated at 180 0C for 30 minutes. GC analysis indicated that at the end of the reaction 27.4 mg of 2,3-dimethylpentane was formed and 267 mg of 2-methylpentane were recovered. A breakdown of the product distribution is shown in Table 8.Table 8: Products from the homologation of 2-methylpentane with MeOH.Product Yield (mg)Iso-butane 23.5Iso-pentane 10.72,3-dimethylbutane 1.762-methylpentane 2673-methylpentane 73.02,4-dimethypentane 12.1Triptane 5.032-methylhexane 5.252,3-dimethylpentane 27.43-methylhexane 8.48Cs alkanes 17.3[0088] The reaction is presumed to initially result in the methylation of 2- methylpentane to 2,3-dimethylpentane. The mechanism is proposed to be analogous to that described above for 2,3-dimethylbutane; initial abstraction of a hydride from 2- methylpentane to form the tertiary 2-methylpentyl carbocation, deprotonation to give 2-methyl-2-pentene, methylation to give the most substituted carbocation, in this case the tertiary 2, 3-dimethylpentyl carbocation, which subsequently picks up a hydride to form 2,3-dimethylpentane. Under the reaction conditions, 2,3- dimethylpentane is unstable and undergoes both isomerization and cracking reactions to form some of the other products observed. Isomerization of 2,3- dimethylpentane results in other C7 alkanes, while products such as iso-butane and iso-pentane form from cracking (these cracking products are also probably formed from the C6 and C8 alkanes present). The reaction is not as selective as the methylation of 2,3-dimethylbutane to triptane because both 2-methylpentane and 2,3-dimethylpentane are more likely to undergo isomehzation reactions than 2,3- dimethylbutane or triptane. This is because 2-methylpentane and 2,3- dimethylpentane can undergo isomerization without a change in the length of main carbon backbone. Despite these isomerization side reactions, 2,3-dimethylpentane comprises approximately 50% of the C7 fraction and highly branched C7 alkanes (2,3- dimethylpentane, 2,4-dimethylpentane and triptane) comprise approximately 75% of the C7 fraction. Furthermore, the presence of C8 alkanes (determined using mass spectrometry) indicates that further methylation of C7 species has occurred. Given the mechanism of methylation, it is believed that these species are also highly branched and will be more significantly more branched than 2-methylpentane. Thus, overall this is a process which increases the branching (often correlated with increased octane number) of the alkanes present. Attempts to homologate hexane with MeOH resulted in only small quantities of C7 products and extremely long reaction times were required.

References:

CALIFORNIA INSTITUTE OF TECHNOLOGY;BP P.L.C. WO2009/64622, 2009, A2 Location in patent:Page/Page column 27-28

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