The catalytic conversion of the isopentenes takes place in two reactions, isomerization and dehydrogenation. Depending on the degree of conversion, the isomeric isopentenes are arranged in the following series: 3-methylbutene-1 >2-methylbutene-1 > 2-methylbutene-2.
Of the three isomeric isopentenes the most stable structure is that of 2-methylbutene-2, where breakdown occurs at the multiple bond, and the least stable is 3-methylbutene-1, breakdown occurring in the saturated portion of the molecule. With respect to the rate of isomerization, the isomets 3-methylbutene-1, 2-methylbutene-1 and 2-methylbutene-2 have the relative values 2.6 ∶ 1.73 ∶ 1, respectively.
2-methylbutene-2 is dehydrogenated at a greater rate than the other two isomers, 2-methylbutene-1 and 3-methylbutene-1, where rate constants are in the ratio 1.44∶ 1.15 ∶1.0. Activation energy of the dehydrogenation reaction is similar in all cases, and amounts to approximately 21–22 kcal/mole.
At temperatures between 580° and 620° the yield of isoprene amounts to 25–41% on the basis of the isopentenes supplied, and to 91–84% on the basis of the isopentenes consumed.
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Bogdanova, O.K., Shcheglova, A.P. & Balandin, A.A. The catalytic dehydrog enation of isomeric isopentenes. Part 3. The catalytic conversions of isopentenes in relation to their structure. Russ Chem Bull 12, 1111–1114 (1963). https://doi.org/10.1007/BF00849666
- Activation Energy
- Stable Structure
- Great Rate