Reaction Equilibrium in the Isomerization of 2,4,4-Trimethyl Pentenes

Abstract

The isomerization reaction of 2,4,4-trimethyl-1-pentene to 2,4,4-trimethyl-2-pentene was studied. In contrast to the general rule for alkene stability, an excess of the R-alkene (2,4,4-trimethyl-1-pentene) was observed in the thermodynamic equilibrium. The result is explained in terms of the molecular structure: the large and bulky substituents in 2,4,4-trimethyl-2-pentene cause steric tension and make the molecule less stable. A reaction enthalpy of 3.51 ( 0.03 kJ mol -1 , i.e., endothermic reaction, and a reaction entropy of -0.47 ( 0.10 J mol -1 K -1 were determined from the experimental data of the isomerization reaction.

Equilibrium of the simultaneous etherification of isobutene and isoamylenes with ethanol in liquid-phase

“…Obtained results are presented in Table 8. Equilibrium constants from Table 8 are comparable to those reported in a specific study of the isomerization reaction between both trimethylpentenes, TMP-1 and TMP-2 (Karinen et al, 2001b). K x5 ranged from 0.242 to 0.286 and K 5 hardly changed in the temperature range from 1.018 to 1.019, which are very close to the unity, as expected, because only two similar olefins are involved in this reaction.…”

“…Slightly different values were found by Karinen et al (2001b), who reported experimental values of 3.51 kJ/mol for r H Besides, Turner et al (1958) published an experimental value of 5.4 kJ/mol for the enthalpy change of reaction, nearby the same value obtained in this work. The similarity between results and the good fit obtained from experimental data for this isomerization reaction between trimethylpentenes enforces the reliability of the present study.…”

“…The chemical equilibrium of the isomerization reaction between C 8 dimers (TMP-1 and TMP-2) is also known to take place (Karinen et al, 2001b). This double bond isomerization reaction of trimethylpentenes does not follow the usual rule of the chemical equilibrium of alkenes, which typically favors the species with the double bond further from the end of the carbon chain, as is the case of the isoamylenes isomerization reaction (Solomons and Fryhle, 2000).…”

“…This double bond isomerization reaction of trimethylpentenes does not follow the usual rule of the chemical equilibrium of alkenes, which typically favors the species with the double bond further from the end of the carbon chain, as is the case of the isoamylenes isomerization reaction (Solomons and Fryhle, 2000). But it follows an opposite trend owing to the size of tert-butyl group, which produces a highly crowded part in the molecule of TMP-2 and promotes then the elimination of the proton from the methyl group in the other part of the molecule (Karinen et al, 2001b). In the case of TMP-1, the tert-butyl group is further away in the position ˇ to the double bond and the largest substituent is in the cis position with hydrogen, which occupies much less CHERD-1418 space.…”

Equilibrium conversion, selectivity and yield optimization of the simultaneous liquid-phase etherification of isobutene and isoamylenes with ethanol over Amberlyst™ 35

“…In addition, isomerization between both diisobutenes (R10) also took place, the formation of TMP-1 being favored, since TMP-1 is a more stable molecule than TMP-2 due to the internal repulsions caused by the large size of the tert-butyl group in the TMP-2 molecule [47,48]. As observed in Figure 9a, when C4 dimers were forms, the TMP-1/TMP-2 molar ratio was around 4 at the end of runs, consistent with published results [47] and with the thermodynamic equilibrium constant for trimethylpentenes isomerization (R10), which are in the range from 0.26 to 0.29 for the assayed temperatures [31]. From IA dimerization (R12 in Figure 1), a wide variety of diisoamylenes can be formed [49].…”