Reactivity of some C8-alkenes in etherification with methanol Original Research Article

This work concerns the reactivity of some tertiary C8-alkenes in the etherification reaction. 2,4,4-trimethyl-1-pentene, 2,4,4-trimethyl-2-pentene, 2-methyl-1-heptene and 2-methyl-2-heptene were chosen as the model compounds and their etherification with methanol was studied in the liquid phase at 50–90°C using a commercial ion-exchange resin as a catalyst. The comparison was made with the reactivity of tertiary C5-alkenes. The reactivity was observed to vary with each molecule: the longer the carbon chain, the slower the reaction rate. Apparent activation energies for the ether formation were determined from the initial reaction rates, being 60–65 kJ/mol for 2,4,4-trimethyl pentenes and 90 kJ/mol for 2-methyl-1-heptene. In addition to the etherification the double bond isomerisation was detected and also some isomerisation experiments without methanol were carried out. An interesting feature in the isomerisation between 2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-2-pentene was observed: the ratio of isomers settled at a value which was independent of the temperature favouring the α-form and thus being far from the expected thermodynamic equilibria. This is probably due to the bulkiness of the trimethyl pentenes and steric hindrances especially in 2,4,4-trimethyl-2-pentene molecule.