Direct esterification of olefins: The challenge of mechanism determination in heterogeneous catalysis

• Linear hexenes and octenes react with heptanoic acid on Amberlyst® 15 via an Eley–Rideal mechanism.
• Olefin is the adsorbed species; heptanoic acid reacts from the bulk phase.
• An LH mechanism was incorrect but could still reproduce much of the kinetic data.
• Hexenes reacted faster than octenes.
• Double bond isomerization was much faster than esterification.

The reversible, direct esterification of 1-hexene and 1-octene with heptanoic acid on Amberlyst® 15 (dry) was studied at 75 °C to determine kinetics and mechanism. The forward surface reaction occurred by an Eley–Rideal mechanism, in which adsorbed olefin reacted with bulk phase heptanoic acid; the reverse reaction, ester decomposition, required just one surface site. While detailed studies pointed to an Eley–Rideal mechanism, a Langmuir–Hinshelwood mechanism was nearly as good as the Eley–Rideal mechanism for reproducing kinetic data observed across several hours of reaction. Authors conclude that a cursory investigation can support a Langmuir–Hinshelwood mechanism, while a detailed investigation supports an Eley–Rideal mechanism in this system.

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