Esterification of camphene over heterogeneous heteropoly acid catalysts: Synthesis of isobornyl carboxylates

Silica supported H3PW12O40 (PW), the strongest heteropoly acid in the Keggin series, is an active and environmentally friendly solid acid catalyst for liquid-phase esterification of camphene, a renewable biomass-based substrate, with C2, C4 and C6 short-chain fatty acids. The reaction provides isobornyl carboxylates, useful as fragrances, in virtually 100% selectivity and 80–90% yield. The reaction is equilibrium-controlled and occurs under mild conditions with a catalyst turnover number of up to 3000. The use of hydrocarbon solvent prevents PW from leaching to allow easy catalyst recovery. The catalyst can be reused several times without loss of activity and selectivity.

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► The catalyst was prepared by supporting of H3PW12O40 on silica (PW/SiO2).
► PW/SiO2 is active in liquid-phase esterification of camphene with C2–C6 fatty acids.
► Commercially important fragrance monoterpenoids were obtained in excellent yields.
► The catalyst is truly heterogeneous and does not undergo PW leaching.