Direct Esterification of Carboxylic Acids with Alcohols Catalyzed by Iron(III) Acetylacetonate Complex

Abstract

Direct condensation of carboxylic acids and alcohols with electronic, steric, and functional group variations was carried out using the environmentally benign, moisture-stable, inexpensive, and recoverable iron(III) acetylacetonate [Fe(acac)₃] as catalyst (5 mol%). This iron salt efficiently catalyzed the esterification of several primary and secondary alcohols in refluxing xylene, without the need for a dehydration reagent. The chemoselectivity of the proposed protocol was demonstrated by the selective esterification of primary alcohol functionality in racemic 1-phenylethane-1,2-diol with benzoic acid. The esterification was also applicable to unmasked α -hydroxyacid, guasiaromatic, heterocyclic, and N-protected amino acids.

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GRAPHICAL ABSTRACT

Keywords:

• Esterification
• iron(III) β-diketonate species
• recoverable catalyst

ACKNOWLEDGMENTS

We acknowledge the financial support by the National Science Council of the Republic of China (NSC-100-2113-M-145-001-MY2). We also thank the mass laboratory of National Taiwan Normal University and the NMR laboratory of National Sun Yat-sen University for assistance in the NMR spectral measurements.

Notes

^a All reactions were performed in refluxed solvent in the presence of 5 mol% iron catalyst.

^b acac: pentan-2,4-dione.

^c hfacac: 1,1,1,5,5,5-hexafluoro- pentan-2,4-dione.

^d tmhd: 2,2,6,6-tetramethyl heptanes-3,5-dione.

^e dbm: dibenzoylmethane.

^f bzac: 1-benzoylacetone.

^g Recovered catalyst from the first cycle was used.

^h Yield of isolated product after chromatography.

^a All reactions were performed with 1 equiv of ester and protic nucleophile in xylene in the presence of 5 mol% Fe(acac)₃ under reflux condition.

^b Isolated yields after column chromatography.