Esterification Catalysis by Pyridinium p-Toluenesulfonate Revisited—Modification with a Lipid Chain for Improved Activities and Selectivities

Abstract

The lipid analogs of pyridinium p-toluenesulfonate (PPTS) were examined for catalysis of the condensation of an equimolar mixture of carboxylic acids and alcohols under mild conditions without removal of water. Although PPTS is a poor catalyst, the introduction of a lipid chain and nitro group significantly improved the activity of PPTS and led to selectivity at suppressing the elimination side reactions of alcohols. 2-Oleamido-5-nitro-pyridinium p-toluenesulfonate (6) is a lead catalyst that promoted various esterification reactions with yields up to 99%.

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GRAPHICAL ABSTRACT

ACKNOWLEDGMENTS

We thank Narsimha Sattenapally for collecting some preliminary laboratory data. This work was supported in part by the NIH (1R15EB007074-01, 2R15EB007074-02) and NSF (CAREER Award CHE-0343440).

Notes

^a Conditions: 4-phenylbutyric acid (2 mmol), 1-octanol (2 mmol), and catalyst (5 mol%) in isooctane (4 mL) at 25 °C for 72 h.

^b Determined by GC analysis.

^c Not detected by GC experiments.

^d The yield of 76% at 25 °C and 99% at 80 °C, respectively.

^a Unless otherwise noted, an acid (2 mmol), and an alcohol (2 mmol) in isooctane (4 mL).