Chromatography-Free Esterification Reactions Using a Bifunctional Polymer

Abstract

A linear polystyrene functionalized with both nucleophilic DMAP groups and sterically hindered tertiary amine groups was synthesized and used homogeneously in a range of esterification reactions between alcohols and various carboxylic acid derivatives. The polymer was highly effective in such reactions where the DMAP groups served as catalytic groups. The ester products of these reactions could be isolated in high purity and yield without the need for chromatographic purification, and the polymer could be recovered and reused numerous times with no apparent decrease in utility.

Key words

DMAP - esterification reactions - organocatalysis - polymer-supported catalysts - polymer-supported reagents

• References and Notes

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• 10 General Procedure for Esterification Reactions Acylating reagent 7 (1.2 equiv) was slowly added dropwise into a stirred solution of alcohol 8 (1.0 equiv) and polymer 6 in dry toluene (30 mL). The reaction mixture was stirred at r.t., and when TLC indicated that 8 had been completely consumed, the reaction mixture was slowly added dropwise into hexane (150 mL). The resulting precipitate was filtered off, and the filtrate was washed with sat. aq Na₂CO₃ (50 mL). The organic layer was washed with brine (50 mL) and dried over anhydrous MgSO₄, and concentrated under reduced pressure to afford product ester 9 in an essentially pure state according to ¹H NMR analysis. The collected precipitate was dissolved MeOH (8 mL), and was slowly added dropwise to a vigorously stirred solution of 0.1 N NaOH dissolved in MeOH (100 mL) at 0 °C. The resulting light yellow precipitate was filtered, washed with MeOH (40 mL), and dried under reduced pressure for reuse in the next reaction. 1-Phenylethyl Acetate (9Aa) ¹H NMR (400 MHz, CDCl₃): δ = 1.49 (d, 3 H, J = 6.8 Hz), 1.98 (s, 3 H), 5.86 (q, 1 H, J = 6.8 Hz), 7.22–7.33 (m, 5 H). 13C NMR (100 MHz, CDCl₃): δ = 21.0. 22.0, 72.0, 125.9 (2 C), 127.6, 128.3 (2 C), 169.8. LRMS: m/z calcd for C₁₀H₁₂O₂: 164.1; found: 164.1.
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