Synthesis and Characterization of Carboxylic Acids Bearing Poly(ethylene glycol) Chains

Abstract

Carboxylic acids 1a and 1b bearing three poly(ethylene glycol) (PEG) chains and carboxylic acid 1c bearing one PEG chain were designed and synthesized. The carboxylic acids 1a–c were fully characterized by NMR and ESI-HRMS analyses. In a Pd-catalyzed aerobic oxidation of 1-phenylethanol, 1a and 1b worked well as carboxylate ligands.

Key words

carboxylic acids - poly(ethylene) glycol - oxidation - alcohol - palladium

• References and Notes

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• 18 General Procedure for the Pd-Catalyzed Aerobic Oxidation of 1-Phenylethanol A 20 mL Schlenk flask was first charged with a CH₂Cl₂ solution (ca. 1 mL) of carboxylic acid (in case it is liquid or sticky solid, 4 mol%). Then, CH₂Cl₂ was removed by gentle heating under vacuum. The flask was further charged with a carboxylic acid (in case it is a solid, 4 mol%), Pd(OAc)₂(py)₂ (1.9 mg, 5.0 μmol, 1.0 mol%), K₂CO₃ (6.9 mg, 50 μmol, 10 mol%), toluene (1.25 mL), and Teflon-coated stirring bar under air. The resulting mixture was stirred under air at room temperature for 1 min, and further at 80 °C for 3 min. Next, 1-phenylethanol (61 mg, 0.50 mmol) was added at 80 °C, and the reaction was carried out at the same temperature for 14 h under air. After the reaction, the mixture was diluted with ethyl acetate (4 mL), and the solution was passed through a pad of Celite. The yield of acetophenone was determined by GC analysis relative to an internal standard (tridecane).
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