Direct Microdroplet Synthesis of Carboxylic Acids from Alcohols by Preparative Paper Spray Ionization without Phase Transfer Catalysts

Abstract

Carboxylic acids are widely used in the production of fine chemicals. This study demonstrates rapid synthesis of carboxylic acids directly from alcohols in microdroplets by paper spray ionization under UV irradiation. Oxidation acceleration was contributed from paper substrate as a thin film format and microdroplets of smaller sizes by paper spray ionization. Yields can reach as high as 100% for all tested alcohols except 4-nitrobenzene alcohol (39%) in microdroplets compared to 1–10% for acids and 2–50% for aldehydes with methylbenzoate byproducts in bulk phase. Preparative paper spray ionization for scaling-up syntheses realized rates of 19 mg h–1. Paper spray-based synthesis not only possesses all merits of microvolume synthesis by electro- and sonic spray, but also owns unique properties of no need for phase-transfer catalysts, and high ease to salt deposition typically occurred at the capillary tips for the latter. All these merits indicate it is a high-efficiency green methodology.