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.

Reaction of chloroauric acid with histidine in microdroplets yields a catalytic Au–(His)2complex

“…40 Recently, there have some technology explored for increasing the yield of the product and scaling-up the microdroplet reaction. 21,38,[40][41][42] Heated ultrasonic nebulization (HUN) has been used successfully for this purpose in our group. 43 We report here the use of ultrasonic nebulization to make a scaled-up preparation the catalytic Au-(His) 2 complex.…”

Microdroplet mass spectrometry: Accelerating reaction and application

“…Then a high voltage is applied, which creates the ions to be analyzed by MS. Microdroplets generated by paper spray ionization were applied to synthesize carboxylic acids from alcohols under UV irradiation without using a phase‐transfer catalysts. The reaction acceleration occurs due to the paper‐thin film format and the microdroplet spray ionization with up to 100% alcohol oxidization yield [11]. Different approaches for paper sample loading, including the single‐tip, dual‐tip, and co‐axial, were tested to limit on‐paper interaction between the reagents.…”

A New World for Chemical Synthesis?

“…al., [64] others have reported the application of the paper spray ionization method for the oxidation of alcohols to carboxylic acids, [65] and a packed-bed photoreactor system containing immobilised Rose Bengal proved useful for photo-oxidation of alkenes using oxygen to avoid downstream processing problems. [66] An enhanced and scalable flow photochemical [2+2] cycloaddition reaction between maleic anhydride and ethylene has been achieved by merging photochemistry with computational methods. Density functional theory (DFT) was applied to calculate the triplet energies of substrates, which were then matched with that of the photosensitizers to provide the optimal conditions.…”