Continuous-flow synthesis of carboxylic acids from alcohols via platinum and silicon dioxide-catalyzed hydrogen peroxide oxidation.

Abstract

A continuous-flow method for the direct oxidation of alcohols to carboxylic acids is reported, employing hydrogen peroxide (H₂O₂) and a platinum (Pt) catalyst within a flow reactor system. This approach allows for precise control over the contact time between the reactants and the catalyst, enabling optimization of reaction conditions. By analyzing the yields of both aldehydes and carboxylic acids as a function of weight hourly space velocity (WHSV), selective synthesis of carboxylic acids was achieved without the formation of corresponding aldehydes. The Pt catalyst exhibited excellent stability, producing 25.2 g of octanoic acid from 1-octanol with a yield exceeding 96% over 210 h at a WHSV of 1.3 h^-1 using a 5 mm inner diameter × 100 mm column. This Pt-catalyzed continuous-flow H₂O₂ oxidation method demonstrates good reactivity for a variety of alcohols, including aliphatic, aromatic, allylic, and heteroaromatic, affording the corresponding carboxylic acids in 19-98% isolated yields with water as the sole byproduct. X-ray photoelectron spectroscopy (XPS) analysis confirmed the preservation of metallic zero-valent Pt (Pt(0)) throughout the reaction.