One-Step, Catalyst-Free Formation of Phenol from Benzoic Acid Using Water Microdroplets

Abstract

Benzoic acid dissolved in water is electrosprayed (−4 kV) by using nitrogen gas at a pressure of 120 psi to form ∼10 μm diameter microdroplets. Analysis with mass spectrometry (MS) and tandem mass spectrometry (MS 2 ) of the resulting microdroplets shows the direct formation of phenol via decarboxylation without any catalyst or added reagents. This process represents an ecofriendly, environmentally benign method for producing phenol and related aromatic alcohols from their corresponding aromatic acids. The mechanism of this transformation was unambiguously characterized using mass spectrometry, radical trapping, and 18 O labeling.

Spontaneous Oxidation in Aqueous Microdroplets: Water Radical Cation as Primary Oxidizing Agent

“…Table 1 summarizes the classification, reaction conditions, and oxidants suggested in various studies. Generally, two types of oxidation have been observed in microdroplets: (i) simple oxidation of substrates, where a single reactant is oxidized by an oxidant to yield the final product, [13,14,16,60,[62][63][64][65][66][67] and (ii) oxidative coupling reactions, in which one reactant is oxidized to generate a radical species (as intermediate) that subsequently couples with another reactant to produce a coupling product. [15,[68][69][70] As shown in table 1, spontaneous oxidation encompasses a wide array of compounds, from organic compounds (most cases), through inorganic compounds (reaction 1.6) to large biomolecules (reactions 1.12 and 1.13).…”

Superfast Formation of C(sp2)−N, C(sp2)−P, and C(sp2)−S Vinylic Bonds in Water Microdroplets

“…Additionally, recent studies explain that hydroxyl radical also forms at the surface of corona bubbles [42] . Furthermore, we leveraged this reactivity to perform catalyst‐free functionalization of both benzoic acids (via decarboxylation) and methylbenzenes (via C−H activation) [43,44] . In our efforts to further expand the utility of water microdroplet chemistry, we disclose here a decarboxylative coupling of vinylic acids with N‐, S‐, and P‐centered nucleophiles.…”

“…[42] Furthermore, we leveraged this reactivity to perform catalyst-free functionalization of both benzoic acids (via decarboxylation) and methylbenzenes (via CÀ H activation). [43,44] In our efforts to further expand the utility of water microdroplet chemistry, we disclose here a decarboxylative coupling of vinylic acids with N-, S-, and P-centered nucleophiles. As with our previous work, these transformations occur under mild, catalyst-free conditions which are made to happen and accelerated by water microdroplets.…”

Spontaneous Oxidation in Aqueous Microdroplets: Water Radical Cation as Primary Oxidizing Agent

“…Table 1 summarizes the classification, reaction conditions, and oxidants suggested in various studies. Generally, two types of oxidation have been observed in microdroplets: (i) simple oxidation of substrates, where a single reactant is oxidized by an oxidant to yield the final product, [13,14,16,60,62–67] and (ii) oxidative coupling reactions, in which one reactant is oxidized to generate a radical species (as intermediate) that subsequently couples with another reactant to produce a coupling product [15,68–70] . As shown in table 1, spontaneous oxidation encompasses a wide array of compounds, from organic compounds (most cases), through inorganic compounds (reaction 1.6) to large biomolecules (reactions 1.12 and 1.13).…”