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Abstract Microdroplets show unique chemistry, especially in their intrinsic redox properties, and to this we here add a case of simultaneous and spontaneous oxidation and reduction. We report the concurrent conversions of several phosphonates to phosphonic acids by reduction (R−P → H−P) and to pentavalent phosphoric acids by oxidation. The experimental results suggest that the active reagent is the water radical cation/anion pair. The water radical cation is observed directly as the ionized water dimer while the water radical anion is only seen indirectly though the spontaneous reduction of carbon dioxide to formate. The coexistence of oxidative and reductive species in turn supports the proposal of a double‐layer structure at the microdroplet surface, where the water radical cation and radical anion are separated and accumulated.
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Electroorganic Synthesis in Aqueous Solution via Generation of Strongly Oxidizing and Reducing Intermediates
Water is the ideal green solvent for organic electrosynthesis. However, a majority of electroorganic processes require potentials that lie beyond the electrochemical window for water. In general, water oxidation and reduction lead to poor synthetic yields and selectivity or altogether prohibit carrying out a desired reaction. Herein, we report several electroorganic reactions in water using synthetic strategies referred to as reductive oxidation and oxidative reduction. Reductive oxidation involves the homogeneous reduction of peroxydisulfate (S2O82–) via electrogenerated Ru(NH3)62+ at potential of –0.2 V vs. Ag/AgCl (3.5 M KCl) to form the highly oxidizing sulfate radical anion (E0′ (SO4•–/SO42–) = 2.21 V vs. Ag/AgCl), which is capable of oxidizing species beyond the water oxidation potential. Electrochemically generated SO4•– then efficiently abstracts a hydrogen atom from a variety of organic compounds such as benzyl alcohol and toluene to yield product in water. The reverse analogue of reductive oxidation is oxidative reduction. In this case, the homogeneous oxidation of oxalate (C2O42–) by electrochemically generated Ru(bpy)33+ produces the strongly reducing carbon dioxide radical anion (E0′ (CO2•–/CO2) = –2.1 V vs. Ag/AgCl), which is capable of reducing species at potential beyond the water or proton reduction potential. In preliminary studies, the CO2•– has used to homogenously reduce the C–Br moiety belonging to benzyl bromide at an oxidizing potential in aqueous solution.
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- Award ID(s):
- 2002158
- PAR ID:
- 10412322
- Date Published:
- Journal Name:
- Faraday Discussions
- ISSN:
- 1359-6640
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D3FD00067B
