Abstract
The lack of understanding of the radical reaction mechanism of Carbon dioxide (CO2) in photo- and electro-catalysis results in the development of such applications far behind the traditional synthesis methods. Using methylbenzophenone as the model, we clarify and compare the photo-enolization/Diels−Alder (PEDA) mechanism for photo-carboxylation and the two-step single-electron reduction pathway for electro-carboxylation with CO2 through careful control experiments. The regioselective carboxylation products, o-acylphenylacetic acid and α-hydroxycarboxylic acid are obtained, respectively, in photo- and electro-chemistry systems. On the basis of understanding the mechanism, a one-pot step-by-step dicarboxylation of o-methylbenzophenone is designed and conducted. Both the experimental results and related density functional theory (DFT) calculation verify the feasibility of the possible pathway in which electro-carboxylation is conducted right after photo-carboxylation in one vessel. This synthesis approach may provide a mild, eco-friendly strategy for the production of polycarboxylic acids in industry.
Highlights
CO2 is one of the main components of greenhouse gases resulting from fossil fuel combustion [1].Researchers have made lots of efforts to convert renewable CO2 to high value-added chemicals, so as to reduce CO2 content in the atmosphere and achieve the recycling of carbon resources [2,3,4]
As a thermodynamically stable molecule, CO2 is usually difficult to be activated under mild conditions
Considering the use of strong reducing reagents, metal catalysts or harsh reaction conditions in the traditional fixation of CO2 into organic compounds, the development of mild but efficient synthesis methods becomes more attractive to researchers [13,14]
Summary
CO2 is one of the main components of greenhouse gases resulting from fossil fuel combustion [1].Researchers have made lots of efforts to convert renewable CO2 to high value-added chemicals, so as to reduce CO2 content in the atmosphere and achieve the recycling of carbon resources [2,3,4]. As a thermodynamically stable molecule, CO2 is usually difficult to be activated under mild conditions. While CO2 is usually converted to small fuel molecules (e.g., CO, CH4 and CH3 OH) [5,6,7,8], it can be used as a C1 building block to form new C−C or C−N bonds with organic molecules and eventually produce more complicated chemical feedstocks [9,10,11,12]. Considering the use of strong reducing reagents, metal catalysts or harsh reaction conditions in the traditional fixation of CO2 into organic compounds, the development of mild but efficient synthesis methods becomes more attractive to researchers [13,14]
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