The successive scale-up of electrochemical reactions is crucial with regard to the implementation of technical electro-organic syntheses. Therefore, we developed a scalable modular parallel-plate electrochemical flow cell. One distinctive feature of this flow cell is that the temperature of the electrodes can be easily controlled from the back side via an external cooling circuit, enabling high reproducibility of electrochemical conversions. Because the gap between the electrodes is kept narrow, small amounts or no supporting electrolyte is required. The practicability and performance of the novel flow cell were validated by three different anodic phenol−phenol cross-couplings as test reactions.
The
electroorganic C,C coupling of phenols to other aryl components
is controlled by the fluoroalcohol–alcohol mixture solvents.
Classical molecular dynamics and static density functional theory
reveal that both kinds of solvents interact with the substrates, influencing
the electronic structure of a phenoxyl radical intermediate in a cooperative
manner to achieve maximal efficiency and selectivity. Simulations
of the electrolyte–electrode interface showed that the substrates
adsorb on the diamond surface in such a way that the repulsive fluorous–lipophilic
interactions can be minimized and the attractive lipophilic–lipophilic
interplay can be maximized, whereas the advantageous hydrogen bonding
with the solvent can be retained. Accordingly, the solvent induces
efficiency through the interaction of hydrogen bonding and the structure
that controls the mesoscopic separation in these fluids. Since these
findings are not specific to electrochemistry, by extending this principle
to other heterogeneous processes, e.g., catalysis, their rate, yield,
and selectivity can be potentially increased as well.
Abstract3,3′,5,5’-Tetramethyl-2,2′-biphenol is well known as an outstanding building block for ligands in transition-metal catalysis and is therefore of particular industrial interest. The electro-organic method is a powerful, sustainable, and efficient alternative to conventional synthetic approaches to obtain symmetric and non-symmetric biphenols. Here, we report the successive scale-up of the dehydrogenative anodic homocoupling of 2,4-dimethylphenol (4) from laboratory scale to the technically relevant scale in highly modular narrow gap flow electrolysis cells. The electrosynthesis was optimized in a manner that allows it to be easily adopted to different scales such as laboratory, semitechnical and technical scale. This includes not only the synthesis itself and its optimization but also a work-up strategy of the desired biphenols for larger scale. Furthermore, the challenges such as side reactions, heat development and gas evolution that arose during optimization are also discussed in detail. We have succeeded in obtaining yields of up to 62% of the desired biphenol.
The symmetric biphenol 3,3′,5,5′‐tetramethyl‐2,2′‐biphenol is a well‐known ligand building block and is used in transition‐metal catalysis. In the literature, there are several synthetic routes for the preparation of this exceptional molecule. Herein, the focus is on the sustainable electrochemical synthesis of 3,3′,5,5′‐tetramethyl‐2,2′‐biphenol. A brief overview of the developmental history of this inconspicuous molecule, which is of great interest for technical applications, but has many challenges for its synthesis, is provided. The electro‐organic method is a powerful, sustainable, and efficient alternative to conventional synthesis to obtain this symmetric biphenol up to the kilogram scale. Another section of this article is devoted to different process management strategies in batch‐type and flow electrolysis and their respective advantages.
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