Interfacial Domain Formation Enhances Electrochemical Synthesis

Abstract

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.

Strong Microheterogeneity in Novel Deep Eutectic Solvents

“…[44] Table 1 also gives the domain count [33,34,43,[45][46][47][48][49] which indicates with numbers close to one high connectivity of different sub-molecular groups and for numbers greater than one dispersed or non-connected parts. The domain count [33,34,43,[45][46][47][48][49] stems from a radical Voronoi tesselation of the investigated systems where the different sub-molecular groups are connected when they share at least one Voronoi face with each other. For a more detailed explanation on the methodology of the used domain analyses the reader is referred to.…”

Electrosynthesis 2.0 in 1,1,1,3,3,3‐Hexafluoroisopropanol/Amine Mixtures

“…Fluorinated alcohols have emerged as excellent choices for a broad range of applications in organic chemistry, due to their high hydrogen-bond donor ability, [1,2] high polarity, [2,3] outstanding (electro-)chemical stability, [4,5] and micro-heterogeneity. [6][7][8] This is illustrated by their use as solvents, co-solvents or promoters in organic syntheses. [2,5,9,10] Several examples have showcased the utility of 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) in transition metal-catalyzed, [10,11] and metal-free reactions.…”

“…[17][18][19][20][21] In particular, the solvate formation modulates nucleophilicity and oxidation potential. [7,17] The unusual electrochemical stability of HFIP is ensured as long as inert anodes are employed for direct electrode processes, [22] whereas hypervalent iodine mediators are capable to convert HFIP to highly toxic hexafluoroacetone. [23] HFIP is corrosive and a strong skin and respiratory irritant, but nevertheless easy to handle.…”

Electrosynthesis of 3,3′,5,5’-Tetramethyl-2,2′-biphenol in Flow

“…In cross-coupling reactions, HFIP is also the key to selectivity, as it ensures decoupling of oxidation potential and nucleophilicity of the used starting material [79]. New results based on molecular dynamics simulations show that HFIP and HFIP-water as well as HFIP-alcohol mixtures have a unique microheterogeneous structure [80,81]. The separation of the polar hydroxyl groups from the fluorinated groups lead to domain formation, which positively influences electrochemical coupling reactions.…”

“…Another effect of microheterogeneity is a very low viscosity of the solution. This results in a positive effect on the mass transfer during electrolysis and can make processes more robust [80,81].…”