Electrochemical Reduction of the Carbonyl Functional Group: The Importance of Adsorption Geometry, Molecular Structure, and Electrode Surface Structure

Abstract

This paper studies the electrochemical hydrogenation of the carbonyl functional group of acetophenone and 4-acetylpyridine at platinum single-crystal electrodes. Comparison with results obtained for the hydrogenation of acetone featuring an isolated carbonyl functional group reveals the influence of the phenyl ring and the pyridine ring, respectively. Lack of acetone adsorption at Pt(111) and Pt(100) due to a weak interaction between surface and carbonyl functional group renders these surfaces inactive for the hydrogenation of acetone. Adsorption through a strong interaction with the phenyl ring of acetophenone activates the Pt(111) and Pt(100) surfaces for hydrogenation of the acetyl substituent. In agreement with previous results for acetone reduction, the Pt(100) surface is specifically active for the hydrogenolysis reaction, breaking the C–O bond, whereas the other surfaces only hydrogenate the carbonyl functionality. In contrast to the phenyl ring, the pyridine ring has a very different effect: due to the dominant interaction of the N atom of the pyridine ring with the platinum electrode, a vertical adsorption mode is realized. The resulting large physical distance between the carbonyl functional group and the electrode surface inhibits the hydrogenation at all platinum surfaces. This also holds for the Pt(110) electrode, which is otherwise active for the electrochemical hydrogenation of the isolated carbonyl functional group of aliphatic ketones. Our results show how the combination of molecular structure of the reactant and surface structure of the catalyst determine the selective electroreduction of functionalized ketones.

Ag Electrodeposited on Cu Open‐Cell Foams for the Selective Electroreduction of 5‐Hydroxymethylfurfural

“…This behavior could be related to the adsorption of organic compounds on the surface of the electrode, likewise for furfural on Cu electrodes, or due to the competition between HER and HMF reduction . At high overpotentials the kinetics of HER increases faster than the kinetics of aldehyde group reduction . Moreover, for the 0.50 M sample a mass transfer limited plateau is observed.…”

“…[6] At high overpotentials the kinetics of HER increases faster than the kinetics of aldehyde group reduction. [31] Moreover, for the 0.50 M sample a mass transfer limited plateau is observed.…”

Electroreductive Olefin–Ketone Coupling

“…4 Although these incredibly robust reactions have been employed countless times, they can indirectly contribute to synthetic inefficiencies as their low chemoselectivity often necessitates the use of protecting groups. 5 This dilemma is nicely illustrated ( Figure 1B) by examining the patented route to steroid derivative 2. 6 Although a Grignard reaction with commercially available ketone 1 is an obvious disconnection, its use introduces several protecting group additions, removals and functional group manipulations throughout the course of a seven-step sequence (only one of which forges a C-C bond).…”

“…Within the specific realm of intermolecular alkyl nucleophile additions to unactivated ketones, Grignard and related organometallic additions are fundamentally limited by their 2-electron mechanisms, which render these nucleophiles both strongly nucleophilic and often highly basic. 4,5,7 Efforts to tone down their reactivity have been explored, with the most successful stemming from nucleophiles bearing activated positions (i.e. allylic, benzylic, propargylic, a-carbonyl, Figure 1C).…”

Flow Process for Ketone Reduction Using a Superabsorber-Immobilized Alcohol Dehydrogenase from Lactobacillus brevis in a Packed-Bed Reactor

“…An enzymatic reaction of particular interest for an application in flow mode due to its matured technology level is asymmetric ketone reduction, having a proven track record underlined by many successful examples demonstrated in the past for the batch mode [10][11][12][13]. Recently, significant process in the biocatalytic [14][15][16][17] reductive synthesis of alcohols starting from ketones, as well as syntheses by non-enzymatic means, have been reported [18][19][20][21]. In recent years, an increasing number of examples of biocatalysis in flow processes have been reported [22][23][24][25][26][27].…”