Kolbe Electrolysis of Mixtures of Aliphatic Organic Acids

Abstract

Kolbe electrolysis of mixtures of n‐butanoic with n‐hexanoic acid and propanoic with n‐hexanoic acid have been performed in aqueous solution at a smooth platinum anode. Typically, hexane production by the oxidation of butanoic acid, or butane production from propanoic acid, in aqueous solution is not observed to exceed a few percent. In the current work, significant increases of these products were observed. In addition, a substantial fraction of the remaining C3 or C4 acids reacted were converted to mixed alkane dimers with hexanoic acid. These results are interpreted by a model in which n‐hexanoic acid and its various oxidation products form a lipophilic layer at the anode surface which provides an environment where further oxidation to carbonium ions is disfavored. This model has been suggested previously to explain pressure effects on Kolbe electrolysis (1). This observation supports the feasibility of producing mixed linear alkanes for use as fuels and chemicals from mixed organic acids which may be produced by anaerobic fermentation of organic matter.

The Dilemma of Supporting Electrolytes for Electroorganic Synthesis: A Case Study on Kolbe Electrolysis

“…Furthermore, increased temperature during Kolbe electrolysisw as reportedt oi ncrease yields of non-Kolbe products [29] and lower the CEs. Thef inding strongly emphasizes the need forac omprehensive and detailed monitoring and controlling of reactionp arameters when evaluating input parameters for Kolbe electrolysis and electroorganic reactions in general.…”

“…[27,29,30,[46][47][48][49] Accordingly,a ni ncreased yield of Kolbe product demands ah igher electric poweri nput (P el )c ompared to non-Kolbe product formation, as the power consumption of an www.chemsuschem.org electrochemical cell is definedb yt he product of the current (i) and the cell voltage (E cell )a ss hown in Equation (1). [27,29,30,[46][47][48][49] Accordingly,a ni ncreased yield of Kolbe product demands ah igher electric poweri nput (P el )c ompared to non-Kolbe product formation, as the power consumption of an www.chemsuschem.org electrochemical cell is definedb yt he product of the current (i) and the cell voltage (E cell )a ss hown in Equation (1).…”

Deterioration of Aqueous n‐Octanoate Electrolysis with Electrolytic Conductivity Collapse Caused by the Formation of n‐Octanoic Acid/n‐Octanoate Agglomerates

“…[7] About 50 years later, it was revealed that the possible reaction pathways of the electrochemical oxidization of carboxylates also include alcohol formation resulting from intermediate carbocations being formed at the anode ( Figure S1). [7,[9][10][11][12][13][14][15][16][17][18] Note that the carboxylate, i. e. the carboxylic acid anion, is the starting compound of the electrochemical reaction [7] (see also Figure S1). [7,[9][10][11][12][13][14][15][16][17][18] Note that the carboxylate, i. e. the carboxylic acid anion, is the starting compound of the electrochemical reaction [7] (see also Figure S1).…”

“…[7,[9][10][11][12][13][14][15][16][17][18] Among others, it was reported that a high current density, a high educt concentration (e. g. 0.5 mol L À1 ) and a neutral or slightly acidic pH promote the Kolbe-reaction over the intermediate formation of carbocations and related follow-up reactions in aqueous media (see Fig-ure S1 for the details on the example of n-octanoic acid/noctanoate). [7,[9][10][11][12][13][14][15][16][17][18] Among others, it was reported that a high current density, a high educt concentration (e. g. 0.5 mol L À1 ) and a neutral or slightly acidic pH promote the Kolbe-reaction over the intermediate formation of carbocations and related follow-up reactions in aqueous media (see Fig-ure S1 for the details on the example of n-octanoic acid/noctanoate).…”

“…[7,[9][10][11][12][13][14][15][16][17][18] Among others, it was reported that a high current density, a high educt concentration (e. g. 0.5 mol L À1 ) and a neutral or slightly acidic pH promote the Kolbe-reaction over the intermediate formation of carbocations and related follow-up reactions in aqueous media (see Fig-ure S1 for the details on the example of n-octanoic acid/noctanoate). [18,19] Especially in biomass derived solutions, mixtures of n-carboxylic acids and n-carboxylates are often found. [18,19] Especially in biomass derived solutions, mixtures of n-carboxylic acids and n-carboxylates are often found.…”