Non-Kolbe electrolysis of N-protected-α-amino acids: a standardized method for the synthesis of N-protected (1-methoxyalkyl)amines

A high-yielding, standardized, electrochemical method for the synthesis of N-protected (1-methoxyalkyl)amines using commercially available, user-friendly kit – not only for “electro-curious” chemists.

Understanding the reaction mechanism of Kolbe electrolysis on Pt anodes

Kolbe electrolysis has been proposed an efficient electrooxidation process to synthesize (un)symmetrical dimers from biomass-based carboxylic acids. However, the reaction mechanism of Kolbe electrolysis remains controversial. In this work, we develop a DFT- based microkinetic model to study the reaction mechanism of Kolbe electrolysis of acetic acid (CH3COOH) on both pristine and partially oxidized Pt anodes. We show that the shift in the rate-determining step of oxygen evolution reaction (OER) on Pt(111)@α-PtO2 surface from OH* formation to H2O adsorption gives rise to the large Tafel slopes, i.e., the inflection zones, observed at high anodic potentials in experiments on Pt anodes. The activity passivation as a result of the inflection zone is further exacerbated in the presence of Kolbe species (i.e., CH3COO* and CH3*). Our simulations find the CH3COO* decarboxylation and CH3* dimerization steps determine the activity of Kolbe reaction during inflection zone. In contrast to the Pt(111)@α-PtO2 surface, Pt(111) shows no activity towards Kolbe products as the CH3COO* decarboxylation step is limiting throughout the considered potential range. This work resolves major controversies in the mechanistic analyses of Kolbe electrolysis on Pt anodes: the origin of the inflection zone, and the identity of the rate limiting step.

Kolbe Electrolysis for the Conversion of Carboxylic Acids to Valuable Products—A Process Design Study

The substitution of fossil resources by renewable alternatives is a major challenge for our society. Kolbe electrolysis converts carboxylic acids to hydrocarbons, which can be used as base chemicals, specialty chemicals, or fuels. Carboxylic acids may be retrieved from biomass or residues and, in consequence, can be a sustainable feedstock. Since the Kolbe electrolysis has only been investigated in lab scale, this work proposes the first basic engineering design study on process development for a continuously working process. Thermophysical data, including solubility and boiling point, are used to gain insight into requirements on process equipment such as separation processes or process parameters such as operating temperature. Furthermore, Aspen Plus was used to retrieve information on acid base equilibria and azeotropes. The process development for three different feedstocks (acetic acid, valeric acid and lauric acid) was performed. The process design shows that most of the process units are rather straightforward and rely on state of the art technologies. The addition of an alkaline catalyst improves the solubility and deprotonation of the carboxylic acid but on the cost of a possibly lower product selectivity. Elevation of the operating temperature above the Krafft point is necessary for long-chain fatty acids. Kolbe electrolysis can be an interesting technology for future production processes based on carboxylic acids and electricity from sustainable sources.

Organic synthesis via Kolbe and related non-Kolbe electrolysis: Enabling electro-strategy

Enabling and environmentally friendly synthetic methodology is preferred over conventional methods that require expensive chemicals & oxidants to achieve value-added organic transformations. Electrochemical conversions encounter the conventional shortcomings and introduce...

(Non-)Kolbe electrolysis in biomass valorization – a discussion of potential applications

The bio-availability of organic acids as platform chemicals and the potential of electrochemistry to directly integrate renewable energy into new value chains drive (Non-)Kolbe electrolysis to become an attractive tool in future electro-bio-refinery.