Selective electrochemical oxidation of primary alcohols to corresponding aldehydes

• Applicant: Dr. Esma Khatun
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Analytical Chemistry
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 533134746

The oxidation of primary alcohols leads to carboxylic acid and/or aldehyde formation. Aldehydes are important reagents in chemical synthesis and critical functions of many physiologically active molecules. However, aldehydes are very unstable and easily get oxidized to carboxylic acids. Also, the aldehyde oxidation rate is higher than that of alcohol. Therefore, during primary alcohol oxidation, it has always been challenging to prevent aldehyde from being over-oxidized to carboxylic acids due to its higher reactivity. Therefore, to prepare aldehydes selectively, it is necessary to control the selectivity during alcohol oxidation. Among various oxidation methods, electrochemical alcohol oxidation is a greener process as it uses electric energy to promote redox reactions at the electrode surface. Also, it produces economically valuable products at both electrodes and decreases the production of waste materials. During the electrochemical oxidation of alcohols, to form aldehyde as the main product, it must get desorbed from the electrode surface and should not be available for further oxidation. However, it is not clear under which parameters this is possible and how the catalysts affect the probability of the aldehyde desorption from the electrode surface. The adsorption mode of alcohol at the surface of catalysts may affect the production of a desorbed aldehyde intermediate. Furthermore, the choice of catalyst might have an effect on determining the adsorption mode of the alcohol, which could then affect the distribution of reaction products. This implies that different adsorption modes are expected to occur on various catalysts which will ultimately determine whether the aldehyde will desorb as an intermediate or it will continuously oxidize to carboxylic acid. Hence, to perform selective oxidation of alcohols, one must know the detailed reaction mechanism. Additionally, it is important to identify how electroactive intermediates develop and adsorb on catalyst surfaces. Therefore, my main focus is to understand the detailed mechanism of alcohol oxidation by identifying the intermediates and their adsorption modes using the in-situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS). Also, differential electrochemical mass spectrometry (DEMS), rotating ring disk electrodes (RRDE) and high-performance liquid chromatography (HPLC) will be used as analytical tools to determine the product distribution during the alcohol oxidation. The product distribution will be correlated with the adsorption mode determined by SERS. The Au and NixOy electrodes will be used as the model catalysts for metal and transition metal oxide-based electrodes.

• DFG Programme: WBP Position