Optimizing semi-hydrogenation of unsaturated hydrocarbons by electrolyte engineering approach

Area of Science:

• Electrochemistry
• Catalysis
• Green Chemistry

Background:

• Electrochemical hydrogenation offers a sustainable alternative to energy-intensive synthetic routes for unsaturated hydrocarbons.
• Electrolyte composition significantly influences the yield, selectivity, and kinetics of semi-hydrogenation reactions.
• Optimizing electrolytes is complex due to their hybrid nature, involving water, organic solvents, and conducting salts.

Purpose of the Study:

• To investigate the impact of electrolyte composition on the electrochemical semi-hydrogenation of alkynes.
• To elucidate the role of water, organic solvents, and conducting salts in reaction outcomes.
• To identify electrolyte conditions that maximize product yield and selectivity.

Main Methods:

• Electrochemical measurements combined with Fourier transform infrared (FTIR) spectroscopy and small-angle X-ray spectroscopy (SAXS).
• Systematic variation of conducting salt, organic solvent, water, and acid concentrations.
• Analysis of electrolyte solvation structure and its correlation with reaction performance.

Main Results:

• Water does not act as a proton source; acid addition is necessary for hydrogenation.
• Increasing acid concentration enhances yield, but high concentrations favor hydrogen evolution.
• Electrolyte solvation structure critically affects yield; homogeneous mixtures (e.g., with dimethylformamide) yield >80%, while heterogeneous mixtures (e.g., with acetonitrile) limit yields.

Conclusions:

• Electrolyte engineering is crucial for optimizing electrochemical alkyne semi-hydrogenation.
• Dimethylformamide-based electrolytes promote homogeneous mixing, enabling high yields by facilitating reactant access to the catalyst.
• Understanding electrolyte solvation structures is key to designing efficient and selective electrochemical hydrogenation processes.