Complete electron economy by pairing electrolysis with hydrogenation

Abstract

Electrosynthesis provides a method of driving organic reaction chemistry under ambient conditions with electricity. Pairing two reactions together enables the synthesis of two valuable chemicals with no waste product. Here we report the paired electrolysis of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde with the concomitant formation of 1-hexene from 1-hexyne in an electrochemical cell. These reaction chambers are separated by a dense palladium membrane that reduces protons formed at the anode to hydrogen atoms that can permeate through the palladium foil to hydrogenate 1-hexyne. The palladium membrane enables two reactions to be performed in distinct reaction conditions: hydrogenation in organic solvents and electrochemical oxidation in aqueous electrolyte. The starting materials in both chambers react quantitatively over 5 hours of electrolysis, and selectivities ≥95% can be achieved for 4-methoxybenzaldehyde and 1-hexene with control of reaction conditions. Exquisite control of the reaction kinetics and selectivities of each of the individual reactions is demonstrated. Electrolysis uses clean electricity to form chemical products but typical water electrolysis produces hydrogen which is hard to store oxygen which is a waste gas. Here, paired electrolysis is performed with an palladium membrane reactor to carry out two organic reactions simultaneously. The dense palladium membrane enables the two reactions to proceed in different solvents and the reaction rates and selectivities can be independently controlled.