Direct Electrosynthesis of an Amino Acid from a Biomass Derivative

TL;DR

This paper presents a two-step electrochemical method to produce an amino acid from a biomass derivative using green sources and renewable energy.

Contribution

A novel electrochemical method to synthesize AFCA from HMF using Ag and MnOx electrodes without product separation.

Findings

AFCA was synthesized from HMF with 35% Faradaic efficiency using MnOx anode oxidation.

Ag electrodes achieved 69% Faradaic efficiency for reductive amination of HMF to HMFA.

Combining cathode and anode reactions in one reactor eliminates energy-wasting side reactions.

Abstract

The
electrochemical synthesis of nitrogen-containing molecules
from biomass-derived compounds under ambient conditions is demonstrated,
relying only on green sources of feedstock, renewable energy, and
water. In this study, we report a two-step method of electrochemically
synthesizing 5-(aminomethyl)furan-2-carboxylic acid (AFCA) from 5-hydroxymethylfurfural
(HMF) using hydroxylamine (NH2OH) as the nitrogen source
in an acidic electrolyte. In the first step, HMF was reductively aminated
into (5-(aminomethyl)furan-2-yl)methanol (HMFA) using NH2OH as the source of nitrogen. This was followed by a second step,
involving the oxidation of HMFA to AFCA on a manganese oxide (MnOx) anode at the same pH. MnOx was able to selectively oxidize the alcohol group on HMFA
to produce AFCA with 35% Faradaic efficiency without affecting the
amine group. As both of these reactions are completed in a pH 1 electrolyte,
it eliminates the need to separate HMFA before proceeding with the
second reaction. Among different metal electrodes (Ag, Au, Cu, Pb,
Pt and Sn) tested for the electrochemical reductive amination reaction,
Ag electrodes displayed the best performance to selectively aminate
HMF to the intermediate species, HMFA, with up to 69% Faradaic efficiency
at mild potentials of −0.50 VRHE. Density functional
theory calculations were carried out to explore a possible reaction
pathway for the reductive amination on Ag(111), which suggests a thermodynamically
feasible reaction even at 0 VRHE. The cathodic experimental
reaction parameters were optimized to reveal that an electrolyte pH
of 1 is optimal for the electrochemical reductive amination reaction.
Our work shapes the future possibility of an electrochemical synthesis
to produce AFCA without the need for any product separation between
steps by combining the Ag cathode reaction to the MnOx anode reaction sharing the same electrolyte. Since
both the cathode and anode reactions both involve four electrons transferred,
combining both half reactions in a single electrochemical reactor
can eliminate the need for energy-wasting auxiliary counter reactions
such as hydrogen evolution or water oxidation.

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