NaBr-Assisted Photoelectrochemical and Photochemical Integrated Process for Isomerization of Maleate Esters to Fumarate Esters

Abstract

We developed a NaBr-assisted photoelectrochemical and photochemical integrated process for the complete isomerization of dimethyl maleate to dimethyl fumarate under solar-simulated light irradiation. This process also produced bulky fumarate ester derivatives at high yields (85–100%). A plausible mechanism of the bromine-initiated radical chain reaction was suggested by the results of the experimental data and density function theory calculations. The photoelectrochemical oxidation of NaBr generated the oxidized bromine species, which were then photolyzed to produce the bromine radical initiators induced by the photochemical process. This resulted in the high faradaic efficiency (98%) in the photoelectrochemical step and internal quantum yield (>100%) in the photoisomerization step. This newly developed process is an innovative and environmentally friendly strategy that goes beyond the conventional thermochemical process to achieve the precise synthesis of fumarate derivatives under mild conditions.

Electronic structure, bonding and stability of fumarate, maleate, and succinate dianions from X-ray spectroscopy

“…Contrarily, the high electronic density on the CQC bond indicates that there are more electrons available for bonding, which makes it as a reaction center for such a reaction like isomerization. As an example, isomerisation reaction can occur via a radical chain reaction mechanism 15 where at the initial step, a bromine radical adds to one of the carbon atoms of the CQC bond in the maleate structure, leading to the formation of a carboncentered radical complex. In contrast, the HOMO orbitals of succinate (16A) and fumarate (12Bu) are delocalized over both carboxylate groups, which potentially would lead to a strong bonding between them and other molecules.…”

“…Previous studies have examined the geometries of fumarate, maleate, and succinate using various experimental and theoretical methods. [11][12][13][14][15] Specifically, trans configuration of fumarate often leads to extended and open structures, while cis configuration of maleate results in more compact topologies. 5,[16][17][18][19][20] In the case of succinate, the absence of a CQC bond allows the molecule to more freely rotate.…”

New Photoelectrochemical Reactor for Hydrogen Generation: Experimental Investigation

“…Therefore, a semiconductor possessing a band gap higher than 1.23 eV and lower than 3 eV is desired to sustain the PEC water-splitting process under visible light spectrum . The use of external bias voltage is another approach to PEC technique. , In this process, the voltage required for water splitting is partially provided from photonic energy absorbed and converted to electrical potential by photoactive electrodes. The process enables to work with low-cost semiconductors, lowering the electricity consumption for water splitting via utilizing free and abundant solar energy and producing totally green hydrogen with respect to the source of the external bias.…”

Experimental Study of a Novel Photoelectrochemical Hydrogen Cell Design for Clean Hydrogen Generation

“…Electrolysis is listed as one of the widely known techniques used for the water-splitting process to produce hydrogen. The photoelectrochemical (PEC) technology is a hydrogen production technique that can enhance the electrolysis process environmentally by combining conventional electrolysis and sunlight energy. − Semiconductor electrodes can convert sunlight (photonic energy) into electrical power for the water-splitting process using a PEC technique. The working photoelectrode absorbs the delivered light to split water via consuming energy from sunlight.…”