Carbon kinetic isotope effects at natural abundances during iron-catalyzed photolytic cleavage of CC bonds in aqueous phase α,ω-dicarboxylic acids

Highlights: • Stable carbon isotope ratios of Fe³⁺/carboxylate mixture exposed to artificial sunlight were measured to gain kinetic isotope effects (KIEs). • Obtained KIEs were used to identify the vailed CC bond cleaving channel of oxalate. • Observed KIEs for the oxalate, malonate, and succinate mixtures were 5.9‰, 11.5‰, and 8.4‰, respectively. • Comparison of the observed KIEs with the proposed photolysis mechanism successfully identified the sequential dissociation of CC and FeO bonds as the CC bond cleaving channel. Carbon kinetic isotope effects (KIEs) at natural abundances during photolysis of Fe³⁺-oxalato, malonato, and succinato complexes in aqueous solution were studied to identify the CC bond cleaving mechanism of Fe³⁺-oxalato complexes under sunlight irradiation. Observed overall KIEs were 5.9‰, 11.5‰, and 8.4‰, respectively. This variation is inconsistent with secondary carbon KIEs for the FeO bond cleavage, but consistent with primary carbon KIEs for sequential cleavage of FeO and CC bonds. Position-specific probability of ¹³C content estimated KIEs of 5.9‰, 17.2‰, and 17‰ for ¹²C¹³C bond cleavage, respectively, indicating the different KIEs for carboxyl-carboxyl and methyl-carboxyl cleavage.