Iron-induced demethoxylation of lignin as an important source for methanol and its oxidation products in the environment

Lignin, the largest source of aromatic carbon in plants and soils, undergoes well-characterized biological demethylation by fungi and bacteria. In industrial applications it is chemically processed at elevated temperatures and pressures to produce bio-based aromatics. Here, we report a novel abiotic demethoxylation mechanism operating under ambient conditions. With Fe ^II/III species and hydrogen peroxide as oxidant, we observe efficient cleavage of methoxy groups from lignin monomers and methoxyphenols, producing methanol and formaldehyde. Isotopic labeling confirms that the entire methoxy group is released intact. Density functional theory (DFT) based computational modeling supports an exergonic oxygen-atom-transfer-initiated demethoxylation mechanism with a low activation barrier (43kJ/mol), consistent with environmentally relevant conditions. Soil incubation experiments with lignin and a variety of natural soils rich in iron and methoxylated organic matter validate the significance of this abiotic pathway. Our findings reveal a so far overlooked mechanism for the release of oxygenated C ₁ compounds from lignin in soils, providing substrates for microbial metabolism and contributing to soil carbon turnover and atmospheric trace gas fluxes with implications for global carbon cycling and atmospheric chemistry.