Binary Fe-containing LDHs and structurally related layered hydroxides are being widely investigated as adsorbents, catalysts, and redox-active nanomaterials. Yet, links among coprecipitation, phase formation, nanostructure, and reactive-site accessibility remain inconsistently interpreted. This critical review evaluates studies published mainly from 2015 to July 2026 on CoFe, NiFe, MgFe, ZnFe, MnFe, CuFe, and CaFe layered hydroxides and Fe(II)/Fe(III) green rust. Coprecipitation is not a single standardized route: local supersaturation, reagent delivery, mixing, complexation, atmosphere, interlayer chemistry, and aging can alter metal incorporation and phase development, while Fe-rich transient precursors may participate under system-specific conditions. The commonly cited Fe(III) fraction of x = 0.20–0.33 is an empirical guideline rather than a universal stability window, and conventional M(II)-Fe(III) LDHs, CaFe hydrocalumite-/AFm-related phases, and green rust require distinct crystal-chemical interpretations. Nominal composition and LDH-like diffraction cannot establish homogeneous cation incorporation or phase purity. In contrast, diffraction broadening, BET area, nanosheet dimensions, and XPS fitting do not provide stand-alone evidence of defects or accessible reactive sites. Progress toward predictive synthesis requires standardized reporting, system-specific synthesis–composition–phase maps, time-resolved studies, quantitative structure–accessibility relationships, and recognition of as-synthesized, working, recovered, and regenerated materials as potentially distinct structural states, supported by uncertainty analysis, negative outcomes, and validation across laboratories.

In this article it was demonstrated that potassium ethyl carbonate can be successfully utilized within the phenol and its derivatives carboxylation. The optimal reaction conditions for m-cresol were determined: substrate to potassium ethyl carbonate ratio 2:1, temperature 180°C, pressure 10 atmospheres and reaction time 6 hours. Importantly, the carboxylation of m-cresol is selective and resulted in the obtaining of 4-methyl-2-hydroxybenzoic acid in 90% yield.To study the impact of the nature and location of substituents in the phenyl ring on the yield of the desired products, carboxylation reactions of various phenol derivatives were carried out with the use of potassium ethyl carbonate. As a result of the investigation, the optimal carboxylation reaction parameters for each of the phenol derivatives were determined.This study may have practical applications in the development of laboratory and manufacturing approaches for the synthesizing of valuable hydroxybenzoic acids and their derivatives. It was discovered that carboxylation of phenol derivatives by potassium ethyl carbonate occurs via electrophilic substitution of the aromatic ring. The most active in this reaction are p-cresol (84%), mcresol (90%), o-cresol (80%) and resorcinol (73%). It was observed that p-chlorophenol (18%), pbromophenol (48%) and p-fluorophenol (58%) showed less pronounced activity.