Two synthesis approaches of Fe-containing intercalated montmorillonites: Differences as acid catalysts for the synthesis of 1,5-benzodeazepine from 1,2-phenylenediamine and acetone

Two approaches were considered for the preparation of Fe-containing composites based on montmorillonite and comparison of their structural, physicochemical and catalytic properties. The first approach (Si,Fex-Mt materials) was based on the intercalation of Cheto montmorillonite (Mt) by 3-aminopropyltriethoxysilane (APTES) and FeCl3 via the sol-gel polymerization technique. Fe/Si atomic ratios were 6:94, 18:82 and 30:70. Then Si,Fex-Mt materials were calcined in air at 400 or 500 °C for the APTES removal. The second approach (Al13 − xFex-Mt materials, x = 1 and 2) was based on the pillaring method using Keggin type mixed Al13 − xFex-polycation (x = 1, 2) and montmorillonite from Cheto, Arizona, USA (Mt) as starting material. The intercalated Al13 − xFex-Mt materials were calcined at 400 or 500 °C. The physicochemical characterization pointed out the effectiveness of the incorporation of Fe and Si into the interlayer space of the clay mineral. The fixation of small amounts of Fe (1.9 wt%) increased the basal space from 9.57 to 13.89 Å, but the further fixation of Fe content slightly decreased the basal space. The specific surface area increased from 80 up to 171 m2/g. The oligomeric state of Fe2O3 particles depended on its content; the larger Fe content, the larger particle size of Fe2O3. Catalytic properties of Si,Fex-Mt and Al13 − xFex-Mt materials were studied in the cyclocondensation of 1,2-phenylenediamine with acetone to 1,5-benzodiazepine. The yield of 1,5-benzodiazepine was found to rise with increasing of the Fe content in Si,Fex-Mt. Catalytic performance of Si,Fex-Mt was lower in comparison with Al13 − xFex-Mt, that is in agreement with the amount of Lewis acid sites.