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

Abstract

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 (1.9wt%) increased the basal space from 9.57 to 13.89Å, but the further fixation of Fe content slightly decreased the basal space. The specific surface area increased from 80 up to 171m2/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.