In situ preparation of a ferric polymeric aluminum chloride–silica gel nanocatalyst by mechanical grinding and its solid-phase catalytic behavior in organic synthesis

Abstract

In recent years, clean and sustainable mechanochemical solvent-free reactions have emerged as a viable alternative to solution chemistry. In order to completely solve the problem of environmental pollution caused by solvents and surfactants in LASC and LASSC systems, a green method for the in situ preparation of environmentally friendly inorganic polymeric Lewis acids and silica gel as nanocatalysts (PLASC) under solvent-free mechanical grinding conditions was designed and realized by mechanochemical means, which is simple to operate and the process generates no other waste. Subsequently, 3-alkylindole derivatives (35–75%), β-amino alcohol derivatives (90%), benzimidazole derivatives (85–90%) and quinoxaline derivatives (93–99%) were synthesized by a one-pot cooking method under continuous grinding conditions. The mechanism of in situ self-assembly of PAFC and silica gel on the silica gel surface under mechanical forces and the new catalytically active species-Si–O–Al(Fe) polynuclear metal complexes resulting from chemical reforming were discovered and confirmed by SEM, HR-TEM, FT-IR, XRD and XPS tests as well as by solution morphology studies. The true active centre –O–Fe–O–Si–O–/–O–Si–O–Al–O– chemical bonding unit was revealed and found to be a nanoscale fibrous structure that is highly stable and can be reused at least 10 times without deactivation. The PLASC catalyst has remarkable green chemistry properties such as easy recycling and a very low E factor, making it a new type of cheap, efficient and green catalyst.