Conducting Polyaniline is an Efficient Catalyst for Synthesis of 3,4-dihydropyrimidin-2-(1H)-one Derivative Under Solvent-Free Conditions

Polyaniline mediated heterogeneous catalysis in the preparation of heterocyclic derivatives through carbon–heteroatom bond formations

Green-bond forming reactions in organic chemistry are very much essential for the sustainability and it is a continuous evolutionary process. Polyaniline (PANI) is one of the catalysts can offer a green-bond forming chemistry. The present chapter is designed to explain PANI mediated reactions leading to the synthesis of heterocycles. PANI and PANI-doped catalyst preparation methods and together with characterization of PANI catalyst using modern analytical tools is explained. Several heterocycles were prepared using PANI or doped-PANI catalyst in a one pot reaction conditions or sometimes multicomponent reaction conditions. Ease of PANI preparation, simple reaction conditions, PANI recovery and reusability and quick-way of product isolation or workup procedure are the highlights of this chapter.

Biginelli Reaction: Polymer Supported Catalytic Approaches

The Biginelli product, dihydropyrimidinone (DHPM) core, and its derivatives are of immense biological importance. There are several methods reported as modifications to the original Biginelli reaction. Among them, many involve the use of different catalysts. Also, among the advancements that have been made to the Biginelli reaction, improvements in product yields, less hazardous reaction conditions, and simplified isolation of products from the reaction predominate. Recently, solid-phase synthetic protocols have attracted the research community for improved yields, simplified product purification, recyclability of the solid support, which forms a special economic approach for Biginelli reaction. The present Review highlights the role of polymer-supported catalysts in Biginelli reaction, which may involve organic, inorganic, or hybrid polymers as support for catalysts. A few of the schemes involve magnetically recoverable catalysts where work up provides green approach relative to traditional methods. Some research groups used polymer-catalyst nanocomposites and polymer-supported ionic liquids as catalyst. Solvent-free, an ultrasound or microwave-assisted Biginelli reactions with polymer-supported catalysts are also reported.

Preparation and Characterization of WS₂@SiO₂ and WS₂@PANI Core-Shell Nanocomposites

Two tungsten disulfide (WS₂)-based core-shell nanocomposites were fabricated using readily available reagents and simple procedures. The surface was pre-treated with a surfactant couple in a layer-by-layer approach, enabling good dispersion of the WS₂ nanostructures in aqueous media and providing a template for the polymerization of a silica (SiO₂) shell. After a Stöber-like reaction, a conformal silica coating was achieved. Inspired by the resulting nanocomposite, a second one was prepared by reacting the surfactant-modified WS₂ nanostructures with aniline and an oxidizing agent in an aqueous medium. Here too, a conformal coating of polyaniline (PANI) was obtained, giving a WS₂@PANI nanocomposite. Both nanocomposites were analyzed by electron microscopy, energy dispersive X-ray spectroscopy (EDS) and FTIR, verifying the core-shell structure and the character of shells. The silica shell was amorphous and mesoporous and the surface area of the composite increases with shell thickness. Polyaniline shells slightly differ in their morphologies dependent on the acid used in the polymerization process and are amorphous like the silica shell. Electron paramagnetic resonance (EPR) spectroscopy of the WS₂@PANI nanocomposite showed variation between bulk PANI and the PANI shell. These two nanocomposites have great potential to expand the use of transition metals dichalcogenides (TMDCs) for new applications in different fields.