Preparation and characterization of Lewis acid grafted sulfonated carbon@titania composites for the multicomponent synthesis of 4H-pyrimido[2,1-b]benzothiazoles and benzoxanthenones under solvent-free conditions

•Design, synthesis and characterization of C/TiO2–SO3M.•4H-Pyrimido[2,1-b]benzothiazoles and benzoxanthenones were synthesised.•Multicomponent synthesis was effectively carried out under solvent-free conditions.•The catalyst showed excellent recyclability with negligible leaching of Lewis acid.

A series of novel and highly efficient Lewis acids covalently grafted over sulfonic acid functionalized carbon@titania composites were successfully synthesized via sulfonation of carbon@titania composites followed by treatment with different Lewis acids like AlCl3, FeCl3, SbCl3, SnCl2, Cu(OAc)2 and Bi(NO3)3. The utility of the developed catalysts was explored for the synthesis of a diverse range of 4H-pyrimido[2,1-b]benzothiazoles and benzoxanthenones, and among various catalysts, C/TiO2–SO3–SbCl2 was found to be the most active. We report here the synthesis of five novel compounds and the structure of one of the compounds has also been confirmed by single-crystal X-ray diffraction. All the five prepared composites were characterized by FTIR and ICP-AES analysis, whereas the most active one, C/TiO2–SO3–SbCl2 was further characterized by XRD, EDX, CHNS, SEM, TEM, HRTEM and TGA. The catalyst can be recovered and reused for atleast five runs without any significant impact on catalytic activity and selectivity. The high catalytic activity, thermal stability, simple recovery and reusability, and eco-friendly nature of the catalyst makes the present method to be particularly attractive from the view point of green chemistry.

Graphical abstractA series of Lewis acid covalently grafted over sulfonated carbon@titania composites have been designed and investigated as sustainable recyclable catalytic system for multicomponent synthesis.Figure optionsDownload full-size imageDownload high-quality image (238 K)Download as PowerPoint slide