Nano BF3·SiO2: A green heterogeneous solid acid for synthesis of formazan dyes under solvent-free condition

•Nano BF3·SiO2 efficiency in synthesis of aryl diazonium salts and their stability.•Solvent- and catalyst-free methodology for synthesis of aldehyde phenylhydrazones.•Room temperature synthesis of formazans via coupling of above mentioned reactants.•No need to buffer solution, solvent, and liquid acid for synthesis of formazans.

A solvent-free, efficient and rapid approach for synthesis of formazan dyes was developed by diazotization of aromatic amines with NaNO2, nano silica-supported boron trifluoride (nano BF3·SiO2), then diazo coupling with aldehyde phenylhydrazones by grinding method at room temperature. This study aimed to overcome the limitations and drawbacks of the previous reported methods such as: low temperature, using corrosive and toxic acids and solvents, using buffer solutions, instability of aryl diazonium salts, modest yields, and long reaction times.

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