NaHSO₄-SiO₂-Promoted Solvent-Free Synthesis of Benzoxazoles, Benzimidazoles, and Benzothiazole Derivatives

Table 1

Preparation of 2-phenyl benzimidazole using various solvents and temperaures^a.

Entry	Solvent	Time/Temp (°C)	Yield (%)^b
1	Ethanol	12 hr/80°C	90
2	1,4-Dioxane	12 hr/100°C	80
3	Toluene	12 hr/100°C	72
4	Solvent-free	12 hr/100°C	92
5	Solvent-free	16 hr/100°C	91
6	Solvent-free	08 hr/100°C	82
7	Solvent-free	12 hr/70°C	68

^aReaction conditions: 𝑜-phenylenediamine (1 mmol), benzoyl chloride (1 mmol),NaHSO₄-SiO₂(25%/wt) were stirred in solvent (3 mL) or neat, the temperature and time indicated in Table 1, ^bisolated yields.