Silica Sulfuric Acid: An Eco-Friendly and Reusable Catalyst for Synthesis of Benzimidazole Derivatives

Table 1

Acid-catalyzed synthesis of 2-(phenyl)benzimidazole.

Entry	Catalyst	Condition/solvent	Time (min)/isolated yield (%)	Ref.
1	Me2S^+BrBr^−(0.5 mmol)^a	r.t./MeCN	10/85	[13]
2	P-TsOH (20 mol%)^a	80°C/DMF	10/85	[9]
3	Alumina-methanesulfnic acid (0.33 g.0.39 g)^b	MW	10/96	[10]
4	BF3.OEt2 (0.1 mmol)^a	r.t./CH2Cl2	30/90	[11]
5	Ceric(IV) ammonium nitrate^a	Reflux/CH2Cl2	45/75	[12]
6	SiO2-OSO3H (0.1 g)	80°C/EtOH	20/91	—
7	SiO2-OSO3H (0.1 g)	25°C/EtOH	60/30	—
8	SiO2-OSO3H (0.1 g)	45°C/—	30/65	—
9	SiO2-OSO3H (0.05 g)	80°C/EtOH	20/82	—
10	SiO2-OSO3H (0.15 g)	80°C/EtOH	20/92	—
11	SiO2-OSO3H (0.1 g) 2nd run	80°C/EtOH	20/85	—
12	SiO2-OSO3H (0.1 g) 3rd run	80°C/EtOH	20/82	—