Zirconyl (IV) Nitrate as Efficient and Reusable Solid Lewis Acid Catalyst for the Synthesis of Benzimidazole Derivatives

Table 1

Optimization of reaction conditions^a for synthesis of substituted benzimidazoles from benzaldehyde/benzoic acid with o-phenylenediamine.

Entry	Solvents	Catalyst conc.; (weight %)	Yield^b (%)/reaction time (h)
			Benzaldehyde	Benzoic acid
1	Ethanol	No catalyst	27/6	45/14
2	Ethanol	0.3	58/3	65/6
3	Ethanol	0.5	96/2	90/3
4	Ethanol	1	94/2.5	94/3
5	Dioxane	0.5	82/3	75/4.5
6	EtOAc	0.5	85/3.5	78/5
7	DCM	1	70/4	80/6

aReflux the reaction mixture. bIsolated yield.