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

Table 2

Synthesis of benzimidazoles catalyzed by silica sulfuric acid^a.

Entry	𝑅^1	𝑅^2	Product^b	Yield/%^c	M.P./°C	Ref.
1	C6H5; 2a	—		91	289–291	[9]
2	4-ClC6H4; 2b	—		87	288–291	[9]
3	2-ClC6H4; 2c	—		89	230-231	[9]
4	4-CH3C6H4; 2d	—		82	262–264	[9]
5	2-OMeC6H4; 2e	—		84	224–227	[10]
6	3,4-OMeC6H3; 2f	—		80	228–230	[13]
7	3-NO2C6H4; 2g	—		85	202–204	[9]
8	4-NO2C6H4; 2h	—		86	308–310	[9]
9	CH3CH2; 2i	—		74	172–174	[10]
10	4-OMeC6H4; 2j	—		89	224–226	[12]
11	C6H5CH=CH; 2k	—		90	199–202	[11]
12	C4H3S; 2l	—		78	327–329	[12]
13	C5H4N; 2m	—		81	218–220	[12]
14	—	4-BrC6H4; 3a		86	283–285	[10]
15	—	C6H5; 3b		85	289–291	[9]
16	—	4-NH2C6H4; 3c		82	202–204	[10]

^aMolar ratio of aldehyde or benzonitrile: 2-amino aniline: SiO₂-OSO₃H(g) was 1: 1 : 0.1. ^bIsolated yield. ^cAll products are known and were identified by their melting points, IR, ¹H NMR, and ¹³C NMR spectra.