Synthesis of benzimidazole and quinoxaline derivatives using reusable sulfonated rice husk ash (RHA-SO3H) as a green and efficient solid acid catalyst

Abstract

In this work, a simple, rapid and efficient method for the preparation of benzimidazoles and quinoxalines from the condensation of o-phenylene diamines with aldehydes and/or 1,2-dicarbonyl compounds in the presence of sulfonated rice husk ash (RHA-SO 3 H) as an efficient green catalyst is reported. RHA-SO 3 H can be easily prepared using a readily available organic compound by simple modification of rice husk ash. All reactions are performed under mild reaction conditions with high to excellent yields. The method is applicable to aromatic, unsaturated and hetero aromatic aldehydes. The advantages of this method are short reaction times, milder conditions, easy work-up, solvent-free conditions and catalyst reusability.

Re(i)[2-aryl-1H-imidazo[4,5-f][1,10]phenanthroline] tricarbonyl chloride complexes for selective cancer therapy via a potential DNA damage mechanism

“…The absorption and emission properties of all the complexes were investigated via the spectrofluorometric method in 1% DMSO-PBS buffer solution. 22 The fluorescence quantum yield ( Φ ) of all the prepared complexes was calculated by employing the comparative Williams method, which involves the use of a well-characterized standard with a known quantum yield value. Quinine sulphate was used as the reference fluorophore excited at 350 nm and emission at 452 nm, quantum yield ( Φ R ) = 0.50 in 1 N H 2 SO 4 .…”

CuAAC “Click”-Derived Luminescent 2-(2-(4-(4-(Pyridin-2-yl)-1H-1,2,3-triazol-1-yl)butoxy)phenyl)benzo[d]thiazole-Based Ru(II)/Ir(III)/Re(I) Complexes as Anticancer Agents

“…Absorption and emission behaviors of all of these complexes were examined by a spectrofluorometric method in 10% DMSO solution . The quantum yield (Φ) of all complexes was determined by the comparative William’s method.…”

“…Then, the reaction mixture was refluxed for 24 h. After completion of the reaction, the solvent was evaporated to obtain the crude complex, which was further crystallized from a diethyl ether/methanol (1:1) solvent system, which yielded a 90% pure crystalline product of complex 7c. 42 The quantum yield (Φ) of all complexes was determined by the comparative William's method. Quinine sulfate was used as the reference fluorophore with excitation at 350 nm and emission at 452 nm; quantum yield (ΦR) = 0.50 in 1N H 2 SO 4 .…”

Recent advances in the transition-metal-free synthesis of quinoxalines

“…Broad functional group tolerance, mild reaction condition, recoverability, and reusability of the catalyst without affecting the outcome of the reaction, are some of the advantages of all of the developed strategies (Table 1). [64][65][66][67][68][69][70] Although their emergence in organic chemistry in only about the last decades, ultrasound irradiation has been considered as a powerful alternative energy source for the construction of value-added compounds to make them sustainable from the perspective of green chemistry. 71 Scheme 2 One-pot reduction and subsequent tandem condensation to access diverse quinoxaline derivatives 7.…”