Deep eutectic solvent prepared from para-toluenesulfonic acid catalised efficiently 2-arylbenzothiazole synthesis reaction

Abstract

Preparation of a new generation ionic liquid (Deep eutectic solvent, DES) was conducted from choline chloride and para-toluenesulfonic acid. Infrared spectroscopy of the prepared DES resulted in the interaction between choline chloride and para-toluenesulfonic acid through hydrogen bonding. This DES was used to catalyze the synthesis of some 2-arylbenzothiazole derivatives from some benzaldehyde derivatives and 2-aminothiophenol under solvent-free conditions. Factors affecting the reaction were investigated such as reaction temperature, reaction time, amount of the catalyst, and ratio of benzaldehyde and 2-aminothiophenol. The best reaction conditions were obtained: reaction temperature of 50oC, reaction time of 30 minutes, ratio of benzaldehyde:2-aminothiophenol=1:1, 1 (mmol), and amount of used catalyst is 20% mol in ratio of benzaldehyde. The used catalysts were collected, purified, and investigated their reusability. The results of the reusability of the catalyst showed that DES can be used 4 times without significant activity decreasing after each use. In addition, synthesis of some other 2-arylbenzothiazole derivatives was also performed by replacing benzaldehyde with its derivatives bearing substituents at the para position, the halogen substituents reduced the reaction yield while the substituents donating electrons did not affect the reaction yield.