Synthesis of Some Derivatives of 4-phenyl-1,3-dihydro-2H-imidazole-2-thion Using Ionic Liquid as Catalyst and Evaluation of Their Antimicrobial Activity

The synthesis of some 1,3-diazoles and thiazoles was realized in different conditions: a) In the presence of PTSA or sulfuric acid as catalyst we obtained only diazole products(4a-d). b) In basic medium such as DABCO or sodium hydroxide and ionic liquid afforded thiazoles. c) Both products, diazoles and thiazoles were collected when using methanol as catalyst and solvent. All structures were confirmed by IR, H NMR and C NMR spectroscopy. The antibacterial activity of some synthesized compounds was investigated against Escherichia Coli (ATCC: 25922) and Serratia marcescens (ATCC: 13880) as gram negative bacteria, Bacillus sabtilis (ATCC: 6633) and Staphylococcus aureus (ATCC: 6338) as gram positive bacteria. Some of these products exhibit good activities to significant antibacterial activity.


Introduction
Diazoles and thiazoles have been attracting special interest because of their various biological activities and clinical applications (Holla, Malini, Rao, Sarojini, & Kumari, 2003).
Heterocyclic compounds containing a 1,3-diazole nucleus are of special interests thanks to their applications in medicinal chemistry as they are the basic skeleton of several bioactive compounds such as antifungal, antibacterial, antitumor and antitubercular (Holla, Malini, Rao, Sarojini, & Kumari, 2003).
According to researches, this critical scaffold can inhibit antibacterial activities of S. aureus and E. coli pathogens (Ghasemi et al., 2016).
Ionic liquids (ILs) are defined as ionic salts with a melting point below 100°C, a high polarity and low vapor pressure (Yavari et al., 2009).These salts are formed of organic cation and inorganic anions (Ratti, 2014).Ionic liquids have been applied widely as alternative solvents to support green chemistry considering particular physical and chemical properties (Selva, Perosa, Guidi, & Cattelan, 2016).
Due to the functional groups of the cation or anion in ILs, they can be considered as acidic, basic or organic catalysts (Ratti, 2014).
In the present research, we have synthesized some of new derivatives of 1, 3-diazoles and thiazoles using water as green and environment friendly solvent and different catalysts such as ionic liquid.The purpose of this study was to investigate the antibacterial activity of the new derivatives comparing to two known antibiotics.

Materials and Equipment
Melting points were determined with an Electrothermal digital apparatus (Thermo Scientific) and were uncorrected.IR spectra were obtained on Shimadzu FT-IR 5000 spectrophotometer in KBr.NMR spectra were recorded on a Brucker 500 and 300 MHz spectrometer, chemical shifts were given in ppm in DMSO-d 6 .

Procedure for the Synthesis of 1,3-Diazoles and Thiazoles
Acetophenone derivatives (1mmol), thiourea (1mmol) and PTSA, DABCO, or sulfuric acid (6-7 drops) as catalysts were transferred to a 100 mL 2-neck round bottom flask and 20 mL distilled water was added as the solvent.Then the mixture was reacted under reflux conditions.The progress of the reaction was monitored by TLC using n -hexane/ ethyl acetate (1/1).After completion of the reaction, the reaction mixture was cooled at room temperature to obtain a precipitate which is considered as the product.

Ionic Liquid Catalyst Synthesis
Choline chloride and urea (2mmol) were heated and stirred for 2 hours.Then the reaction mixture was cooled and the desired product (choline chloride urea) was gained.

Antibacterial Activities of Synthesized Compounds
Four microorganisms were used to test the antibacterial activity of the synthesized compounds.

Results and Discussion
As shown in scheme (1), we quickly and efficiently synthesized 1,3-diazole and thiazole derivatives ( 4 a-d , 3 a-d ) by refluxing some 2-holo acetophenone derivatives (1 a-e ) and thiourea (2) using water as reaction solvent and different kinds of catalysts.Compared to reported methods of thiazole and 1,3-diazole synthesis (Ghodse & Telvekar, ,2015;Zhao et al., 2002) which employed toxic organic solvents and they were time-taking or expensive, this procedure is less hazardous, less toxic, cheap and environment friendly.The occurred reactions in this procedure, lead to produce desired compounds with high yields of 85-94% (table 1).The reaction time was short (6h).All reaction mixtures were cooled at room temperature and the precipitate was filtered easily.In FT-IR spectra of the synthesized 1, 3-diazole derivatives, the adsorption bands of C=S and NH were observed respectively within 1629.74_1649.02cm -1 and 3122.54_3450.41cm -1 .In 1 H-NMR spectra of 1, 3-diazole-2-thion and thiazole 2-amine derivatives, the aromatic hydrogens of phenyl ring and 1,3-diazole-2-thion and thiazole 2-amine rings appeared within 7-8 ppm as singlets, doublets, doublet of doublets or multiplets according to the type of hydrogen.The absorption band of NH and NH 2 groups in 1,3-diazole-2-thion and thiazole 2-amine derivatives were observed in the region of higher than 8 ppm (8-10 ppm) and these absorption bands were disappeared in D 2 O shake-1 H-NMR which can confirm the predicted structures of the synthesized compounds. 13C-NMR chemical shifts for the compounds were displayed in their expected regions.
Using an ionic liquid as catalyst, the reaction yields the same compounds as the case of using DABCO and sodium hydroxide, but the reaction time was decreased and the yield was increased significantly.
As it was shown in the table 1 and scheme 1, thiazole derivatives were synthesized in basic pH using basic catalysts or solvent such as DABCO, NaOH, ionic liquid and diazole derivatives were obtained in acidic PH when PTSA and H 2 SO 4 were applied as catalysts.In contrast of above conditions when we used methanol as catalyst and solvent both products, diazoles and thiazoles were appeared.

ults have y against
Escherichia Coli compared to tetracycline and imipenem antibiotics.The compound 3a showed the best antibacterial activity against gram positive bacterias Staphylococcus aureus and Bacillus Subtilis compared to both applied antibiotics and acceptable antibacterial activity against gram negative bacteria Serratia marcescens compared to tetracycline.The results of this part have been shown in the table2.In conclusion, we have developed a facile, efficient and green method for the synthesis of 1,3-diazole and thiazole derivatives by refluxing acetophenone derivatives and thiourea in water medium and various types of catalysts.Then, in a second part, antibacterial activities of the resulting compounds were studied.The antibacterial activities of the compounds have demonstrated appropriate results compared to common antibiotics.Compared to the previously reported methodologies, our protocol offers considerable benefits, including that it has a simple procedure, is environmentally friendly, produces high yields.
They were: Escherichia Coli (ATCC: 25922) and Serratia marcescens (ATCC: 13880) as gram negative bacteria and Bacillus sabtilis (ATCC: 6633), and Staphylococcus aureus (ATCC: 6338) as gram positive bacteria.Antibacterial activities of the compounds were tested by Disc Diffusion method and Minimum Inhibitory Concentration (MIC) using agar dilution method.Yield 92% Formation of this synthesized compound was confirmed by thin layer chromatography (TLC) and comparing with the synthesized compound when MeOH was applied as the catalyst.

Table 2 .
Antibacterial activities of synthesized compounds