Synthesis and Characterization of Benzimidazole by Using o-Phenylenediamine with Different Aldehydes and Carboxylic Acids in the Presence of ρ-TSOH as a Catalyst

Introduction

Benzimidazole is one of the heterocyclic compounds that shows different biological qualities such as antibacterial and antifungal.¹ Also, some Benzimidazoles have an effect on human viruses such as cytomegalovirus.² There are two procedures for the synthesis of 2-substituted Benzimidazoles. The first is the reaction of phenylenediamines and carboxylic acids or its derivatives by heating³ in strong drying conditions.⁴ The second includes a two-step procedure that includes the oxidative cyclodehydrogenation of Schiff bases, which are often generated from the condensation of phenylenediamines and aldehydes³ and with aryl-aldehydes by using an acidic agent and also with silica gel at room temperature.⁴ p-TsOH has been used as a neutral acid catalyst to synthesize a number of benzimidazoles.⁵ It is considered as an important, effective, available and inexpensive incentive.⁶ Also, there are many ways to synthesize benzimidazole by using different catalysts such as Nanocrystalline oxides (MgO) with iodine,⁷ H₂O₂/HCl and Cu (OTf)₂,⁸ HCl.⁹ In this work, the aim was the synthesis of benzimidazole rings by using one catalyst is p-TsOH as in previous studies above, which are used one catalyst in different circumstances.

Instruments

Melting points have been determined by using Melting point SMP3 apparatus.

F.T.I.R spectra have been recorded by using Fourier Transform Infrared Spectrophotometre (F.T.I.R) 8400 S Shimadzu apparatus.

HNMR spectra have been recorded by using NMR Spectrometer 400 MHz, Avance III 400 Bruker, Germany.

U.V. spectra havebeen recorded by using U.V-Visible Spectrophotometer 1650 PC Shimadzu apparatus.

Experimental Section

The General Method for Synthesizing Benzimidazoles from Aldehydes

A solution of Aldehyde (0.01 mole), o-phenylenediamine(0.01 mol) and DMF (3 ml) has been mixed with  p-TsOH (20 ml). The mixture has been heated and stirred at 80°C for 2-3hr., then cooled to reach room temperature, the mixture has been added dropwise  with stirring into mixture of  Na₂CO₃ (0,01mole) and H₂O (20 ml), the product has been filtered, washed by H2O, then dried² to yield A, B and C compounds.

The General Method for Synthesizing Benzimidazole from Carboxylic Acids

A solution of Carboxylic acid (0.01 mole), o-phenylenediamine(0.01 mole) and toluene (10 ml) has been mixed with p-TsOH (20 ml). The mixture has been refluxed for 2-3 hr. then cooled, filtered and dried¹⁰ to yield D, E and F compounds.

Table 1: Physical Properties of Compounds

Compounds	Molecular formula	Solvent	Yield %	M. P. Cº	Color
A	C13H9N2Cl	DMF	78	294-298	Brown
B	C15H15N3	DMF	72	237-240	Nutty
C	C6H6N2	DMF	85	115-118	Yellow
D	C13H10N2O	Toluene	81	151-157	Yellow
E	C8H8N2	Toluene	72	Oil	Nutty
F	C10H12N2	Toluene	68	249 dec.	Nutty

 

Scheme 1 Click here to View scheme

 

Result and Discussion

Synthesis compounds characterized by F.T.I.R. and H-NMR spectroscopy have showed an important absorption packs of functional groups for the synthesis Benzimidazole derivatives from aldehydes and carboxylic acids with presence of p-TSOH as a catalyst in the different conditions.

2-(4-Chlorophenyl) -1H-Benzimidazole

The F.T.I.R spectrum of this compound shows appearance of an absorption pack at 3379cm^-1 refers to (N-H) group and appearance of an absorption pack at 686 cm^-1 refers to (C-Cl) bond. HNMR (400 MHz ) δ(ppm) Benzi. (7.26t 2H) and (7.71t 2H), Ar (7.31 and 7.61), N-H(3.42s). Table (2) shows the other absorption packs of the compound in the F.T.I.R spectrum.

2-(4-N,N- Dimethylaniline)-1H-Benzimidazole

The F.T.I.R spectrum of this compound shows an absorption pack at 3301cm^-1 refers to (N-H) group and appearance of an absorption pack at 2916 cm^-1 refers to (C-H) aliphatic. H-NMR (400 MHz) δ(ppm) Ar (6.91 and 7.31), Benzi. (7,26t 2H 7.69t 2H), N-H(4.42d), CH₃(2.91). Table(2) shows the other absorption packs of the compound in the F.T.I.R spectrum.

1H-Benzimidazole

The F.T.I.R spectrum of this compound shows an absorption pack at 3409 cm^-1 refers to (N-H) group and an absorption pack at 2923 cm^-1 refers to (C-H) aliphatic. HNMR (400 MHz ) δ(ppm) Benzi. (7.68t 2H) and (7.26-7.30t 2H), N-H(2.9Hz), Benz.-CH(7.90Hz). Table (2) shows the other absorption packs of the compound in the F.T.I.R spectrum.

2-(2-hydroxy phenyl)-1H-Benzimidazole

F.T.I.R spectrum of this compound shows an absorption pack at 3425 cm^-1 refers to (O-H) group and appearance of an absorption pack at 1157 cm^-1 refers to (C-O) bond in addition to an absorption pack (N-H) group at 3240 cm^-1. HNMR (400 MHz ) δ(ppm) Benz. (7.26t 2H) and (7.75t 2H), Ar (7.35- 7.00), N-H(2,93s), O-H(7.97). Table (2) shows the other absorption packs of compound in F.T.I.R spectrum.

2-Methyl-1H-Benzimidazole

The F.T.I.R spectrum of this compound shows an absorption pack at 3178 cm^-1 refers to (N-H) group and an absorption pack at 2916 cm^-1 refers to (C-H) aliphatic. HNMR (400 MHz ) δ(ppm) Benz. (7.26t 2H and 7.71t 2H), N-H(2.45), CH₃ (2.20s). Table (2) shows the other absorption packs of the compound in the F.T.I.R spectrum.

2-Propyl-1H-Benzimidazole

The F.T.I.R spectrum of this compound shows an absorption pack at 3209 cm^-1 refers to (N-H) group and an absorption pack at 2962 and 2931 cm^-1 to (C-H) aliphatic. HNMR (400 MHz ) δ(ppm) Benz. (7.29t 2H) and (7.71t 2H), N-H(4.28s), -CH₂-CH₂(2.42_S), CH₂-CH₂-(1,43_S), CH₃(0.92_S). Table (2) shows the other absorption packs of the compound in the F.T.I.R spectrum.

Figure 1: (F.T.I.R) Spectrum of Compound (A) Click here to View figure

 

Figure 2: (H-NMR) Spectrum of Compound (B) Click here to View figure

Figure 3: (F.T.I.R) Spectrum of Compound (C) Click here to View figure

Figure 4: (F.T.I.R) Spectrum of Compound (D) Click here to View figure

Figure 5: (F.T.I.R) Spectrum of Compound (E) Click here to View figure

Figure 6: (F.T.I.R) Spectrum of Compound (F) Click here to View figure

 

Table 2: Other Absorption Pecks of Compounds in F.T.I.R. Spectroscopy.

Compounds	Name of compound	UV (nm)	(C-H) aromatic cm-1	(C=N)(C=C)	(C-N)
A	2-(4-Chlorophenyl) -1H-Benzimidazole	318-379	3062	1512-1604	1311
B	2-(4-N,N– Dimethylaniline)-1H-Benzimidazole	293-374	3039	1496-1604	1365
C	1H-Benzimidazle	316	3062	1512-1604	1303
D	2-(2-Hydroxy Phenyl)-1H-Benzimidazole	293-396	3024	1666-1612	1249
E	2-Methyl-1H-Benzimidazole	357	3062	1519-1681	1311
F	2-Propyl-1H-Benzimidazole	357	3070	1512-1620	1157

 

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