Introduction of a New Analytical Reagent of Azo Compound

Introduction

In recent years, the detectability of instrumental analysis methods has been continuously and rapidly improved. On the one hand, it depends on the improvement and updating of analytical instruments, and on the other hand, it depends on the development of new analytical reagents. Azo compounds are an important group of organic chemicals that contain at least one azo chromophore as (-N=N-) which gives the color to this famous type of compounds. And thus, these compounds can be used as analytical reagents for the determination of micro quantities of elements in multiple specimens. Very recently, a new azo ligand derivative from 4,5-bis(4-methoxyphenyl) imidazole, (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid, was synthesized by Radhi ^[1]. It can act as an analytical reagent to determine Hg (II) in trace amounts by a simple and low cost spectrophotometric method. Here, Alfa Chemistry briefly introduces the synthesis, properties and application of (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid according to the Radhi's report, which may inspire you to develop new analytical reagents, and may also help you to detect more metal ions and other analytes for your research.

Synthesis

The synthesis of the (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid can be schematically described as follows:

In short, the synthesis of (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid is divided into three steps: the synthesis of 4,5-bis(4-methoxy phenyl) imidazole, the preparation diazonium solution and the synthesis of final product. The synthesis of 4,5-bis(4-methoxy phenyl) imidazole can be referenced in previous reports ^[2]. Diazonium solution can be prepared by following. Dissolving 4-Amino benzoic acid (0.428g, 0.001mol) in a mixture solution (3 mL concentrated HCl + 20 mL distilled water), and keeping the mixture in an ice bath (0-5) ℃. Then add 10 mL of the aqueous solution of NaNO₂ (0.70 g, 0.01 mol) drop by drop with stirring, and finally, leaving the solution for 30 minutes to obtain diazonium solution. The final product can be synthesized by followings. Diazonium solution is mixed with (2.80 g, 0.01 mol) of 5,4-di (4-methoxyphenyl) imidazole solution and dissolved in a mixture of 150 mL methyl alcohol and 5 mL of NaOH (10%). Let the solution for 24 hours, and then adjust the pH value to 7 by adding drops of 0.1N HCl. Leave the solution to settle, then filter, wash, dry and re-crystallize to obtain (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid.

Fig. 1. Preparation steps of the (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid.

Properties

Fig. 2. The structure of Hg (II)-azo ligand complex.

The UV-Vis spectrum of the reagent (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid shows a maximum absorption peak (λmax) at 470 nm. And when it chelates with mercury, the absorption spectra show a bathochromic shift with maximum absorption peak (λmax) of 546 nm. In addition, (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid forms complexes with mercury in molar ratio of 1:2 (metal: ligand). Based on this and the properties of the imidazole compounds, the complex structure can be suggested as Fig.2.

Application

(E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid can be used as analytical reagents for the determination of micro quantities of mercury ion by spectrophotometric method. The results showed that the Beer`s-Lambert law was obeyed in the range of (0.5-10) µg mL-1, and the limit of detection LOD and the limit of quantification LOQ were 0.190 and 0.634 µg mL^-1, respectively. The molar absorptivity and sandell's sensitivity are 7.963 ×10³ L mol^-1 cm^-1 and 0.025 µg cm^-2, respectively. The relative standard deviation RSD% for n=10 was 1.607%. These results demonstrated that (E)-2-(4,5-bis(4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid can be used as a good analytical reagent for the rapid and efficient determination of mercury (II) without the treatments of heating or extraction.

Fig. 3. The calibration curve of mercury ion detection experiment.

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References

Radhi E R. Spectrophotometric Determination of Hg (II) Using (E)-2-(4, 5-bis (4-methoxyphenyl)-1H-imidazol-4-yl) diazenyl) benzoic acid as analytical reagent[J]. Journal of Pharmaceutical Negative Results, 2022: 530-536.
Abd Z. G. and Ali A. M. Preparation and Identification of Some New Mixed Ligand Complexes Containing Imidazole and 1, 10-phenanthroline Compounds[J]. Journal of Kufa for Chemical Science, Vol, 2020, 2(6).

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