Synthesis of some azo dyes by using phenolics

Introduction

Azo dyes are the most significant and versatile class of synthetic organic compounds with enormous variety of applications. The azo dyes contain heterocyclic rings results in brighter and often deeper shades than their benzene analogs. Usually azo compounds are prepared by diazotization of the aromatic amine in mineral acid at about 0^oC followed by coupling with nucleophiles. Textile industry is a major consumer of these dyes. They can be obtained easily and economically by using a wide variety of different aromatic coupling components. They have high drying and good fastness properties and thus wide applications in areas such as dyeing of textile fibres, paper, plastics, leather and bio-medical studies. The synthetic, spectroscopic and dyeing properties of these compounds were studied in last fifty years. They show variety of interesting biological activities such as antifungal, pesticidal and antibacterial activities. [1-8]

In this paper, it is aimed to synthesize azo dyes from aniline with the reaction of different phenolic compounds and to find out their colors. Their structures were confirmed through different spectral studies.

Materials and Methods

General

All the chemicals used were of analytical grade and were used without further purification. All the products were synthesized and characterized by their spectral analysis.

Infrared spectra were obtained on a JASCO A-302 spectrophotometer. Ultraviolet spectra were recorded on a Hitachi-U-3200 spectrophotometer. The EI-MS were recorded on Finnigan MAT-112 spectrometer respectively. The ¹H-NMR (1D) spectra were recorded on Bruker Avance spectrometers operating at 400, 500 and 600 MHz. The Chemical shifts are expressed in (ppm) referenced to the residual solvent signal and the coupling constants (J) are in Hz.

Silica gel 9385 (Merck) was used for column chromatography. TLC was performed on Kieselgel 60 F₂₅₄ precoated aluminium cards (0.2 mm thickness, Merck) and spots were visualized under UV light at 254/365 nm and by spraying iodine and 5% H₂SO₄.

Synthesis of Oleanolic Acid Derivatives

Diazotization

First take 2g of NaNO₂ in 10 ml distill water and cool it at (0-5 ^oC) in ice bath. Take another flask in which take 8 ml distill water now add 8 ml of HCL in it and maintain temp at (0-5 ^oC). Now add 2.5 mL aniline in the second flask and maintain temp at (0-5 ^oC). Then add cooled NaNO₂ solution and again maintain temperature at (0-5 ^oC) the change of color indicates formation of diazonium salt.

Coupling with Phenolic Compounds

Ina flask take, 18 pellets of NaOH in 13 ml of distill water and stir well. Add 2.1g of phenolic compound (beta-naphthol, alpha-naphthol, phenol and 3-methoxy phenol) in it and stir well. Now put this flask in ice bath and maintain temperature at (0-5 ^oC). After maintaining temperature of coupling mixture, add diazonium salt in coupling solution. Again maintain temperature at (0-5 ^oC). Finally now add HCL, with continuous stirring in ice bath. Stir it until color changes. Filter wash and dry precipitates.

Naphthalene-1-ol phenyldiazene (1a) : purplish red color. UV l_max (MeOH) nm : 229, 495. IR n_max (KBr) cm^-1 : 3448.1 (br. OH), 3052 (N-H), 1606.9 (N=N), 1503 (C=N) and 2925 (CH=CH). EI-MS m/z (rel. int., %) :  77 (72.1), 92 (95.5), 106.1 (32.2), 169.1 (28.6), 197.1 (54.4), 255.2 (26.5). ¹H-NMR (CDCl₃, 600 MHz): 8.42 (2H, d, J = 12.6, H-3), 7.60 (2H, d, J = 12.6, H-2a, H-2b), 7.58 (2H, t, J = 12.6, 10.8, H-1a, 1b), 7.41 (3H, t, J = 10.8, 12.6, H-6a, 6b, 6c), 7.20 (2H, d, J = 11.4, H-5a, 5b), 6.90 (1H, d, J = 13.8, H-4), 3.50 (OH,s,).

Naphthalene-2-ol phenyldiazene (1b) : reddish maroon color. UV l_max (MeOH) nm : 418, 426. IR n_max (KBr) cm^-1 : 3447.2 (br. OH), 3051 (N-H), 1608(N=N), 1505 (C=N) and 2923 (CH=CH). EI-MS m/z (rel. int., %) :  77.1 (18.4), 92.1 (5.6), 115.1 (23.1), 171.1 (8.4), 219.1 (4.5), 248.1 (100). ¹H-NMR (CDCl₃, 600 MHz): 8.420 (1H, d,  J = 8, H-5), 7.566 (4H, m, H-3a, H-3b, H-3c, H-3d ), 7.386 ( 3H, m, H-1a, H-1b, H-1c), 7.229 ( 2H, d, J = 9.2, H-2a, H-2b),  7.010 (1H, d,  J = 9.6, H-4), 3.471 (OH, s).

3-methoxy benzenol phenyl diazene (1c) : red color. UV l_max (MeOH) nm : 333. IR n_max (KBr) cm^-1 : 3448.9 (br. OH), 3058.3 (N-H), 1598.1 (N=N), 1486.0 (C=N) and 2928 (CH=CH), 1144.2 (C-O). EI-MS m/z (rel. int., %) :  77 (80.6), 92.1 (100.0), 106 (20.5), 169.1 (18.8), 197.1 (35.2), 227.1 (8.3). ¹H-NMR (CDCl₃, 600 MHz) : 7.789 (3H, m, H-2a, 2b, 2c), 7.493 (1H, m, H-4), 7.415 (1H, d, J = 10.8, H-3), 6.60 (2H, dd, J = 9.1, 4.2, H-1a, 1b), 6.490 (1H, d, J = 3.6, H-5), 4.566 (OH, s), 3.03 (3H, O-CH₃, s).

Benzenolphenyldiazene (1d) : brownish yellow color. UV l_max (MeOH, nm) : 346. IR n_max (KBr) cm^-1 : 3137.9 (br. OH), 3065.1 (N-H), 1591.1 (N=N), 1499.0 (C=N) and 2929.0 (CH=CH). EI-MS m/z (rel. int., %) :  77.0 (59.7), 93.0 (100), 105.0 (5.7), 121.1 (43.5), 141 (7.3), 198.1 (68.1). ¹H-NMR (CDCl₃, 400 MHz) : 7.889 (2H, d, J = 4.4, H-1a, 1b), 7.864 (2H, d, J = 2.8, H-2a, 2b), 7.503 (3H, m, H-3a, 3b, 3c), 6.942 (2H, d, J = 2.2, H-4a, 4b), 3.30 (OH, s).

Result and Discussion

            Azo dyes are synthetic compounds (It is known that only one occurs in environment) containing azo bond –N=N–, are obtained mainly from the aromatic amine, nitro and nitroso substrate. Methods of their synthesis rely on the use of a suitable oxidative/reductive reactions or diazotization/coupling reaction. We have synthesized azo dyes using Aniline with four different phenolic compounds 1-Napthol, 2-Napthol, Phenol and 3 Methoxy phenol. The synthesized dye were in shades of red and yellow the following dyes were characterized by IR, ¹H-NMR, UV and mass spectroscopy the synthesized dyes can have may applications.

Naphthalene-1-ol phenyldiazene (1a) : Compound had a molecular formula C₁₆H₁₂N₂O obtained from its EI-MS (m/z 255.2), purplish red in color. Significat fragment ion peaks at m/z 106.0 and 197.1 arising from the breaking of azo bond from naphthol compound and aniline respectively. The UV absorption maximum (229, 495 nm). The IR spectra shows in cm^-1 that 3448.1 (br. OH), 3052 (N-H), 1606.9 (N=N), 1503 (C=N) and 2925 (CH=CH). While the ¹H-NMR spectra shows a total of 10 proton signals including a singlet of OH at 3.30 ppm. The presence of doublet of two protons H-3 at 8.42 ppm having (J = 12.6 Hz) confirms presence of 2 proton of aniline. A doublet of two protons H-2a, 2b at 7.60 ppm (J = 12.6 Hz) corresponds to the other two protons of phenol. Because of the presence of OH group, two protons of aniline H-1a, 2b are present in triplet form at 7.58 ppm (J = 12.6, 10.8 Hz). A triplet of 3 protons H-6a, 6b, 6c (J = 10.8, 12.6 Hz) at 7.41 ppm. A doublet of two protons H-5a, 5b (J = 11.4 Hz) at 7.20 ppm. A doublet of one proton H-4 (J = 13.8 Hz) at 6.90 ppm.

Naphthalene-2-ol phenyldiazene (1b) : Compound had a molecular formula C₁₆H₁₂N₂O obtained from its EI-MS (m/z 248.1), marronish red in color. Significant fragment ion peaks at m/z 143.1 arising from the breaking of azo bond from aniline compound. The UV absorption maximum (418,426 nm). The IR spectra shows in cm^-1 that 3448.1 (br. OH), 3052 (N-H), 1606.9 (N=N), 1503 (C=N) and 2925 (CH=CH). While the ¹H-NMR spectra shows a total of 12 proton signals including a singlet of OH at 3.471 ppm. The presence of three doublet at 7.010 ppm, 7.229 ppm and 8.420 ppm confirms the presence of azo group at proton H-2a and H-2b. While protons of H-1a, 1b, 1c and H-3a, 3b, 3c, 3d are present as multiplets at 7.386 ppm and 7.566 ppm respectively.

3-Methoxy benzenol phenyl diazene (1c) : Compound had a molecular formula C₁₃H₁₂N₂O₂ obtained from its EI-MS (m/z 227.1), red in color. Significant fragment ion peaks at m/z 197.1 and 227.1 arising from the breaking of azo bond from O-CH₃ and phenolic OH repectively. The UV absorption maximum (333 nm). The IR spectra shows in cm^-1 that 3448.9 (br. OH), 3058.3 (N-H), 1598.1 (N=N), 1486.0 (C=N) and 2928 (CH=CH), 1144.2 (C-O). While the ¹H-NMR spectra shows a total of 13 proton signals including a singlet of OH at 4.566 ppm. The presence of multiplet of three protons H-2a, 2b, 2c at 7.789 ppm. A triplet of one proton H-4 at 7.493 ppm. A doublet of 1 protons H-3 at 7.415 ppm (J = 10.8 Hz). A doublet of doublet of 2 protons of C-1a, 1b at 6.60 ppm (J = 9.0, 4.2 Hz) and a doublet of 1 proton of H-5 at 6.490 ppm (J = 3.6 Hz).

Benzenolphenyldiazene (1d) : Compound had a molecular formula C₁₂H₁₀O obtained from its EI-MS (m/z 198.1), brownish yellow in color. Significant fragment ion peaks at m/z 105.0 and 121.1 arising from the breaking of azo bond from phenolic compound and aniline respectively. The UV absorption maximum (346 nm). The IR spectra shows in cm^-1 that 3448.9 (br. OH), 3058.3 (N-H), 1598.1 (N=N), 1486.0 (C=N) and 2928 (CH=CH), 1144.2 (C-O). While the ¹H-NMR spectra shows a total of 10 proton signals including a singlet of OH present at 3.30 ppm. The presence of doublet of two protons H-1a and H-1b at 7.889 ppm having J = 4.0 Hz confirms presence of two proton of aniline. A doublet of two protons H-2a, 2b at 7.864 ppm (J = 2.8 Hz) corresponds to the other two protons of phenol because of the presence of OH group. Three protons of aniline H-3a, 3b, 3c are present in multiplet form at 7.503-7.402 ppm. A doublet of 2 protons H-4a, 4b (J = 2 Hz) confirms the presence of two protons of phenol.

Conclusion

In the present study, four azo dyes were prepared. The color of these dyes was observed and characterized through UV, IR, EI-MS and ¹H-NMR spectroscopy. Through this analysis we also noticed that how the use of different phenolic compound with aniline produces different colored dyes. These dyes can be further used in variety of applications such as in Textile and Pharmaceutical Industries.

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