Journal of Spectroscopy

Volume 2013 (2013), Article ID 276413, 6 pages

http://dx.doi.org/10.1155/2013/276413

Research Article

Synthesis and Evaluation of Changes Induced by Solvent and Substituent in Electronic Absorption Spectra of New Azo Disperse Dyes Containig Barbiturate Ring

Hooshang Hamidian,¹ Najmeh Zahedian,² Dadkhoda Ghazanfari,² and Samieh Fozooni³

¹Department of Chemistry, Payame Noor University (PNU), Tehran 19395-4697, Iran

²Department of Chemistry, Azad University, Kerman, Iran

³Zarand High Education Center, Mining Engineering Department, Shahid Bahonar University, Kerman, Iran

Received 29 June 2012; Revised 14 September 2012; Accepted 17 September 2012

Academic Editor: Damien Boyer

Copyright © 2013 Hooshang Hamidian et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Six azo disperse dyes were prepared by diazotizing 4-amino hippuric acid and coupled with barbituric acid and 2-thiobarbituric acid. Then, the products were reacted with aromatic aldehyde, sodium acetate, and acetic anhydride, and oxazolone derivatives were formed. Characterization of the dyes was carried out by using UV-Vis, FT-IR, ¹H NMR and ¹³C NMR, and mass spectroscopic techniques. The solvatochromic behavior of azo disperse dyes was evaluated in various solvents. The effects of substituents of aromatic aldehyde, barbiturate, and thiobarbiturate ring on the color of dyes were investigated.

1. Introduction

It is well known that azo compounds are the most widely class of industrial synthesized organic dyes due to their versatile application in various fields, such as dyeing textilefiber, biological-pharmacological activities, and advanced application in organic synthesis [1–3]. Many heterocyclic compounds are used extensively in disperse dye chemistry for textile or nontextile applications. These dyes are now marketed to produce a full range of dispersed dyestuffs without the use of colorants based on heteroaromatic diazo components. Most of the heterocyclic dyes are derived from the diazo components consisting of five-membered rings containing one or more nitrogen heteroatoms, with the rings being fused into another aromatic ring [4].

The azo dyes containing heterocyclic rings result in brighter and often deeper shades than their benzene analogs. On the other hand, they are very important in applications such as disperse dyes for polyester fibers, reprography, functional dye and nonlinear optical systems, photodynamic therapy, and lasers [5–10].

Barbituric acid (pyrimidine 2,4,6(1H,3H,5H)-trione) is widely used in the manufacturing of plastics, pigments, dyes, polymers, and the Vitamin B₂ (riboflavin) synthesis [11–14]. Barbiturates are a class of drugs that are utilized as anesthetics and sleeping agents and are used for the treatment of anxiety, epilepsy, and other psychiatric disorders and possess effects on the motor and sensory functions [15]. 2-Thiobarbituric acid is also used in the 2-thioxo-2,3-dihydro-4,6(1H,5H)-pyrimidinedione pharmacological and analytical fields [16, 17]. Therefore, several studies have been published on the synthesis and spectral properties of several azo barbituric acids so far [18–22]. We report the synthesis of a series of new azo dyes based on barbituric acid (Scheme 1).

Scheme 1: Chemical structures of new azo dyes (4a–4f).

The visible absorption spectra in various solvents of these dyes and effects of substituents of aromatic aldehyde, barbiturate, and thiobarbiturate ring on the color of dyes were also discussed.

2. Experimental

2.1. Materials and Apparatus

The chemicals used for the synthesis of the compounds were obtained from Merk Chemical Company and used without further purification.

The solvents used were of spectroscopic grade. IR spectra were determined using a Bruker tensor 27 Fourier Transform-infrared (FT-IR) spectrophotometer on a KBr disc. Nuclear magnetic resonance (¹H NMR) spectra were recorded on a Bruker-Spectrospin 400 Shimadzu QP-1100EX in dimethylsulphoxide (DMSO); chemical shifts were given in ppm. The microanalyses for C, H, and N were performed on perkin-elmer elemental analyzer. Ultraviolet-visible (UV-vis) absorption spectra were recorded on an Perkin Elmer spectrophotometer at the wavelength of maximum absorption in a range of solvents, that is, dimethylsulphoxide (DMSO), dimethylformamide (DMF), and ethanol, at same concentrations .

2.2. Synthesis and Characterization

2.2.1. Preparation of Azo Dyes

NaNO₂ (70 mg, 1 mmol) was added to concentrated HCl (3.0 mL) with external cooling. The suspension was heated to 60°C and again cooled to 0–5°C.

To a cooled basic solution of 4-Amino hippuric acid (1.94 g, 0.01 mol) in sodium carbonate (2.5%, 20 mL) the prepared diazonium solution was added drop-wise and the mixture was stirred for 50 min at reaction pH 7 (neutralized with sodium acetate). The precipitated product was filtered and purified by recrystallization from DMF/water .

(1) 2-[(4-{2-[2,4,6-trioxotetrahydro)-5(2H)-pyrimidinyliden]hydrazino} benzoyl) amino] acetic acid (3a). Yellow solid, yield 89%, m.p. 289–291°C; IR (KBr): 3423, 3264, 1750, 1710, 1654 cm⁻¹; ¹H NMR (ppm): 12.33 (broad, 2H, NH and OH), 11.23 (s, 2H, 2NH), 8.36 (d, 2H, Ar-H), 7.63 (d, 2H, Ar-H), 6.41 (t, 1H, NH), 3.93 (d, 2H, CH₂); ¹³C NMR (ppm): 172.7, 168.0, 163.0, 154.1, 142.1, 131.3, 123.5, 119.1, 115.1, 38.1; Anal. Calcd for C₁₃H₁₁N₅O₆: C, 46.85; H, 3.30; N, 21.02. Found: C, 47.01; H, 3.18; N, 20.95.

(2) 2-[(4-{2-[4,6-dioxo-2-thioxotetrahydro)-5(2H)-pyrimidinyliden]hydrazino} benzoyl) amino] acetic acid (3b). Orange solid, yield 81%, m.p. 306–308°C; IR (KBr): 3424, 3252, 1703, 1653 cm⁻¹; ¹H NMR (ppm): 12.38 (broad, 2H, NH and OH), 11.49 (s, 2H, 2NH), 8.42 (d, 2H, Ar-H), 7.67 (d, 2H, Ar-H), 6.41 (t, 1H, NH), 3.92 (d, 2H, CH₂); ¹³C NMR (ppm): 178.2, 171.9, 167.8, 154.3, 143.1, 131.9, 122.9, 122.1, 115.0, 38.1; Anal. Calcd for C₁₃H₁₁N₅O₅S: C, 44.70; H, 3.15; N, 20.06. Found: C, 44.48; H, 2.94; N, 19.89.

2.2.2. General Synthesis of Azo Dyes Containing Barbiturate Ring (4a–4f)

A general preparative procedure is described below for the preparation of all dyes. 2-[(4-{2-[2,4,6-trioxotetrahydro)-5(2H)-pyrimidinyliden]hydrazino} benzoyl) amino] acetic acid or 2-[(4-{2-[4,6-dioxo-2-thioxotetrahydro)-5(2H)-pyrimidinyliden]hydrazino} benzoyl) amino] acetic acid (3.35 g or 3.50 g, 0.01 mole) was refluxed in a mixture of sodium acetate (1.50 g), acetic anhydride (15 mL) and aromatic aldehydes (0.03 mole) for 6 h. The precipitated products were filtered off, washed with ethanol several times, dried, and recrystallized from dimethylformamide and water.

(1) 5-{2-[4-(4-benzyl-5-oxo-2,5-dihydro-1,3-oxazol-2-yl)-2,5-cyclohexadienyliden]hydrazono}-2,4,6(1H,3H,5H)-pyrimidinetrione (4a). Yellow solid, yield 32%, m.p. 326-327°C; IR (cm⁻¹): 3343 and 3265 (N–H), 1754 (C=O, oxazolone ring), 1710 and 1653 (C=O, barbiturate ring); ¹H NMR (ppm): 11.56 (s, 1H, NH), 11.33 (s, 1H, NH), 7.41–8.85 (m, 9H, Ar-H and CH=C), 4.15 (s, 2H, CH₂); ¹³C NMR (ppm): 171.8, 169.2, 166.1, 162.4, 160.2, 150.2, 144.1, 135.7, 131.4, 131.1, 130.1, 129.4, 126.9, 119.2, 116.5, 21.0; MS: m/z (%) (70 ev EL) 403 (M⁺), 257 (0.75), 211 (3), 105 (22), 57 (88), 43 (100). Anal. Calcd for C₂₀H₁₃N₅O₅: C, 59.55; H, 3.22; N, 17.40. Found: C, 59.71; H, 3.46; N, 17.05.

(2) 5-(2-{4-[4-(4-chlorobenzyl)-5-oxo-2,5-dihydro-1,3-oxazol-2-yl]-2,5-cyclohexadienyliden}hydrazono)-2,4,6(1H,3H,5H)-pyrimidinetrione (4b). Orange solid, yield 48%, m.p. 325–328°C; IR (cm⁻¹): 3343 and 3264 (N–H), 1753 (C=O, oxazolone ring), 1710 and 1652 (C=O, barbiturate ring); ¹H NMR (ppm): 11.57 (s, 1H, NH), 11.33 (s, 1H, NH), 7.63–8.85 (m, 8H, Ar-H and CH=C), 3.92 (s, 2H, CH₂); ¹³C NMR (ppm): 171.8, 169.1, 167.1, 162.4, 160.2, 150.2, 145.1, 131.5, 131.1, 129.4, 128.9, 128.3, 120.5, 117.1, 116.6, 21.5; MS: m/z (%) (70 ev EL) 437 (M⁺), 257 (29.6), 171 (26.97), 105 (90), 85 (64), 43 (100). Anal. Calcd for C₂₀H₁₂ClN₅O₅: C, 54.86; H, 2.74; N, 16.00. Found: C, 55.08; H, 2.94; N, 15.88.

(3) 5-(2-{4-[4-(4-fluorobenzyl)-5-oxo-2,5-dihydro-1,3-oxazol-2-yl]-2,5-cyclohexadienyliden}hydrazono)-2,4,6(1H,3H,5H)-pyrimidinetrione (4c). Yellow solid, yield 61%, m.p. 334-335°C; IR (cm⁻¹): 3342 and 3265 (N–H), 1753 (C=O, oxazolone ring), 1710 and 1655 (C=O, barbiturate ring); ¹H NMR (ppm): 11.55 (s, 1H, NH), 11.33 (s, 1H, NH), 7.24–8.85 (m, 8H, Ar-H and CH=C), 3.91 (s, 2H, CH₂); ¹³C NMR (ppm): 171.8, 169.1, 166.1, 162.5, 160.2, 150.2, 144.1, 132.2, 131.5, 131.1, 130.2, 129.4, 129.3, 119.3, 116.1, 21.0; MS: m/z (%) (70 ev EL) 421 (M⁺), 393 (1.66), 313 (14.58), 247 (3.33), 135 (80), 109 (35.42), 57 (91.66), 43 (100). Anal. Calcd for C₂₀H₁₁₂ FN₅O₅: C, 57.01; H, 2.85; N, 16.63. Found: C, 56.79; H, 3.03; N, 16.47.

(4) 5-(2-{4-[5-oxo-4-[1-phenylmethylidene]-1,3-oxazol-2(5H)-yl]phenyl}hydrazono)-2-thioxodihydro-4,6(1H,5H)-pyrimidinedione (4d). Orange solid, yield 73%, m.p. 322–325°C; IR (cm⁻¹): 3316 and 3262 (N–H), 1792 (C=O, oxazolone ring), 1689 (C=O, thiobarbiturate ring); ¹H NMR (ppm): 14.2 (s, 1H, N–H), 12.36 (s, 1H, NH pyrimidine), 12.47 (s, 1H, NH pyrimidine), 7.43–8.9 (m, 10H, Ar-H, CH=C); ¹³C NMR (ppm): 178.1, 171.5, 169.3, 166.1, 163.5, 161.1, 159.0, 144.0, 135.3, 131.5, 130.9, 126.9, 120.2, 117.1, 116.4, 115.3; MS: m/z (%) (70 ev EL) 419 (M⁺), 211 (4.16), 105 (91.66), 77 (68.3), 43 (100). Anal. Calcd for C₂₀H₁₃N₅O₄S: C, 57.28; H, 3.12; N, 16.71. Found: C, 57.41; H, 2.97; N, 16.58.

(5) 5-(2-{4-[4-[1-(4-chlorophenyl)methylidene]-5-oxo-1,3-oxazol-2(5H)-yl]phenyl}hydrazono)-2-thioxodihydro-4,6(1H,5H)-pyrimidinedione (4e). Dark red solid, yield 40%, m.p. 335-336°C; IR (cm⁻¹): 3342 and 3246 (N–H), 1792 (C=O, oxazolone ring), 1688 (C=O, thiobarbiturate ring); ¹H NMR (ppm): 14.14 (s, 1H, N–H), 12.50 (s, 1H, NH pyrimidine), 12.47 (s, 1H, NH pyrimidine), 7.51–8.50 (m, 9H, Ar-H, CH=C); ¹³C NMR (ppm): 178.0, 171.8, 169.1, 166.1, 162.4, 160.2, 158.6, 144.9, 134.8, 131.4, 131.1, 129.4, 119.2, 117.1, 116.6, 114.1; MS: m/z (%) (70 ev EL) 435 (M⁺), 297 (4.68), 271 (3.57), 158 (62.5), 139 (91.5), 111 (32.18), 43 (100). Anal. Calcd for C₂₀H₁₂ClN₅O₄S: C, 52.92; H, 2.65; N, 15.44. Found: C, 53.03; H, 2.69; N, 15.28.

(6) 5-(2-{4-[4-[1-(4-fluorophenyl)methylidene]-5-oxo-1,3-oxazol-2(5H)-yl]phenyl}hydrazono)-2-thioxodihydro-4,6(1H,5H)-pyrimidinedione (4f). Orange solid, yield 67%, m.p. 320–322°C; IR (cm⁻¹): 3323 and 3260 (N–H), 1791 (C=O, oxazolone ring), 1688 (C=O, thiobarbiturate ring); ¹H NMR (ppm): 14.2 (s, 1H, N–H), 12.63 (s, 1H, NH pyrimidine), 12.46 (s, 1H, NH pyrimidine), 7.23–8.85 (m, 9H, Ar-H and CH=C); ¹³C NMR (ppm): 178.1, 171.7, 169.1, 166.1, 164.3, 160.2, 158.7, 145.1, 131.5, 131.1, 129.4, 128.3, 120.4, 119.6, 117.1, 115.9; MS: m/z (%) (70 ev EL) 347 (M⁺), 393 (93.8), 378 (3.5), 336 (15.5), 296 (59.5), 280 (31.2), 135 (9.5), 43 (100). Anal. Calcd for C₂₀H₁₂FN₅O₄S: C, 54.92; H, 2.75; N, 16.02. Found: C, 55.10; H, 2.64; N, 15.91.

3. Results and Discussion

2-[(4-{2-[2,4,6-trioxotetrahydro)-5(2H)-pyrimidinyliden]hydrazino} benzoyl) amino] acetic acid (3a) and 2-[(4-{2-[4,6-dioxo-2-thioxotetrahydro)-5(2H)-pyrimidinyliden]hydrazino} benzoyl) amino] acetic acid (3b) were prepared by diazotization of 4-amino hippuric acid (1) in nitrosyl hydrochloric acid followed by coupling with barbituric acid and 2-thiobarbituric acid. Then oxazolone azo dyes (4a–4f) were synthesized by classical Erlenmeyer reaction, involving condensation of azo dye products with corresponding aldehydes in presence of acetic anhydride and sodium acetate under refluxing condition (Scheme 2).

Scheme 2: Synthetic route for azo dyes containing barbiturate ring 4a–4f.

3.1. The UV-Visible Spectra and Solvatochromic Studies of New Dyes

In order to study of solvent effects on spectral features of the dyes, we recorded their absorption spectra in three solvents with different polarity at a concentration 10⁻⁶ M in the range of 250–700 nm (Table 1), in which the solvents are arranged in the order of decreasing polarity. Also, refractive index , dielectric constant , and the solvatochromic parameters (, α, and β) were taken from the literature [23–25]. As shown in Table 1, the electronic absorption spectra of all studied compounds in different solvents exhibit maximum absorption band in the range of 390.51–425.12 nm which can be attributed to and/or electronic transitions of azo chromophores.

Table 1: Experimental electronic absorption maxima for investigated dyes and solvent parameters [21–23].

Solvents
π *

(30)
(nm)

293 K
293 K
Dye (a)
Dye (b)
Dye (c)
Dye (d)
Dye (e)
Dye (f)

DMSO
1.00
0.00
0.76
47.24
1.4770
45.0
394.48
394.38
396.26
424.71
425.12
422.48

DMF
0.87
0.00
0.69
38.25
1.4305
43.8
393.04
392.85
393.39
423.04
424.64
421.57

Ethanol
0.54
0.83
0.77
25.33
1.3611
51.9
392.34
390.51
392.41
421.99
423.25
419.31

The dyes displayed a single main absorption peak without a shoulder in all solvents. The of all compounds were found to show a weak solvent dependency, denoting bathochromic effect (positive solvatochromism) in more polar solvents. The spectral shift is mainly due to solute-solvent interactions that give rise to a better stabilization of the orbital as compared to the orbital in polar solvents (Figure 1).

(a)

(b)

(c)

(d)

(e)

(f)

Figure 1: Electronic absorption spectra of azo dyes (4a–4f) at room temperature . (red) DMSO, (green) DMF, (blue) EtOH; (a) 4a, (b) 4b, (c) 4c, (d) 4d, (e) 4e, (f) 4f.

3.2. Substituent Effects

The absorption spectra of these azo dyes 4a–4f were recorded in various solvents at the concentration of 10⁻⁶, M, and the results are given in Table 1. We found that the electronic absorption of these azo dyes indicated a regular variation with the polarity of solvents, which did not change significantly. These dyes, apparently, did not exhibit a strong solvent dependence. The maximum absorption of these dyes shifted in the order: DMSO > DMF > Ethanol. The spectral shifts of dyes 4a–4f in various solvents are shown in Figure 1. The maximum absorption of dye 4a showed bathochromic shift in DMSO and DMF, with respect to the maximum absorption in ethanol (e.g., is 394.48 nm in DMSO, 393.04 nm in DMF, and 392.34 nm in ethanol). The same trends of absorption shifts in various solvents were observed for the entire series of dyes 4a–4f, as shown in Table 1. The substituent effects of the heterocyclic azo dyes 4a–4f were evaluated. The spectral shifts of dyes 4a–4f in solvents at a concentration of 10⁻⁶ are given in Table 2. We found that the dyes 4a–4f did not exhibit a strong solvent dependence to substituent effects on the phenyl ring but exhibited a strong solvent dependence to thiobarbiturate or barbiturate ring. Therefore dyes 4d–4f showed bathochromic shift in comparison with dyes a–c in all studied solvents as shown in Table 2.

Table 2: Substituent effect of dyes 4a–4f in DMSO, DMF, and ethanol.

Dyes
X
R
DMSO
DMF
Ethanol

(a)
O
H
394.48
—
6.07
393.04
—
6.17
392.34
—
5.07

(b)
O
Cl
394.38
−0.10
6.25
392.85
−0.19
5.93
390.51
−1.83
5.68

(c)
O
F
396.26
+1.78
6.05
393.39
+0.35
6.17
392.41
+0.07
5.68

(d)
S
H
424.71
+30.23
5.40
423.04
+30.00
6.04
421.99
+29.65
5.69

(e)
S
Cl
425.12
+30.64
6.11
424.64
+31.60
6.17
423.25
+30.91
5.70

(f)
S
F
422.48
+28.00
6.11
421.57
+28.53
6.09
419.31
+26.97
6.09

aRelative to dye (a).

4. Conclusions

In summary, we have synthesized six disperse azo dyes containing barbiturate and thiobarbiturate ring (4a–4f) in this paper. The structures of prepared dyes were confirmed by ¹H NMR, ¹³C NMR, mass spectroscopy, FT-IR, and UV-vis spectra. The electronic absorption spectra of disperse dyes were recorded in solvents with different physical-chemical properties. A large bathochromic shift (positive solvatochromism) of these compounds was observed upon increasing the solvent polarity and the dyes 4a–4f did not exhibit a strong solvent dependence to substituent effects on the phenyl ring but exhibited a strong solvent dependence to thiobarbiturate or barbiturate ring.

Acknowledgment

The authors are very grateful to Azad University of Kerman for providing financial support of this study.

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