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

Six azo disperse dyes were prepared by diazotizing 4-amino hippuric acid and coupled with barbituric acid and 2-thiobarbituric acid.en, the products were reactedwith 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, H NMR and C NMR, and mass spectroscopic techniques. e solvatochromic behavior of azo disperse dyes was evaluated in various solvents. e effects of substituents of aromatic aldehyde, barbiturate, and thiobarbiturate ring on the color of dyes were investigated.


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 �elds, such as dyeing tex-tile�ber, biological-pharmacological activities, and advanced application in organic synthesis [1][2][3].Many heterocyclic compounds are used extensively in disperse dye chemistry for textile or nontextile applications.ese 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 �ve-membered rings containing one or more nitrogen heteroatoms, with the rings being fused into another aromatic ring [4].
e azo dyes containing heterocyclic rings result in brighter and oen deeper shades than their benzene analogs.On the other hand, they are very important in applications such as disperse dyes for polyester �bers, reprography, functional dye and nonlinear optical systems, photodynamic therapy, and lasers [5][6][7][8][9][10].
e 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.Transform-infrared (FT-IR) spectrophotometer on a KBr disc.Nuclear magnetic resonance ( 1 H NMR) spectra were recorded on a Bruker-Spectrospin 400 Shimadzu QP-1100EX in dimethylsulphoxide (DMSO); chemical shis were () given in ppm.e microanalyses for C, H, and N were performed on perkin-elmer elemental analyzer.Ultravioletvisible (UV-vis) absorption spectra were recorded on an Perkin Elmer spectrophotometer at the wavelength of maximum absorption ( max ) in a range of solvents, that is, dimethylsulphoxide (DMSO), dimethylformamide (DMF), and ethanol, at same concentrations (1 × 10 −6 M).
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).e precipitated product was �ltered and puri�ed by recrystallization from DMF�water (8 ∶ 2). (
( (   1) in nitrosyl hydrochloric acid followed by coupling with barbituric acid and 2-thiobarbituric acid.en 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 re�uxing condition (Scheme 2).

e 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 ( * , , and ) were taken from the literature [23][24][25].As shown in Table 1, the electronic absorption spectra of all studied compounds in different solvents exhibit maximum absorption band ( max ) in the range of 390.51-425.12nm which can be attributed to    * and/or  −  * electronic transitions of azo chromophores.
e dyes displayed a single main absorption peak without a shoulder in all solvents.e  max of all compounds were found to show a weak solvent dependency, denoting bathochromic effect (positive solvatochromism) in more polar solvents.e spectral shi is mainly due to solutesolvent interactions that give rise to a better stabilization of the  * orbital as compared to the  orbital in polar solvents (Figure 1).

Substituent
Effects.e 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 signi�cantly.ese dyes, apparently, did not exhibit a strong solvent dependence.e maximum absorption of these dyes shied in the order: DMSO > DMF > Ethanol.e spectral shis of dyes 4a-4f in various solvents are shown in Figure 1.e maximum absorption of dye 4a showed bathochromic shi in DMSO and DMF, with respect to the maximum absorption in ethanol (e.g.,  max is 394.48 nm in DMSO, 393.04 nm in DMF, and 392.34 nm in ethanol).e same trends of absorption shis in various solvents were observed for the entire series of dyes 4a-4f, as shown in Table 1.e substituent effects of the heterocyclic azo dyes 4a-4f were evaluated.e spectral shis 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.erefore dyes 4d-4f showed bathochromic shi in comparison with dyes a-c in all studied solvents as shown in Table 2.

Conclusions
In summary, we have synthesized six disperse azo dyes containing barbiturate and thiobarbiturate ring (4a-4f) in this paper.e structures of prepared dyes were con�rmed  by 1 H NMR, 13 C NMR, mass spectroscopy, FT-IR, and UVvis spectra.e electronic absorption spectra of disperse dyes were recorded in solvents with different physicalchemical properties.A large bathochromic shi (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.

2. 1 .
Materials and Apparatus.e chemicals used for the synthesis of the compounds were obtained from Merk Chemical Company and used without further puri�cation.esolvents used were of spectroscopic grade.IR spectra were determined using a Bruker tensor 27 Fourier : R = H, (4e): R = Cl, (4f): R = F S 1: Chemical structures of new azo dyes (4a-4f).