Synthesis, dyeing performance on polyester fiber and antimicrobial studies of some novel pyrazolotriazine and pyrazolyl pyrazolone azo dyes

1 Introduction

It has been known for many years that the azo compounds are the most widely used class of dyes due to their versatile applications in various fields such as dyeing of textile fibers, coloring of different materials, biological medical studies and advanced applications in organic synthesis (Bareini 2009; Karipcin et al., 2010). Disperse dyes are very popular and important class for dyeing polyester fibers due to their brilliancy, wide range of hue excellent fastness properties, in addition to the environmental and economic reasons (Metwally et al., 2012). 5-Aminopyrazoles are very important class of heterocycles due to their biological and pharmacological activities (Tsai and Wang, 2005; Yang et al., 2009). These compounds often exhibit anti-inflammatory, herbicidal, fungicidal, bactericidal, and antipyretic activities (Kumar et al., 2005; Yang et al., 2009; Jung et al., 2002; Gudmundsson et al., 2005; Sung et al., 2011; Gyorgy et al., 2008; Chimichi et al., 2006). The pyrazolotriazine compounds have received much attention owing to their antibacterial, antiviral and antihypertensive activities. Moreover, they are used as key starting material for the synthesis of commercial arylazopyrazole dyes which have found application in dyes, biological, pharmacological and complexmetric titration (Lister et al., 1970; Ahmed et al., 2012; Menegatti et al., 2006; Tsai and Wang, 2005; Y W Ho 2005; Kandil et al., 2001). As a part of our continuous interest on 5-amino pyrazole derivatives we report here the synthes of some novel azo and disazo dyes having pyrazole moiety and study their applications as disperse dyes to polyester fabrics (M A El-Borai et al. 2011; M A El-Borai et al. 2011; M A El-Borai et al. 2010).

2 Experimental

Commercially available polyester fabrics were used for dyeing. The chemicals used for synthesis were obtained from Sigma–Aldrich and used without further purification, and the solvents were of spectroscopic grade.

3 Results and discussion

We report here the synthesis of a series of monoazo dyes based on pyrazolo[5,1-c][1,2,4] triazine (3a–d) by coupling of 5-amino-3-phenyl-1H-pyrazole 1 with a variety of heterocyclic diazonium salts to give the corresponding 3-phenyl-5-amino-4-heteroazo-1H-pyrazoles (2a–d) in good yield (Scheme 1). The IR spectra of compound (2a–d) showed the characteristic absorption bands at γ1554–1597 cm⁻¹ for the azo group and at γ 3378–3427 cm⁻¹ for the amino group at position 5. The diazotization of 2a–d was followed by coupling with malononitrile in pyridine at pH 7–8, the formed solid was filtered quickly and refluxed in glacial acetic acid to give compounds 3a–d (Scheme 1). Azo dyes 3a–d can exist in two possible tautomeric forms, namely the azo-enamine form A and the hydrazo-imine form B as shown in (Scheme 1). The IR spectra of compounds 3a–d showed the characteristic absorption band group at γ 2207–2216 cm⁻¹ for the Cyano group, at γ 1583–1587 cm⁻¹ for the azo group and a broad band at 3159 cm⁻¹ for the amino group. Furthermore, the ¹H NMR spectra of compounds 3a–d showed the presence a singlet attributed to amino protons at δ 8.40–9.47 ppm and multiplet at δ 7.05–8.30 ppm corresponding to heteroaromatic moieties, which confirm the azo-enamine form B for these compounds. The heterocyclic diazo pyrazolone dyes (4a–h) were prepared by coupling 3-phenyl-1H-pyrazole-5-one and 1, 3-diphenyl-pyrazole-5-one with diazotized 5-amino-3-phenyl-4-hetarylazo-1H-pyrazoles (Scheme 1). The ¹H NMR spectra of dyes 4a–h showed a singlet at δ 2.07–2.40 ppm (CH₃ of pyrazolone ring), a broad peak at δ 12.5–14.5 ppm for –OH or –NH protons (enol or hydrazo forms of pyrazolone ring), a broad peak at δ 11.7–14.00 ppm for –NH protons (1-H of pyrazolone ring) and a broad peak at δ 10.54–11.20 ppm for –NH protons (1-H of pyrazole ring). The obtained results revealed that the prepared dyes are in favor of the predominantly single tautomeric form (T1 or T2 as shown in scheme 1), the mass spectral data confirm the structure of all the synthesized compounds (see. Experimental).

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Scheme 1

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4 UV–vis spectroscopic analysis of dyes 2a–d, 3a–d, and 4a–h

It is well known that heterocyclic based azo disperse dyes tend to gave a pronounced bathochromic shift compared to the corresponding benzenoid compounds (Hallas and Choi, 1999; Joerg et al., 1988), with larger solvatochromic effects due to the increasing polarity of the dye system, especially in the excited state.

The electronic spectra showed λmax at 400–474 nm for dyes 2a–d, and λ_max 463–514 nm for the prepared dyes 2a–d, and 3a–d respectively (Table 1). These bands were due to electronic transitions involving the whole conjugate system (both of the phenyl rings, heterocyclic moieties and the azo group which assigned to a transition of π–π∗ type).The introduction of the cyano group as an electron withdrawing subsistent onto compounds 3a–d produces a bathochromic shift of the absorption band. This is attributed to more extensive electron delocalization and small steric requirements of the rod-like cyano group (Hiremith et al., 2002), the obtained results are depicted in (Table 1).

The electronic spectra of the compounds 4a–h showed a band at λ_max 375–406 nm due to the π–π∗excitation of the electrons of the azo groups. It is worthy to note that the absorbance bands for biazopyrazolyl pyrazolone dyes 4a–h located in the region λ_max 375–406 nm are due to deformation of the functional groups.

5 The dyeing properties of the prepared dyes on polyester fabrics

The results obtained are depicted in (Table 2), having the following observations:

1. The dyed fabrics 3b, 3c, 3d, 4a exhibit excellent (4–5) washing, perspiration, sublimation and rubbing fastness properties, while dyes 2a–d, 3a, 4b–h exhibit good (3–4) washing, perspiration, sublimation and rubbing fastness properties.

2. The light fastness of dyed fabrics exhibit moderate to very good (5–6) fastness properties for all the synthesized dyes.

Table 2 Fastness properties of dyes 2a-d, 3a-d, and 4a-h on polyester fabric^a.

a Rate for light fastness: 4–8 (acceptable), 1–3 (not acceptable); rate for different fastness: 3–4 (acceptable), 1–2 (not acceptable).

6 Color assessment

The assessment of color-dyed fabrics was made in terms of tristimulus colorimetry. The following CIELAB coordinates are measured, lightness (L∗), chroma (c∗), hue angle from 0 °C to 360 °C (h), (a∗) value represents the degree of redness (positive) and greenness (negative) and (b∗) represents the degree of yellowness (positive) and blueness (negative). The measured K/S values given by the reflectance spectrometer are directly correlated with the dye concentration on the dye substrate according to the KubelkaeMunk equation: K/S = (1−R)²/2R. Where K = absorbance coefficient, S = scattering coefficient, R = reflectance ratio. The color coordinates indicate that the dyes have good affinity to polyester fabrics with the following conclusions (Table 3):

1. The color hues of the dyes under investigation on polyester fabric are shifted to the yellowish direction on the yellow-blue axis according to the positive values of b∗, while the color hues of the 2a (−0.49) are shifted to the bluish direction on the yellow-blue axis as according to the negative values of b∗ for these dyes.

2. The color hue of the dye 2a, 4a, 4b on polyester fabric is shifted to the greenish direction on the red green axis as indicated from the negative value of a∗ (−1.11, −1.62, −8.97 respectively), while the color hues of the other synthesized dyes on polyester fabrics are shifted to the reddish direction on the red green axis as according to the positive values of a∗ for the prepared dyes.

3. The 2b, 4a–e, 4e, 4h, 4g, dyes are more light than the corresponding dyes 2a, 2c, 2d, 4a–d, 5f according to the color lightness values (L∗).

4. The 2c, d, 3c, 4b, e, f, h dyes are brighter than the corresponding dyes 2a, b, 3a, b, d, 4a, c, d, g according to the color brightness value (C∗).

5. K/S values in the dyes under investigation 2a–d, 3a–d and 4a–h vary from 0.47 to 15.51. Dyes 2a, c and 3a–d are characterized by higher K/S values compared with the other dyes, indicating that the color strength on polyester fabrics increases at high temperature and gave generally deep and bright intense hues, ranging from yellow to reddish brown, while dyes 4a–h showed less affinity due to large and asymmetric structure of the dyes which prevent the substantivity of dyes on fiber.

7 Antimicrobial activity

The antibacterial and anti-fungal activities of the dyes were determined against four bacteria S. aureus, P. aeruginosa (Gram positive), B. subtitles, E. coli (Gram negative) and C. albicans, A. niger (fungi). Results of the antimicrobial tests are presented in (Table 4). All the tested compounds except 2a, 2b, 2d, 4d, 4e exhibited strong activity against all strains of tested organisms. For antifungal activity among the compounds tested only compounds 3a, 3b were active against the A. niger fungi. On the other hand 2d, 4d, 4e exhibited inactivity against C. albicans.

8 Conclusions

In this work, a series of new monoazo dyes based on pyrazolo [5, 1-c] [1, 2, 4] triazine ring 3a–d, the heterocyclic series of disazo pyrazolone dyes 4a–h have been synthesized. The characterization and the absorption ability of novel disperse dyes 3a–d, 4a–h were studied. All the synthesized compounds were applied to polyester fabrics as disperse dyes. The fastness and colorimetric properties were measured. The results revealed that the monoazo dyes have good fastness and good to moderate affinity to polyester fiber than diazo dyes and also significant antimicrobial activity, the results revealed that all compounds except 2a, 2b, 2d, 4d, 4e compounds exhibited antibacterial activity of high order against all strains of the bacteria used. For antifungal activity the tested compounds except 2d, 4d, 4e exhibited activity against C. albicans, while only compounds 3a, 3b were active against A. niger fungi.