Green Synthesis,Printing Performance,and Antibacterial Activity of Disperse Dyes Incorporating Arylazopyrazolopyrimidines

Abstract

Novel heterocyclic arylazo-disperse dyes containing pyrazolo[1,5-a]pyrimidine structures were prepared via conventional refluxing and microwave heating. Starting from cyanoacetic acid, 4-arylazo-2H-pyrazol-3-ylamine was obtained from a sequence of reactions. This pyrazole intermediate afforded the target arylazo-pyrazolo[1,5-a]pyrimidines and pyrazolo[1,5-a] pyrimidin-7-ones upon cyclization with 3-piperidinylacrylonitrile, ethyl acetoacetate, ethyl(arylhydrazono)acetoacetates, or (arylhydrazono)propanals. The structures of these compounds were confirmed by ¹ H and ¹³ C nuclear magnetic resonance (NMR) spectroscopy, mass spectroscopy, infrared (IR) analysis, and elemental analysis. The disperse colorants produced were applied to printing on polyester fabrics to give satisfactory results. All the synthesized products were tested as antimicrobial agents. Most compounds exhibited relatively strong antibacterial activity against a panel of Gram-positive and Gram-negative bacteria.

Introduction

Many nitrogen-containing heterocyclic materials^1,2 have biological activity and their role as pharmacophores are of considerable historical importance.^3–5 Nitriles have been broadly used as intermediates in the synthesis of various heterocycles, such as aminopyrazoles, that can be easily prepared by the reaction of nitrile derivatives with hydra-zine.^6,7 The reaction of aminopyrazole derivatives with electrophilic reagents affords a variety of fused heterocycles with a broad spectrum of antimicrobial activity.^8–14 Furthermore, these fused heterocycles are also used as intermediates in the dye industry.^15–17 Arylazopyrazolo[1,5-a]pyrimidines were prepared by condensing aminoarylazopyrazoles with β-bifunctional reagents using methodologies initially established in our laboratories.^18–20

In the present work, we report the synthesis of arylazopyrazolo[1,5-a]pyrimidines and their potential application as disperse dyes for printing polyester fabrics. These fused systems displayed considerable antimicrobial activity and gave satisfactory printing results on polyester fabrics. A comparison of conventional and microwave heating use during syntheses was also made. Fastness properties and spectral data for these new dyes were also evaluated. The UV-Vis absorption spectra of these dyes with electron-withdrawing and electron-donating groups were also examined in detail.

Experimental

Materials and Apparatus

All melting points are uncorrected and are expressed in °C. They were determined on a Stuart melting point apparatus. Infrared (IR) spectra were recorded as KBr pellets on a Fourier transform infrared (FTIR) Nicolet 670 spectrometer and ¹ H nuclear magnetic resonance (NMR) spectra were recorded on a Varian GEMINI 200 MHz NMR spectrometer, using tetramethylsilane (TMS) as the internal standard, and chemical shifts were given in δ (ppm). ¹³ C NMR spectra were obtained on a JEOL EX-400 MHz NMR spectrometer, the chemical shifts are expressed in δ (ppm) using TMS as the internal standard. Mass spectra were obtained from a Shimadzu GCMS-QP-1000 EX spectrometer (70 eV). The maximum absorption wavelength (λ_max) of dye solutions (1 × 10^–4 M) in dimethylformamide (DMF) were recorded on an UNICAM UV-Vis 300 instrument. Microanalysis for C, H, and N were performed on a Perkin-Elmer 2400 III platina. The color strength was recorded using an UltraScan PRO Spectrophotometer (light source D₆₅/10° observer). A Domestic 34L Microwave Stainless Steel oven (ME6124ST) was used as a microwave source.

Unless otherwise noted, all chemicals were supplied by Sigma Aldrich. Dry solvents for syntheses and spectroscopic measurements (spectroscopic grade) were used without further purification. Scoured and bleached 100% polyester fabrics were supplied by El-Mahalla El-Kobra Co. The fabrics were scoured in and aqueous solution having a liquor ratio (LR) of 1:50 and containing 2 g/L of non-ionic detergent solution (Hostapal, Clariant) and 2 g/L of sodium carbonate at 50 °C for 30 min to remove waxes and impurities, followed by rinsing in cold water, and finally drying at room temperature (RT).

Printing

Dyes were ground up using a small mortar and pestle and then sieved using a USA standard sieve with 0.0029 in. (75 μm) holes. A paste composed of synthetic thickener stock paste (3.5 g Alcoprint DT-CS with 95 g water) and the ground dye (1.5 g) was prepared by stirring the mixture well. The printing paste was applied to the fabrics using the fat screen printing technique. White polyester fabric (100%) plain weave (149 g/m²) was supplied by Miser Co. Print fixation was done by thermofixation at 180–200 °C for 2–3 min in an automatic thermostatic oven (Werner Mathis Co.). Washing of involved cold water rinsing, followed by washing with soap at 40 °C using 1 g/L Ciba Eriopon OS. Reduction clear was performed at 50 °C using 1–2 g/L sodium hydrosulfite, 1–2 g/L caustic soda at 66 °Tw (36 °Bé), and 1 g/L Ciba Eriopon OS. The printed fabric was rinsed at 50 °C, then with cold water, and finally dried. ⁶

Colorfastness

Fastness to washing, perspiration, light, and sublimation was tested according to the reported methods.^21–24

Color Strength

The color strength of the printed samples, expressed as K/S, was evaluated by the high reflectance technique. Reflectance measurements of the printed fabrics were performed on a Perkin-Elmer Lambda 3B, UV/Vis spectrophotometer. K/S values were calculated using the Kobelka-Munk equation (Eq. 1)

$$K/S={\left(1-R\right)}^2/2R-{\left(1-R_0\right)}^2/2R_0$$

(Eq. 1)

K is the absorption coefficient, S is the scattering coefficient, and R and R₀ are decimal fractions of the reflectance of the printed and unprinted fabrics, respectively. ²⁵

Crockfastness

Crockfastness was determined according to the ISO test meth-od. ²² In this test, the color is transferred from the surface of the colored fabric to another surface by rubbing. A colored test specimen fastened to the base of a crockmeter (SDL Atlas) was rubbed on a white crock test cloth under controlled conditions.

Dry Crocking Test

The test specimen was placed on the base of the crockmeter. A white testing cloth was mounted. The covered finger was lowered onto the test specimen and caused to slide back and forth 20 times by making ten complete turns at a rate of one turn per second. The white test sample was then removed for evaluation using the Gray Scale for Staining.

Wet Crocking Test

The white test sample was thoroughly wetted out in water to a 65% pickup. The procedure was run as before and the white test samples were then air dried before evaluation.

Washfastness

Washfastness was determined according to ISO 105-C02:1989 using a Launder-Ometer (SDL-Atlas). ²¹ The specimens (5 × 10 cm) were sewn between two similar pieces of bleached cotton fabric. The composite specimen was immersed into an aqueous solution containing 5 g/L soap and 2 g/L of sodium carbonate at an LR of 50:1. The bath was thermostatically adjusted to 45 °C. The test was run for 30 min at 42 rpm. The samples were then removed, rinsed twice with occasional stirring or hand squeezing, and then dried. Washfastness was assessed using the Gray Scale for Color Change.

Colorfastness to Perspiration

Alkaline Solution

L-Histidine monohydrochloride monohydrate (0.25 g/L), sodium chloride (10 g/L), and sodium dihydrogen phosphate (1 g/L) were dissolved in 1 L of distilled water. The pH was adjusted to 8 with sodium hydroxide solution (0.1N).

Acidic Solution

L-Histidine monohydrochloride monohydrate (0.25 g/L), sodium chloride (10 g/L), and sodium dihydrogen phosphate (1 g/L) were dissolved in 1 L of distilled water. The pH was adjusted to 4.3 with an acetic acid solution (10%). The colored specimen (5 × 4 cm) was sewn between two pieces of uncolored specimens to form a composite specimen. The composite specimen was then immersed for 15–30 min in each solution with occasional agitation and squeezing to insure complete wetting. The test specimen was placed between two glass plates under a force of ∼4–5 kg. The plates containing the composite specimen were then held vertical in the oven at 37 ± 2 °C for 4 h. The effect on the color of the test specimen was determined by reference to the Gray Scale for Color Change.

Lightfastness

Lightfastness was determined according to AATCC TM 16A-1989 (ISO 105-B02:1988). ²⁴ The evaluation was established using the blue scale (SDL Atlas) as the reference of color change. For lightfastness testing, a Fade-Ometer 18-F (Aldrich) equipped with a UV lamp was used, with light exposures conducted for 35 h.

Antimicrobial Activity Evaluation of Synthesized Dyes

Some of the synthesized compounds were evaluated for antimicrobial activity against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeu-roginosa. Each compound was dissolved in acetone and a solution at 1 mg/mL was prepared separately. Paper discs of Whatman filter paper were cut to a standard size (5 cm) and sterilized in an autoclave. The paper discs were soaked in the desired concentration of the dye solution and were placed aseptically in Petri dishes containing nutrient agar media (agar, 20 g + beef extract, 3g + peptone, 5g) seeded with S. aureus, B. subtilis, E. coli, and P. aeuroginosa. The Petri dishes were incubated at 36 °C and the inhibition zones were recorded after 24 h of incubation. Each treatment was replicated three times. ²⁶

Synthesis-Intermediates

Note that data relating to the characterization of the following intermediates are available from the authors. All proper safety precautions, including wearing safety glasses, use of fume hoods, and shielding, must be observed when working in the laboratory.

3-Piperidin-1-yl-acrylonitrile

A mixture of cyanoacetic acid (0.05 mol), triethyl orthofor-mate (0.05 mol), and piperidine (0.5 mL) was heated under reflux for 2 h, allowed to cool to RT, then poured into cold water. The reaction mixture was treated with 1 M sodium carbonate solution (50 mL), extracted with dichlorometh-ane (100 mL), and the extract was left overnight to dry. The solvent was evaporated in vacuo. Piperidin-1-yl-acrylonitrile (1) was obtained as buff crystals.

Phenyl Substituted and Unsubtituted 2-(phenylhydrazono)-3-oxo-propionitriles

An aryldiazonium salt (0.01 mol) solution was prepared by adding sodium nitrite solution (0.7 g in 10 mL H₂O) to a chilled solution of arylamine hydrochloride (0.01 mol of arylamine in 5 mL conc. HCl) with stirring. The resulting aryldiazonium solution was then added to a cold solution of 1 in acetic acid (50 mL) containing sodium acetate (3.8 g). The reaction mixture was stirred for 1 h. The solid product so formed was collected by filtration and crystallized from ethanol to give substituted and unsubstituted 2-(phenylhydrazono)-3-oxo-propionitriles (2).

Ethyl 2-(4-nitrophenylhydrazono)acetoactate

4-Nitroaniline (1.38 g, 0.01 mol) was dissolved in conc. HCl (10 mL) and the solution was then cooled to 0–5 °C. Sodium nitrite (0.01 mol) in water (3 mL) was then added to this solution dropwise with vigorous stirring over 1 h, while cooling at 0–5 °C. The clear diazonium salt solution was then added dropwise to a well-cooled (0–5 °C) and stirred solution of ethyl acetoacetate (1.3 g, 0.01 mol) in sodium acetate (2 g, dissolved in 10 mL of 50% aqueous ethanol). The pH of the coupling mixture, in each case, was maintained at 5–6 throughout the coupling process by adding sodium acetate. Stirring was continued for 4 h at 0–5 °C and the precipitated products separated upon dilution with cold water (50 mL) were filtered of, washed with water several times, dried, and recrystallized from ethanol-H₂O to give ethyl 2-(4-nitrophenylhydrazono)acetoactate (9).

4-(Arylazo)-2H-pyrazol-3-ylamine

A mixture of 2 (0.01 mol) and hydrazine hydrate (0.01 mol) in ethanol (25 mL) was refluxed for 2 hours then poured into H₂O. The solid 4-(arylazo)-2H-pyrazol-3-ylamine (3) was collected by filtration and then crystallized.

Synthesis-Dyes

3-Phenylazo-pyrazolo[1,5-a]pyrmidin-7-ylamine

A mixture of 3-piperidinoacrylonitrile 1 (0.01 mol) and 3 (0.01 mol) was refluxed in dioxane (20 mL) for 2–3 h. The reaction mixture was then poured into crushed ice with stirring. The solid 3-phenylazo-pyrazolo[1,5-a]pyrmidin-7-ylamine (6) was collected by filtration and crystallized from DMF to give dark brown crystals (34%), mp > 300 °C. IR (KBr) ν_max: 3412, 3282 (NH₂), 2936 (CH, aromatic) cm^–1. MS m/z 238 (M⁺). ¹ H NMR (DMSO-d₆, δ): 6.11 (d, 1H, pyrimidin-H), 6.85 (s, 1H, pyrazol-H), 7.45–7.50 (m, 5H, Ar-H), 7.70 (s, 2H, NH₂), 8.05 (d, 1H, pyrimidin-H). Anal. Calcd for C₁₂H₁₀N₆: C, 60.50; H, 4.23; N, 35.27. Found: C, 60.53; H, 4.22; N, 35.26.

5-Methyl-3-(4-nitro-phenylazo)-4H-pyrazolo[1,5-a] pyrimidin-7-one

A mixture of ethyl acetoacetate 7 (0.01 mol), 4-(4-nitrophenylazo)-1H-pyrazol-3-ylamine 3 (0.01 mol) and pyridine (0.5 mL) was refluxed in ethanol for 6 h. The mixture was then poured into cold water and acidified with conc. HCl. The solid 5-methyl-3-(4-nitro-phenylazo)-4H-pyrazolo[1,5-a]pyrimidin-7-one (8) was collected by filtration and crystallized from ethanol to give dark brown crystals (59%), mp 260 °C. IR (KBr) ν_max: 3445 (OH), 2887 (CH, aliphatic), 1681 (CO) cm^–1. MS m/z 298 (M⁺). ¹ H NMR (DMSO-d₆, δ): 2.35 (s, 3H, aliphatic-H), 5.85 (s, 1H, pyrim-idinone-H), 7.75–8.30 (m, 4H, Ar-H). ¹³ C NMR (DMSO-d₆, δ): 19.08 (aliphatic CH), 99.93 (pyrazole CH), 122.65, 124.95 (aromatic CH), 125.35 (pyrimidinone CH), 134, 140.35 (aromatic CH), 147.20, 152, 155.23 (pyrimidinone CH), 156.30 (CO). Anal. Calcd for C₁₃H₁₀N₆O₃: C, 52.35; H, 3.38; N, 28.18. Found: C, 52.33; H, 3.37; N, 28.19.

Procedures for 3,6-Bis(arylazo)pyrazolo[1,5-a]pyrimidin-7-ylamine Syntheses

Method A

A mixture of 3 (0.01 mol) and 2 (0.01 mol) was refluxed in acetic acid (15 mL) for 2–3 h. The reaction mixture was then poured into water with stirring. The solid 3,6-bis(arylazo) pyrazolo[1,5-a]pyrimidin-7-ylamine (4) was collected by filtration and crystallized.

Method B

A mixture of 2 (0.02 mol) and hydrazine hydrate (0.01 mol) was refluxed in ethanol (15 mL) for 5-6 h. The reaction mixture was then poured into crushed ice with stirring. The solid 3,6-bis(arylazo)pyrazolo[1,5-a]pyrimidin-7-ylamine (4) was collected by filtration and crystallized.

Method C

A solution of the aryldiazonium salt, which was prepared from the appropriate aniline derivative (0.01 mol), sodium nitrite (0.01 mol), and concentrated HCl (25 mL) in water (10 mL) was added slowly to a cold 5 °C solution of 6 (0.01 mol) in pyri-dine (10 mL). The resulting solid was filtered, washed with cold water, dried, and recrystalized.

6-(4-Nitrophenylazo)-3-phenylazo-pyrazolo[1,5-a] pyrimidin-7-ylamine

6-(4-Nitrophenylazo)-3-phenylazo-pyrazolo[1,5-a]pyrim-idin-7-ylamine (4a) was obtained as dark brown crystals from ethanol-DMF (39%), mp >300 °C. IR (KBr) ν_max: 3398 (NH₂), 1595 (C=N). MS m/z 387 (M⁺) cm^–1. ¹ H NMR (DMSO-d₆, δ): 7.45–8.35 (m, 10H, Ar-H, pyrazolo-H), 8.65, 8.95 (s, 1H, pyrimidinyl-H), 9.62, 9.92 (s, 1H, NH₂). Anal. Calcd for C₁₈H₁₃N₉O₂: C, 55.81; H, 3.38; N, 32.54. Found: C, 55.83; H, 3.37; N, 32.54.

3,6-Bis-(2-nitrophenylazo)-pyrazolo[1,5-a]pyrimidin-7-ylamine

3,6-Bis-(2-nitrophenylazo)-pyrazolo[1,5-a]pyrimidin-7-ylamine (4b) was obtained as reddish-brown crystals from ethanol-DMF (48%), mp 297 °C. MS m/z 432 (M⁺). Anal. Calcd for C₁₈H₁₂N₁₀O₄: C, 50.00; H, 2.80; N, 32.40. Found: C, 49.98; H, 2.81; N, 32.39.

3,6-Bis-(phenylazo)-pyrazolo[1,5-a]pyrimidin-7-ylamine

3,6-Bis-(phenylazo)-pyrazolo[1,5-a]pyrimidin-7-ylamine (4c) was obtained as dark red crystals from DMF (72%), mp 276 °C. IR (KBr) ν_max: 3424 (NH2), 2946 (CH aromatic) cm^–1. MS m/z 342 (M⁺). ¹ H NMR (DMSO-d₆, δ): 6.62 (s, 1H, pyrazolo-H), 7.35–8.04 (m, 10H, Ar-H), 8.71, 9.0 (s, 1H, pyrimidinyl-H), 9.38, 9.76 (s, 1H, NH₂). Anal. Calcd for C₁₈H₁₄N₈: C, 63.15; H, 4.12; N, 32, 73. Found: C, 63.10; H, 4.11; N, 32.74.

3,6-Bis-(4-nitrophenylazo)-pyrazolo[1,5-a]pyrimidin-7-ylamine

3,6-Bis-(4-nitrophenylazo)-pyrazolo[1,5-a]pyrimidin-7-yl-amine (4d) was obtained as dark brown crystals from DMF (57%), mp 234 °C. IR (KBr) ν_max: 3435 (overtone and combination bands), 1627 (C=N) cm^–1. MS m/z 431 (M⁺). Anal. Calcd for C₁₈H₁₂N₁₀O₄: C, 50.00; H, 2.80; N, 32.40. Found: C, 50.03; H, 2.79; N, 32.42.

3,6-Bis-(p-tolylazo)-pyrazolo [1,5-a]pyrimidin-7-ylamine

3,6-Bis-(p-tolylazo)-pyrazolo [1,5-a]pyrimidin-7-ylamine (4e) was obtained as brown crystals from DMF (58%), mp > 300 °C. IR (KBr) ν_max: 3283 (NH₂), 2833 (CH, aliphatic) cm^–1. MS m/z 370 (M⁺). ¹ H NMR (DMSO-d₆, δ): 7.36–8.67 (m, 9H, Ar-H, pyrazolo-H), 8.96 (s, 1H, pyrimidinyl-H), 11.56 (s, 2H, NH₂). Anal. Calcd for C₂₀H₁₈N₈: C, 64.85; H, 4.90; N, 30.25. Found: C, 64.77; H, 4.89; N, 30.28.

Procedure for 3,6-bis-(arylazo)pyrazolo[1,5-a]pyrimidin-7-one Syntheses

A mixture of 3 (0.01 mol), pyridine (0.5 mL) and 9 (0.01 mol) was refluxed in ethanol (15 mL) for 6 h. The reaction mixture was then poured into cold water and acidified with concentrated HCl. 3,6-Bis-(arylazo) pyrazolo[1,5-a]pyrimidin-7-one (10) was collected by filtration and then crystallized.

5-Methyl-6-[(4-nitrophenyl)-hydrazono]-3-phenyl-azo-6H-pyrazolo[1,5-a]pyrimidin-7-one

5-Methyl-6-[(4-nitrophenyl)-hydrazono]-3-phenylazo-6H-pyrazolo[1,5-a]pyrimidin-7-one (10a) was obtained as red crystals from DMF (49%), mp 156 °C. MS m/z 386 (M⁺). ¹ H NMR (DMSO-d₆, δ): 2.51 (s, 3H, aliphatic-H), 6.91 (s, 1H, pyrazolo-H), 7.29-8.24 (m, 9H, Ar-H), 11.97 (s, 1H, NH). Anal. Calcd for C₁₉H₁₄N₈O₃: C, 56.72; H, 3.51; N, 27.85. Found: C, 56.77; H, 3.50; N, 27.83.

5-Methyl-3-(4-nitrophenylazo)-6-[(4-nitrophenyl)-hydrazono]-6H-pyrazolo[1,5-a]pyrimidin-7-one

5-Methyl-3-(4-nitrophenylazo)-6-[(4-nitrophenyl)-hydrazono]-6H-pyrazolo[1,5-a]pyrimidin-7-one (10b) was obtained as dark brown crystals from DMF (68%), mp 174 °C. IR (KBr) ν_max: 3200 (NH), 2842 (CH, aliphatic), 1672 (CO), 1596 (C=N) cm^–1. MS m/z 449 (M⁺). ¹ H NMR (DMSO-d₆, δ): 2.41 (s, 3H, CH aliphatic), 6.52 (d, 1H, pyrazolo-H), 7.11–8.32 (m, 8H, Ar-H). Anal. Calcd for C₁₉H₁₃N₉O₅: C, 51.01; H, 2.93; N, 28.18. Found: C, 51.06; H, 2.91; N, 28.21.

(11,12,14,15-tetraaza-cyclopenta[a]phenanthren-17-yl) -p-tolyl-diazene

Aqueous sodium nitrite (0.7 g in 5 mL H₂O) was added to a cold (0 °C) stirred solution of 3 (0.01 mol) in conc. HCl (5 mL). The pyrazolediazonium salt solution was then added to a cold solution of β-naphthol (20) in ethanol (50 mL) containing sodium acetate (3 g). This was stirred at RT for 1 h and the solid (11,12,14,15-tetraaza-cyclopenta[a] phenanthren-17-yl)-p-tolyl-diazene (15) was collected by filtration and crystallized from ethanol-DMF to give dark brown crystals (81%), mp 249 °C. IR (KBr) ν_max: 2921 (CH, aromatic), 2956 (CH, aliphatic) cm^–1. MS m/z 337 (M⁺). ¹ H NMR (DMSO-d₆, δ): 2.50 (s, 3H, CH₃), 6.63 (s, 1H, pyrazolo-H), 7.15-7.88 (m, 10H, Ar-H). Anal. Calcd for C₂₀H₁₄N₆: C, 70.99; H, 4.17; N, 24.84. Found: C, 70.96; H, 4.15; N, 24.82.

Results and Discussion

Synthesis

The structures of synthesized compounds were confirmed by a variety of spectroscopic techniques, including ¹ H and ¹³ C NMR, mass spectroscopy, IR, and elemental analysis. Elnagdi et al.^6,18–20 reported that the reaction of enaminoni-trile 1 with aromatic diazonium salts affords arylhydrazones 2, which are readily converted into arylazoaminopyrazoles 3. Our work wanted to determine if 4-arylazo-2H-pyr- azol-3-ylamine derivatives could be used as precursors to arylazo-pyrazolo[1,5-a]pyrimidin-7-ylamines (and pyrimi-din-7-ones). Compound 2 reacted with 3 to yield products that may be formed as 4 or the isomeric 5. Structure 4 was preferred for these products, based on their synthesis via coupling of 6 with aromatic diazonium salts. Compound 6 in turn was prepared from reaction of 3 with 1. Such a reaction, which leads to 7-amino-pyrazolo[1,5-a]pyrimidines, was established earlier by X-ray single crystal structure, ²⁷ and more recently by ¹⁵ N heteronuclear multiple bond correlation (HMBC) measurements^18,28 (Scheme 1).

Scheme 1

Synthesis of arylazo-pyrazolo[1,5-a]pyrimidin-7-ylamines starting from piperidinylacrylonitrile (1).

Product 4 was also prepared in a direct one-pot experiment by reacting 2:1 moles of propanals 2 and hydrazine hydrate, respectively, for 5–6 h in refluxing ethanol. This methodology was available only for symmetrical bisarylazo-pyrazolo[1,5-a]pyrimidin-7-ylamines 4 (Scheme 2).

Scheme 2

One-pot synthesis of arylazo-pyrazolo[1,5-a]pyrimidin-7-ylamines (4).

Aminopyrazoles 3 reacted with ethyl acetoacetate 7 to yield pyrazolo[1,5-a]pyrimidin-7-ones 8. IR spectra of compound 8 showed a band at 1681 cm^–1 (C=O) and a band at 3445 cm^–1 (NH-pyrimidinone), while ¹ H NMR spectra showed a single peak at 2.43 ppm and 5.86 ppm for methyl and CH-pyrimidinone groups, respectively. Also, 3 reacted with ethyl 2-(4-nitrophenylhydrazono)acetoactate 9, yielding the corresponding arylazo-pyrazolo[1,5-a]pyrimidin-7-ones 10. Structures proposed for products 8 and 10 were based on analogy to the well-established chemistry of aminopyr-azoles, as well as spectral and analytical data.^29,30 The ¹ H NMR spectrum of compound 10a showed a single peak at ∼12 ppm (NH-hydrazone group) and a single peak at 2.50 ppm (methyl group). The IR spectrum of 10b showed a band at 3200 cm^–1 (NH-hydrazone) and at 1672 cm^–1 (C=O group) (Scheme 3).

Scheme 3

Synthesis of arylazo-pyrazolo[1,5-a]pyrimidin-7-ones (10a-b).

Consistent with the previously reported reactivity of β-naphthol toward heterocyclic diazonium salts, ³¹ compound 13 also coupled with the pyrazolediazonium chloride 11 to yield the pyrazolo[5,1-c]triazines 15.

Trials to isolate acyclic hydrazones failed. It is believed that direct formation of 15 resulted from the cycloaddition reaction of the diazo compound 11 to 13 to yield 14, which was then condensed and aromatized into 15. A similar assumption was made to account for direct formation of pyrazolo[5,1-c]-1,2,3-triazines upon reacting 13 with diazo-tized aminopyrazoles (Scheme 4). ³²

Scheme 4

Synthesis of pyrazolo[5,1-c]-1,2,3-triazines (15).

Use of microwave heating has environmental advantages over use of conventional energy resources, such as low energy consumption, milder reaction conditions, acceleration of reaction rates, increased reaction yield, and less or solvent-free reaction conditions.^6,9,33 Products 4, 6, 8, and 10 were also obtained using microwave heating of reactants in DMF for 1–2 min and subsequent treatment with water. Better yields were generally obtained at greatly shortened reaction times compared to conventional heating (Table I).

Table I

Yield and Time Comparison between Conventional and Microwave Heating

Compound	Conventional Heating		Microwave Heating
	Yield (%)	Time (h)	Yield (%)	Time (min)
6	34.1	2–3	56	1–2
8	59.2	6	71	2
4a	38.8	2-3	44	1-2
4b	47.7	2-3	73	1-2
4c	71.7	2-3	77	1-2
4d	57	2-3	52.9	1-2
4e	58.1	2-3	71	1-2
10a	48.8	6	61.4	2
10b	68	6	61.7	2

Dyeing Polyester Fabrics

Color Properties

The arylazopyrazolopyrimidines synthesized in this work can be considered disperse dyes because they are water-insoluble, small molecules able to dye polyester fibers. Polyester has a high affinity for disperse dyes compared to other hydrophobic textile fibers. ³⁴ Therefore, these arylazopyrazolo[1,5-a]pyrimidine disperse dyes were applied to polyester fabrics.

K/S values for each dye on the printed substrates are listed in Table II, together with the hues of the polyester samples and the λ_max values in DMF. Dyes 4a-e, 6, and 8 built up well, yet dyes 10a, b failed to build up to deep shades on the substrate. The behavior of dyes 10a, b may be attributed to their low melting points and, consequently, degradation during the thermofixaton process. Dyes 4d and 8 showed a slight increase in color strength due to the presence of electron-withdrawing groups (X = p-NO₂), while the opposite occurred with electron-donating groups (X = CH₃).

Table II

UV-Vis Absorption Spectra and Color Strength of the Prepared Dyes

Compound	λmax (DMF)	Shade	K/S
6	441	Yellow	12.53
8	500	Orange	14.17
4a	476	Orange	16.87
4b	486	Orange	12.91
4c	494	Orange	14.17
4d	556	Orange-red	15.14
4e	459	Yellow	11.84
10a	469	Orange	6.18
10b	503	Orange	7.23

The hues of the printed polyester fabrics were consistent with the observed λ_max values of the dyes in solution. The present dyes give yellow, orange, and orange-red shades. Dye 4d was the most bathochromic. The presence of a nitro group at the ortho-position to the azo linkage did not seem to affect the color shift. It was also observed that the strong (p-NO₂) electron-withdrawing substituent, at the arylazopy-rimidine moiety, did not highly affect the color shift either.

Fastness Properties

The fastness of the printed polyester samples was generally satisfactory; the depths of shade and dye structure influenced the fastness results.

Washfastness

The rate of movement of dyes out of polyester fibers during the washing process depends on the molecular size of dye, the nature of mechanical link formed between the dye and the fiber, and the dye's charge, which is affected by presence of electron donating or electron withdrawing substituents. The washfastness of the printed polyester fabrics tested, including color change and stain on cotton, ranged from poor to very good (Table III). Better washfastness results were obtained for dyes with electron-donating substituents, indicating their higher substantivity to hydrophobic fibers. On the other hand, poorer washfastness results were obtained for dyes with electron-withdrawing substituents that consequently had poor substantivity to hydrophobic fibers.

Table III

Fastness Properties of the Synthesized Dyes on Polyester Fabrics ^a

Cpd.	Washfastness		Perspiration Fastness				Crockfastness		LF
	Alt.	St.	Acidic		Basic		Dry	Wet
			Alt.	St.	Alt.	St.
6	4	4	4-5	4-5	3	3	4-5	4-5	5-6
8	4-5	4-5	4	4	4-5	4-5	4-5	4-5	6-7
4a	4	4	4-5	4-5	4-5	4-5	4-5	4-5	3
4b	4	4	4-5	4-5	4	3-4	4-5	4-5	5-6
4c	3-4	3-4	4	4-5	4	3-4	4-5	4	5
4d	3-4	3-4	4	4-5	3-4	3-4	4	4	2-3
4e	4-5	4-5	4-5	4-5	4-5	4-5	4-5	4-5	4
10a	4-5	4-5	4	4	3-4	3-4	4	4	5
10b	4	3-4	4	4	4	3-4	4	4-5	4-5

a

Cpd. = compound; LF = lightfastness; Alt. = alteration in color; St. = staining on cotton.

Perspiration Fastness

The extent of dye removal from polyester fabric due to perspiration is shown in Table III. The results show that dye removal was mostly dependent on the dye substituents. Dyes with electron-withdrawing groups were less stable to perspiration. The perspiration fastness values varied from poor to very good, with higher ratings for dyes with electron-donating groups.

Crockfastness

Crockfastness evaluates the removal of loosely adhered dye molecules from the surface of the polyester fabric. The higher molecular weight dyes had the higher crockfastness values. All of the dyed fabrics tested generally gave good crockfastness results as shown in Table III.

Lightfastness

Lightfastness values for the dyed fabrics tested varied from poor to very good depending on the dye‘s molecular structure and depth of shade (Table II). For the aminoazobenzene derivatives, an increase in the electron-withdrawing effect of the diazo component led to a decrease in the electron density on the amino nitrogen atom with photofading taking place due to singlet oxygen attack at this site.^16,17 Generally, the same photofading effect was observed with the dyes containing the electron-withdrawing p-nitro substituent, except for dyes 8, 10a, and 10b, which contain a carbonyl group that did not participate in conjugation. As mentioned before, the o-nitro group did not affect conjugation, and hence, this phenomenon did not affect dye 4b.

Antibacterial Activity and Structure-Activity Relationship

Dyes 4, 6, 8, and 10 were individually tested against S. aure-us, B. subtilis, E. coli, and P. aeuroginosa. The antibacterial activity of a standard antibiotic Ampicillin was also reported using the same procedures as above.

The percentage activity index was calculated by the formula shown in Table IV. Compared to the bisazo dyes 4 and 10, the monoazo dyes 6 and 8 showed relatively stronger antibacterial activity against all four bacteria. The highly-substituted dyes 10a and 10b demonstrated relatively stronger antibacterial activities than dyes 4a-e. Furthermore, dye 8, containing a highly electron-withdrawing functional group, demonstrated weaker antibacterial activities than dye 6. Similarly, dyes 4a, 4b, and 4d, containing higher electron-withdrawing substituents, demonstrated weaker antibacterial activities than dyes 4c and 4e.

Table IV

Dye Antibacterial Properties

Compound	E. coli	P. aeuroginosa	S. aureus	B. subtilis
6	66.7	73.0	63.4	83.7
8	61.0	48.9	41.1	67.2
4a	26.3	40.1	32.0	55.3
4b	33.2	42.0	28.0	57.0
4c	60.5	31.2	45.6	36.4
4d	13.3	22.3	11.8	32.4
4e	50.5	41.5	36.4	65.2
10a	47.6	57.8	43.5	72.0
10b	20.4	47.3	28.7	33.1
Ampicillin	100	100	100	100
$$\text{\% Activity index }=\frac{\text{Inhibition zone of compound tested (diameter) x 100}}{\text{Inhibition zone of standard (diameter)}}$$

It is notable that these dyes exhibited antimicrobial activity. For this to be useful in practice, it would be necessary that, once applied, the dyes migrate out of the polyester. The generally good fastness results suggest that this migration would be limited. Future work is needed that tests the antimicrobial activity of the dyed material (as opposed to the dyes present on a paper substrate) to substantiate this conclusion. ³⁵

Conclusion

In this work, a series of arylazo-pyrazolo[1,5-a]pyrimdin-7-ylamine and arylazo-pyrazolo[1,5-a]pyrimidin-7-one disperse dyes have been synthesized using both conventional refluxing and microwave heating. Use of microwave heating reduced the time required for synthesis from hours to minutes and reduced energy consumption. These yellow, orange, and orange-red dye printed polyester fabrics gave solid shades with satisfactory depth of shade, levelness, and fastness properties. The fastness properties tested (lightfast-ness, crockfastness, washfastness, and perspiration fastness) were, in most cases, rated acceptable to very good. Furthermore, most of these compounds showed relatively strong antibacterial activity.

Footnotes

Acknowledgement

We are grateful to National Research Centre, Cairo, Egypt; for their financial support.