Ecotoxicology and Environmental Safety ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach M. Ganapathi a, D. Jayaseelan b, S. Guhanathan b,n a b
PG & Research Department of Chemistry, Government Arts College, Tiruvannamalai, Tamil nadu, India PG & Research Department of Chemistry, Muthurangam Government Arts College (Autonomous), Vellore, Tamil nadu, India
art ic l e i nf o
a b s t r a c t
Article history: Received 2 November 2014 Received in revised form 1 May 2015 Accepted 5 May 2015
A conventional and microwave assisted efficient synthesis of diphenyl substituted pyrazole using PEG 600 as green solvent has been described. A relatively shorter reaction time with excellent yield of the piperidine mediated protocol has been attracted economically attractive and eco-friendly. All newly synthesized compounds were characterized by standard spectroscopic techniques viz., UV–visible, FT-IR, 1 H-NMR and Mass spectra. The anti-microbial activities of compounds have also been tested using Minimum Inhibitory Concentration (MIC) method with two different microorganisms Staphylococcus aureus (MTCC3381) and Escherichia coli (MTCC739). The results of the antimicrobial activity revealed that the diphenyl substituted pyrazole derivatives have nice inhibiting nature against both types of bacteria of present investigation than corresponding chalcones. Since, the work has been focused on green chemical approach towards the synthesis, this protocol may be recommended for eco-friendly applications. & 2015 Elsevier Inc. All rights reserved.
Keywords: Chalcones Pyrazole Piperidine Antimicrobial activity PEG-600 Microwave irradiation (MWI)
1. Introduction Chalcones comprise a class of compounds with important therapeutic potential. The ease of preparation, the potential of oral administration, and safety protocol enable chalcone-based compounds as therapeutic agents. Chalcones (α, β-unsaturated ketones) possess a wide range of pharmacological activities such as anti-inflammatory (Hsieh et al., 1998), anticancer (Shibata, 1994), analgesic (Viana et al., 2003), antiulcerative (Murakami et al., 1991), antiviral (Wu et al., 2003), antimalarial (Liu et al., 2001) and antibacterial (Bekhit et al., 2001). The presence of a reactive α, βunsaturated keto group in chalcones is found to be responsible for their pharmacological activities. Pyrazole derivatives have been reported to possess diverse biological activities such as antibacterial (Abdel-Hafez et al., 2009) antifungal (Ali, 2009) herbicidal (Witschel, 2009), insecticidal (Lahm et al., 2007) anti-inflammatory (Youssef et al., 2010), anticonvulsant (Abdel-Aziz et al., 2009) anti-oxidant (Oliver and Dallinger, 2006) and so on. Considerable interest has been focused on the pyrazole structure which has been known to possess a broad spectrum of biological activities. Designing of safer chemicals which prevents the environmental n
pollution found to be a greater environmental impact in minimizing the use and disposal of organic solvents into the environment. In view of this, polyethylene glycol (PEG) has found to be an interesting solvent system. PEG is an environmentally benign reaction solvent, it is inexpensive, potentially recyclable and water soluble, which facilitates its removal from there action product. Microwave-assisted synthesis is an eco-friendly and efficient method of synthesis of organic compounds as compared to the conventional method of synthesis. In this method, reaction occurs more rapidly, safely and with higher chemical yields due to which this method becomes superior to the conventional method. The conventional method, requiring a longer reaction time and larger quantities of solvents and reagents, causes environmental pollution and contributes to the health hazards (Oliver and Dallinger, 2006). Based on the careful analysis of the literature, present investigation was aimed to focus on the PEG-600 solvent system. The series of chalcones and diphenyl substituted pyrazoles compounds were synthesized by both conventional and microwave irradiation methods. The synthesized compounds were characterized on the basis of UV–visible, FTIR, 1HNMR and mass spectral data. Further, the present investigation have also been recommended for the antibacterial activities of the synthesized
Corresponding author. E-mail address: [email protected] (S. Guhanathan).
http://dx.doi.org/10.1016/j.ecoenv.2015.05.002 0147-6513/& 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
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compound with some selected gram positive and gram negative bacteria viz., Staphylococcus aureus, and Escherichia coli respectively.
2. Experimental 2.1. Methods and materials The chemicals acetophenone (1), 4-chloroacetophenone (2), 4nitroacetophenone (3), 4-hydroxybenzaledehyde (4), PEG-600 (5), hydrazine hydrate (6), sodium hydroxide and piperidine were obtained from Avra chemicals, Hyderabad and were used as such without further purification. Silica gel (TLC and Column grade) were purchased from Merck. The solvents were purified as per the standard procedure reported elsewhere. FTIR spectra (KBr pellets) were measured using Alpha Bruker FTIR instrument scanning with the entire region of 4000–400 cm 1 with typical resolution of 1.0 cm 1. UV–visible spectra were also recorder using Alpha Bruker UV spectrophotometer. The NMR spectra of the compounds have been recorded on Bruker AV400 spectrometer operating at 400 MHz for recording 1H spectra in DMSO solvent using TMS as internal standard. Mass spectra have been recorded on SHIMADZU spectrometer using chemical ionization technique. Melting points of all synthesised compounds have been determined in open glass capillaries on Mettler FP51 melting point apparatus and are uncorrected. Microwave reactions are carried out commercially available IFB domestic microwave oven having a maximum power output of 110 W operating at 450 Hz. 2.2. Synthesis of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one (7) 2.2.1. Method-A (conventional method) A mixture of acetophenone (0.01 mol) and 4-hydroxy benzaldehyde (0.01 mol) and NaOH (0.02 mol) were stirred in PEG-600 (20 mL) as solvent at 65 °C for 1 h. The completion of the reaction was monitored by TLC and the crude mixture was worked up in ice-cold water (100 mL). The product was separated out and filtered. The filtrate was evaporated to dryness to remove water leaving behind PEG-600. The recovered PEG-600 has been utilized for the synthesis of chalcones. Synthesised compounds were recrystallised from ethanol to afford pure compound (5). (Yield – 80% and melting point: 100–102 °C). 2.2.2. Method-B (microwave irradiation method) A mixture compounds 1 (0.01 mol) and 4 (0.01 mol) and NaOH (0.02 mol) were grinded in to the mortar. Then it was mixed with 20 mL of PEG-600. The mixed compounds were taken in a 100 mL beaker and it was irradiated in a microwave oven for the 3–5 min at 110 W operating at 2450 Hz at 30 s of intervals. After completion of reaction as followed by T.L.C examination, chilled water was added to the reaction mixture and neutralized by an acid. The solid product was obtained, which was filtered, dried and crystallized from an ethanol. The filtrate was evaporated to dryness to remove water leaving behind PEG-600. (Yield – 98% and melting point: 101–102 °C).
and filtered. A synthesised compound (6) was recrystallised from ethanol. (Yield – 75% and melting point: 110–111 °C) 2.3.2. Method-B (microwave irradiation method) A mixture of compounds (5) (0.01 mol), (6) (0.01 mol) and 2–3 drops piperidine catalyst were mixed thoroughly in mortar. Then it was dissolved into minimum amount of PEG-600. The mixed compounds were taken in a 100 mL beaker and it was irradiated in a microwave oven for the 4–5 min at 110 W operating at 2450 Hz at 30 s of intervals. The completion of the reaction was monitored by TLC and the crude mixture was worked up in ice-cold water. The filtrate was evaporated to dryness to remove water leaving behind PEG-600. Yield: 90% and 110–112 °C. The rest of the compounds of 8, 9 and 11, 12 were synthesised by the above mentioned same procedures.
3. Results and discussion 3.1. Results 3.1.1. Spectral details of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1one (7) Melting point : 101–102 °C UV–visible (λmax:nm) : 226 (π → π * transition), 314 (n → π * transition) FTIR (cm 1) : 3203 (O–H), 3184 (Aromatic C–H str), 1271(–C–C str.), 1644 (C ¼ O), 1554 (C ¼C str), 828 (C–H out plane bending 1 H NMR (ppm) : 6.82-6.91 (2d, 2H, – CH ¼ CH–), 7.42–8.08 (m, 9H, Ar–H), 10.41 (s, 1H, Ar–OH) Mass (m/z) : Calculated M.W 224.25, Observed M.W 225.2
Suppl. Fig. S1
Fig. 1
Suppl. Fig. S2
3.1.2. Spectral details of 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl) phenol (10) : 110–112 °C UV–visible (λmax:nm) : 204 (π → π * transition), 314 (n → π * transition) Suppl. FTIR (cm 1) : 3378(O–H), 2090(Aromatic C–H str), 1649(C ¼N), 1333(– Fig. S3 C ¼ C–str.), 1108(C–N str. ), 824(N–H bending vib.) 1 Fig. 2 H NMR (ppm) : 2.48–3.429 (2H, m, –CH2 protons–), 4.7–4.77 (q, 1HC– H Protons adjacent to N–H), 6.62–6.626 (d, 1H, N–H), 6.72 to 7.63 (m, 9H, Ar–H), 9.35(s, 1H, Ar–OH)` Mass (m/z) : Calculated M.W 238.11, Observed M.W 239.0 Melting point
2.3. Synthesis 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl)phenol (10) 2.3.1. Method-A (conventional method) A mixture of compound (5) (0.01 mol) in ethanol (20 mL) was refluxed with hydrazine hydrate (0.01 mol) in the presence of piperidine (2–3 drops) as catalyst for an hour. The completion of reaction was monitored by TLC. The reaction mixture was quenched by poured into ice-cold water. The product was separated out
3.1.3. Spectral details of 1-(4-chlorophenyl)-3-(4-hydroxyphenyl) prop-2-en-1-one (8) Melting point : 90–92°C UV–visible (λmax:nm) : 230 (π → π * transition), 345 (n → π * transition)
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
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FTIR (cm 1)
1
H NMR (ppm)
Mass (m/z)
: 3222 (O–H), 3029 (Aromatic C–H str), 2899 (C–H), 1677 (C ¼O), 1580 (C ¼ C str), 1089 (C–Cl chloro aromatic), 815 (C–H out plane bending) : 6.8–6.9 (2d, 2H, –CH ¼CH–), 7.41–8.08 (m, 8H, Ar–H), 10.44 (s, 1H, Ar–OH) : Calculated M.W 258.0448.402, Observed M. W 259.6
Suppl. Fig. S4
Suppl. Fig. S5 Suppl. Fig. S6
3.1.4. Spectral details of 4-(3-(4-chlorophenyl)-4,5-dihydro-1 Hpyrazol-5-yl)phenol (11) Melting point : 110–111 °C UV–visible (λmax:nm) : 229 (π → π * transition), 268 (n → π * transition) FTIR (cm 1) : 3284 (O–H), 2938 (Aromatic C–H str), 1652 (C ¼N), 1091 (C–Cl chloro aromatic), 824 (N–H bending vib.) 1 H NMR (ppm) : 2.48–3.42 (2 H, m, –CH2 protons–), 4.7–4.77 (q, 1H C– H Protons adjacent to N–H), 6.62 to 6.626 (d, 1 H, N–H), 6.72–7.63 (m, 8 H, Ar–H), 9.35 (s, 1 H, Ar–OH) Mass (m/z) : Calculated M.W 272.07, Observed M.W 273.2
3
3.1.5. Spectral details of 3-(4-hydroxyphenyl)-1-(4-nitrophenyl) prop-2-en-1-one (9) Melting point : 63.5–65.0 °C UV–visible (λmax:nm) : 227 (π → π * transition), 269 (n → π * transition) FTIR (cm 1) : 3441 (O–H), 2938 (Aromatic Suppl. Fig. S9 C–H str), 2605 (C–H), 1652 (C ¼O), 1505 (NO2 str), 1342 (C–N str.), 824 (C–H out plane bending) 1 H NMR (ppm) : 6.8-6.9 (2d, 2H, –CH ¼CH–), Fig. 3 7.41–8.08 (m, 8H, Ar–H), 10.44 (s, 1H, Ar–OH) Mass (m/z) : Calculated M.W 269.09, Observed M.W 270.10
3.1.6. Spectral details of 4-(4,5-dihydro-3-(4-nitrophenyl)-1H-pyrazol-5-yl)phenol (12) Suppl. Fig. S7
Fig. 4
Suppl. Fig. S8
Melting point : 56–57 °C UV–visible (λmax:nm) : 239 (π → π * transition), 312 (n → π * transition) FTIR (cm 1) : 3421 (O–H), 2938 (Aromatic C–H str), 1602 (C ¼N), 1512 (C–NO2 str.), 835 (N–H bending vib.) 1 H NMR (ppm) : 2.48–3.01 (2H, (m, –CH2 protons–), 4.83–4.89 (q, 1HC–H Protons adjacent to N–H), 6.8 to 6.9 (d, 1H, N–H), 7.72 to 7.87 (m, 8H, Ar–H), 11.10(s, 1H, Ar–OH) Mass (m/z) Calculated M.283.1, Observed M.W 284.3
Fig. 1. 1HNMR spectrum of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one.
Suppl. Fig. S10 Suppl. Fig. S11
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Fig. 2. 1HNMR spectrum of 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl)phenol.
Fig. 3. 1HNMR spectrum of 3-(4-hydroxyphenyl)-1-(4-nitrophenyl)prop-2-en-1-one.
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
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Fig. 4. 1HNMR spectrum of 4-(3-(4-chlorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenol.
3.2. Discussion Fig. 1 revealed the 1HNMR of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one respectively using compound 1 and 4 with compound 5 in the presence of sodium hydroxide has been shown in the scheme. Fig. 2 revealed the 1HNMR spectra of 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl)phenol respectively using compound 7 with compound 6 in the presence of piperidine as catalyst has also been presented in the scheme. UV absorption and FTIR spectra of compound 7 has been provided a preliminary idea in confirmation the formation of product. According to the UV spectrum, presence of peaks at 226 and 314 nm clearly showed that the compound (7) has –CH ¼ CH– group and hetero atom respectively. According to the FTIR, presence of peak at 1580 cm 1 has clearly noticed the utilization of starting materials transforms into the product. Further, the corresponding peaks at 3203, 3184, 1271, 1644 and 1554 cm 1 have been related to –OH, C–H aromatic, C–C, C ¼O stretching and aliphatic C ¼C stretching respectively in the compound 7. The concerned mass of the compound 7 is in good agreement with the observed (224.25 m/z) and calculated value (225.2 m/z). Similarly, proton NMR strongly empowered for the formation of the product by its δ value at 10.41, 7.42–8.8, and 6.82–6.91 ppm corresponding to the O–H, Ar–H and –CH ¼CH– protons of compound 7 were mentioned in Fig. 1. UV absorption and FTIR spectra of compound 10 has provided a preliminary idea in confirmation the formation of product. According to the UV spectrum of compound 10, presence of peaks at 204 and 314 nm has been related to aromatic double bond and hetero atom respectively. According to the FTIR spectrum, absence of peak at 1644 cm 1 clearly observed the complete utilization of starting materials transformed into the product. Further, the corresponding peaks at 3378, 2090, 1649, 1331 and 824 cm 1 for – OH, C–H aromatic stretching, C ¼N, C ¼C stretching and N–H bending vibrations respectively in the compound 10. All such stretching and bending peaks have also been supported for the
formation of the product. The concern mass of compound 10 are in good agreement with the observed (238.11 m/z) and calculated value (239 m/z). Similarly, proton NMR strongly empowered for the formation of the product by its δ value at 9.35, 6.75–7.63, 6.62– 6.65, 4.72–4.77 and 2.48–2.82 ppm corresponding to the O–H, Ar– H, N–H, C–H and CH2 protons of compound 10 were mentioned in Fig. 2. Similarly, the rest of the compound structures have also been determined using spectroscopic techniques.
4. Antimicrobial activity The Minimum Inhibitory Concentration (MIC), which is considered as the least concentration of the sample which inhibits the visible growth of a microbe was determined by the broth dilution method. All the synthesized compounds were evaluated for their antimicrobial activity using broth dilution method to find the MIC value were tested against one gram positive and one gram negative bacterial strains namely S. aureus and E. coli, respectively. The MIC values of synthesized compounds were given in Table 1. According to Table 1, the chloro-substituted compounds both chalcones and pyrazoles found to have excellent antibacterial activities than that of corresponding unsubstituted and nitro substituted Table 1 : Minimum Inhibiting Concentration (MIC) (μg/ml) of the synthesized compounds Substituent (R) Compound Staphylococcus aureus (S. a)
Escherichia coli (E. c)
H Cl NO2 H Cl NO2
31.25 62.50 15.63 31.25 125.00 31.25
7 10 8 11 9 12
31.25 62.50 7.81 15.63 62.50 15.63
Chalcones
Pyrazoles
(Compound, 7,8,9 – Chalcones, and 10,11, 12 – Pyrazole compounds).
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
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compounds of present investigation. This is might be due to the presence of electron donating (Chloro) and electron withdrawing (nitro) action of the substituent present in the compound. Further, the unsubstituted chalcones has nice antibacterial activity than corresponding unsubstituted pyrazole compound. However, the reciprocal relationship was noticed for nitro-substituted pyrazole than nitro-substituted chalcones. In overall observation, the antibacterial activities have been listed as order decreasing activity: For Gram positive bacteria: (S. aureus) Chloro-substituted chalcone4Chloro-substituted pyrazole¼Nitrosubstituted pyrazole4Unsubstituted chalcone4Nitro-substituted chalcones¼Unsubstituted pyrazole For Gram negative bacteria: (E. coli) Chloro-substituted chalcone4Chloro-substituted pyrazole¼Nitrosubstituted pyrazole4Unsubstituted chalcone4Unsubstituted pyrazole4Nitro-substituted chalcones
5. Conclusions
In the present work diphenyl substituted pyrazole derivatives were synthesized via Claisen–Schmidt condensation using PEG600 as solvent for both conventional and microwave irradiation methods. Since, the PEG-600 is non-toxic, eco-friendly, inexpensive, water soluble and potentially recyclable which may be recommended for safer greener reactions. Use of piperidine as catalyst in the synthesis the pyrazole found to have shorter reaction time than that of non-catalyzed reaction which has been progressed more than eight hours. Synthesizing of chalcones and pyrazole compounds via microwave assisted method of reaction; it is clean with shorter reaction time, mild reaction condition, eco-friendly, excellent yield as compared to conventional methods and reduces the use of volatile organic compounds (VOCs) and finally, it is agreement with the green chemistry protocols. The chemical structures of compounds 7, 8, 9, 10, 11 and 12 have been confirmed using standard spectral techniques viz., FTIR, UV–visible, Mass and 1H-NMR spectra and were found to be in agreement with the chemical structures as expected. The microbial activities substituted chalcones and diphenyl substituted pyrazole derivatives were checked against the two microbes S. aureus and E. coli. The report of antimicrobial activity clearly showed that, the synthesized compounds of 8 and 11 has excellent activities towards the tested bacterial strains of both gram positive and gram negative. This is due to the compounds 8
and 11 has electron donation group of chlorine, whereas the compounds 9, 12 and 7, 10 has electron withdrawing group of nitro and without substitution of any groups respectively.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2015.05. 002.
References Abdel-Aziz, M., Abuo-Rahma, G.E.D.A., Hassan, A.A., 2009. Synthesis of novel pyrazole derivatives and Evaluation of their antidepressant and anticonvulsant activities. Eur. J. Med. Chem. 44, 3480. Abdel-Hafez, E.S.M.N., Abuo-Rahma, G.E.D.A.A., Abdel-Aziz, M., Radwan, M.F., Farag, H.H., 2009. Design, Synthesis and biological investigation of certain pyrazole-3carboxylic acid derivatives as novel carriers ofnitiric oxide. Bioorg. Med. Chem. 17, 3829. Ali, T.E., 2009. Synthesis of some new pyrazolfuropyrimidinethiones and trizolofuropyrimidinethiones. Eur. J. Med. Chem. 44, 4385. Bekhit, A.A., Habib, N.S., El-Din, A., Bekhit, A., 2001. Synthesis, characterization and antibacteiral activity of (E)-chalcone derivatives. Boll. Chim. Farm. 140, 297–301. Hsieh, H.K., Lee, T.H., Wang, J.P., Wang, J.J., Lin, C.N., 1998. Redox Behavior of anticancer chalcone on a glassy carbon electrode and Evaluation of its Interaction parameters with DNA. Pharm. Res. 15, 39–46. Lahm, G.P., Stevenson, T.M., Selby, T.P., et al., 2007. A new insecticidal anthranilic diamide that acts as a potent and selective ryanodine receptor activator. Bioorg. Med. Chem. Lett. 17, 6274. Liu, M., Wilairat, P., Go, M.L., 2001. Antimalarial alkoxylated and hydroxylated chalcone: structure–activity relationship analysis. J. Med. Chem. 44:, 4443–4452.. Murakami, S., Muramatsu, M., Aihara, H., Otomo, S., 1991. Synthesis, characterization and antibacterial activity of (E) -chalcone derivatives. Biochem. Pharmacol. 42, 1447–1451. Oliver, K.C., Dallinger, D., 2006. The impact of microwave synthesis on drug discovery. Nat. Rev. Drug Discov. 5, 51–63. Shibata, S., 1994. Anti-tumorigenic chalcones. Stem Cells 12, 44–52. Viana, G.S., Bandeira, M.A., Matos, F.J., 2003. Analgesic and anti-inflammatory effects of chalcones isolated from Myracrodruon urundeuva allemao. Phytomedicine 10, 189–195. Witschel, M., 2009. Synthesis and antimicrobial activities of some novel bis-pyrazole derivatives containing a hydrophosphoryl unit. Bioorg. Med. Chem. 17, 4221. Wu, J.H., Wang, X.H., Yi, Y.H., Lee, K.H., 2003. Anti-AIDS agents 54-A potent anti-HIV chalcone and flavonoids genus Desmos. Bioorg. Med. Chem. Lett. 13, 1813–1815. Youssef, A.M., Sydney White, M., Villanueva, E.B., El-Ashmawy, I.M., Klegeris, A., 2010. Synthesis and biological evaluation of novel pyrazolyl-2- Bioorg. Med. Chem 18, 2019.
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
Contents lists available at ScienceDirect
Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv
Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach M. Ganapathi a, D. Jayaseelan b, S. Guhanathan b,n a b
PG & Research Department of Chemistry, Government Arts College, Tiruvannamalai, Tamil nadu, India PG & Research Department of Chemistry, Muthurangam Government Arts College (Autonomous), Vellore, Tamil nadu, India
art ic l e i nf o
a b s t r a c t
Article history: Received 2 November 2014 Received in revised form 1 May 2015 Accepted 5 May 2015
A conventional and microwave assisted efficient synthesis of diphenyl substituted pyrazole using PEG 600 as green solvent has been described. A relatively shorter reaction time with excellent yield of the piperidine mediated protocol has been attracted economically attractive and eco-friendly. All newly synthesized compounds were characterized by standard spectroscopic techniques viz., UV–visible, FT-IR, 1 H-NMR and Mass spectra. The anti-microbial activities of compounds have also been tested using Minimum Inhibitory Concentration (MIC) method with two different microorganisms Staphylococcus aureus (MTCC3381) and Escherichia coli (MTCC739). The results of the antimicrobial activity revealed that the diphenyl substituted pyrazole derivatives have nice inhibiting nature against both types of bacteria of present investigation than corresponding chalcones. Since, the work has been focused on green chemical approach towards the synthesis, this protocol may be recommended for eco-friendly applications. & 2015 Elsevier Inc. All rights reserved.
Keywords: Chalcones Pyrazole Piperidine Antimicrobial activity PEG-600 Microwave irradiation (MWI)
1. Introduction Chalcones comprise a class of compounds with important therapeutic potential. The ease of preparation, the potential of oral administration, and safety protocol enable chalcone-based compounds as therapeutic agents. Chalcones (α, β-unsaturated ketones) possess a wide range of pharmacological activities such as anti-inflammatory (Hsieh et al., 1998), anticancer (Shibata, 1994), analgesic (Viana et al., 2003), antiulcerative (Murakami et al., 1991), antiviral (Wu et al., 2003), antimalarial (Liu et al., 2001) and antibacterial (Bekhit et al., 2001). The presence of a reactive α, βunsaturated keto group in chalcones is found to be responsible for their pharmacological activities. Pyrazole derivatives have been reported to possess diverse biological activities such as antibacterial (Abdel-Hafez et al., 2009) antifungal (Ali, 2009) herbicidal (Witschel, 2009), insecticidal (Lahm et al., 2007) anti-inflammatory (Youssef et al., 2010), anticonvulsant (Abdel-Aziz et al., 2009) anti-oxidant (Oliver and Dallinger, 2006) and so on. Considerable interest has been focused on the pyrazole structure which has been known to possess a broad spectrum of biological activities. Designing of safer chemicals which prevents the environmental n
pollution found to be a greater environmental impact in minimizing the use and disposal of organic solvents into the environment. In view of this, polyethylene glycol (PEG) has found to be an interesting solvent system. PEG is an environmentally benign reaction solvent, it is inexpensive, potentially recyclable and water soluble, which facilitates its removal from there action product. Microwave-assisted synthesis is an eco-friendly and efficient method of synthesis of organic compounds as compared to the conventional method of synthesis. In this method, reaction occurs more rapidly, safely and with higher chemical yields due to which this method becomes superior to the conventional method. The conventional method, requiring a longer reaction time and larger quantities of solvents and reagents, causes environmental pollution and contributes to the health hazards (Oliver and Dallinger, 2006). Based on the careful analysis of the literature, present investigation was aimed to focus on the PEG-600 solvent system. The series of chalcones and diphenyl substituted pyrazoles compounds were synthesized by both conventional and microwave irradiation methods. The synthesized compounds were characterized on the basis of UV–visible, FTIR, 1HNMR and mass spectral data. Further, the present investigation have also been recommended for the antibacterial activities of the synthesized
Corresponding author. E-mail address: [email protected] (S. Guhanathan).
http://dx.doi.org/10.1016/j.ecoenv.2015.05.002 0147-6513/& 2015 Elsevier Inc. All rights reserved.
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
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2
compound with some selected gram positive and gram negative bacteria viz., Staphylococcus aureus, and Escherichia coli respectively.
2. Experimental 2.1. Methods and materials The chemicals acetophenone (1), 4-chloroacetophenone (2), 4nitroacetophenone (3), 4-hydroxybenzaledehyde (4), PEG-600 (5), hydrazine hydrate (6), sodium hydroxide and piperidine were obtained from Avra chemicals, Hyderabad and were used as such without further purification. Silica gel (TLC and Column grade) were purchased from Merck. The solvents were purified as per the standard procedure reported elsewhere. FTIR spectra (KBr pellets) were measured using Alpha Bruker FTIR instrument scanning with the entire region of 4000–400 cm 1 with typical resolution of 1.0 cm 1. UV–visible spectra were also recorder using Alpha Bruker UV spectrophotometer. The NMR spectra of the compounds have been recorded on Bruker AV400 spectrometer operating at 400 MHz for recording 1H spectra in DMSO solvent using TMS as internal standard. Mass spectra have been recorded on SHIMADZU spectrometer using chemical ionization technique. Melting points of all synthesised compounds have been determined in open glass capillaries on Mettler FP51 melting point apparatus and are uncorrected. Microwave reactions are carried out commercially available IFB domestic microwave oven having a maximum power output of 110 W operating at 450 Hz. 2.2. Synthesis of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one (7) 2.2.1. Method-A (conventional method) A mixture of acetophenone (0.01 mol) and 4-hydroxy benzaldehyde (0.01 mol) and NaOH (0.02 mol) were stirred in PEG-600 (20 mL) as solvent at 65 °C for 1 h. The completion of the reaction was monitored by TLC and the crude mixture was worked up in ice-cold water (100 mL). The product was separated out and filtered. The filtrate was evaporated to dryness to remove water leaving behind PEG-600. The recovered PEG-600 has been utilized for the synthesis of chalcones. Synthesised compounds were recrystallised from ethanol to afford pure compound (5). (Yield – 80% and melting point: 100–102 °C). 2.2.2. Method-B (microwave irradiation method) A mixture compounds 1 (0.01 mol) and 4 (0.01 mol) and NaOH (0.02 mol) were grinded in to the mortar. Then it was mixed with 20 mL of PEG-600. The mixed compounds were taken in a 100 mL beaker and it was irradiated in a microwave oven for the 3–5 min at 110 W operating at 2450 Hz at 30 s of intervals. After completion of reaction as followed by T.L.C examination, chilled water was added to the reaction mixture and neutralized by an acid. The solid product was obtained, which was filtered, dried and crystallized from an ethanol. The filtrate was evaporated to dryness to remove water leaving behind PEG-600. (Yield – 98% and melting point: 101–102 °C).
and filtered. A synthesised compound (6) was recrystallised from ethanol. (Yield – 75% and melting point: 110–111 °C) 2.3.2. Method-B (microwave irradiation method) A mixture of compounds (5) (0.01 mol), (6) (0.01 mol) and 2–3 drops piperidine catalyst were mixed thoroughly in mortar. Then it was dissolved into minimum amount of PEG-600. The mixed compounds were taken in a 100 mL beaker and it was irradiated in a microwave oven for the 4–5 min at 110 W operating at 2450 Hz at 30 s of intervals. The completion of the reaction was monitored by TLC and the crude mixture was worked up in ice-cold water. The filtrate was evaporated to dryness to remove water leaving behind PEG-600. Yield: 90% and 110–112 °C. The rest of the compounds of 8, 9 and 11, 12 were synthesised by the above mentioned same procedures.
3. Results and discussion 3.1. Results 3.1.1. Spectral details of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1one (7) Melting point : 101–102 °C UV–visible (λmax:nm) : 226 (π → π * transition), 314 (n → π * transition) FTIR (cm 1) : 3203 (O–H), 3184 (Aromatic C–H str), 1271(–C–C str.), 1644 (C ¼ O), 1554 (C ¼C str), 828 (C–H out plane bending 1 H NMR (ppm) : 6.82-6.91 (2d, 2H, – CH ¼ CH–), 7.42–8.08 (m, 9H, Ar–H), 10.41 (s, 1H, Ar–OH) Mass (m/z) : Calculated M.W 224.25, Observed M.W 225.2
Suppl. Fig. S1
Fig. 1
Suppl. Fig. S2
3.1.2. Spectral details of 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl) phenol (10) : 110–112 °C UV–visible (λmax:nm) : 204 (π → π * transition), 314 (n → π * transition) Suppl. FTIR (cm 1) : 3378(O–H), 2090(Aromatic C–H str), 1649(C ¼N), 1333(– Fig. S3 C ¼ C–str.), 1108(C–N str. ), 824(N–H bending vib.) 1 Fig. 2 H NMR (ppm) : 2.48–3.429 (2H, m, –CH2 protons–), 4.7–4.77 (q, 1HC– H Protons adjacent to N–H), 6.62–6.626 (d, 1H, N–H), 6.72 to 7.63 (m, 9H, Ar–H), 9.35(s, 1H, Ar–OH)` Mass (m/z) : Calculated M.W 238.11, Observed M.W 239.0 Melting point
2.3. Synthesis 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl)phenol (10) 2.3.1. Method-A (conventional method) A mixture of compound (5) (0.01 mol) in ethanol (20 mL) was refluxed with hydrazine hydrate (0.01 mol) in the presence of piperidine (2–3 drops) as catalyst for an hour. The completion of reaction was monitored by TLC. The reaction mixture was quenched by poured into ice-cold water. The product was separated out
3.1.3. Spectral details of 1-(4-chlorophenyl)-3-(4-hydroxyphenyl) prop-2-en-1-one (8) Melting point : 90–92°C UV–visible (λmax:nm) : 230 (π → π * transition), 345 (n → π * transition)
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
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FTIR (cm 1)
1
H NMR (ppm)
Mass (m/z)
: 3222 (O–H), 3029 (Aromatic C–H str), 2899 (C–H), 1677 (C ¼O), 1580 (C ¼ C str), 1089 (C–Cl chloro aromatic), 815 (C–H out plane bending) : 6.8–6.9 (2d, 2H, –CH ¼CH–), 7.41–8.08 (m, 8H, Ar–H), 10.44 (s, 1H, Ar–OH) : Calculated M.W 258.0448.402, Observed M. W 259.6
Suppl. Fig. S4
Suppl. Fig. S5 Suppl. Fig. S6
3.1.4. Spectral details of 4-(3-(4-chlorophenyl)-4,5-dihydro-1 Hpyrazol-5-yl)phenol (11) Melting point : 110–111 °C UV–visible (λmax:nm) : 229 (π → π * transition), 268 (n → π * transition) FTIR (cm 1) : 3284 (O–H), 2938 (Aromatic C–H str), 1652 (C ¼N), 1091 (C–Cl chloro aromatic), 824 (N–H bending vib.) 1 H NMR (ppm) : 2.48–3.42 (2 H, m, –CH2 protons–), 4.7–4.77 (q, 1H C– H Protons adjacent to N–H), 6.62 to 6.626 (d, 1 H, N–H), 6.72–7.63 (m, 8 H, Ar–H), 9.35 (s, 1 H, Ar–OH) Mass (m/z) : Calculated M.W 272.07, Observed M.W 273.2
3
3.1.5. Spectral details of 3-(4-hydroxyphenyl)-1-(4-nitrophenyl) prop-2-en-1-one (9) Melting point : 63.5–65.0 °C UV–visible (λmax:nm) : 227 (π → π * transition), 269 (n → π * transition) FTIR (cm 1) : 3441 (O–H), 2938 (Aromatic Suppl. Fig. S9 C–H str), 2605 (C–H), 1652 (C ¼O), 1505 (NO2 str), 1342 (C–N str.), 824 (C–H out plane bending) 1 H NMR (ppm) : 6.8-6.9 (2d, 2H, –CH ¼CH–), Fig. 3 7.41–8.08 (m, 8H, Ar–H), 10.44 (s, 1H, Ar–OH) Mass (m/z) : Calculated M.W 269.09, Observed M.W 270.10
3.1.6. Spectral details of 4-(4,5-dihydro-3-(4-nitrophenyl)-1H-pyrazol-5-yl)phenol (12) Suppl. Fig. S7
Fig. 4
Suppl. Fig. S8
Melting point : 56–57 °C UV–visible (λmax:nm) : 239 (π → π * transition), 312 (n → π * transition) FTIR (cm 1) : 3421 (O–H), 2938 (Aromatic C–H str), 1602 (C ¼N), 1512 (C–NO2 str.), 835 (N–H bending vib.) 1 H NMR (ppm) : 2.48–3.01 (2H, (m, –CH2 protons–), 4.83–4.89 (q, 1HC–H Protons adjacent to N–H), 6.8 to 6.9 (d, 1H, N–H), 7.72 to 7.87 (m, 8H, Ar–H), 11.10(s, 1H, Ar–OH) Mass (m/z) Calculated M.283.1, Observed M.W 284.3
Fig. 1. 1HNMR spectrum of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one.
Suppl. Fig. S10 Suppl. Fig. S11
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Fig. 2. 1HNMR spectrum of 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl)phenol.
Fig. 3. 1HNMR spectrum of 3-(4-hydroxyphenyl)-1-(4-nitrophenyl)prop-2-en-1-one.
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Fig. 4. 1HNMR spectrum of 4-(3-(4-chlorophenyl)-4,5-dihydro-1H-pyrazol-5-yl)phenol.
3.2. Discussion Fig. 1 revealed the 1HNMR of 3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one respectively using compound 1 and 4 with compound 5 in the presence of sodium hydroxide has been shown in the scheme. Fig. 2 revealed the 1HNMR spectra of 4-(4,5-dihydro-3-phenyl-1H-pyrazol-5-yl)phenol respectively using compound 7 with compound 6 in the presence of piperidine as catalyst has also been presented in the scheme. UV absorption and FTIR spectra of compound 7 has been provided a preliminary idea in confirmation the formation of product. According to the UV spectrum, presence of peaks at 226 and 314 nm clearly showed that the compound (7) has –CH ¼ CH– group and hetero atom respectively. According to the FTIR, presence of peak at 1580 cm 1 has clearly noticed the utilization of starting materials transforms into the product. Further, the corresponding peaks at 3203, 3184, 1271, 1644 and 1554 cm 1 have been related to –OH, C–H aromatic, C–C, C ¼O stretching and aliphatic C ¼C stretching respectively in the compound 7. The concerned mass of the compound 7 is in good agreement with the observed (224.25 m/z) and calculated value (225.2 m/z). Similarly, proton NMR strongly empowered for the formation of the product by its δ value at 10.41, 7.42–8.8, and 6.82–6.91 ppm corresponding to the O–H, Ar–H and –CH ¼CH– protons of compound 7 were mentioned in Fig. 1. UV absorption and FTIR spectra of compound 10 has provided a preliminary idea in confirmation the formation of product. According to the UV spectrum of compound 10, presence of peaks at 204 and 314 nm has been related to aromatic double bond and hetero atom respectively. According to the FTIR spectrum, absence of peak at 1644 cm 1 clearly observed the complete utilization of starting materials transformed into the product. Further, the corresponding peaks at 3378, 2090, 1649, 1331 and 824 cm 1 for – OH, C–H aromatic stretching, C ¼N, C ¼C stretching and N–H bending vibrations respectively in the compound 10. All such stretching and bending peaks have also been supported for the
formation of the product. The concern mass of compound 10 are in good agreement with the observed (238.11 m/z) and calculated value (239 m/z). Similarly, proton NMR strongly empowered for the formation of the product by its δ value at 9.35, 6.75–7.63, 6.62– 6.65, 4.72–4.77 and 2.48–2.82 ppm corresponding to the O–H, Ar– H, N–H, C–H and CH2 protons of compound 10 were mentioned in Fig. 2. Similarly, the rest of the compound structures have also been determined using spectroscopic techniques.
4. Antimicrobial activity The Minimum Inhibitory Concentration (MIC), which is considered as the least concentration of the sample which inhibits the visible growth of a microbe was determined by the broth dilution method. All the synthesized compounds were evaluated for their antimicrobial activity using broth dilution method to find the MIC value were tested against one gram positive and one gram negative bacterial strains namely S. aureus and E. coli, respectively. The MIC values of synthesized compounds were given in Table 1. According to Table 1, the chloro-substituted compounds both chalcones and pyrazoles found to have excellent antibacterial activities than that of corresponding unsubstituted and nitro substituted Table 1 : Minimum Inhibiting Concentration (MIC) (μg/ml) of the synthesized compounds Substituent (R) Compound Staphylococcus aureus (S. a)
Escherichia coli (E. c)
H Cl NO2 H Cl NO2
31.25 62.50 15.63 31.25 125.00 31.25
7 10 8 11 9 12
31.25 62.50 7.81 15.63 62.50 15.63
Chalcones
Pyrazoles
(Compound, 7,8,9 – Chalcones, and 10,11, 12 – Pyrazole compounds).
Please cite this article as: Ganapathi, M., et al., Microwave assisted efficient synthesis of diphenyl substituted pyrazoles using PEG-600 as solvent – A green approach. Ecotoxicol. Environ. Saf. (2015), http://dx.doi.org/10.1016/j.ecoenv.2015.05.002i
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compounds of present investigation. This is might be due to the presence of electron donating (Chloro) and electron withdrawing (nitro) action of the substituent present in the compound. Further, the unsubstituted chalcones has nice antibacterial activity than corresponding unsubstituted pyrazole compound. However, the reciprocal relationship was noticed for nitro-substituted pyrazole than nitro-substituted chalcones. In overall observation, the antibacterial activities have been listed as order decreasing activity: For Gram positive bacteria: (S. aureus) Chloro-substituted chalcone4Chloro-substituted pyrazole¼Nitrosubstituted pyrazole4Unsubstituted chalcone4Nitro-substituted chalcones¼Unsubstituted pyrazole For Gram negative bacteria: (E. coli) Chloro-substituted chalcone4Chloro-substituted pyrazole¼Nitrosubstituted pyrazole4Unsubstituted chalcone4Unsubstituted pyrazole4Nitro-substituted chalcones
5. Conclusions
In the present work diphenyl substituted pyrazole derivatives were synthesized via Claisen–Schmidt condensation using PEG600 as solvent for both conventional and microwave irradiation methods. Since, the PEG-600 is non-toxic, eco-friendly, inexpensive, water soluble and potentially recyclable which may be recommended for safer greener reactions. Use of piperidine as catalyst in the synthesis the pyrazole found to have shorter reaction time than that of non-catalyzed reaction which has been progressed more than eight hours. Synthesizing of chalcones and pyrazole compounds via microwave assisted method of reaction; it is clean with shorter reaction time, mild reaction condition, eco-friendly, excellent yield as compared to conventional methods and reduces the use of volatile organic compounds (VOCs) and finally, it is agreement with the green chemistry protocols. The chemical structures of compounds 7, 8, 9, 10, 11 and 12 have been confirmed using standard spectral techniques viz., FTIR, UV–visible, Mass and 1H-NMR spectra and were found to be in agreement with the chemical structures as expected. The microbial activities substituted chalcones and diphenyl substituted pyrazole derivatives were checked against the two microbes S. aureus and E. coli. The report of antimicrobial activity clearly showed that, the synthesized compounds of 8 and 11 has excellent activities towards the tested bacterial strains of both gram positive and gram negative. This is due to the compounds 8
and 11 has electron donation group of chlorine, whereas the compounds 9, 12 and 7, 10 has electron withdrawing group of nitro and without substitution of any groups respectively.
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.ecoenv.2015.05. 002.
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