Home Physical Sciences A highly efficient eco-friendly AFO reaction using grinding technique: synthesis of 3-hydroxy-2-phenyl-4H-chromen-4-ones
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A highly efficient eco-friendly AFO reaction using grinding technique: synthesis of 3-hydroxy-2-phenyl-4H-chromen-4-ones

  • Ashish Kumar

    Dr. Ashish Kumar received his PhD degree in Organic Chemistry in 2013 from Maharshi Dayanand University, Rohtak, India. He has worked on synthesis of organic compounds using eco-friendly methods. His research interests are synthetic organic chemistry, green chemistry, grinding technique, microwave synthesis, and aqueous chemistry.

     EMAIL logo     , Surender Kumar

    Dr. Surender Kumar received his PhD degree in Organic Chemistry in 2005 and is currently working as Associate Professor in the Department of Chemistry, Technological Institute of Textile and Sciences, Bhiwani-127021, India. His research interests are the development of green methods of organic synthesis and phase transfer catalysis.

         and Jagdish K. Makrandi

    Prof. J.K. Makrandi received his PhD degree in 1978 from Delhi University, India and he did his post doctoral work in Germany. He is working as a Professor at Maharshi Dayanand University, Rohtak-124001, India. His research interests are development of eco-friendly methods for the synthesis of organic compounds, grinding technique, phase transfer catalysis, microwave synthesis, and aqueous chemistry.
Published/Copyright: July 31, 2013
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Green Processing and Synthesis
From the journal Green Processing and Synthesis Volume 2 Issue 4

Abstract

2′-Hydroxychalcones, on reaction with urea-hydrogen peroxide complex (UHP) and potassium hydroxide moist with ethanol, under grinding conditions, provided 3-hydroxy-2-phenyl-4H-chromen-4-ones (3-hydroxyflavones or flavonols) in excellent yields. Epoxidation followed by oxidative cyclization takes place simultaneously in a single pot reaction.

Keywords: 2′-hydroxychalcones; alkaline medium; eco-friendly; grinding technique; urea-hydrogen peroxide complex (UHP)

1 Introduction

Flavonoids are the polyphenolic compounds widely distributed in plants. In recent years, 3-hydroxyflavones (flavonols) and their derivatives have received considerable attention of chemists, due to their presumed role in the prevention of various degenerative diseases, such as cancer and cardiovascular diseases [1, 2]. Quercetin (3,3′,4′,5,7-pentahydroxyflavone) and related compounds are known to inhibit the growth of tumor cells and potentiate the cytotoxicity of DNA damaging anticancer drugs, such as cisplatin[1]; they have also been found to exhibit various pharmacological properties, such as antimicrobial, ATP synthesis inhibitory, antiplatelet, gastroprotective, antitumor, antiallergic, antidiabetic, cytotoxic, therapeutic, hepatoprotective, and antiemetic activities [3–14].

Due to their pharmacological importance, much emphasis has been laid on synthesis of these compounds, which have been obtained by following the Allan-Robinson method [15]; this involves heating 2-hydroxy-ω-methoxyacetophenones with aromatic acid anhydrides in the presence of the potassium salt of the acids. 3-Hydroxyflavones are obtained by demethylation of the 3-methoxy group. A more convenient route is the Algar-Flynn-Oyamada (AFO) reaction [16–18],which involves the base catalyzed epoxidation of 2′-hydroxychalcones using hydrogen peroxide, followed by oxidative cyclization, which takes place simultaneously in the same step. The later method has been found to be practically more useful being a single step reaction. This reaction suffers from many disadvantages, as the reaction is carried out with hydrogen peroxide, which is available only in the form of an aqueous solution (10–30%). This makes the 2′-hydroxychalcones completely insoluble and a sufficient amount of pyridine[17], a highly toxic substance, is added to homogenize the reaction mixture and the bulk of the reaction mixture greatly increases, which makes its handling difficult. Also, as the reaction is carried out under heating conditions, formation of 2-arylidene-3-(2H)-benzofuranone (aurone) is accompanied during the reaction, making the purification difficult.

In recent years, there has been much emphasis on developing green methods for the synthesis of organic compounds. A reaction using the grinding technique is one of the modes which provides green synthesis of the compounds. It has been employed successfully to a number of organic transformations, such as aldol condensation [19], cyclopropanation reaction [20], Knoevenagel condensation [21], the Reformatsky reaction [22], asymmetric hydrogenation of enamines [23], conversion of epoxides to thiocyanohydrins [24], oxidative bromination of alkanones [25], synthesis of 2-phenylchromones [26], modified Pechmann condensation [27], synthesis of 1,3,4-oxadiazoles [28], etc. It has been well established that energy produced at the surface of the molecules by friction caused by grinding, provides activation energy for the reaction [29], etc.

Moreover this technique can be employed on industrial scale very easily, by using an electric food mixer with stainless steel rotors, or by using a ball mill [29]. Therefore, it was thought that synthesizing flavonols, a useful class of compounds, using the grinding technique, would be worthwhile.

2 Experimental section

Melting points were determined in open capillary tubes. A mortar and pestle made of porcelain was used to carry out the reactions. Chalcones were prepared using the method available in the literature and the rest of the chemicals (>99%) were purchased from Sigma-Aldrich Chemicals, New Delhi, India. IR, NMR, and mass spectral studies were carried out with a Perkin Elmer-Spectrum RX-IFTIR, 400 MHz Avance II (Bruker) and Waters Micromass Q-Tof Micro, respectively, at SAIF, Central Instrumentation Laboratory, Panjab University, Chandigarh, India.

2.1 General procedure

A mixture of 2′-hydroxychalcone (2 mmol), urea-hydrogen peroxide complex (UHP) (2 mmol) and pulverized potassium hydroxide homogenized with 6–10 drops of ethanol (approximately 0.1–0.2 ml) was ground with a mortar and pestle at room temperature for 5 min and completion of the reaction was checked with TLC, which confirmed the presence of a single product. The reaction mixture was left at room temperature for digestion for 10 min, diluted with ice-cold water, and acidified with concentrated HCl. The solid product thus obtained was filtered, washed with water, and recrystallized from ethanol to give flavonol.

3 Results and discussion

Herein, we wish to report a facile and efficient protocol for the synthesis of 3-hydroxyflavones (Scheme 1) making use of UHP[30] as a source of hydrogen peroxide, which avoids the bulk of the reaction solution and thus the reaction could be carried out avoiding pyridine under grinding conditions.

Scheme 1 Synthesis of flavonols at room temperature using grinding technique.
Scheme 1

Synthesis of flavonols at room temperature using grinding technique.

A mixture of 2′-hydroxychalcone, UHP and potassium hydroxide moist with a few drops of ethanol, on grinding with a mortar and pestle at room temperature, afforded flavonol in excellent yield in one step, after acidification of the reaction mixture in cold concentrated HCl. As the reaction is being carried out at room temperature, it suppresses the formation of aurones as side products, generally formed at elevated temperatures; this is confirmed by using TLC, thus resulting in flavonols in higher yields. An IR spectrum of the product formed showed an absorption at 3209 cm-1 due to O-H stretching and an absorption at 1608 cm-1 due to C=O stretching. An 1H NMR spectrum showed a singlet and a multiplet at δ 7.01 and 7.06–8.25, due to OH and aromatic protons, respectively. Further, the formation of flavonol was confirmed by comparing the melting point with the literature value [31]. The physical data of all the flavonols prepared are presented in Table 1. The present method is simple, as UHP has been used as a source of hydrogen peroxide, which avoids the bulk volume of the reaction and makes handling easy. Moreover, the present method avoids the use of hazardous solvents, making the reaction eco-friendly.

Table 1

Physical data of synthesized compounds.

CompdRR1R2R3R4Time (min, a+b)M.P. (°C)Lit. M.P. (°C)Yield (%)
1HHHHH(5+10)169–70170[31]92
2HOCH3HHH(5+15)176–78178–79 [32]89
3HHHHOCH3(5+15)226–28224–25[33]91
4HOCH3HHOCH3(10+15)186–87190[34]92
5CH3HHHH(5+10)200–02201–02 [35]92
6CH3HHHOCH3(10+20)190–91192–93 [32]90
7HHHHCH3(5+20)192–93192–93 [36]88
8HHOCH3HH(5+15)130–32–90
9HHOCH3HOCH3(10+15)189–91–89
10HHHOCH3OCH3(10+20)202–03200–02 [36]87

(a+b)=(grinding time+digestion time).

4 Spectral details of the flavonols synthesized

3-Hydroxyflavone (flavonol; 1) IR (KBr): 3209 cm-1(O-H), 1608 cm-1 (C=O); 1H NMR (CDCl3): δ 7.01 (s, 1H, OH) 7.06–8.25 (m, 9H, H-5, H-6, H-7, H-8, H-2′, H-3′, H-4′, H-5′, H-6′).

3-Hydroxy-7-methoxyflavone (7-methoxyflavonol; 2) IR (KBr): 3292 cm-1 (O-H), 1618 cm-1 (C=O); 1H NMR (CDCl3): δ 3.93 (s, 3H, OCH3), 6.80 (s, 1H, OH), 6.95–7.10 (m, 2H, H-6, H-8), 7.43–7.55 (m, 3H, H-3′, H-4′, H-5′), 8.12 (d, 1H, J=9.00 Hz, H-5), 8.22 (m, 2H, H-2′, H-6′).

3-Hydroxy-4′-methoxyflavone (4′-methoxyflavonol; 3) IR (KBr): 3184 cm-1 (O-H), 1602 cm-1 (C=O); 1H NMR (CDCl3): δ 3.90 (s, 3H, OCH3), 6.95 (dd, 1H, J=8.74 and 2.46 Hz, H-8), 7.00 (d, 2H, J=9.00 Hz, H-3′, H-5′), 7.09 (s, 1H, OH), 7.39–7.59 (m, 2H, H-6, H-7), 7.70 (dd, 1H, J=9.00 and 3.00 Hz, H-5), 8.24 (d, 2H, J=9.00 Hz, H-2′, H-6′).

3-Hydroxy-7,4′-dimethoxyflavone (7,4′-dimethoxyflavonol; 4) IR (KBr): 3269 cm-1 (O-H), 1608 cm-1 (C=O); 1H NMR (CDCl3): δ 3.89 and 3.93 (each s, 6H, 2×OCH3), 6.70 (dd, 1H, J=8.00 and 3.00 Hz, H-6), 6.93 (d, 1H, J=3.00 Hz, H-8), 7.00 (d, 2H, J=9.00 Hz, H-3′, H-5′), 7.18 (s, 1H, OH), 8.12 (d, 1H, J=8.72 Hz, H-5), 8.19 (d, 2H, J=9.00 Hz, H-2′, H-6′).

3-Hydroxy-6-methylflavone (6-methylflavonol; 5) IR (KBr): 3250 cm-1 (O-H), 1610 cm-1 (C=O); 1H NMR (CDCl3): δ 2.21 (s, 3H, CH3), 6.75 (s, 1H, OH) 6.80–7.23 (m, 5H, H-7, H-8, H-3′, H-4′, H-5′), 7.76 (d, 1H, J=2.46 Hz, H-5), 8.18 (m, 2H, H-2′, H-6′).

3-Hydroxy-4′-methoxy-6-methylflavone (4′-methoxy-6-methylflavonol; 6) IR (KBr): 3269 cm-1 (O-H), 1612 cm-1 (C=O); 1H NMR (CDCl3): δ 2.25 (s, 3H, CH3), 3.92 (s, 3H, OCH3), 6.80 (d, 2H, J=9.00 Hz, H-3′, H-5′), 6.86–6.92 (m, 2H, H-7, H-8), 7.03 (s, 1H, OH), 7.80 (d, 1H, J=2.64 Hz, H-5), 8.21 (d, 2H, J=9.00 Hz, H-2′, H-6′).

3-Hydroxy-4′-methylflavone (4′-methylflavonol; 7) IR (KBr): 3284 cm-1 (O-H), 1608 cm-1 (C=O); 1H NMR (CDCl3): δ 2.45 (s, 3H, CH3), 7.06 (s, 1H, OH), 7.36 (d, 2H, J=8.16 Hz, H-3′, H-5′), 7.39–7.77 (m, 3H, H-6, H-7, H-8), 8.17 (d, 2H, J=8.16 Hz, H-2′, H-6′), 8.27 (dd, 1H, J=8.04 and 1.52 Hz, H-5).

3-Hydroxy-2′-methoxyflavone (2′-methoxyflavonol; 8) IR (KBr): 3262 cm-1 (O-H), 1611 cm-1 (C=O);1H NMR (CDCl3): δ 3.71 (s, 3H, OCH3), 7.03 (dd, 1H, J=8.32 and 2.32 Hz, H-3′) 7.13 (s, 1H, OH), 7.39–7.92 (m, 6H, H-6, H-7, H-8, H-4′, H-5′, H-6′), 8.27 (dd, 1H, J=8.52 and 2.34 Hz, H-5); m/z: 269.06 (M+1).

3-Hydroxy-2′,4′-dimethoxyflavone (2′,4′-dimethoxyflavonol; 9) IR (KBr): 3309 cm-1 (O-H), 1611 cm-1 (C=O); 1H NMR (CDCl3): δ 3.88 and 3.90 ( each s, 6H, 2×OCH3), 6.61 (d, 1H, J=2.24 Hz, H-3′), 6.67 (dd, 1H, J=8.54 and 2.24 Hz, H-5′) 7.38–7.74 (m, 4H, H-6, H-7, H-8, H-6′), 8.29 (dd, 1H, J=7.12 and 2.40 Hz, H-5), 9.01 (s, 1H, OH); m/z: 299.04 (M+1).

3-Hydroxy-3′,4′-dimethoxyflavone (3′,4′-dimethoxyflavonol; 10) IR (KBr): 3268 cm-1 (O-H), 1603 cm-1 (C=O); 1H NMR (CDCl3): δ 3.87 (s, 6H, 2×OCH3), 6.98 (d, 1H, J=8.64 Hz, H-5′), 7.28–7.72 (m, 3H, H-6, H-7, H-6′), 7.79 (d, 1H, J=2.00 Hz, H-2′), 7.87 (dd, 1H, J=8.60 and 2.00 Hz, H-8), 8.09 (dd, 1H, J=8.00 and 1.32 Hz, H-5), 9.01 (s, 1H, OH).

5 Conclusion

The present method for the synthesis of flavonols is eco-friendly, as it avoids the use of hazardous organic solvents at any stage of the reaction. It is also efficient, as the yields of the flavonols are very good and avoids the formation of aurones as side products.

Corresponding author: Ashish Kumar, Department of Chemistry, Maharshi Dayanand University, Rohtak, 124001, India

About the authors

Ashish Kumar

Dr. Ashish Kumar received his PhD degree in Organic Chemistry in 2013 from Maharshi Dayanand University, Rohtak, India. He has worked on synthesis of organic compounds using eco-friendly methods. His research interests are synthetic organic chemistry, green chemistry, grinding technique, microwave synthesis, and aqueous chemistry.

Surender Kumar

Dr. Surender Kumar received his PhD degree in Organic Chemistry in 2005 and is currently working as Associate Professor in the Department of Chemistry, Technological Institute of Textile and Sciences, Bhiwani-127021, India. His research interests are the development of green methods of organic synthesis and phase transfer catalysis.

Jagdish K. Makrandi

Prof. J.K. Makrandi received his PhD degree in 1978 from Delhi University, India and he did his post doctoral work in Germany. He is working as a Professor at Maharshi Dayanand University, Rohtak-124001, India. His research interests are development of eco-friendly methods for the synthesis of organic compounds, grinding technique, phase transfer catalysis, microwave synthesis, and aqueous chemistry.

The authors are grateful to CSIR, India for providing research fellowship to Ashish Kumar.

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Received: 2013-5-26
Accepted: 2013-6-27
Published Online: 2013-07-31
Published in Print: 2013-03-01

©2013 by Walter de Gruyter Berlin Boston

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https://doi.org/10.1515/gps-2013-0042
Keywords for this article
2′-hydroxychalcones; alkaline medium; eco-friendly; grinding technique; urea-hydrogen peroxide complex (UHP)
Creative Commons
BY-NC-ND 3.0

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