An optimized method for synthesis of 2’hydroxy chalcone

 

Nikunj Patadiya1*, Vipul Vaghela2

1Research Scholar, Department of Pharmaceutical Chemistry,

A.R College of Pharmacy and G.H Patel Institute of Pharmacy, Vallabh Vidhyanagar, Anand, Gujarat, India.

2Professor, Department of Pharmaceutical Chemistry,

A.R College of Pharmacy and G.H Patel Institute of Pharmacy, Vallabh Vidhyanagar, Anand, Gujarat, India.

*Corresponding Author E-mail: nikunj20899@gmail.com

 

ABSTRACT:

The main aim of present work is to develop optimised method for synthesis of 2’hydroxy chalcone. 2’hydroxy chalcone was synthesized by Claisen–Schmidt condensation between o-hydroxy acetohenone and benzaldehyde. Variety of bases tried as catalyst for synthesis of 2’hydroxy chalcone. Calcium hydroxide and magnesium hydroxide proved ineffective for synthesis. Lithium hydroxide slightly converts reactant to product. Sodium hydroxide shows best catalytical activity compare to other bases. Isopropyl alcohol proved better solvent then other solvents like methanol, ethanol, acetonitrile, dichloromethane and tetrahydrofuran. In optimization step, effect of solvent and base quantity, stirring time and temperature was examined. Temperature shows drastic effect on product yield and purity. At 0˚C best yield was obtained. Amount of base catalyst also shows significant effect on yield. 20ml of 40% NaOH gives best results for 0.05mol reactants. 50ml IPA was needed for the best results for 0.05mol reactant. In approximate 4h, reaction should be completed. Further stirring was not too much effective.

 

KEYWORDS: 2’ hydroxyl chalcone, Claisen–Schmidt condensation, IPA, NaOH.

 

 


INTRODUCTION:

Chalcones are very versatile compounds in field of medicinal chemistry. Chalcones shows variety of biological activities. Most common and widely used method for synthesis of 2’hydroxy chalcone is Claisen–Schmidt condensation. In Claisen–Schmidt condensation substituted acetophenone are react with substituted benzaldehydes in presence of strong base and alcohol use as solvent.1-12 Microwave assisted methods are also reported for synthesis of 2’hydroxy chalcone.13-17 Chalcone analogs are widely use for synthesis of variety of heterocyclic compounds.17-27

 

Chemistry:

In present work, synthesis of 2’hydroxy chalcone was carried out by Claisen–Schmidt condensation using different solvent and variety of strong bases.

 

In this study, lithium hydroxide, sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide and magnesium hydroxide screened as base catalyst for synthesis. Methanol, ethanol, isopropyl alcohol (IPA), tetrahydrofuran (THF), dichloromethane (DCM) and acetonitrile (ACN) was screened as solvent. Highest yield condition was selected for the optimization. In optimization step effect of solvent and base quantity, stirring time and temperature were screened.

 

RESULTS AND DISCUSSION:

Table 1. Effect of base catalyst and solvent on product (2’hydroxy chalcone) yield.

Sr. No.

Base

Solvent

%yield

1

LiOH

Methanol

1.24%

2

NaOH

Methanol

70.56%

3

KOH

Methanol

68.25%

4

Ba(OH)2

Methanol

5.25%

5

Ca(OH)2

Methanol

No Reaction

6

Mg(OH)2

Methanol

No Reaction

7

LiOH

Ethanol

2.28%

8

NaOH

Ethanol

75.74%

9

KOH

Ethanol

72.95%

10

Ba(OH)2

Ethanol

4.35%

Sr no.

Base

Solvent

%yield

11

Ca(OH)2

Ethanol

No Reaction

12

Mg(OH)2

Ethanol

No Reaction

13

LiOH

IPA

No Reaction

14

NaOH

IPA

80.56%

15

KOH

IPA

76.34%

16

Ba(OH)2

IPA

6.23%

17

Ca(OH)2

IPA

No Reaction

18

Mg(OH)2

IPA

No Reaction

19

LiOH

THF

No Reaction

20

NaOH

THF

1.56%

21

KOH

THF

1.42%

22

Ba(OH)2

THF

No Reaction

23

Ca(OH)2

THF

No Reaction

24

Mg(OH)2

THF

No Reaction

25

LiOH

DCM

No Reaction

26

NaOH

DCM

1.36%

27

KOH

DCM

2.04%

28

Ba(OH)2

DCM

No Reaction

29

Ca(OH)2

DCM

No Reaction

30

Mg(OH)2

DCM

No Reaction

31

LiOH

ACN

No Reaction

32

NaOH

ACN

No Reaction

33

KOH

ACN

No Reaction

34

Ba(OH)2

ACN

No Reaction

35

Ca(OH)2

ACN

No Reaction

36

Mg(OH)2

ACN

No Reaction

Reaction Condition: Temperature 28˚C; Stirring Time: 24hr; Amt. of Solvent: 50ml; Amt. of reactants:0.05mol; Amt. of base: 40% W/V 30ml

 

Table 2. Effect of base and solvent quantity, temperature and stirring time on product (2’hydroxy chalcone) yield.

Sr No.

Amount of 40% NaOH (ml)

Amount of IPA (ml)

Temp. (˚C)

Stirring time (hr)

%

yield

1

15

50

28

24

50.75%

2

20

50

28

24

81.54%

3

25

50

28

24

81.35%

4

30

50

28

24

80.56%

5

35

50

28

24

*

6

40

50

28

24

*

7

20

10

28

24

10.56%

8

20

20

28

24

15.75%

9

20

30

28

24

34.12%

10

20

40

28

24

60.78%

11

20

60

28

24

81.24%

12

20

50

0

24

92.04%

13

20

50

10

24

84.21%

14

20

50

15

24

83.41%

15

20

50

20

24

81.12%

16

20

50

25

24

81.01%

17

20

50

0

1

15.25%

18

20

50

0

2

40%

19

20

50

0

4

92%

20

20

50

0

8

92%

21

20

50

0

10

92%

22

20

50

0

12

92%

23

20

50

0

15

92%

24

20

50

0

18

92%

25

20

50

0

20

92.%

26

20

50

0

22

92.04%

*By product formation. After stirring the mixture, refrigerated it for 2h; Amt. of reactants: 0.05mol

 

 

 

 

Variety of bases and solvents was screened for synthesis of 2’hydroxy chalcone. NaOH gives highest yield and purity compare to other bases. IPA was proved beneficial solvent compare to methanol, ethanol, DCM, ACN and THF. Excess amount of base shows byproduct formation. 20ml of 40% W/V NaOH amount show good result compare to other concentration. Sufficient amount of IPA was necessary for synthesis of 2’hydroxy chalcone, 50ml IPA show best result compare to lower concentration and no major change screened after increasing amount of IPA. Temperature change gives significant effect on %yield. At 0˚C highest yield obtained without formation of any by product. %yield drastically decreased upon temperature increases, also byproduct formation occurred. For the completion of reaction minimum 4h was required, after stirring not more effective.

 

Scheme 1. Synthesis of 2’hydroxy chalcone

 

CONCLUSION:

2’hydroxy chalcone were successfully synthesized by Claisen–Schmidt condensation between benzaldehyde and 2’hydroxy chalcone. Variety of bases and solvent were tried for synthesis of 2’hydroxy chalcone. Lithium hydroxide shows slight catalytic activity in methanol and ethanol, in other solvent catalytic activity lost. Barium hydroxide also show slight catalytic in methanol, ethanol and IPA, in other solvent no product was formed. Calcium and magnesium hydroxide shows no catalytic activity in any solvent. Sodium hydroxide shows better activity than potassium hydroxide in all solvents. IPA proved better solvent than other solvents. In optimization process effect of solvent and base quantity, stirring time and temperature were screened. Product yield increases with amount of base level, but higher amount of base leads to byproduct formation. Amount of solvent also shows significant effect on product yield. Temperature shows significant effect on product yield. At 0˚C, best results obtained. In 4h, reaction mostly completed, further stirring was not effective. So the main aim of study, to develop optimized method for synthesis of 2’hydroxy chalcone was successfully completed.

 

EXPERIMENTAL:

Chemistry:

General:

All purchased chemicals were of analytical grade and used without further purification. The synthesis of 2’ Hydroxy chalcone were carried out as per the procedure detailed in Scheme 1. The progress of the reactions was monitored by thin‐layer chromatography analysis (Silica gel G60 F254; Merck). Melting points of the synthesized compounds were determined in open capillary tubes using Veego Melting Point Apparatus model VMP-D. Infrared spectra were recorded on Perkin Elmer spectrum GX FTIR spectrophotometer using KBr discs. 1H-NMR was recorded on Bruker Advance–II NMR-400MHz instrument using DMSO as a solvent and tetra methyl silane (TMS) as internal standard. Mass spectra were recorded on LCQ Fleet and TSQ quantum surveyor plus HPLC system spectrophotometer.

 

General procedure for the synthesis of 2’ Hydroxy Chalcone:

Mixed benzaldehyde (0.05mol, 5.3gm) and o-hydroxy acetophenone (0.05mol, 6.8gm) in 50ml of isopropyl alcohol and stirred for 15min at 0˚C. Add 40% NaOH 20ml dropwise (1ml/min) with stirring. After 6h stirring at 0˚C solution kept refrigerate for 2h. Add 100ml water in reaction mixture so pale-yellow precipitate observed. Filter the precipitate and recrystallized using methanol. Pale yellow needles shape; %yield 92% (9.56gm); mp 88-90˚C; IR (KBr, cm-1) vmax: 3432 (-OH),3026 (C-H Aromatic), 2926 (C-H Aliphatic), 1639 (C=O), 1485 (C=C Aromatic); 1H NMR (400 MHz, DMSOd6) δ ppm: 13.05 (s, 1H, OH), 7.94 (d, 1H alkene), 7.86 (d, 1H alkene), 6.90-8.31 (m, 9H Aromatic CH). MS (ESI+): m/z 224[M+], 225[M+1].

 

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Received on 29.01.2022                    Modified on 26.03.2022

Accepted on 23.05.2022                   ©AJRC All right reserved

Asian J. Research Chem. 2022; 15(3):210-212.

DOI: 10.52711/0974-4150.2022.00036