Studies on Synthesis of Aromatic Schiff Bases. Part-VI. Synthesis, Characterization and Biological Activity of Ketimines from

5-Chloro-2-hydroxy-4-methyl-acetophenone with substituted anilines

 

S. B. Salve, C. J. Patil, H. A. Mahajan

Smt. G. G. Khadse College, Muktainagar, Dist-Jalgaon-425 306, M.S., India 

*Corresponding Author E-mail: sanjivsalve@gmail.com, drcjpatil@yahoo.com

The condensed reaction of aromatic ketone, 5-Chloro-2-hydroxy-4-methyl-acetophenone with aniline and its derivatives each separately viz. Aniline, 4-Amino-phenol, 2-Amino-thiophenol, 4-Amino-thiophenol, 4-Chloro-2-nitro-aniline, 2-Amino-benzonitrile and 4-Amino-benzonitrile and reacted efficiently to produced a series of ketimines in high yield and purity. These were analyzed by employing the TLC technique. All the products were characterized by their colour, physical constant, TLC, elemental analysis and spectral(UV-Vis and FTIR) method. After confirming their desired molecular studies, these ketimines were studied for their antifungal activity using A. alternata, and F. oxysporum.

 

INTRODUCTION:

Schiff bases are the compounds carrying imine or azomethine (>C=N–) functional group.The azomethines are very important synthetic intermediates. Survey of the past literature [1-2] revealed that the chemistry of multiple bonds has achieved an enormous developments, as these compounds are useful in industrial and biological field via cycloaddition reaction[3], ring closure[4] and condensation reactions[5-6]. Ketimines or Schiff bases also play role as antimicrobial [7], anticonvulsant [8], antitubercular [9], anticancer [10], antioxidant [11] and antihelmintic [12]. Further, to summarize, reports from this lab includes different ketimines viz. from o-Hydroxy-acetophenone[13], benzophenone[14], a rare ketone, 5-Chloro-4-methyl-2-hydroxy-acetophenone by conventional [15-17] and by microwave method[18] for the antibacterial[19-20] and antifungal studies[17-18].

 

Literature shows that many researchers have used reflux with D. S. Trap to synthesize the ketimines and aldimines. Looking to this we have planned to synthesize and to study of the antifungal behaviour of ketimines.

 

In the present study we have proposed a reflux with D. S. Trap for the condensation of a ketone, 5-Chloro-2-hydroxy-4-methyl-acetophenone with each separately seven different aromatic amines viz. Aniline, 4-Amino-phenol, 2-Amino-thiophenol, 4-Amino-thiophenol, 4-Chloro-2-nitro-aniline, 2-Amino-benzonitrile and 4-Amino-benzonitrile were of synthesis grades and used for synthesis of ketimines in high purity.

 

Scheme of Synthesis:

The proposed structures of the compounds are shown in Scheme-1.

 

 

 

 

 

 

 

EXPERIMENTAL:

The raw materials ketone, 5-Chloro-2-hydroxy-4-methyl-acetophenone and the Aniline, 4-Amino-phenol, 2-Amino-thiophenol, 4-Amino-thiophenol, 4-Chloro-2-nitro-aniline, 2-Amino-benzonitrile and 4-Amino-benzonitrile were of synthesis grades used for synthesis of ketimines. The solvents The solvents absolute alcohol(ethanol), toluene and methanol used for synthesis, TLC and spectra purpose were of the synthesis and spectroscopic grade. The reactions were monitored by employing the techniques such as TLC on aluminium plates coated with silica gel and UV monitored on Shimadzu-1800 spectrophotometer.

 

The condensation reaction of aromatic rare ketone, 5-Chloro-2-hydroxy-4-methyl-acetophenone and anilines viz. Aniline, 4-Amino-phenol, 2-Amino-thiophenol, 4-Amino-thiophenol, 4-Chloro-2-nitro-aniline, 2-Amino-benzonitrile and 4-Amino-benzonitrile, each of equimole in absolute alcohol or toluene on reflux with D. S. Trap for about 6 hrs(clear TLC), gave formation of ketimines. The reaction completion is monitored by employing the techniques such as TLC on aluminium plates coated with silica gel. The obtained products were recrystallized in absolute alcohol. The UV-Vis spectra were recorded on Shimadzu-1800 spectrophotometer in alcohol.

 

After confirming their desired molecular studies, these ketimines were studied for their antifungal activity using A. alternata, and F. oxysporum were purchased from National Collection of Industrial Microorganisms (NCIM) NCL, Pune.

 

General Procedure for the Synthesis of Ketimines:

The condensation reaction of aromatic ketone, 5-Chloro-2-hydroxy-4-methyl-acetophenone with each separately seven different aromatic amines viz. Aniline, 4-Amino-phenol, 2-Amino-thiophenol, 4-Amino-thiophenol, 4-Chloro-2-nitro-aniline, 2-Amino-benzonitrile and 4-Amino-benzonitrile, each in mole 0.033 for S-I, S-II, S-IV, S-VI and S-VII) or 0.0165 (for S-III and S-V) and using absolute alcohol or toluene on reflux for about 5 hrs, gave formation of ketimines. The reaction completion is monitored by employing the techniques such as TLC on aluminium plates coated with silica gel. The obtained products were recrystallized in absolute alcohol. The physical constants were determined on the Digital m. p. apparatus of Equiptronics, Model, EQ-670.

 

The UV-Vis spectra were recorded on Shimadzu-1800 spectrophotometer in alcohol. Stock solutions prepared in absolute ethanol and were of 0.01 M concentration. These solutions were diluted serially and were used for the UV-Vis spectral determinations. The FTIR spectra were recorded on a Shimadzu FTIR 8400 spectrophotometer (Model-IRAffinity-1) using sample mixed in powder form with KBr powder, the frequency values, ‘υ’, are in the range of 4000-350 cm^-1. The structural assignment of the products was based respectively on the elemental (CHN) analysis.

 

After confirming their desired molecular studies, these ketimines were studied for their antifungal activity by subjecting to in vitro antifungal activity against fungi viz. A. alternata, and F. oxysporum using disc diffusion method[5].

 

RESULTS AND DISCUSSION:

The condensation products of ketone and primary aromatic amines called as ketimines. In the present study, Ketimines from 5-Chloro-2-hydroxy-4-methyl-acetophenone with Aniline, 4-Amino-phenol, 2-Amino-thiophenol, 4-Amino-thiophenol, 4-Chloro-2-nitro-aniline, 2-Amino-benzonitrile and 4-Amino-benzonitrile were synthesized and abbrivated respectively as S-I to S-VII. The progress of reactions was monitored by Silica gel TLC 60F₂₅₄ Merck, visualized by UV cabinet or iodine vapour. These products were of yellow to brown in colour. The obtained products were purified by column chromatography on 60-120 Silica Gel. The purity of the compounds was ascertained by melting point determinations. Their TLCs were recorded on aluminium plates coated with silica gel. The physical and analytical data for synthesized ketimines is shown in Table-1. The analytical results and % yields for synthesized ketimines are given in Table-1. The experimental yields are in the range 72.34 % to 55.38 %.

 

All compounds gave satisfactory elemental analysis. Values are in the close agreement with the values calculated for expected molecular formulae assigned to these compounds and are in 5 % in statistics. The colour, physical constant and their purity was confirmed by TLC. The TLC of amine and the final product is monitored, indicated the single spots and obtained data is given in the Table-2.

 

In addition to this the compounds, S-I to S-VII were also characterized by spectral analysis viz. UV-Vis, and FTIR and the obtained results are reported in the Table 3.

 

 

 

 

Table 1: Physical and Analytical data for Synthesized Ketimines,S-I to S-VII.

Sr. No.	Product Code	Aniline used	Mol. Wt. of Aniline	Product, Mol. Wt.	Product Wt.,gm.	% Yield*
1	S-I	Aniline	93.13	259.63	5.72	66.75
2	S-II	4-Amino-phenol	109.13	275.63	5.75	63.86
3	S-III	2-Amino-thiophenol	125.19	291.69	5.50	57.55
4	S-IV	4-Amino-thiophenol	125.19	291.69	6.85	71.23
5	S-V	4-Chloro-2-nitro-aniline	172.57	339.07	7.35	65.12
6	S-VI	2-Amino-benzonitrile	118.14	284.64	5.18	55.38
7	S-VII	4-Amino-benzonitrile	118.14	284.64	6.85	72.34

*isolated yield

 

Table-2:Data for Elemental Analysis of the Synthesized Ketimines, S-I to S-VII, derived from 5-Chloro-2-hydroxy-4-methyl-acetophenone.

Product ID	Colour	m.p. °C	Results of TLC analysis	Micro-anal (Elemental) of Ketimines
				% C		% H		% N
				obs.	cal.	obs.	cal.	obs.	cal.
S-I	Moss Green	82-91	Single Spot product	69.14	69.33	5.24	5.39	5.30	5.39
S-II	Dark brown	155-158	Single Spot product	65.21	65.31	5.02	5.08	5.03	5.08
S-III	Dark green	133-135	Single Spot product	62.01	61.71	4.66	4.80	4.68	4.80
S-IV	Light brown	122-123	Single Spot product	61.48	61.71	4.71	4.80	4.73	4.80
S-V	Yellow orange	75-77	Single Spot product	52.99	53.09	3.55	3.54	8.23	8.26
S-VI	Chocolate brown	106-108	Single Spot product	67.31	67.45	4.59	4.57	9.76	9.84
S-VII	Shiny brown	48-50	Single Spot product	67.39	67.45	4.51	4.57	9.86	9.84

 

 

Table 3: The Spectral Data for Synthesized Ketimines, S-I to S-VII, derived from 5-Chloro-2-hydroxy-4-methyl-acetophenone.

 

 

All the studied Ketimine compounds showed 2-3 peaks in UV-Vis spectra in ethanol in the studied range 600 nm to 250 nm. In the UV-Vis spectral analysis of ketimines shows the two to three peaks in the studied range. These are attributed to n-p* and p-p* transitions due to presence of varied auxochrom group (auxochrome) and >C=N- group transitions and aromatic phenyl ring transition of moderate energy. The spectral data are in close agreement, similar to previous reports[13-19] with the structures of the synthesized compounds.

 

The Table 3 also indicates the assigned structures from the spectral results. The typical UV-Vis Spectra for the series of Ketimines synthesized, S-I to S-VII, is depicted in the Fig.-1, is shown below,

 

 

Fig.-1 Typical UV-Vis Spectra for the series of Ketimines synthesized, S-I to S-VII.

 

The typical FTIR Spectra for the series of Ketimines synthesized, S-I to S-VII, is depicted in the Fig.-2, is shown below,

 

 

Fig.-2 The Typical FTIR Spectra for the series of Ketimines synthesized, S-I to S-VII.

 

 

On the basis of the foregoing discussion and based on the TLC spectral observations, the structures of the synthesized compounds are assigned.

 

The FTIR spectra of the studied Ketimines, S-I to S-VII, indicated the absorption at different frequencies as n_-OH  = 3100; n_Ar-C-H =  1562 and 1460; n_Ar-C-H  =  2820; n_>C=N-  = 1641; n_-NO2 = 1446 and 1367and  n_C-Cl  = 810 and 772for the respective functional groups as indicated.

 

Antifungal Activity:

After confirming the desired molecular studies, these Ketimines, S-I to S-VII, were studied for their antifungal activity by subjecting to in vitro antifungal activity against plant pathogenic fungi viz. A. alternata, and F. oxysporum using disc diffusion method[5]. The results of zone of inhibition(in mm) are depicted in Table 4.

 

Table 4: The Antifungal activity screening for Synthesized Ketimines, S-I to S-VII, derived from 5-Chloro-2-hydroxy-4-methyl-acetophenone.

Name of Strain	A. alternata				F. oxysporum
Concn.(µg/ml)  → Comp. ID ↓	100	150	200	500	100	150	200	500
S1	0	0	0	0	0	0	10	10
S2	10	11	14	13	8	11	12	14
S3	8	10	11	14	10	11	10	12
S4	6	6	12	13	8	11	12	14
S5	8	8	10	10	8	11	14	16
S6	9	10	11	12	8	11	13	17
S7	5	8	10	14	7	10	12	15
Fluconazole, standard Drug	16	17	17	19	17	19	20	22

 

Fig. 3: Antifungal activity screening for Synthesized Ketimines, S1 to S7, against A. alternata

 

Fig. 4: Antifungal activity screening for Synthesized Ketimines, S1 to S7, against F. oxysporume

Glimpses of Antifungal Activity:

All the compounds studied are less potential than the standard drug, Fluconazole.

S-I compound active against Fusarium oxysporum at higher concn. (200 and 500 mg/ml) and inactive against Alternaria alternata.

S-II more active against Fusarium oxysporum than Alternaria alternata.

S-III more active against Alternaria alternata than Fusarium oxysporum.

S-IV more active against Fusarium oxysporum than Alternaria alternata.

S-V more active against Fusarium oxysporum than Alternaria alternata.

S-VI more active against Fusarium oxysporum than Alternaria alternata.

S-VII more active against Fusarium oxysporum than Alternaria alternata.

The standard drug, Fluconazole has also shown more activity against Fusarium oxysporum than Alternaria alternata.

 

 

 

 

CONCLUSION:

Seven Ketimines were synthesized and characterized on the basis of analytical and spectral data. These compounds will be useful as building block by organic researchers in the near future. Screening of these compounds against pathogenic microorganism reveals that these compounds have the capacity of inhibiting metabolic growth of some microorganisms to different extent. The antimicrobial activity of the compound is also dependent on the nature of substituent present on the aromatic ring.

 

ACKNOWLEDGEMENTS:

The authors(S.B.S. and H.A.M.) are thankful to WRO, UGC, Pune for sanctioning the Minor research project[F.No.47-2049/11(WRO) dated 23^rd Feb. 2012] under UGC Scheme (XIth Plan). They are also thankful to the Management and Principal of their College for the permission of the present work. Help of Kishor Vasudeo Patil is duly acknowledged.

 

 

 

 

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Received on 16.09.2017         Modified on 04.12.2017

Accepted on 15.01.2018         © AJRC All right reserved