INTRODUCTION:

Macrocyclic crown ethers forms extractable ion-pairs between the positively charged metal ion crown ether complexes with some simple or complex anions. These can be very selective extracting agents for metal ions and are now often used for the determination of alkali, alkaline earth and transition elements. Solvent extraction is extensively used as an indirect method for determining the complexing behavior of various polyether-salt systems.¹ Their chemistry and analytical use including extraction have been comprehensively reviewed.^2-9 The extraction properties and complexation are controlled by the ring size, the cavity in the structure of the reagent which is influenced by the number and position of oxygen donor atoms, by the position and nature of the substituents and the stability of the ion-pairs. Thus crown ethers containing incorporated groups and also crown ether complex ion-pairs with selected dye anions are suitable for the sensitive extraction followed by spectrophotometric determination of alkali, alkaline earth and transition elements. The macrocyclic polyethers show a remarkable range of specificity for a wide variety of cations.^10-13

The cation selectivity of macrocyclic ligands can be determined by various types of experiments among which, solvent extraction,^14-16 stability constant determination and permeabilities of cations through macrocycle containing liquid membranes¹⁷ are important.Sandwiching complexation, substitution effect, ring size effect, uncommon complex stoichiometry of a series of crown ethers by solvent extraction experiments have been reported.^18-20 Present paper reports cation binding behavior of synthesized benzocrown ether derivatives (fig-1.1) with silver metal ion (Ag⁺) by using solvent extraction method.

MATERIALS AND METHODS:

All chemicals used were of AR grade. The commercially available regents were used without further purification. The metal contents were estimated by flame photometric method. Results of elemental analysis of synthesized compounds agreed with required value within experimental error. The melting points of synthesized compounds were determined on electrical tempo T-1150 apparatus. Molar conductivities of the compounds were measured using Systronic conductivity meter-306. The conductivities of the compounds were measured at the concentration 10^-3 M in methanol solvent at 30(±0.5)⁰C. IR spectra were recorded by Perkin Elmer spectrometer RX1 (4000-450 cm^-1). UV-visible spectral data were recorded through Systronic double beam spectrophotometer-2203 (600-200 nm). The ¹H−NMR spectra of ligand and crown ether complexes were recorded in CDCl₃ by Bruker DRX-300.

EXPERIMENTAL:

Preparation of silver salt of 2,4,6-trinitrophenol, Ag(TNP) :

About 4 mmol (1.004gm) of sodium salt of 2,4,6-trinitrophenol was taken in a conical flask and 25 ml of dry ethanol was added to it. The ethanolic solution of sodium salt of 2,4,6-trinitrophenol was heated on a water bath and continuously shaken till gets completely dissolved and the solution becomes homogeneous. Then, 4 mmol of AgNO₃ (0.68gm)was dissolved in 25 ml of dry ethanol. The freshly prepared ethanolic solution of silver nitrate was slowly added to the ethanolic solution of sodium salt of 2,4,6-trinitrophenol and continuously shaken. On adding the ethanolic solution of silver nitrate, yellow coloured silver salt of 2,4,6-trinitrophenol (AgTNP) precipitated out. The mixture was continuously stirred on hot plate equipped with magnetic stirrer for 45 minutes to ensure complete precipitation. Product was filtered, washed with absolute ethanol and dried in an electric oven at 80⁰C. Some physical properties of synthesized silver salt are given in table-1.1.

Table – 1.1-Physical properties of alkaline siver salt

Compound

Colour

Melting point (⁰C)

% Nitrogen

Found

Ag(TNP)

Yellow

245e

17.36

e – explosion temp

Preparation of crown ethers:

Preparation of crown ether which may work as a host molecule was one of the important part of this research work. Crown ethers, were prepared by the known synthetic methods as reported in literature. Benzo-15-crown-5 (1)^21-25, 4′-iodo-benzo-15-crown-5 (2), 4′-amino-benzo-15-crown-5 (3),²⁶dibenzo-18-crown-6 (5),^21-25 2,14-diamino-6,7,9,10,17,18,20,21-octahydro-5,8,11,16,19,22-hexaoxadibenzo[b,k]cyclooctadecene(6),²⁷ 2,13-diamino-6,7,9,10,17,18,20,21-octahydro-5,8,11,16,19,22-hexaoxadibenzo[b,k]cyclooctadecene (7)²⁷ and benzocrown ether derivative 4,²⁸ were prepared according to the reported procedure.

Figure: 1.1

Extraction experiments were undertaken to evaluate the ability of the synthesized macrocycles to extract silver ion from aqueous solutions. In solvent extraction method, metal cations were extracted from an aqueous phase into an organic phase by complexation with a macrocycle crown ether present in the organic phase.^29-32 It is a method of separation based on the transfer of a solute from one immiscible solvent into another. The solvents, CH₂Cl₂/CHCl₃ and H₂O were saturated with each other prior to use for preventing volume changes of both phases during extraction. Equal volumes of CH₂Cl₂/CHCl₃solution (10 ml) of the respective crown ether (0.3 mmol/l) and an aqueous solution of silver metal picrate (0.03 mmol/l) were introduced into a stoppered Erlenmeyer flask and the mixture was shaken for 30 minutes in an incubater thermostated at (28.0±0.2)^oC. This mixture was then allowed to stand for 6 hour at that temperature for complete phase separation. The concentration of silver picrate in the aqueous phase was determined through measuring the absorbance at 354 nm by UV-vis spectrometer. The extractability of silver ion (Ag⁺) by synthesized crown ethers is listed in table-1.2.

Table – 1.2-Solvent extraction of aqueous silver salt with benzocrown ether derivatives^a

Ligand	Extractability^b % (CH₂Cl₂)	Extractability^c % (CHCl₃)
Ligand	Ag⁺	Ag⁺
1	0.58	0.76
2	0.72	0.77
3	1.44	1.89
4	0.48	0.44
5	0.44	0.46
6	3.68	3.92
7	4.34	5.64

^aTemperature (28.0±0.2) ^oC; aqueous phase (10 ml), [picrate] = 0.03 mmol/l; organic phase (CH₂Cl₂/CHCl₃, 10 ml), [Ligand] = 0.3 mmol/l. ^bPercent of picrate extracted into CH₂Cl₂ (average of two independent runs). ^cPercent of picrate extracted into CHCl₃ (average of two independent runs).

RESULTS AND DISCUSSION:

The obtained results, when compared with the relevant data for compounds 1–4 and 5–7, have furnished further understanding of the complexation behavior of the benzocrown ether derivatives with Ag⁺ion.^33-35 In the solvent extraction of silver picrates, crown ethers 1-7 generally show low extractability as expected. Modified single armed crown ether 4, shows very low extraction effect in CHCl₃, indicating very weak complexation between 4 and Ag⁺ ion. Crown ether 3 shows high extractability with Ag⁺ion in both the organic phases. The crown ether 7 gives high extractability for Ag⁺ion in the case of CHCl₃ indicating high selectivity. It shows strong complexation behavior of crown ether 7. Comparison of the data given in the table-1.2 reveals that the stability of the resulting cation-macrocycle complexes in CH₂Cl₂ follows order 7>6>3>2>1>4>5, where as in CHCl₃,stability varies in the order 7>6>3>2>1>5>4.

ACKNOWLEDGEMENT:

I am thankful to the Chairman, UGC, New Delhi, for providing financial assistance to this research project under UGC-Minor Research Programme. I further extend my sincere thank to the Head, SAIF, CDRI, Lucknow, for providing necessary facilities.

REFERENCES:

1 Frensdorff HK, J. Am. Chem. Soc., 93, 1971, 4684

2. Kolthoff IM, Anal. Chem., 51, 1979, 1R

3. Takagi M and Ueno K, Topics in Current Chem., 121, 1984, 39

4. Christensen JJ, Eatough JD and Izatt RM, Chem. Rev., 74, 1979, 351

5. Poonia NS, and Bajaj AV, Chem. Rev., 79, 1979, 389

6. Nelson GA, Coordination Chemistry of Macrocyclic Compounds, Ed Plenum Press, New York, 1979

7 Takagi M and Nakamura H, J. Coord. Chem., 15, 1986, 53

8. Blasius E and Janzen KP, Topics in Current Chem., 98, 1981, 163

9. Bubnis BP, Steger JL, Wu YP, Meyers LA and Pacey GE, Anal. Chim. Acta., 139, 1982, 307

10 (a) Part 20: Zhang HY, Yang YW and Liu Y, Chem. j. Chin. Univ., 21, 1858, 2000

(b) Part 21 : Liu Y, Zhang HY, Bai XP, Wada T and Inoue Y, J. Org. Chem., 65, 7105, 2000

11 Takeda Y, In The Solvent Extraction of Metal Ions by Crown Compounds: Host-Guest Complex Chemistry III, Topics in Current Chemistry, Eds. : Vogtle E and Wiber E, Springer-Verlag, Berlin, pp. 1-38, 1984

12 Ma SL, Zhu WX, Dong SJ, Guo QL and She YB, Chin. J. Chem., 21, 2003, 1178

13. Liu SH, Wu XY and Wu CT, Acta. Chim. Sinicica., 57, 1999, 1167

14. Zhao M and Ford WT, J. Incl. Phenom., 17, 1994, 53

15 Inoue Y, Liu Y, Tong LH, Tai A and Hakushi T, J. Chem. Soc. Chem. Commun., 1989, 1556

16 Inoue Y, Wada D, Liu Y, Ouchi M, Tai A and Hakushi T, J. Org. Chem., 54, 1989, 5268

17. Schwind RA, Gilligan TJ and Cussler EL, in "Synthetic Multidentate Macrocyclic Compounds"; Izatt RM and Christensen JJ, Ed. Academic Press, New york, 289-308, 1978

18. Izatt RM, Bruening RL, Turbet BJ, Griffin LD, Bruening ML, Krakowiak KE and Bradshaw JS, Pure Appl. Chem., 62, 1990, 1115

19. (a) Kato M and Ito T, Inorg. Chem., 24, 1985, 504

(b) Kato M and Ito T, Inorg. Chem., 24, 1985, 509

20. Liu Y and Zhang HY, Chin. J. Chem., 18, 2000, 66

21 Pedersen CJ, J. Am. Chem. Soc., 89, 1967, 7017

22 Pedersen CJ, J. Am. Chem. Soc., 92, 1970, 386

23. Pedersen CJ, J. Org. Chem., 36, 1971, 254

24. Pedersen CJ, J. Org. Chem., 36, 1971, 1690

25. Pedersen CJ and Frensdorff HK, Angew. Chem. Int. Edn. (England), 11, 1972, 10

26. Ungaro R, Haj BE and Smid J, J. Am. Chem. Soc., 98, 1976, 5198

27. Pannell KH, Yee W, Lewandos GS and Hambrick DC, J. Am. Chem. Soc., 99, 1977, 1457

28. Yang YW, Li CJ, Zhang HY and Liu Y, Chin. J. Chem., 22, 2004, 616

29 Gokel GW, Dishong DM and Diamond CJ, J. Chem. Soc., Chem. Comm., 1053, 1980

30. Dishong DM, Diamond CJ and Gokel GW, Tetrahedron Letter, 22, 1981, 1663

31 Schultz RA, Dishong DM and Gokel GW, Tetrahedron Letter, 22, 1981, 2623

32. Schultz RA, Dishong DM and Gokel GW, J. Am. Chem. Soc., 104, 1982, 625

33 Levason, Willian, Popham, Michael C, Reid, Gillian and Webster, Dalton Trans., 3, 2003, 291

34 Zhu YH, Du MX, Li DC, Wang DQ and Dou JM, Chem. J. Chin. Univ., 21(1), 2005, 123

35 Song XM, Li DL, Wei JF and Dou JM, Z. Kristallogr NCS., 220, 2005, 231

Received on 16.07.2013 Modified on 24.07.2013

Asian J. Research Chem. 6(9): September 2013; Page 819-821