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A stoichiometric study on the reaction between ferric ion and p-Chloro--N- Phenyl--p-Chlorobenzo hydroxamic acid.

Introduction

The chemistry of hydroxamic acids has received considerable attention [5, 6], and this interest is also connected with a variety of their pharmaceutical and industrial applications [7, 8]. Particularly important in their role as siderophores, as well as a model system for natural siderophores. [9,10] Siderophores are low- molecular weight multidentate ligands.

Experimental

All chemicals used were AnalaR grade. All solutions were prepared according to the usual analytical procedures using double distilled water.

pH-determining solutions

1.0M, 2.0 M, 3.0M and 3.5 M HCl.

Acetate Buffer Solutions

A series of buffer solutions ranging from pH 1.0 to pH 7.0 were prepared. Buffer solutions of pH 1.0 and pH 2.0 were prepared from a mixture of 0.2 M hydrochloric acid and 0.2 M potassium chloride in different proportions; solutions ranging from pH 3.0 to pH 7.0 were prepared using 0.2M acetic acid and 0.2M sodium acetate in different proportions. They were all adjusted to the exact value by some drops of sodium hydroxide or hydrochloric acid using a pH -meter.

Oxidation of Fe (II) to Fe (III) with hydrogen peroxide

25 [cm.sup.3] of [10.sup.-3] g/[cm.sup.3] Fe (II) were transferred to a 400 [cm.sup.3] beaker.

10 [cm.sup.3] of 20 % V / V hydrogen peroxide and 2 [cm.sup.3] of concentrated hydrochloric acid were added. The mixture was heated to boil to expel the excess of hydrogen peroxide.

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII]

The oxidized solution was transferred to a 250 [cm.sup.3] volumetric flask and was diluted to volume by double distilled water. The concentration was [10.sup.-4] g / [cm.sup.3] Fe (III).

A\ Extraction and spectrophotometric determination of Iron(III) (determination of the pH at maximum extraction)

5 [cm.sup.3] portions of [10.sup.-4] g / [cm.sup.3] Fe (III) were pipetted into a series of 25 [cm.sup.3] volumetric flasks and completed to the mark with adjusted pH--determining solutions ((acetate buffer solutions ranging from pH 1.0 to pH 7.0 and pH--determining solutions 1.0M, 2.0 M, 3.0M and 3.5 M HCl)). The solutions were transferred to a series of 100 [cm.sup.3] seperatory funnels and were extracted with an equal volume (25 [cm.sup.3]) of 0.5 % w/v

PCNPPCBHA in chloroform, with vigorous shaking for two minutes. Blood red colour was observed. The two layers were separated : (1) The organic layer (lower phase) and (2) the aqueous layer (upper phase). The aqueous layers were taken for further analysis to determine the pH at maximum extraction.

Analysis of the aqueous layer of by spectrophotometric procedure (11)

The standard ((calibration curve)) for [iron.sup.+3] and the sample ((aqueous layer)) were carried out at the same time for spectrophotometric procedure.

B \ The standard ((calibration)) curve

0.0, 5.0, 7.5, 10.0, 12.5, and 15.0 [cm.sup.3] of [10.sup.-5] g / [cm.sup.3] (w/v) Fe (III) solution, 20.0 [cm.sup.3] double distilled water, 5.0 [cm.sup.3] of concentrated hydrochloric acid, 1.0 [cm.sup.3] of 2 % w/v potassium persulphate and 10.0 [cm.sup.3] of 20 % w/v potassium thiocynate solution were transferred to seperatory funnels successively. The solutions were extracted with five 10.0 [cm.sup.3] portions of (1:1) isobutyl alcohol and carbon tetrachloride (50 % v /v), with vigorous shaking for two minutes each. The organic layers were combined in 50 [cm.sup.3] volumetric flasks. The absorbance was measured at 485 nm using 1 cm cell. Results are shown in table (1) and represented graphically in figure (1).

[FIGURE 1 OMITTED]

C\ The sample

From the aqueous layer in A, 5[cm.sup.3] were transferred to a seperatory funnel. The analysis was carried out as in B. Results are shown in table (2)

Results and Discussion

Spectrophotometric studies on [Iron.sup.+3]--p-Chloro-- N- Phenyl--p-Chlorobenzohydroxamic acid complex:

(I) The Continuous Variation Method:

The ratio of the ligand: metal i.e. PCNPPCBHA:[Fe.sup.+3] was determined by the application of the continuous variation method (12), (13). Results are shown in table (3) and represented graphically in figure (2). The blank used was chloroform.

(II) The Slope Ratio Method:

The ratio of the metal [Iron.sup.+3] to the ligand PCNPPCBHA was confirmed by the application of the slope ratio method (14) which was found 1:2. Results are shown in table (4) and represented graphically in figure (3).

(III) The Calibration curve of [Iron.sup.+3]--PCNPPCBHA system:

A standard calibration curve of [Iron.sup.+3]--PCNPPCBHA system was carried out against chloroform as blank. Results are shown in table (5) and represented graphically in figure (4).

Jop (12) has pointed out, that the method of continuous variation is simple and rapid for determining the formula of a compound, provided that only a single compound is formed. If more than one compound is formed, the method can still help in giving information about the formulae of compounds if the compounds are sufficiently stable. Caution is necessary in such cases. The shape of the curves in the continuous variation method sometimes may give indication to the existence of more than one compound. (13)

Many of the relation in this paper presuppose the validity of Beer-Lambert law (15). True variations of the law can arises when moderately concentrated solutions are used, but can usually be neglected when working with dilute solutions. The ligand PCNPPCBHA forms 1:2 complex with Fe (III)

at pH 5.0 ((the minimum value of the absorbance table (2))) that corresponds the maximum absorption in a value of 0.35 M / M + L in the continuous variation method curve figure (2), and this confirmed by the slope ratio curve figure (3). This system is closely resemble the systems [CO.sup.+2]: PCNPPCBHA and [Cu.sup.+2]: PCNPPCBHA i.e. forms 1:2 complex. (16)

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

References

[1] Vogel, A.I., 1951, "A text book of practical organic chemistry", Longmans, London, 2nd. Ed.

[2] Usha, P. Tandon. S. G, 1967, J. of Chem. and Eng.data, 12, (1), 143.

[3] Abdalla, H.H., 1992, M.SC. thesis, Fac.of Science, University of Khartoum.

[4] Openshow, H. T., 1995, "A laboratory Manual Of Qualitative Organic Analysis" Cambridge University Press, 3rd ed.

[5] Miller, M.J, 1989, Chem. Rev, 89, P 1536.

[6] Crunbliss, A.L; 1990, Coord.Chem., 105, P 155.

[7] Musser, J.H; Kreft, A.F; Bender, R.H. W; Kubrak, D.M; Grimes, D; Carlson, R.P; Hand, H.M; Chang, J; 1990, J.Med. Chem., 33, P 240.

[8] Yamamoto, K; Shinoki, Y; Nishio, M; Matsuda, Y; Inouye Y; Nakamura, S; 1990, J. Antibio., 43, P 1012.

[9] Matzanke, B.F., 1989, "Siderophore Mediated Iron Transport; Chemistry, Biology and Physical Properties", VCH Publishers, New York.

[10] Hider, R.C., Hall, A.D., 1991, "Perspectives on Bioinorganic Chemistry", JAI Press, London, Vol.1.

[11] Sandell, E.B., 1960, "Colorimetric Determination of Trace Metal" interscience, New York.

[12] Job, 1928, Ann. Chem. Paris, 9, P 113.

[13] Warren, C. Vosburgh and Gerald R.Cooper, 1941, J. of Am.Chem. Soc., 63, P 437.

[14] Harvey, A. E, and Manning, D. L. 1952, J.Am.Chem.Soc., 74, P4744.

[15] Brown, G. H and Sallee, E. M. 1963, "Quantitative chemistry" 1st ed. Prentice-hall Inc. USA.

[16] A Mageed, M.J., 1995, M.SC. thesis, Faculty of Science, University Of Khartoum, Sudan.

M. J. A. Abualreish

Department of Chemistry, Faculty of Science and Technology, Umdurman Islamic University, Umdurman, Sudan
Table 1: Absorbance of the standard solutions
for the calibration curve of [Iron.sup.+3] at
[lambda] 485 nm.

Concentration   Medium   Absorbance
of Fe (III)
in ppm

1.0              HCl       0.150
1.5               "        0.275
2.0               "        0.389
2.5               "        0.521
3.0               "        0.625

Table (2): Absorbance of the aqueous layer from
the extraction of [Iron.sup.+3] with PCNPPCBHA.

      pH         Absorbance at
                 [lambda] 485 nm

    1M HCl            0.120
    2M HCl            0.125
    3M HCl            0.271
   3.5M HCl           0.215
Acetate pH 1.0        0.109
     2.0              0.122
     3.0              0.044
     4.0              0.019
     5.0              0.017
     6.0              0.018
     7.0              0.045

* pH at maximum extraction implies the lowest
value of the of the absorbance i.e. at pH = 5.0

Table (3): Continuous variation method for
[Iron.sup.+3]--PCNPPCBHA system.

Solution           1      2      3      4      5      6      7

Vol. of            2      3      4      5      6      7      8
[Fe.sup.+3]
1 x [10.sup.-3]
in [cm.sup.3]

Vol. of Acetate    2      2      2      2      2      2      2
pH 5 in
[cm.sup.3]

Vol. of Dist.      6      5      4      3      2      1      0
[H.sup.2]O in
[cm.sup.3]

Vol. of ligand     8      7      6      5      4      3      2
1 x [10.sup.-3]
in [cm.sup.3]

Vol. of            2      3      4      5      6      7      8
chloroform
added to
the ligand
before added
to the metal
in [cm.sup.3]

M                0.20   0.30   0.40   0.50   0.60   0.70   0.80
M+L

Absorbance at    0.314  0.459  0.583  0.455  0.315  0.205  0.081
[lambda] 520 nm

Table 4: Slope--ratio method for [Iron.sup.+3]--PCNPPCBHA system.

Set (A)

Solution                1       2       3       4       5       6

Vol. of [Fe.sup.+3]     1       2       3       4       5       6
1 x [10.sup.-3]
in [cm.sup.3]

Vol. of Acetate pH      3       3       3       3       3       3
5 in [cm.sup.3]

Vol. of Dist.           6       5       4       3       2       1
[H.sub.2]O in
[cm.sup.3]

Vol. of ligand          5       5       5       5       5       5
1 x [10.sup.-3]
in [cm.sup.3]

Vol. of chloroform      5       5       5       5       5       5
added to the ligand
before added to the
metal in [cm.sup.3]

[Fe+3 ] x               1       2       3       4       5       6
[10.sup.-4] M

Absorbance            0.131   0.187   0.252   0.315   0.395   0.449
at [lambda]
485 nm

Set (B)

Solution                1       2       3       4       5       6

Vol. of                 5       5       5       5       5       5
[Fe.sup.+3] 1 x
[10.sup.-3]
in [cm.sup.3]

Vol. of Acetate pH      3       3       3       3       3       3
5 in [cm.sup.3]

Vol. of Dist.           2       2       2       2       2       2
[H.sup.2]O in
[cm.sup.3]

Vol. of ligand          1       2       3       4       5       6
1 x [10.sup.-3]
in [cm.sup.3]

Vol. of chloroform      9       8       7       6       5       4
added to the ligand
before added to
the metal in
[cm.sup.3]

[PCNPPCBHA]             1       2       3       4       5       6
x[10.sup.-4]M

Absorbance            0.104   0.218   0.342   0.458   0.571   0.962
at [lambda]
485 nm

Table 5: Calibration curve for Iron+3--PCNPPCBHA system.

Solution                 1       2       3       4       5

Vol. of [Fe.sup.+3]
  1 x [10.sup.-3]
  in [cm.sup.3]          1       2       3       4       5
Vol. of Acetate
  pH 5 in [cm.sup.3]     5       5       5       5       5
Vol. of Dist.
  [H.sup.2]O in
  [cm.sup.3]             4       3       2       1       0
Vol. of ligand
  1 x [10.sup.-3]
  in [cm.sup.3]         10      10      10      10      10
[Fe.sup.+3] x
  [10.sup.-4] M          1       2       3       4       5
Absorbance at
  [lambda] 485 nm      0.378   0.446   0.515   0.578   0.641
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Author:Abualreish, M.J.A.
Publication:International Journal of Applied Chemistry
Article Type:Report
Geographic Code:1USA
Date:Jan 1, 2009
Words:1952
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