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Studies with dithizone analogues—II
Tahta,
Vol. 22, pp 931-932
Pergamon
Press, 1975 Pnnted
m Great Br~tam
ANNOTATION STUDIES WlTH DITHIZONJ.! ANALOGUES-II PREPARATION AND CHARACTERIZATION OF 2,2’-DICHLORODlTHIZONE AND THE INVESTIGATION OF ITS REACTIONS WKH SOME METAL IONS A. M.
KIWAN
and A. Y. KASSIM
Department of Chemistry, The University of Kuwait, Kuwait (Received 15 August 1974. Accepted 7 March 1975) 2,2’-Dichlorodithizone [l,S-di-(2chlorophenyl)-3-mercaptoformazan] was first described by Pelkis, Dubenko and Pupko’ who prepared it by the nitroformazyl method* and reported that its electronic absorption spectrum exhibits two characteristic peaks at 645 (1, ,,,) and 465 (d, m) nm. More recently, Ramakrishna and Fernandopulle3 have repeated its preparation by the same method, and reported different wavelengths for the absorption maxima, namely, 670 and 470nm respectively. They have also given data for the molar absorptivities of 2,2’-dichlorodithizone and some of its metal complexes. However, during our current studies on dithizone analogues, we have found that Ramakrishna and Fernandopulle’s data are radically different from ours and so a reinvestigation seemed desirable. This paper describes the preparation and characterization of 2J’dichlorodithizone (abbreviated hereafter as Cl,H,Dz) and reports the results of an investigation of its reactions with Ag(I), Hg(II), Cu(II), Bi(III), Zn(II), Cd(H), Co(II), Ni(II) and Pb(II) ions. EXPERIMENTAL
Reagent
The 2,2’-dichlorodithizone was prepared by the nitroformazy1 method.’ It was purified by dissolving it in dilute isopiestically distilled ammonia solution4 followed by extraction into analytical-grade chloroform and finally precipitation with 2% isopiestically prepared hydrochloric acid. It was washed free from acid and dried in vacua; m.p. 138-139” (literature values: 112-l 13”;’ 13803).Found: C 47.9x, H 3.4x, N 17.2x, Cl 21.7%; C,3H,,Cl,N,S requires C 48.290/, H 3.09x, N 17.33x, Cl 21.98%. Reagent grade salts were used and the usual precautions were taken with dithizone. Procedures
The methods used for the determination of the molar absorptivities of 2,2’-dichlorodithizone and its metal complexes, their compositions, and the effect of pH on their extractabilities into CCL, were those which were used for dithizone.5m7 The acid dissociation constant and the partitron coefficient P, of 2,2’-dichlorodithizone were measured by applying the technique used by Sandell.* The average value of pK, calculated from six determinations was found to be 475 f 0.5. The average value of the partition coefficient between carbon tetrachloride and water was 6.1 f 1 x 104. The partition coefficients, PM,_for copper(I1) and zinc(H) complexes between carbon tetrachloride and water were determined by the technique used by Geiger and SandelLg The average values were 3.5 x lo4 and 1.5 x 10“ respectively. The extraction constants K,,, for M(Cl,HDz), were
determined for the Zn(II), Cd(I1) and Pb(I1) complexes by performing extractions from 1M perchlorate solutions, and calculating the equilibrium concentrations of M(Cl,HDz),, M”+, Cl,H,Dz and H+. The concentrations of 2,2’-dichlorodithizone and it3 metal complex were determined spectrophotometrically, M”+ from the degree of extraction, and H+ from the pH of the aqueous phase. The extraction constants of Hg(Cl,HDz), and Cu(Cl,HDz), were determined by following the procedures given by Takei and Kato.‘O RESULTS
AND
DISCUSSION
Visible absorption spectra of 2,2’-dichlorodithizone and its metal complexes
The introduction of chlorine atoms into the ortho positions of the phenyl nuclei of dithiione was found to shift both absorption bands bathochromically to 644 and 462 nm respectively (vs. 620 and 450 nm for dithizone). Our values are quite close to those (645 and 465nm respectivelv) renorted bv Pelkis. Dubenko and Puoko.’ but thev are-different from the values 670 and 476 nm given by Ramakrishna and Fernandopulle,3 which for reasons given later, appear to be incorrect. The positions of I max for the metal complexes were also found to undergo various shifts as shown in Table 1. The molar absorptivities of 2,2’-dichlorodithizone were also affected (Table 1). E, __.. for 2,2’-dichlorodithizone has increased to 2.97 x i06~le.cm- ’ whereas I, msxhas decreased to onlv 3.34 x 104. Ramakrishna and Fernandopulle’s l2 ,,J3.83 x 10“ talc. by us from their peak ratio) is too high. Further, the anamolous shape of the shorter wavelength band, the displaced positions of both absorption peaks and the low peak ratio reported by them, cast serious doubts on the purity of their materials and/or the reliability of their data. The molar absorptivities of the metal complexes undergo analogous changes. compared with the corresponding metal dithizonates.’ ’ The spectral data which were given by Ramakrishna and Fernandopulle3 for the Hg(II), Ag(I), Bi(III), Pb(II), Zn(II), Cu(II), Cd(H), Co(I1) and Ni(II) complexes of 2,2’-dichlorodithizone, given in Table 1, appear to be in serious disagreement with ours. Reaction between 2,2’-dichiorodithizone and metal ions
2,2’-Dichlorodithizone was found to react with various metal ions in a stoichiometrically identical way to dithizone, giving primary and secondary 2,2’-dichlorodithizonates. The former are formed when the reagent is in excess, the latter when the pH and the proportion of metal to ligand are increased. The extraction data for metal complexes with 2,2’-dichlorodithizone are included in Table 1, inspection of which reveals the following features. 931
932
ANNOTATION
Table 1. Characteristic absorption and extraction data for 2,2’-dichlorothizone and some of its metal complexes. Some values for the corresponding dithizone complexes are included for comparison. Values in parentheses are the molar absorptivities (l.mole- ’ .cm- ‘) x 10m3
Lax (4 This work* 2,2-Dichlorodithizone Cu(Cl,HDz), Cu(HDz), Zn(Cl,HDz), Zn(HDz), Hg(Cl,HDz), Hg(HI% Cd(&HDz), Cd(HDz), Pb(Cl,HDz), PqHDz), Ag(Cl,HDz) Bi(Cl,HDz),
644 (33.4) 462 (29.8) 541 (65.8) 550 (45)” 533 (97.2) 538 (92)” 485 (86.3) 485 (71)” 527(111.4) 520 (88)’ ’ 514 (70.8) 520 (69)” 460 (39) 490(1047) 539 (55.7) 669 (26.7) 545 (37.4) 428 (41.3)
Ref. 3 670(33.1) 470 570 (77.4) 560(105) 425 (70) 500 (80.9) 550 (94.6) 530 (90.3) 430 sh.
pH for complete extn.
log K,,,
PML
log
BML
4.3-7
6.88 10.48 0.4 2.18” 26.18 26.8113 1.47 1.8813 1.85
3.5 x lo4 1.5 x lo4
21.1 22.3’ 14.9 15.05’4
-0.05’3
470 (38.7) 520(76.1) 5 14 (708) 460
* Except where indicated by reference number.
(1) The ranges of pH for the complete extraction of 2,2’dichlorodithizone complexes with copper( zinc(H) and cadmium(I1) are relatively narrower than the corresponding values for dithizone complexes. (2) The range of pH where mercury(I1) is completely extracted was practically unaffected by the presence of chlorine atoms in the ortho positions of the phenyl nuclei of dithizone. The extraction constant of the mercury(I1) complex has barely decreased from that for Hg(HDz)*.13 (3) Both the extraction and the stability constants of Cu(Cl,HDz), are lower than those for Cu(HDz),. The corresponding constants for Zn(Cl,HD,), are also slightly lower than those of Zn(HDz),. That copper(I1) is more sensitive than zmc(I1) to the substitution by chlorine in the ortho positions of the phenyl nuclei of dithizone, may be explained on the assumption that copper(I1) complexes are square planar, whereas the zinc(I1) complexes are tetrahedral. The metal atom in a square planar environment would be subjected to relatively more steric hindrance from the substituents than in a tetrahedral one, and hence the stability constant of the former complex may be more adversely affected than that of the latter. The centrosymmetric square planar configuration of Cu(I1) dithizonate” and the tetrahedral configuration of Zn(I1) dithizonate16 which have been established by X-ray structure determination, lend further support to our argument. REFERENCES
1. P. S. Pelkis, R. G. Dubenko and L. S. Pupko, Zh. Obsch. Khim., 1957, 27, 2134; Chem. Abstr., 1958, 52, 6230.
2. D. M. Hubbard and E. W. Scott, J. Am. Chem. Sot., 1943, 65, 2390. 3. R. S. Raniakrishna and M. Femandopulle, Anal. Chim. Acta, 1968, 41. 35. 4. H. M. N. H. Irving and J. J. Cox, Analyst, 1958, 83, 526. 5. A. M. Kiwan and M. F. Fouda, J. Organomet. Chem., 1970, 23, 9. 6. A. M. Kiwan and H. M. N. H. Irving, Anal. Chim. Acta, 1971, 57, 59.
7. H. M. N. H. Irving and A. M. Kiwan, ibid., 1969, 45, 255.
8. E. B. Sandell, J. Am. Chem. Sot., 1950, 72, 4660. 9. R. G. Geiger and E. B. Sandell, Anal. Chim. Acta, 1952, 8, 197.
10. S. Takei and T. Kato, Tech. Repts. Tohoku Univ., 1957, 21, 319; 1961, 25, 55; 1962, 26, 19. 11. G. IwantscheR, Das Dithizon und seine Anwendung in der Mikro- und Spurenanalyse, 2nd Ed., p. 13. Verlag Chemie, Weinheim, 1972. 12. H. M. N. H. Irving and A. M. Kiwan, Anal. Chim. Actu, 1971, 56, 435 and references therein. 13. Y. Marcus and A. S. Kertes, Ion Exchange and Solvent Extraction of Metal Complexes, p. 513. Wiley-Interscience, London. 1969. 14. C. B. Honaker and H. Freiser, J. Phys. Chem., 1962, 66, 127. 15. R. F. Bryan and P. M. Knopf, Proc. Chem. Sot., 1961, 203.
16. A. Mawby and H. M. N. H. Irving, Anal. Chim. Actu, 1971, 55, 269.
Surnmary-l,5-Di-(2-chlorophenyl)-3-mercaptoformazan (2,2’-dichlorodithizone) has been synthesized and characterized. Its acid dissociation constant and its partition coefficient between carbon tetrachloride and water have been determined. The introduction of chlorine atoms into the ortho positions of the phenyl nuclei of dithizone was found to affect the visible electronic spectra of the reagent and its metal complexes. The ranges of pH for complete extraction, and the extraction constanta for the Hg(II), Cu(II), Zn(II), Cd(II), and Pb(I1) complexes have been determined. The stability constants of the Cu(I1) and Zn(I1) complexes were also determined. Discrepancies between the present extensive data and the corresponding earlier data have been attributed to use of impure materials and/or inaccuracy of measurements in the earlier work.
Vol. 22, pp 931-932
Pergamon
Press, 1975 Pnnted
m Great Br~tam
ANNOTATION STUDIES WlTH DITHIZONJ.! ANALOGUES-II PREPARATION AND CHARACTERIZATION OF 2,2’-DICHLORODlTHIZONE AND THE INVESTIGATION OF ITS REACTIONS WKH SOME METAL IONS A. M.
KIWAN
and A. Y. KASSIM
Department of Chemistry, The University of Kuwait, Kuwait (Received 15 August 1974. Accepted 7 March 1975) 2,2’-Dichlorodithizone [l,S-di-(2chlorophenyl)-3-mercaptoformazan] was first described by Pelkis, Dubenko and Pupko’ who prepared it by the nitroformazyl method* and reported that its electronic absorption spectrum exhibits two characteristic peaks at 645 (1, ,,,) and 465 (d, m) nm. More recently, Ramakrishna and Fernandopulle3 have repeated its preparation by the same method, and reported different wavelengths for the absorption maxima, namely, 670 and 470nm respectively. They have also given data for the molar absorptivities of 2,2’-dichlorodithizone and some of its metal complexes. However, during our current studies on dithizone analogues, we have found that Ramakrishna and Fernandopulle’s data are radically different from ours and so a reinvestigation seemed desirable. This paper describes the preparation and characterization of 2J’dichlorodithizone (abbreviated hereafter as Cl,H,Dz) and reports the results of an investigation of its reactions with Ag(I), Hg(II), Cu(II), Bi(III), Zn(II), Cd(H), Co(II), Ni(II) and Pb(II) ions. EXPERIMENTAL
Reagent
The 2,2’-dichlorodithizone was prepared by the nitroformazy1 method.’ It was purified by dissolving it in dilute isopiestically distilled ammonia solution4 followed by extraction into analytical-grade chloroform and finally precipitation with 2% isopiestically prepared hydrochloric acid. It was washed free from acid and dried in vacua; m.p. 138-139” (literature values: 112-l 13”;’ 13803).Found: C 47.9x, H 3.4x, N 17.2x, Cl 21.7%; C,3H,,Cl,N,S requires C 48.290/, H 3.09x, N 17.33x, Cl 21.98%. Reagent grade salts were used and the usual precautions were taken with dithizone. Procedures
The methods used for the determination of the molar absorptivities of 2,2’-dichlorodithizone and its metal complexes, their compositions, and the effect of pH on their extractabilities into CCL, were those which were used for dithizone.5m7 The acid dissociation constant and the partitron coefficient P, of 2,2’-dichlorodithizone were measured by applying the technique used by Sandell.* The average value of pK, calculated from six determinations was found to be 475 f 0.5. The average value of the partition coefficient between carbon tetrachloride and water was 6.1 f 1 x 104. The partition coefficients, PM,_for copper(I1) and zinc(H) complexes between carbon tetrachloride and water were determined by the technique used by Geiger and SandelLg The average values were 3.5 x lo4 and 1.5 x 10“ respectively. The extraction constants K,,, for M(Cl,HDz), were
determined for the Zn(II), Cd(I1) and Pb(I1) complexes by performing extractions from 1M perchlorate solutions, and calculating the equilibrium concentrations of M(Cl,HDz),, M”+, Cl,H,Dz and H+. The concentrations of 2,2’-dichlorodithizone and it3 metal complex were determined spectrophotometrically, M”+ from the degree of extraction, and H+ from the pH of the aqueous phase. The extraction constants of Hg(Cl,HDz), and Cu(Cl,HDz), were determined by following the procedures given by Takei and Kato.‘O RESULTS
AND
DISCUSSION
Visible absorption spectra of 2,2’-dichlorodithizone and its metal complexes
The introduction of chlorine atoms into the ortho positions of the phenyl nuclei of dithiione was found to shift both absorption bands bathochromically to 644 and 462 nm respectively (vs. 620 and 450 nm for dithizone). Our values are quite close to those (645 and 465nm respectivelv) renorted bv Pelkis. Dubenko and Puoko.’ but thev are-different from the values 670 and 476 nm given by Ramakrishna and Fernandopulle,3 which for reasons given later, appear to be incorrect. The positions of I max for the metal complexes were also found to undergo various shifts as shown in Table 1. The molar absorptivities of 2,2’-dichlorodithizone were also affected (Table 1). E, __.. for 2,2’-dichlorodithizone has increased to 2.97 x i06~le.cm- ’ whereas I, msxhas decreased to onlv 3.34 x 104. Ramakrishna and Fernandopulle’s l2 ,,J3.83 x 10“ talc. by us from their peak ratio) is too high. Further, the anamolous shape of the shorter wavelength band, the displaced positions of both absorption peaks and the low peak ratio reported by them, cast serious doubts on the purity of their materials and/or the reliability of their data. The molar absorptivities of the metal complexes undergo analogous changes. compared with the corresponding metal dithizonates.’ ’ The spectral data which were given by Ramakrishna and Fernandopulle3 for the Hg(II), Ag(I), Bi(III), Pb(II), Zn(II), Cu(II), Cd(H), Co(I1) and Ni(II) complexes of 2,2’-dichlorodithizone, given in Table 1, appear to be in serious disagreement with ours. Reaction between 2,2’-dichiorodithizone and metal ions
2,2’-Dichlorodithizone was found to react with various metal ions in a stoichiometrically identical way to dithizone, giving primary and secondary 2,2’-dichlorodithizonates. The former are formed when the reagent is in excess, the latter when the pH and the proportion of metal to ligand are increased. The extraction data for metal complexes with 2,2’-dichlorodithizone are included in Table 1, inspection of which reveals the following features. 931
932
ANNOTATION
Table 1. Characteristic absorption and extraction data for 2,2’-dichlorothizone and some of its metal complexes. Some values for the corresponding dithizone complexes are included for comparison. Values in parentheses are the molar absorptivities (l.mole- ’ .cm- ‘) x 10m3
Lax (4 This work* 2,2-Dichlorodithizone Cu(Cl,HDz), Cu(HDz), Zn(Cl,HDz), Zn(HDz), Hg(Cl,HDz), Hg(HI% Cd(&HDz), Cd(HDz), Pb(Cl,HDz), PqHDz), Ag(Cl,HDz) Bi(Cl,HDz),
644 (33.4) 462 (29.8) 541 (65.8) 550 (45)” 533 (97.2) 538 (92)” 485 (86.3) 485 (71)” 527(111.4) 520 (88)’ ’ 514 (70.8) 520 (69)” 460 (39) 490(1047) 539 (55.7) 669 (26.7) 545 (37.4) 428 (41.3)
Ref. 3 670(33.1) 470 570 (77.4) 560(105) 425 (70) 500 (80.9) 550 (94.6) 530 (90.3) 430 sh.
pH for complete extn.
log K,,,
PML
log
BML
4.3-7
6.88 10.48 0.4 2.18” 26.18 26.8113 1.47 1.8813 1.85
3.5 x lo4 1.5 x lo4
21.1 22.3’ 14.9 15.05’4
-0.05’3
470 (38.7) 520(76.1) 5 14 (708) 460
* Except where indicated by reference number.
(1) The ranges of pH for the complete extraction of 2,2’dichlorodithizone complexes with copper( zinc(H) and cadmium(I1) are relatively narrower than the corresponding values for dithizone complexes. (2) The range of pH where mercury(I1) is completely extracted was practically unaffected by the presence of chlorine atoms in the ortho positions of the phenyl nuclei of dithizone. The extraction constant of the mercury(I1) complex has barely decreased from that for Hg(HDz)*.13 (3) Both the extraction and the stability constants of Cu(Cl,HDz), are lower than those for Cu(HDz),. The corresponding constants for Zn(Cl,HD,), are also slightly lower than those of Zn(HDz),. That copper(I1) is more sensitive than zmc(I1) to the substitution by chlorine in the ortho positions of the phenyl nuclei of dithizone, may be explained on the assumption that copper(I1) complexes are square planar, whereas the zinc(I1) complexes are tetrahedral. The metal atom in a square planar environment would be subjected to relatively more steric hindrance from the substituents than in a tetrahedral one, and hence the stability constant of the former complex may be more adversely affected than that of the latter. The centrosymmetric square planar configuration of Cu(I1) dithizonate” and the tetrahedral configuration of Zn(I1) dithizonate16 which have been established by X-ray structure determination, lend further support to our argument. REFERENCES
1. P. S. Pelkis, R. G. Dubenko and L. S. Pupko, Zh. Obsch. Khim., 1957, 27, 2134; Chem. Abstr., 1958, 52, 6230.
2. D. M. Hubbard and E. W. Scott, J. Am. Chem. Sot., 1943, 65, 2390. 3. R. S. Raniakrishna and M. Femandopulle, Anal. Chim. Acta, 1968, 41. 35. 4. H. M. N. H. Irving and J. J. Cox, Analyst, 1958, 83, 526. 5. A. M. Kiwan and M. F. Fouda, J. Organomet. Chem., 1970, 23, 9. 6. A. M. Kiwan and H. M. N. H. Irving, Anal. Chim. Acta, 1971, 57, 59.
7. H. M. N. H. Irving and A. M. Kiwan, ibid., 1969, 45, 255.
8. E. B. Sandell, J. Am. Chem. Sot., 1950, 72, 4660. 9. R. G. Geiger and E. B. Sandell, Anal. Chim. Acta, 1952, 8, 197.
10. S. Takei and T. Kato, Tech. Repts. Tohoku Univ., 1957, 21, 319; 1961, 25, 55; 1962, 26, 19. 11. G. IwantscheR, Das Dithizon und seine Anwendung in der Mikro- und Spurenanalyse, 2nd Ed., p. 13. Verlag Chemie, Weinheim, 1972. 12. H. M. N. H. Irving and A. M. Kiwan, Anal. Chim. Actu, 1971, 56, 435 and references therein. 13. Y. Marcus and A. S. Kertes, Ion Exchange and Solvent Extraction of Metal Complexes, p. 513. Wiley-Interscience, London. 1969. 14. C. B. Honaker and H. Freiser, J. Phys. Chem., 1962, 66, 127. 15. R. F. Bryan and P. M. Knopf, Proc. Chem. Sot., 1961, 203.
16. A. Mawby and H. M. N. H. Irving, Anal. Chim. Actu, 1971, 55, 269.
Surnmary-l,5-Di-(2-chlorophenyl)-3-mercaptoformazan (2,2’-dichlorodithizone) has been synthesized and characterized. Its acid dissociation constant and its partition coefficient between carbon tetrachloride and water have been determined. The introduction of chlorine atoms into the ortho positions of the phenyl nuclei of dithizone was found to affect the visible electronic spectra of the reagent and its metal complexes. The ranges of pH for complete extraction, and the extraction constanta for the Hg(II), Cu(II), Zn(II), Cd(II), and Pb(I1) complexes have been determined. The stability constants of the Cu(I1) and Zn(I1) complexes were also determined. Discrepancies between the present extensive data and the corresponding earlier data have been attributed to use of impure materials and/or inaccuracy of measurements in the earlier work.