Metal dithizonates

It functions as a monoprotic acid (pKa = 4.7) up to a pH of about 12 the acid proton is that of the thiol group in (C). Primary metal dithizonates are formed according to the reaction ... 

Alternatively, an aqueous solution of sodium diethyldithiocarbamate (3.5%, 2 ml) or freshly prepared solution of dithizone in chloroform (0.1%, 10 ml) was added to sample A. The metal diethyldithiocarbamates (termed sample B) or metal dithizon-ates (termed sample C) thus formed were extracted in chloroform. The volume of chloroform extract was reduced to 1.0 ml. Aliquots (10 pi) each of sample B and sample C were chromatographed on plates coated with 0.25-mm layer of silica gel G using benzene -t methyl isopropylketone (50 1) and toluene -r chloroform (50 1), respectively, as mobile phases. Metal dithizonates were self-detected. The namral colored metal diethyldithiocarbamates were converted into brown spots by spraying... 

The enol-ioxm of Dithizone (I) behaves as monoprotic acid having a dissociation constant pKa = 4.7 upto a pH range of about 12 obviously, the acid proton is inherited due to the thiol moiety in (I). In reality, two kinds of metal dithizonates are invariably formed, namely ... 

The separation of five metal dithizone complexes extracted from a standard metal solution, is illustrated in Fig. 4.13. 

Diphenylthiocarbazone ( dithizone ) forms intensely colored complexes with, for example, Mn, Fe, Co, Ni, Cu, Zn, Pd, Ag, Cd, Pt, Au, and Hg, which are soluble in CCLi and CHCI3, a property which facilitates then-separation and individual determination.Solutions ofmost metal dithizonates in organic solvents have the interesting property of being photochromic (see Photochromism), and the relatively long half-life of the photoexcited mercury(II) dithizonate complexes (ti/2 ca. 1 min) has facilitated then-investigation by conventional specttoscopic techniques. ... 

In addition to distribution chromatographic of ions on paper by utilization of various spray reagents to help detection, thin-layer chromatography of metal chromatography of metal chelates, more than any other technique, has been widely applied with metal dithizonates in particular ... 

Gregorowicz, Z., Kulicka, J., Suwinska, T. Separation and detection of trace amounts of some heavy metal dithizonates by thin-layer chromatography. Chem. Anal. (Warsaw) 16,... 

Suzuki, M., Kaiho, F., Takitani, S. Thin-layer chromatography of inorganic compounds. XIV. Colorimetric determination of metal dithizonates by elution from the thin-layer plate. Eisei Kagaku (J. Hyg. Chem.) 21, 47 (1975) C. A. 83, 187 955u (1975)... 

Tewari, S. N., Bhatt, N. Separation and identification of metal dithizonates by thin-layer chromatography and its application in toxicological analysis. Mikrochim. Acta 337 (1973)... 

Hydrogen transfer (tautomerism) (e.g., metal dithizonates, A-salicylidene-anilines, etc.)... 

C. Geosling, A. W. Adamson, and A. R. Gutierrez, Photochemical and kinetic studies of some metal dithizonate complexes, Inorg. Chim. Acta 29, 279-287 (1978). 

The solubility of metal dithizonates, like that of dithizone itself, is higher in CHCI3 in CCI4 (10- -10 I sparingly soluble in CCI4. 

Solutions of metal dithizonates in organic solvents are intensely coloured, their colour differing considerably from that of dithizone. An exception is the grey-green solution of Pd(HDz)2. Figure 4.4 shows the absorption spectra of dithizone and several dithizonates dissolved in CCU. The presence of CHCI3 admixtures in carbon tetrachloride affects the molar absorptivity of dithizone [90]. 

The most frequently applied method for determining metals with dithizone consists in extracting the metal from aqueous solutions with an excess of dithizone solution in CCI4 (CHCI3), removing the free dithizone from the non-aqueous phase by shaking with an alkaline aqueous solution, and measuring the absorbance of the coloured metal dithizonate solution. 

Unlike other metal-dithizone systems, for palladium there is only a slight difference between the colours of the complex and the free reagent. Pd(HDz)2 is formed rather slowly. The extraction rate increases with increasing excess of dithizone and in the presence of SnCl2 (in small amounts) or f. 

From the carbon tetrachloride extract containing Zn, Cd, Ni, and Co (all of which form soluble ammine complexes), Zn and Cd can be separated quantitatively by utilizing the differences in resistance of the four metal dithizonates to acid treatment. Ni and Co dithizonates begin to form at pH 4, but once formed are rather hard to decompose even... 

In solution the photochromism of coordination compounds can result from photoinduced isomerization e.g. metal dithizonates " ), substitution e.g. iron(II) phthalocyanine in the presence of benzyl isocyanide ) and oxidation—reduction e.g. tris(diethyldithiocarbamato)-nickel(rV) bromide ). 

Table 5 Use of Masking Agents in the Extraction of Metal Dithizonates - ...

Figure 20.3. Qualitative extraction curves for metal dithizonates. From G. H. Morrison and H. Preiser in C. L. Wilson and D. Wilson, eds.. Comprehensive Analytical Chemistry, vol. lA, Amsterdam Elsevier, 1959, by permission of the publisher.

Fig. 1, Qualitative extraction curves for metal dithizonates in carbon tetrachloride. From Morrison and Freiser (M7, p. 161). Reproduced by permission of Ekevier Publishing Co.

Intramolecular hydrogen transfer Intramolecular hydrogen transfer is found in anils, benzylpyridines, triazoles, oxazoles, metal dithizonates, and perimidinespirohexadienones... 

Figure 9 The extraction percentage versus pH diagram for some metal dithizonates extracted by carbon tetrachloride.

Since the spectrophotometric determination of Hg by means of di-thizone can be falsified by other heavy metals and oxidation products of the dithizone, it is best to purify the dithizone extract by TLC beforehand. The various metal dithizonates, dithizone and its oxidation products are separated from one another on the chromatogram. In particular the ubiquitous Cu-dithizonate can be separated. The spots of Hg-dithizonate may be scraped off, eluted and evaluated colorimetric-ally. The order of migration distances is ... 

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