Dithizone complexes with

The determination of an analyte s concentration based on its absorption of ultraviolet or visible radiation is one of the most frequently encountered quantitative analytical methods. One reason for its popularity is that many organic and inorganic compounds have strong absorption bands in the UV/Vis region of the electromagnetic spectrum. In addition, analytes that do not absorb UV/Vis radiation, or that absorb such radiation only weakly, frequently can be chemically coupled to a species that does. For example, nonabsorbing solutions of Pb + can be reacted with dithizone to form the red Pb-dithizonate complex. An additional advantage to UV/Vis absorption is that in most cases it is relatively easy to adjust experimental and instrumental conditions so that Beer s law is obeyed. 

The measurment in twophase systems is discussed by the example of dithizonate of zinc, in pseudomonophase systems - by the example of zinc and cadmium complexes with l-(2-pyridylazo)-2-naphthol, lanthanoid ion complexes with l-(2-pyridylazo)-resorcin. 

The nature of the donor atoms in the chelating agent. Ligands which contain donor atoms of the soft-base type form their most stable complexes with the relatively small group of Class B metal ions (i.e. soft acids) and are thus more selective reagents. This is illustrated by the reagent diphenylthiocarbazone (dithizone) used for the solvent extraction of metal ions such as Pd2+, Ag+, Hg2+, Cu2+, Bi3+, Pb2+, and Zn2 +. ... 

Multi-element analyses involving solvent extraction and high performance liquid chromatography (HPLC) have also been described. The extracts, containing metal-chelate complexes with sulphur-containing reagents, such as dithizone and diethyldithiocarbamate, were used directly for determination of the metals by HPLC.14... 

The cobalt complex is usually formed in a hot acetate-acetic acid medium. After the formation of the cobalt colour, hydrochloric acid or nitric acid is added to decompose the complexes of most of the other heavy metals present. Iron, copper, cerium(IV), chromium(III and VI), nickel, vanadyl vanadium, and copper interfere when present in appreciable quantities. Excess of the reagent minimises the interference of iron(II) iron(III) can be removed by diethyl ether extraction from a hydrochloric acid solution. Most of the interferences can be eliminated by treatment with potassium bromate, followed by the addition of an alkali fluoride. Cobalt may also be isolated by dithizone extraction from a basic medium after copper has been removed (if necessary) from acidic solution. An alumina column may also be used to adsorb the cobalt nitroso-R-chelate anion in the presence of perchloric acid, the other elements are eluted with warm 1M nitric acid, and finally the cobalt complex with 1M sulphuric acid, and the absorbance measured at 500 nm. 

Keeping in mind the above work, experiments were carried out to examine the effects of ultrasound, on the dissolution of zinc metal in an alkaline medium and the decomposition of zinc-dithizone complex in the presence of an ultrasonic field. To examine the effect of power ultrasound on the dissolution of zinc metal in alkaline media, 0.0480 g zinc metal was treated with 10 ml of 5 M NaOH solution. Two samples of this solution were exposed to ultrasound for 15 and 30 min, while, control samples were also kept in the similar condition and for the same duration. To compare their spectra and concentration of dissolved zinc in sonicated and control conditions, zinc-dithizone complex was formed by adding 0.5 ml of 0.005% dithizone solution. The red coloured complex, thus obtained, was extracted in chloroform and made upto to the mark in 25 ml volumetric flask with chloroform. 

Zn-dithizone complex gradually decreased (Fig. 9.2). Mechanism for the decomposition of this complex could thus be explained that the complex was broken into zinc ions and dithizone before dithizone molecules were oxidised to S=C (N=NC6H5)2, which, however, did not react further with metal ions [114] and therefore, the Zn-dithizone complex was decomposed. The decomposition of Zn-dithizone complex could thus be attributed to the oxidation of dithizone molecule in ultrasonic field. 

Analysis by GC of the various organolead species present in gasoline requires special detectors because of the profusion of species with retention times near those of the organometaHic compounds. An old determination method consisted of scrubbing the separated species in iodine solution, foHowed by spectrophotometric determination of the complex with dithizone (2)133,134 (see also Table 2). 

In actual practice, an excess of the standard solution of disodium edetate is added to the sample, pH is adequately adjusted for the residual titration with a metal-ion solution e.g., ZnS04 and employing an appropriate indicator which is sensitive enough to the respective titrant. However, the metal ion under estimation remains firmly complexed with the EDTA and offers little interference with the Zn-EDTA complex formed. It has been established experimentally that bismuth readily yields a highly stable complex which may be titrated conveniently between pH 1 and 2. Bismuth forms a stable complex by reacting with EDTA quantitatively at pH 4.0 and, therefore, dithizone is employed as an indicator to detect the end-point for it has a transition state of colour at pH 4.6. 

It has been observed that the complex formed by Mn2+ with dithizone alone is of no practical analytical utility because of the fact that it undergoes decomposition very quickly. However, the addition of a base, such as pyridine into the Mn2+ plus dithizone complex yields a red-complex, which is fairly stable to oxidation and light and, therefore, forms the basis for a very sensitive photometric method employed in estimating trace amounts of Mn2+. 

The i.r. and n.m.r. spectra of copper(ii) dithizonate together with other physicochemical data indicate that the complex is dimeric with structure (201). " The Schiff bases S-methyl-N-isopropylidenedithiocarbazate (NSH) and S-methyl-7V-(2-pyridyl)methylenedithiocarbazate (NNSH) form the square-... 

Dithizone (diphenylthiocarbazone) is a green compound that is soluble in nonpolar organic solvents and insoluble in water below pH 7. It forms red, hydrophobic complexes with most di- and trivalent metal ions. 

The crystal structures of methyl- and phenyl-mercury(II) dithizonates have been determined as part of a study on the photochroism of such compounds.149 In both structures the chelate is planar, with an irregular three-coordination at the metal including N and S of the ligand. The article provides a short structural review of dithizone complexes. 

Fig. 4.13 Separation of a standard trace metal sample (extracted with dithizone solution). Divisions on baseline 1 min per division peaks, dithizone complexes of (a) Hg, (b) Cu, (c) Ni,...

The most widely applied reagents have been chelating agents which will complex with many metals, e.g. dithizone and the various thiocarbamate derivatives such as diethyldithiocarbamate and pyrrolidine dithiocarbamate. The latter agent as the ammonium salt (APDC) has been shown to complex some thirty elements [19] most of which can be readily extracted into various solvents. 4-Methylpentane-2-one (methyl isobutyl ketone or MIBK) is usually the favoured solvent because of its excellent compatibility with flames. The solubility of MIBK in water is not negligible and this limits the available concentration factor to ten higher molecular weight ketones (e.g. decan-2-one) offer better concentration factors and chloroform up to fifty times, but this latter solvent is only really suitable for electrothermal atomisation. 

Dithizone test Dithizone (diphenyl thiocarbazone) forms complexes with a number of metal ions, which can be extracted with carbon tetrachloride. The zinc complex, formed in neutral, alkaline or acetic acid solutions, is red ... 

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. ... 

Other extraction agents such as dithizone, diethyl dithiocarbamates, and 8-hydroxy-quinoline (oxine) are also useful as chelating agents and extract several metals including transition metals, alkali and alkaline metals. The dithizone can extract up to 20 elements and these complexes behave the same and there is no additional advantage of using one over the other. The compound 8-hydroxyquinoline will form stable complexes with Al, Ca, Sr and Mg at pH 8.0 these metals form unstable complexes with APDC. At carefully controlled pH the oxidation states of metals may also separated, e.g. Fe[II] and Fe[III], The stmcture of 8-hydroxyquinoline is ... 

In an indirect method, thiocyanate and Hg(II) form a mixed-ligand mercury complex with quinoline, which can be extracted into chloroform. This complex can be treated with a CHCI3 solution of dithizone to form the Hg(HDz)2 complex [45]. 

In the indirect methods of determining iodide, use has been made of the exchange of ligands between iodide and a Hg(II) complex with diphenylcarbazone [20], the Ag complex with DDTK (in the presence of Cu ions) [21], the Hg(II) complex with dithizone [22], the Ag complex with 4-(2-quinolyl)phenol [23], and the Pd complex with 2-nitroso-5-diethylaminophenol (e = 2.3-10 at 540 nm) [24]. 

After the extraction of the Pb complex with crown ether by CHCI3 from 2 M HNO3 medium, dithizone in CHCb-ethanol solutions was added to the extract [7]. 

Dithizone (in the presence of pyridine or phen as synergistic agents) forms an extractable (CCI4) complex with manganese (e = 5.7-10 at 510 nm) [39 2]. Manganese can also be determined with HTTA (e = 6.1-10 at 420 nm) [43,44] and 8-hydroxyquinoline (extraction in the presence of quaternary bases) [45]. 

Two methods are presented in detail an extractive dithizone method and the thio-Michler s ketone method. Both of them have good selectivity but the latter is more sensitive. Methods based on ion-associates formed by anionic mercury complexes with basic dyes are also noteworthy. 

---