Dithizone metal complexes

The reactions of silver(I) with 1,5-diphenyl thiocarbazone (56 dithizone = HaDz) by comparison to thiosemicarbazones have been thoroughly investigated.442,444 Dithizone has for many years been used as a colorimetric reagent for trace metal ions. Its metal complexes are of two types, the so-called primary and secondary dithizonates. Primary dithizonates are generally formed at low pHs where the ligand becomes mono depronated (pA = 4.5) but retains the NH proton. Secondary dithizonates are formed in the presence of an excess of metal and/or at higher pH values where the ligand becomes fully deprotonated. Since it has been estimated that for free dithizone pK2 > 15, the second proton obviously becomes labilized in the presence of metal ions. 

I, 5-diphenylcarbazide and chromium(III). P. Cazeneuve (1900), and F. Feigl and F. L. Lederer (1925) later used the procedure for certain separations.5 However, the most pregnant discovery was made by Helmuth Fischer (1925) when he pioneered the analytical applications of dithizone, PhNHNHCSN==NPh. Here both the reagent and its metal complexes are intensely coloured, soluble in organic solvents but insoluble in water. Only a small number of metals react and the procedures can readily be made highly selective.7 8... 

The selectivity of spectrophotometric methods has been greatly increased by the development of derivative spectrophotometry (see Chapter 1.5). Derivative spectrophotometry enables one to single out, by means of various mathematical algorithms of data processing, a separate signal due to a selected component, from the sum of absorbances of the analysed mixture. This technique was successfully applied in determinations of a number of elements in mixtures such as Pd, Pt and Au [37], Pd and Pt in iodide solutions [38], Au, Pd and Pt in bromide solutions [39], Ru(IIl) and Rh(IIl) in the form of octadecyldithiocarbamate complexes [40], Ru and Os in chloride solutions [41], Cu, Hg and Pb as dithizonates [42], complexes of various metals with 4-(2-pyridylazo)resorcinol [43], Fe(IIl) with EDTA in the presence of Cr(III), A1 and Mn [44], Cr(III) and Cu(II) with EDTA [45], and Cu and Co in a flow system [46]. Derivative spectrophotometry was also used in the study of Sr- complexing reactions with various crown ethers [47]. 

A redetermination of the structure of the commonly encountered oxidation product of the metal complexing agent dithizone (PhN=NC(S)NHNHPh) has confirmed it to be 3-phenylazo-l//-4,1,2-benzothiadiazine (21) <69CC392, 82AJC2157). The crystals of the azo-compound are orthorhombic and the substantially planar molecule is present as the 1 //-tautomer in the solid state. 

IR studies of metal xanthates and dithizonates, including complexes of Zn, Cd and Hg, have been reported. 

Diphenylthiocarbazone (dithizone) test dithizone forms complexes with a number of metal ions, which can be extracted with chloroform. The zinc complex, formed in neutral, alkaline or acetic acid solutions, is red ... 

There are two overlapping absorbance bands for dithizone (Dz) metal complexes and free dithizone. The Cd(Dz)2 complex absorbs strongly at 520 nm but very weakly at 606 nm (e -100 M cm at 606 nm). Thus, the 606 nm absorbance was used to monitor free dithizone. 

Lead can conveniently be separated quantitatively from all other metals except bismuth, by the method of Allport and Skrimshire. Diphenyl-thiocarbazone (dithizone) forms a metallic complex with lead, which is insoluble in water and can be extracted by organic solvents. Other metals can give a similar complex, but in most cases potassium cyanide prevents their formation. The method is of particular value in the presence of iron in quantity, which does not form a compound with the reagent. 

A series of papers dealing with the preparation and properties of metal complexes of l-coumariloyl-4-arylthiosemicarbazides, N-phenylthiocar-bamoyl-N -guanylhydrazine, " 4-aryl-3-thiourazoles, S-methyl-dithizone, " and arylazothioformamides may be of interest to workers in that field. 

Dithizone (PhN=NCSNHNHPh) forms uncharged, water insoluble complexes with most heavy metals, especially Hg (forming HgL2), Ag and Cu, which can be extracted into organic solvents and measured spectrophotometrically. Various derivatives of dithizone have been prepared in an attempt to improve on its analytical properties and its stability. Its metal complexes are subject to photochemical decomposition. Dithizones are potentially capable of tautomerism to SH-forms, leading to difficulties of nomenclature and CAS registration (see note on pagexi). 

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... 

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