13C NMR spectra and the structure of dithizone

The structural characteristics of dithizone in the solid state and in solution were studied by a high-resolution¹³C NMR method. A highly symmetrical structure of dithizone was established in the crystalline state, and it was suggested that it exhibits dual behavior in complexation reactions with metal ions.V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 113–117, January, 1992.     

Studies with dithizone: Part 35. A new look at the structure of dithizone in solution

The traditional view that solutions of dithizone in organic solvents comprise equilibrium mixtures of thione- and thiol-forms which are individually responsible for the characteristic strong absorption bands around 620 and 440 nm is examined critically. It is shown that experimental values of pH_{$\text{1}\text{2}$}, pK and R (the peak ratio) can legitimately be used in calculations although they are compounded of parameters (partition coefficients, acid dissociation constants, etc.) relating to both of the alleged tautomeric forms and the equilibrium constant, K_T governing the interconversion. Published attempts to calculate K_T from spectral data alone are shown to be unreliable.     

Electron spectra and structure of dithizone and its ions

Energies and intensities of electron transition of different forms of dithizone were calculated by the method of molecular orbitals (LCAO MO SCF LCI) and compared with the measured spectra of dithizone and its ions. It has been found that the spectrum of nondissociated dithizone corresponds to a compound which is close to the structure of the enol form. The spectrum of dithizone in moderate alkaline solutions corresponds to the enol form with the SH- group dissociated and in strongly alkaline solutions (approx. 2N NaOH) to the enol form with both hydrogen atoms dissociated. The spectrum of dithizone in 60% H₂SO₄ corresponds to the enol form with the imine group protonated.     

The reaction of gold and dithizone

On thermodynamic grounds gold(III) and gold(I) are likely to oxidize dithizone rather than to form complexes. Conditions are described to obtain all the spectra previously ascribed to “gold dithizonate” both in a single system and separately. Oxidation products are responsible for several of the peaks, and it is unlikely that any of the species obtained is a gold dithizonate except possibly that giving the transitory peak at 490 nm. Analytical processes based on the reaction of gold and dithizone should be recognised as involving oxidation and treated with extreme caution.     

Spectrophotometric determination of selenium with dithizone

Microgram amounts of selenium(IV) are determined by measuring the decrease in absorbance of dithizone in carbon tetrachloride solution at 620 nm. Relative standard deviations for samples containing 0.20 and 1.00 μg of selenium(IV) are 0.6% and 0.4%, respectively. Of several metals tested only copper (at the 1.0-μg level) and iron (at the 100-μg level) interfere but high concentrations of nitric or perchloric acid cause low results. A reinvestigation of the reaction of selenium(IV) with dithizone suggests a formula Se(HDz)₄ for the dithizonate.     

Investigations on the redox character of dithizone by voltammetric methods: Part II. The elucidation of the deterioration of dithizone solutions

The electrochemical redox behaviour of dithizone and its oxidation products have been examined in detail and the mechanisms of the electrochemical and aerial oxidation of dithizone are considered. All the oxidation products (tetrazolium and disulphide compounds) can be followed by voltammetric methods. The results of the electrochemical investigation of dithizone are useful for practical analytical and electroanalytical applications of dithizone.     

Investigations on the redox character of dithizone by voltammetric methods : Part I.The reduction of dithizone in aqueous solutions

The mechanism of the electrochemical reduction of dithizone to the corresponding hydrazo compound, diphenylthiocarbazide, has been examined in detail by polarographic and voltammetric techniques over a wide pH range. The reaction is reversible and dithizone can be determined polarographically in the range 10^-3–10^-5M. This polarographic behaviour suggests new applications of dithizone as an electroanalytical reagent.     

The solvent extraction of zinc with dithizone

The extraction of 10^-5M zinc ion from aqueous solution into an organic solvent 1.8 . 10–3m in dithizone has been investigated. The effects of pH, other ions in the aqueous phase including ions which complex with zinc, and various organic solvents have been investigated. Ions which complex with zinc (citrate, oxalate, nitrilotriacetate, ethylenediaminetetracetate) change the position and/or shape of the extraction curve. Changes in the organic solvent alter the position of the curve, this alteration being qualitatively related to the solubility of dithizone in the organic solvent. Spectra for dithizone and for zinc dithixonate in several organic solvents have also been determined.     

双硫腙水溶液的极谱研究

用单扫描极谱法和循环伏安法研究了双硫腙在酸性和碱性水溶液中的极谱行为.在碱性介质中,有三个还原波-0.63,-0.52和-0.45V,分别对应于双硫腙阴离子,它的氧化产物四氮化合物和二硫化合物的还原过程,在酸性介质中,只有一个-0.18V的双硫腙还原波.上述波的电极反应和特征也讨论了.     

A fast photometric titration for the standardization of dithizone solutions

A simple method is reported for standardizing 10^?5–10^?4 M dithizone solutions for titrimetric analysis. Dithizone in an anhydrous acetic acid/chloroform (4% v/v) medium is titrated with 2 × 10^?4 M mercury(II) acetate in the same medium. The titratioin takes only a few minutes. The accuracy (+0.2%) and precision (r.s.d. = 0.7%) achieved are similar to those obtained by the classical extractive titration with silver(I).     

Chemical and electrochemical oxidation and reduction of dithizone

A non-aqueous electrochemical study of dithizone, H₂Dz, 1, is compared with the chemical oxidation and reduction profile of this versatile ligand. Chemical oxidation of 1 by I₂ initially leads to an isolatable disulfide-bridged species, (HDz)₂, 2₂, but ultimately monomeric dehydrodithizone, Dz, 3, is formed. Electrochemically, in CH₂Cl₂/0.1 mol dm⁻³ [N(ⁿBu)₄][B(C₆F₅)₄], two oxidation processes are observed for 1. Evidence of the electrochemical formation of the dimer 2₂ was found, but on a CV timescale the fully oxidized species, 2_2oxidized, did not convert to the chemically stable species 3. Regeneration of 1 during an irreversible electrochemical reduction of the electrochemically generated fully oxidized species, 2_2oxidized, was detected. Two further one-electron electrochemical irreversible reduction steps were also identified to ultimately generate H₃Dz⁻, 8, one of the synthetic precursors to 1. In contrast, resolution and identification of the electron transfer steps of 1 in both dimethylsulfoxide, DMSO, or in CH₂Cl₂/0.1 mol dm⁻³ [N(ⁿBu)₄][PF₆] were hampered by solvation and ion paring of [PF₆]⁻ especially with the oxidized species of 1. A metathesis of water-soluble potassium dithizonate, KHDz, 4b, led to lipophilic [N(ⁿBu)₄][HDz], 4c.     

Reaction of tellurium(iv) with dithizone

With an excess of dithizone over tellurium, the extraction of Te(IV) from 1 M perchloric acid solutions into a carbon tetrachloride solution (o) of dithixone follows the relation

When the acidity is varied, again with a sufficiently large excess of dithissone, the following relation seems to be approached;

(μ=1.0).     

Preferential solvation of dithizone in chloroform in cyclohexane

The molar absorptivity of diphenylthiocarbazone in cyclohexane is dramatically enhanced by the addition of small quantities of chloroform. This has been attributed to the formation of a 1:2 dithizone chloroform complex (formation constant 10^4.0) rather than simple nonspecific solvent effects.     

Extraction and spectrophotometric determination of cobalt with dithizone

Cobalt(II) in acetate-tartrate buffer (pH 6.0-7.3) is extracted quantitatively as cobalt(III) dithizonate with excess of dithizone in CCl(4). The molar absorptivity in the CCl(4) phase is 4.6 x 10(4) 1.mole(-1).cm(-1) at the absorption maximum 550 nm. The calibration graph is linear for 1-10 mug of cobalt in 10 ml of CCl(4) when excess of dithizone is removed by back-extraction with 0.01M aqueous ammonia. Most interferences can be overcome by (a) initial extraction with dithizone at pH 1.3, (b) selective back-extraction into hydrochloric acid (pH 1 to 2), (c) oxidation of iron and tin to iron(III) and tin(IV) and addition of fluoride to complex the former, and (d) selective reaction of nickel dithizonate with 1,10-phenanthroline in the CCl(4) phase followed by back-extraction of nickel into 0.1M acid. The method has been applied to determination of cobalt in a copper-nickel-zinc alloy and a nimonic alloy.     

More light on the low electronic transition energy bands of dithizone

The visible electronic spectral behaviour of different concentrations of dithizone in pure and mixed various organic solvents has been investigated. It is identified that in dilute basic solvents solutions, dithizone (H₂DZ) exists mainly in monovalent anionic form (HDZ⁻), where its extent of ionization is largely dependent on the solvent basicity effect. The visible absorption band belonging to absorption of HDZ⁻ form and the shorter visible one belonging to absorption of H₂DZ form are assigned to a transition involving the whole solute associated with intramolecular CT interaction. On the other hand, the longer wavelength visible band observed in the spectrum of the H₂DZ form is assigned to absorption of hydrogen bonding solvated molecular complex. This involves an electron transfer from the lone pair of electrons belonging to solvent molecule to the σ*-antibonding orbital of the acidic NH bond belongs to H₂DZ form.     

Studies with dithizone : Part 26. The interaction of thallium(III) with solutions of dithizone in organic solvents

The strong oxidising capacity of thallium(III) dominates its reaction with solutions of dithizone (H₂Dz) in organic solvents. When carbon tetrachloride is used as solvent, the unstable thallium(III) complex Tl(HDz)³ is found in the organic phase but it very quickly disproportionates to the thallium(I) complex [Tl(HDz)], and bis-1,5-diphenylformazan-3-yl-disulphide. This reaction is notably faster in chloroform, in which thallium(I) dithizonate is the first identifiable product. In contact with an acidic aqueous phase, thallium(I) dithizonate is reverted to regenerate dithizone in the organic phase and Tl⁺ ions appear in the aqueous phase. Organic solutions of the disulphide disproportionate spontaneously by first-order kinetics to give an equimolar mixture of dithizone and the mesoionic compound, 2,3-diphenyl-2,3-dihydrotetrazolium-5-thiolate: this change is much slower in carbon tetrachloride than in the more polar chloroform and is catalysed by both Tl⁺ and Tl³⁺. If thallium(III) is present in excess, the mesoionic compound is the principal oxidation product of the dithizone although a dication may also be formed. The mesoionic compound does not react with thallium(I) but forms a water-soluble 2:1 complex with thallium(III); partition of this complex into the organic phase is uninfluenced by chloride ions. Because of the large number of competing reactions, the composition of the reaction mixture at any stage of the reaction between thallium(III) and dithizone depends on the relative concentrations of the components, the order in which they are brought together, the time elapsed after mixing, the pH of the aqueous phase, and the nature of the organic solvent.