From Dithizone

From Dithizone. Dithizone, PhNHN=C(SH)N=NPh, undergoes iSiV-dialkyl-ation on treatment with di-iodomethane, with simultaneous cyclization, to give the substituted 1,3,4-thiadiazoline (135), a reaction that occurs also under the influence of formaldehyde.  

The action of iron pentacarbonyl on the meso-ionic dehydrodithizone (136), expected to yield (137) by carbonyl-insertion, produces the 1,3,4-thiadiazoline derivative (138) (54%), the structure of which has been established by JT-ray analysis. The mechanism of its formation is not yet clear.  

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Many organic spectrophotometric reagents for Pd incorporate sulphur as a ligand atom. Apart from dithizone and thio-Michler s ketone, which have been discussed above, examples include the thiourea derivatives [33-36] p-dimethylaminobenzylidene-rhodanine (rhodanine) (e = 4.9 10 ) [37] and its derivatives [38], thiodibenzoylmethane [39,40], and thiosemicarbazone derivatives [41—47]. 

Procedure. To 10 mL of a solution (Note 2) containing from 1 to 10 pg of nickel(II) add 5mL of a phthalate or acetate (ethanoate) buffer of pH 6.0 or, if the sample solution is acidic, use dilute ammonia to adjust the pH. To this solution now add 15mL of a chloroform solution of dithizone (7 x 10-5M) and 1,10-phenanthroline (3 x 10-5M). Shake the phases for five minutes in a... 

Notes. (1) The reagent solution should be freshly prepared using analytical-grade dithizone and 1,10-phenanthroline, preferably taken from new or recently opened reagent bottles. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

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. 

The extraction system which was measured by the HSS method for the first time was the extraction kinetics of Ni(II) and Zn(II) with -alkyl substituted dithizone (HL) [14]. The observed extraction rate constants linearly depended on both concentrations of the metal ion [M j and the dissociated form of the ligand [L j. This seemed to suggest that the rate determining reaction was the aqueous phase complexation which formed a 1 1 complex. However, the observed extraction rate constant k was not decreased with the distribution constant Kj of the ligands as expected from the aqueous phase mechanism. 

FIG. 4 Dependence of the extraction rate constants, k, of Zn(II) and Ni(II) on the number of carbon atoms in the substitution of w-alkyl dithizones. The solid lines trace the observed values and the broken lines the values predicted from the aqueous mechanism. 

Traces of copper and lead are separated [301] from macro amounts of calcium, magnesium, sodium, and potassium by adsorption from the sample onto active carbon modified with hydroxyquinoline dithizone or diethyldithiocarbamate. 

In many applications, such as the analysis of mercury in open ocean seawater, where the mercury concentrations can be as small as 10 ng/1 [468,472-476], a preconcentration stage is generally necessary. A preliminary concentration step may separate mercury from interfering substances, and the lowered detection limits attained are most desirable when sample quantity is limited. Concentration of mercury prior to measurement has been commonly achieved either by amalgamation on a noble-metal metal [460,467, 469,472], or by dithizone extraction [462,472,475] or extraction with sodium diethyldithiocarbamate [475]. Preconcentration and separation of mercury has also been accomplished using a cold trap at the temperature of liquid nitrogen. 

In these procedures 1 litre of seawater was shaken with 60 mg charcoal for 15 min. Complexing agents were added in amounts of 1 mg, dissolved in 1 ml of acetone. The pH was 5.5, or it was adjusted to 8.5 by addition of 0.1 M ammonia. The charcoal was filtered off and irradiated. Results of three sets of experiments with charcoal alone, charcoal in the presence of dithizone, and charcoal in the presence of sodium diethyldithiocarbamate are compared. The following elements are adsorbed to an extent from 75 to 100% silver, gold, cerium, cadmium, cobalt, chromium, europium, iron, mercury, lanthanum, scandium, uranium, and zinc. The amount of sodium is reduced to about 10 6, bromine to about 10 5, and calcium to about 10 2. 

Lead Lead extracted from water with chloroformic dithizone Graphite furnace AAS - [364]... 

Methylmercury has been preconcentrated from seawater by extraction with a solution of dithizone prior to analysis by gold foil cold vapour atomic absorption spectrometry [126]. 

EDTA salts are used for the treatment of heavy metal poisoning. Roosels and Vanderkeel142) were able to extract lead from urine in the presence of EDTA with dithizone by adding calcium to presumably release the lead from EDTA. In view of the fact that the formation constant of the lead-EDTA chelate is 20,000,000 times larger than that of the corresponding calcium chelate, it is doubtful that the calcium actually releases the EDTA from the lead. 

In a similar procedure [32] the sediment is wet oxidised with dilute sulphuric acid and nitric acids in an apparatus in which the vapour from the digestion is condensed into a reservoir from which it can be collected or returned to the digestion flask as required. The combined oxidised residue and condensate are diluted until the acid concentration is IN and nitrate is removed by addition of hydroxylammonium chloride with boiling. Fat is removed from the cooled solution with carbon tetrachlodithizone in carbon tetrachloride. The extract is shaken with 0.1M hydrochloric acid and sodium nitrite solution and, after treatment of the separated aqueous layer with hydroxylammonium chloride a solution of urea and then EDTA solution are added to prevent subsequent extraction of copper. The liquid is then extracted with a 0.01% solution of dithizone in carbon tetrachloride and mercury estimated in the extract spectrophotometrically at 485nm. 

It is, however, pertinent to mention here that dithizone is an extremely sensitive reagent and, therefore, helps in the determination of lead either from a neutral or faintly alkaline medium to the extent of a few micrograms. 

Excess dithizone may be removed from the chloroform layer by back-extraction with 10 ml of 0.1 M NaOH, (a through shaking for 60 seconds will suffice this extraction),... 

Results(79) from a Round Robin analyses for the lead content of air particulate filters were given along with the average values obtained from 65 laboratories participating in the study. The procedures used by the other laboratories included x-ray, FAA, flameless atomic absorption, emission spectrometric, and dithizone-spectropho-tometric. The overall analytical agreement was very good. 

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