1,5-diphenylcarbazone

Oxidation of diphenylcarbazide (Section VII,3) with hydrogen peroxide in the presence of alcoholio potassium hydroxide affords diphenylcarbazone  

Phenylhydrazine condenses with carbon disulphide to yield the phenylhydrazine salt of p-phenyldithiocarbazic acid (I), whioh on heating at 96-98° until the first evolution of ammonia is detectable affords diphenylthiocarb-azide (II)  

Upon heating diphenylthiocarbazide with methyl alcoholic potassium hydroxide dithizone (or diphenylthiocarbazone) (III) is produced  

Equip a 500 ml. three-necked flask with a dropping funnel, a mechanical stirrer and a reflux condenser. Place a solution of 72 g. (65 ml.) of redistilled phenylhydrazine (Section IV,89) (CAUTION poisonous) in 300 ml. of ether in the flask, stir vigorously, and add 33 g. (26 ml.) of A.R. carbon disulphide slowly during about 30 minutes. A precipitate is formed immediately upon the addition of the carbon disulphide, the mixture becomes warm and the temperature soon approaches the boiling point maintain the temperature just below the b.p. by cooling with ice water if necessary. When the addition is complete, stir for a further 30 minutes, then Alter the precipitate at the pump, wash it with about 25 ml. of ether, and spread it upon Alter paper for 20 minutes to permit of the evaporation of the ether. The yield of the salt (I) is 92 g. 

---

Chloride is determined by titrating with Hg(N03)2, forming soluble HgCb-The sample is acidified to within the pH range of 2.3-3.8 where diphenylcarbazone, which forms a colored complex with excess Hg +, serves as the visual indicator. Xylene cyanol FF is added as a pH indicator to ensure that the pH is within the desired range. The initial solution is a greenish blue, and the titration is carried out to a purple end point. 

The concentration of Ch in a 100.0-mL sample of water drawn from a fresh water acquifer suffering from encroachment of sea water, was determined by titrating with 0.0516 M Hg(N03)2. The sample was acidified and titrated to the diphenylcarbazone end point, requiring 6.18 mb of the titrant. Report the concentration of Cb in parts per million. 

Chloride. Chloride is common in freshwater because almost all chloride salts are very soluble in water. Its concentration is generally lO " to 10 M. Chloride can be titrated with mercuric nitrate. Diphenylcarbazone, which forms a purple complex with the excess mercuric ions at pH 2.3—2.8, is used as the indicator. The pH should be controlled to 0.1 pH unit. Bromide and iodide are the principal interferences, whereas chromate, ferric, and sulfite ions interfere at levels greater than 10 mg/L. Chloride can also be deterrnined by a colorimetric method based on the displacement of thiocyanate ion from mercuric thiocyanate by chloride ion. The Hberated SCN reacts with ferric ion to form the colored complex of ferric thiocyanate. The method is suitable for chloride concentrations from 10 to 10 M. 

Barbiturate metabolites are more heavily colored by the mercury(I) nitrate reagent (exception allobarbital), while unaltered barbiturates react more sensitively to the mercury(II)-diphenylcarbazone reagent (q.v.) [1]. 

In the titrmetric procedure, the serum is diluted in 0.07 N nitric acid and titrated with a dilute mercuric nitrate solution in the presence of diphenylcarbazone (34). A purple color forms when excess mercury ions appear, over that needed to complex the chloride. Using an ultramicro buret this method has found wide use in the past. The microburets which are available such as the Rehburg buret are typified in Figure 22. 

Diphenylcarbazone and diphenylcarbazide have been widely used for the spectrophotometric determination of chromium [ 190]. Crm reacts with diphenylcarbazone whereas CrVI reacts (probably via a redox reaction combined with complexation) with diphenylcarbazide [ 191 ]. Although speciation would seem a likely prospect with such reactions, commercial diphenylcarbazone is a complex mixture of several components, including diphenylcarbazide, diphenylcarbazone, phenylsemicarbazide, and diphenylcarbadiazone, with no stoichiometric relationship between the diphenylcarbazone and diphenylcarbazide [192]. As a consequence, use of diphenylcarbazone to chelate Crm selectively also results in the sequestration of some CrVI. Total chromium can be determined with diphenylcarbazone following reduction of all chromium to Crm. 

In another procedure [522] the sample of seawater (0.5-3 litres) is filtered through a membrane-filter (pore size 0.7 xm) which is then wet-ashed. The nickel is separated from the resulting solution by extraction as the dimethylglyoxime complex and is then determined by its catalysis of the reaction of Tiron and diphenylcarbazone with hydrogen peroxide, with spectrophotometric measurement at 413 nm. Cobalt is first separated as the 2-nitroso-1-naphthol complex, and is determined by its catalysis of the oxidation of alizarin by hydrogen peroxide at pH 12.4. Sensitivities are 0.8 xg/l (nickel) and 0.04 xg/l (cobalt). 

Chromium Chromium Immobilised diphenylcarbazone Cr(III) converted to Tris (1,1,1, trifluoro 2,4 pentanediono) chromium(III), extracted with hexane Zeeman AAS Isotope dilution GC-MS [178] [181,183, 867]... 

---