1.5- diphenylcarbazide

Diphenylcarbazide is prepared by heating a mixture of phenylhydrazine and urea at 155°  

In a 500 ml. Pyrex rovind-bottomed flask, provided with a reflux condenser, place a mixture of 40 g. of freshly-distilled phenylhydrazine (Section IV,89) and 14 g. of urea (previously dried for 3 hours at 100°). Immerse the flask in an oil bath at 155°. After about 10 minutes the urea commences to dissolve accompanied by foaming due to evolution of ammonia the gas evolution slackens ai r about 1 hour. Remove the flask from the oil bath after 135 minutes, allow it to cool for 3 minutes, and then add 250 ml. of rectifled spirit to the hot golden-yellow oil some diphenylcarbazide will crystallise out. Heat under reflux for about 15 minutes to dissolve the diphenylcturbazide, filter through a hot water funnel or a pre heated Buchner funnel, and cool the alcoholic solution rapidly in a bath of ice and salt. After 30 minutes, filter the white crystals at the pump, drain well, and wash twice with a little ether. Dry upon filter paper in the air. The 3deld of diphenylcarbazide, m.p. 171 °, is 34 g, A further 7 g. may be obtained by concentrating the filtrate under reduced pressure. The compound may be recrystallised from alcohol or from glacial acetic acid. 

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

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

Dpon heating diphenylthiocarbazide with methyl alcohohc potassium hydroxide dithizone (or diphenylthiocarbazone) (III) is produced  

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Abbreviations DPC, diphenylcarbazide HDMG, dimethylglyoxime PAN, 1 -(2-pyridylazo)-2-naphthol. 

To determine moderate amounts of Cr(III) and Cr(VI) in samples that have both oxidation states present, Cr(VI) is analyzed by direct titration in one sample, and the total chromium is found in a second sample after oxidation of the Cr(III). The Cr(III) concentration is determined as the difference. Trace quantities of Cr(VI) in Cr(III) compounds can be detected and analyzed by (3)-diphenylcarbazide. Trace quantities of Cr(III) in Cr(VI) may be detected and analyzed either photometrically (102) or by ion chromatography using various modes of detection (103). 

Instrumental Quantitative Analysis. Methods such as x-ray spectroscopy, oaes, and naa do not necessarily require pretreatment of samples to soluble forms. Only reUable and verified standards are needed. Other instmmental methods that can be used to determine a wide range of chromium concentrations are atomic absorption spectroscopy (aas), flame photometry, icap-aes, and direct current plasma—atomic emission spectroscopy (dcp-aes). These methods caimot distinguish the oxidation states of chromium, and speciation at trace levels usually requires a previous wet-chemical separation. However, the instmmental methods are preferred over (3)-diphenylcarbazide for trace chromium concentrations, because of the difficulty of oxidizing very small quantities of Cr(III). 

Chromium (hexavalent) in chromium plating mists Colorimetric field method using 1,5-diphenylcarbazide 52/3... 

Other dyestuffs have been recommended as adsorption indicators for the titration of halides and other ions. Thus cyanide ion may be titrated with standard silver nitrate solution using diphenylcarbazide as adsorption indicator (see Section 10.44) the precipitate is pale violet at the end point. A selection of adsorption indicators, their properties and uses, is given in Table 10.8. 

In the second method diphenylcarbazide is employed as an adsorption indicator. The end-point is marked by the pink colour becoming pale violet (almost colourless) on the colloidal precipitate in dilute solution (ca 0.01 M) before the opalescence is visible. In 0.1M solutions, the colour change is observed on the precipitated particles of silver cyanoargentate. 

Method B. Prepare the solution and transfer 25 mL of it to a 250 mL conical flask as detailed under Method A. Add two to three drops of diphenylcarbazide indicator and titrate with standard 0.1M silver nitrate solution until a permanent violet colour is just produced. 

A more sensitive method is to employ 1,5-diphenylcarbazide CO(NHNHC6H5)2 in acid solution (ca 0.2M), chromates give a soluble violet compound with this reagent. 

Molybdenum(VI), vanadium(V), mercury, and iron interfere permanganates, if present, may be removed by boiling with a little ethanol. If the ratio of vanadium to chromium does not exceed 10 1, nearly correct results may be obtained by allowing the solution to stand for 10-15 minutes after the addition of the reagent, since the vanadium-diphenylcarbazide colour fades fairly rapidly. Vanadate can be separated from chromate by adding oxine to the solution and extracting at a pH of about 4 with chloroform chromate remains in the aqueous solution. Vanadium as well as iron can be precipitated in acid solution with cupferron and thus separated from chromium (III). 

Procedure. Prepare a 0.25 per cent solution of diphenylcarbazide in 50 per cent acetone as required. The test solution may contain from 0.2 to 0.5 part per million of chromate. To about 15 mL of this solution add sufficient 3M sulphuric acid to make the concentration about 0.1M when subsequently diluted to 25 mL, add 1 mL of the diphenylcarbazide reagent and make up to 25 mL with water. Match the colour produced against standards prepared from 0.0002M potassium dichromate solution. A green filter having the transmission maximum at about 540 nm may be used. 

Diphenylcarbazide as adsorption indicator, 358 as colorimetric reagent, 687 Diphenylthiocarbazone see Dithizone Direct reading emission spectrometer 775 Dispensers (liquid) 84 Displacement titrations 278 borate ion with a strong acid, 278 carbonate ion with a strong acid, 278 choice of indicators for, 279, 280 Dissociation (ionisation) constant 23, 31 calculations involving, 34 D. of for a complex ion, (v) 602 for an indicator, (s) 718 of polyprotic acids, 33 values for acids and bases in water, (T) 832 true or thermodynamic, 23 Distribution coefficient 162, 195 and per cent extraction, 165 Distribution ratio 162 Dithiol 693, 695, 697 Dithizone 171, 178... 

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. 

Aliphatic amines have been determined by a number of methods. Batley et al. [290] extracted the amines into chloroform as ion-association complexes with chromate, then determined the chromium in the complex colorimetri-cally with diphenylcarbazide. The chromium might also be determined, with fewer steps, by atomic absorption. With the colorimetric method, the limit of detection of a commercial tertiary amine mixture was 15ppb. The sensitivity was extended to 0.2 ppb by extracting into organic solvent the complex formed by the amine and Eosin Yellow. The concentration of the complex was measured fluorometrically. Gas chromatography, with the separations taking place on a modified carbon black column, was used by Di Corcia and Samperi [291] to measure aliphatic amines. 

Diphenic acid, bl41 Diphenolic acid, b205 Diphenyl, bl38 Diphenylacetone, d767 Diphenylbenzenes, t7 thru t9 sym-Diphenylcarbazide, d746 Diphenyldiazene, a312... 

Reagent iodine vapour phosphomolybdic acid fluorescein/bromine sulphuric acid ninhydrin or isotin 2,4 -dinitropheny lhy drazine H2S water, diphenylcarbazide or... 

Strongly basic antibiotics may be precipitated by formation of the coloured reineckate salt which may then be determined spectrophotometri-cally 65. Bickfordl66 dissolved the precipitated neomycin reineckate in acetone and has successfully used this procedure to assay neomycin extracted from topical formulations. Roushdi et al 73 preferred to oxidise the precipitate with potassium permanganate and then colorimetrically estimate the chromate produced with diphenylcarbazide. 

Miller and Zittef have used 1,5-diphenylcarbazide (0.25% solution in acetone) for the spectrophotometric determination of technetiiun. 1 to 15 /ig of technetium in 10 ml solution can be ascertained by measuring the extinction at 520 nm of the Tc (IV) complex in 1.5 M sulfuric acid. The development of the most intense color takes about 35 min the reduction of pertechnetate to Tc (IV) is effected by the reagent itself before complexation occurs. The molar extinction coefficient of the complex at 520 nm is 48,600. The relative standard deviation is 2%. Fe ", Ce ", and CrOj" clearly disturb measurements, VO , MoOj ,... 

Trace polonium is extracted from aqueous acetate solution by 8-hy-droxyquinoline in chloroform, probably forming a 1 1 compound this sublimes at 140°C (81). The thionalide complex appears to have 2 molecules of ligand to each polonium atom volatile complexes with thiourea, thio-semicarbazide, diphenylcarbazide, and analogous reagents have also been reported (81). 

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