A simple, selective and sensitive method for the extractive
spectrophotometric determination of vanadium(V) using N-p-chlorophenyl-
2-naphthohydroxamic acid (CP-2-NHA) is described. Vanadium(
V) is quantitatively extracted from 3-8.4 M HCl as a violet
complex with CP-2-NHA into chloroform. Beer\u27s law is applicable
in the concentration range 34 and 224 fig of vanadium(V) per 25 ml
of chloroform extract. The Sandell sensitivity of the system is
0.0089 μg/cm2 at 530 nm. The method has been satisfactorily
employed for the determination of vanadium in steel.
The solid complex, VOCI (C11H11N02Cl)2, was prepared and
characterised by melting point, elemental analysis, visible and
infrared spectra

S . G. Tandon

V. C. Koshy

English

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CROATICA CHEMICA ACTA CCACAA 54 (4) 459-464 (1981) CCA-1304 YU ISSN 0011-1643 UDC 546.881 Originai Scientific Paper Extractive Spectrophotometric Determination of Vanadium(V) with N-p-Chlorophenyl-2-naphthohydroxamic Acid and Investigation of Its Solid Complext V. C. Koshy and S . G. Tandon Department of Chemistry, Ravishankar University, Raipur, 492.010, India Received April 20, 1981 A simple, selective and sensitive method for the extractive spectrophotometric determination of vanadium(V) using N-p-chloro-phenyl-2-naphthohydroxamic acid (CP-2-NHA) is described. Vana-dium(V) is quantitatively extracted from 3-8.4 M HCl as a violet complex with CP-2-NHA into chloroform. Beer's law is applicable in the concentration range 34 and 224 fig of vanadium(V) per 25 ml of chloroform extract. The Sandell sensitivity of the system is 0.0089 µg/cm2 at 530 nm. The method has been satisfactorily employed for the determination of vanadium in steel. The solid complex, VOCI (C11H11N02Cl)2, was prepared and characterised by melting point, elemental analysis, visible and infrared spectra. INTRODUCTION The years since the introduction of N-phenylbenzohydroxamic acid, PBHA, as a reagent for the detection and determination of vanadium(V)1•2 have seen an explosive growth in this field . The upsurge of interest in the application of this method to a variety of problems3- 6 owes much of its impetus to the search for better reagents from the family of hydroxamic acids. A number of hydroxamic acids have been prepared by varying the nature and position of the substituent groups attached to the carbon a:nd nitrogen atoms of -CON(OH)-, and their reaction with vanadium(V) in concentrated hydro-chloric add media studied7- 14• In a further extension of this work, fourteen new N-arylhydroxamic acids with typical range of structural variations have been prepared15• Out of these, N-p-chlorophenyl-2-naphthohydroxamic acid has shown an encouraging combination of good sensitivity with better selectivity for vanadium(V). Hence, the optimum conditions for the colour reaction have been studied and the vanadium content in samples of B.C.S~ analysed steels determined· with satisfactory results. Although a large number of hydroxamic acids have been reported as reagents for the spectrophotometric determination of vanadium(V), their solid complexes have not been isolated. In this work, the ,solid vanadium(V)--CP-2-NHA complex has been prepared and characterised by elemental ana-lysis, melting point, visible and infrared spectra. t Part of Ph. D. Thesis of V. C. K. Ravishankar University, Raipur, 1981. 460 V. C. KOSHY AND 1S. G. TANDON EXPERIMENTAL Apparatus Absorption spectra were scanned on UV-VIS Carl Zeiss Jena SPECORD re-cording spectrophotometer, and fixed wavelength measurements made with E. C., India Model GS-865 spectrophotometer. The infrared spectra were recorded as nujol mulls on Perkin Elmer Model-377 infrared spectrophotometer. Reagents CP-2-NHA was prepared as reported earlier15• Its 0.10/o w/v solution in ethanol free chloroform1 was used for extraction;1 saturated solution in chloroform (2.2 X X 10-2 M) was used for preparing solid vanadium(V) complex. A stock solution of ammonium metavanadate (AR, Hungary) was prepared1 and diluted as required. For the preparation of the solid vanadium(V) complex of CP-2-NHA, a saturated solution of ammonium metavanadate in glass distilled water was used. Solutions of diverse ions, 20 mg/ml, were prepared from analytical grade salts.16 Procedure for Development of Colour The procedure adopted here was the same as reported earlier11 • The absorbance of the chloroform extract of VOCl (C17H11N02Cl)2 was measured at 530 nm using chloroform as blank. Procedure for Isolation of Solid Complex To 100 ml of saturated solution of ammonium metavanadate in a 500 ml separat-ory funnel · was added 55 ml of hydrochloric acid (11.4 M). To this was added 10 ml of saturated solution of CP-2-NHA in chloroform and 200 ml of n-hexane. On shaking for about two minutes. the solid vanadium(V) complex was obtained. It was filtered off, washed with water (5 X 15 ml) and dried in a vacuum over P205; m. p., 122-123 °c. The complex was analysed and the results are in agreement with the molecular formula, VOCI (C17H11N02Cl)2. (Analysis: calculated for VOCI (C11H11N02Cl)2; Mol. wt., 695.86; C, 58.69; H, 3.19; N, 4.03; Cl, 15.28; V, 7.32. Found : C, 58.26; H, 3.10; N, 4.10; Cl, 15.00; V, 7.25) . RESULTS AND DISCUSSION A.bsorption Spectra and Solvents for Extraction The solution of the VOCI (C17H 1.1N02Cl)2 in chloroform has a maximum absorbance of at 530 nm. The position of the absorption band remains •intact on varying (i) the concentration of vanadium(V) or (ii) the acid concentration (2-10 M), thus indicating the presence of one type of complex. The coloured complex is extracted into benzene, chloroform, chlorobenzene, carbontetra-chloride, o-dichlorobenzene, ethyl acetate, etc. readily, but chloroform is the most efficient solvent. Effect of Acidity, Time of Shaking and Stability of Colour Maximum colour develops if the acidity of the aqueous phase is maintained between 3.0 and 8.4 M HCL Usually, measurements were made from 4 M HCl solutions. The colour is extracted into the chloroform layer in less than one minute and is stable for several days. Volume of Aqueous Phase The absorbance readings remain unchanged on varying the volume of the aqueous phase from 2 to 30 ml; however, a slight decrease in absorbance was observed thereafter. Usually the volume of the aqueous phase was 10 ml or smaller for 10 ml of organic phase. DETERMINATION OF VANADIUM(V) 461 TABLE I 1etermination of Vanadium in the Presence of Diverse Ions. Fixed Amount of Vanadium(V) = 87.02 µg Amount of Error, Ion Added as ion added, O/g mg I II III IV Al(III) Al(NOa)s · 9H20 40 0.0 120 + 2.5 Ba(II) Ba(N0a)2 40 + 1.3 60 0.0 Bi(III) Bi(NOa)a · 5H20 20 0.0 40 4.8 Ce(IV) Ce(S04)2 40 + 0.8 60 1.3 Cd(II) 3CdS04 · 8H20 40 + 0.8 60 0.0 Co(II) CoS04·7H20 40 1.3 60 2.5 Cu(II) Cu(N0a)2 · 3H20 10 0.8 Fe(III) FeCl~ · 5H20 13 2.8 15 0.0 Li(!) (Li)2S04 · H20 120 + 2.5 200 1.3 Mg(II) Mg(N03)2 · 6H20 20 0.0 40 0.0 80 1.3 Mo(VI) (NH4)2Mo04 20 1.3 30 8.9 40 -15.2 Ni(II) Ni(N0s)2 · 6H20 20 + 0.8 Pb(II) Pb(NOa)2 40 0.0 60 0.8 Th(IV) Th(N03)4 · 6H20 40 + 1.3 60 0.3 Ti(IV) K2TiO(C204)2 5 0.0 10 0.5 U(VI) U02(NOs)2 · 6H20 40 + 0.8 50 1.3 W(VI) Na2 W04 · 2H20 10 2.5 20 -39.2 40 -59.5 Zn(II) ZnS04 · 7H20 40 + 0.8 80 0.8 Zr(IV) Zr(N0s)4 7 0.0 10 1.8 13 8.9 CHscoo- CHsCOOH 3N 0.0 5N 1.3 7N -10.9 Cl04- HCl04 0.5N - 1.3 1N - 5.6 2N -12.9 Nos- HNOs lN 0.0 2N 4.1 PQ43- HaP04 2N 0.8 3N 4.1 4N 6.8 8042- H2S04 3N 0.0 6N 4.1 462 V. C. KOSHY AND S. G. TANDON A.mount of Reagent A 1 : 8 mole ratio of vanadium(V) to reagent ensures maximum colour. The reagent is colourless and its large excess is tolerated. Beer's Law Beer's law is obeyed in the concentration range 34 to 224 µg of vana-dium(V) per 25 ml by Ringbom plot17• The molar absorptivity of the violet vanadium(V)-CP-2-NHA complex in chloroform is 5750 ± 100 litre mole-1 cm-1 at 530 nm. The Sandell sensitivity18 of the system is 0.0089 µg /cm2• Effect of Diverse Ions Fixed amounts of vanadium(V) were determined in the presence of varying amounts of diverse ions. Large amounts of Al(III), Ba(II), Bi(III), Cd(II), Co(II), Cu(II), Fe(III), Li(I), Mg(II), Ni(II) , Pb(II), Th(IV), U(VI), Zn(II), acetate, perchlorate, nitrate, phosphate and sulphate are tolerated {Table I). Tolerance of large amounts of sulphuric acid will permit the use of potassium pyrosulphate fusion of those vanadium bearing minerals which are not attacked satisfactorily by hydrofluoric acid. Ce(IV), Mo(VI), Ti(IV) and Zr(IV) form a light yellow chloroform extract with absorption bands at a shorter wavelength and having practically no absorption at 530 nm. Hence, relatively large quantities of these ions are tolerated. This explains the high selectivity of the v anadium(V) reaction with CP-2-NHA. Lead(II) and tung-sten(VI) yield a precipitate with hydrochloric acid and are removed by repeated centrifuging and washing before the extraction of vanadium(V). Strong oxidising agents such as potassium dichromate and potassium per-manganate interfered in the determination of vanadium(V); however, such interference could be easily eliminated by the ready conversion of these oxidants to noninterfering oxidation states, viz., Cr(VI) to Cr(III) and Mn(VII) to Mn(II). Determination of Vanadium in Steel The results obtained in the analysis of B.C.S. steels, using CP-2-NHA, are in excellent agreement with the certified values (Table - II). Thus, both the accuracy and the precision of the newly developed method are established. TABLE II Determination of Vanadium ·in B. C. S. Steels B. C. S. Steels Certified 0/o of 0/o of vanadium vanadium found 241/1 1.570 1.564 High Speed Steel Cr-V 0.242 0.241 No. 224 Low Alloy Steel 0.460 0.458 No. 252 DETERMINATION OF VANADIUM(V) 463 Investigation of VOC1 (C11H11N02Cl), The complex is a purple solid and is freely soluble in benzene, chloroben-zene, chloroform, o-dichlorobenzene, etc. It is sparingly soluble in water, n-hexane a:nd cyclohexane. The solid complex is fairly stable if kept in a cool dark place. The molar absorptivity of the chloroform solution of the complex is exactly the same as that of its chloroform extract used for the spectrophotometric determination of vanadium. The purple solid complex gives a red colouration which gradually turns golden yellow and ultimately colourless with all alcohols. The infrared spectrum of VOCI (C11H 1'1N02Cl)2 is compared with the spectrum of CP-2-NHA. The b and of the free ligand at 3200 cm-1 is ascribed to 0 - H stretching vibration since it disappears in the spectrum of its vana-dium(V) complex. The disappearance of this strong band indicates that the 0-H bond has broken in the formation of the metal complex. The car-bonyl stretching vibration in CP-2-NHA appears at 1615 cm-1, as a very strong band, and on complexation with vanadium, this is shifted to 1600 cm-1• A band of medium intensity at 905 cm- 1 in CP-2-NHA has been assigned to N-0 stretching vibration. In the spectrum of its vanadium(V) complex, this is transformed to two very close bands of medium intensity at 900 and 930 cm-1, r espectively. The appearance of a strong band around 975 cm-1 in the VOCI (C17H 111N02Cl) 2 indicates the presence of a V = 0 bond, since in structurally analogous complexes, (19-22), it has been observed in the range 965 ± 50 cm-1• Acknowledgement. - The authors are grateful to the authorities of the Uni-versity Grants Commission, New Delhi for awarding a Junior Research Fellowship to one of them (V. C. K.). REFERENCES 1. U. Pr i y ad a rs hi n i, S. G. Tandon, Anal. Chem. 33 (1961) 435. 2. D. E. Ryan, Analyst, 85 (1960) 569. 3. E. M. D o n a I d s o n, Talanta, 17 (1970) 583. 4. A. A. Sh ah id, Analyst, 101 (1979) 209. 5. M. Uh r ova and L. Ka b rt, Sb. Vys. Sk. Chem. Technol. Praze. Anal. Chem., HU (1976) 91. 6. R. R. Nan e war, Usha T an don, Talanta, 25 (1978) 352. 7. S. G. Tandon and S. C. Bhattacharya, J. Ind. Chem. Soc. 47 (1970) 583. 8. U. Tan d on and S. G. Tandon, J. Ind. Chem. Soc., 46 (1969) 983. 9. D. C. B h u r a and S. G. Tan don, AnaL. Chim. Acta, 53 (1971) 379. 10. V. K. Gupta and S. G. Tandon, Anal. Chi m . Acta, 66 (1973) 39. 11. Ram a P a n de and S. G. Tandon, Croat. Chem. Acta, 51 (1978) 353. 12. E. K. Ab du s a I am ova and B. G. 0 st rob r o d, Tr. Task. Politekh. Inst., 119 (1974) 17. 13. A. A. Sh ah id, Anal. Chem., 48 (1976) 714. 14. V. C. Bass and J. H. Yoe, Talanta, 13 (1966) 735. 15. V. C. K o s h y and S. G. T a n d o n, J. Chem. Eng. Data, Accepted, 16. P. W. We st, J. Chem. Educ., 18 (1941) 528. 17. A. Ring b om, Z. Anal. Chem., 115 (1939) 332. 18. E. B. S and e 11, Colorimetric Determination of Traces of Metals, Intersience Publishers, Inc., New York, 3rd ed., p-83, 97, 217 (1959). 19. J. S e I b in, Coard. Chem. Rev., 1 (1966) 293. 20. A. Sy am a I and K. S. Ka I e, Inorg. Chem., 18 (1979) 992. 21. R. L. Farmer and F. L. Urbach, Inorg. Chem., 13 (1974) 587. 22. J. J. R. Frausto d a Si 1 v a, R. W o t to n, and R. D. G i 11 a rd, J . Chem. Soc., (1970) 3369. 464 V. C. KOSHY AND S. G . TANDON SAZETAK Ekstrakcijsko spektrofotometrijsko odredivanje vanadija(V) primjenom N-p-klorofenil-2-naftohidroksamne kiseline i istrazivanje njihovog krutog kompleksa V. C. Koshy i S. G. Tandon Opisana je selektivna i osjetljiva metoda za ekstrakcijsko spektrofotometrijsko odredivanje vanadija(V) pomoeu N-p-klorofenil-2-naftohidroksamne kiseline (CP-2--NHA). Vanadij(V) se kvantitativno ekstrahira s CP-2-NHA u kloroform u obliku ljubieastog kompleksa iz otopina koje su 3- 8.4 mol dm-3 s obzirom na HCl. Sistem slije~i Beerov zakon u podrucju koncentracija 34 do 224 µg vanadija u 25 cm3 klo-roformnog ekstrakta. Osjetljivost metode izrazena Sandellovim indeksom iznosi 0.0089 µg cm-2 kod 530 nm. Postupak je uspjesno primjenjen za odredivanje vana-dija u celicima. Kruti kompleks, VOCl(C11H11N02Cl)2 je sintetiziran i karakteriziran talistem, elementarnom analizom i pomocu vidljivih i infracrvenih spektara. DEPARTMENT OF CHEMISTRY, RA VISHANKAR UNIVERSITY, RAIPUR, 492010, INDIA Prispjelo 20. travnja 1981 

Extractive Spectrophotometric Determination of Vanadium(V) with N-p-Chlorophenyl-2-naphthohydroxamic Acid and Investigation of Its Solid Complex

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