N-hydroxy-N-p-tolyl-N′-(3-chloro-4-methylphenyl)-p-toluamidine as a sensitive and selective reagent for vanadium(V): Synergic extraction and photometric determination in the presence of various phenols

Journal of the Less-Common Metals, 64(1979) 155 - 161 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands

155

N-HYDROXY-N-p-TOLYL-N’-(3-CHLORO-4-METHYLPHENYL)-~TOLUAMIDINE AS A SENSITIVE AND SELECTIVE REAGENT FOR VANADIUM(V): SYNERGIC EXTRACTION AND PHOTOMETRIC DETERMINATION IN THE PRESENCE OF VARIOUS PHENOLS

R. S. KHARSAN, Department (Received

K. S. PATEL and R. K. MISHRA

of Chemistry, Rauishankar University, Raipur, M.P. (India)

June 27, 1978)

Summary Vanadium(V) reacts with N-hydroxy-N-p-tolyl-N’-(3-chloro-4-methylphenyl)-p-toluamidine to give a 1:2 VO(20Am)OH complex, having E = 1600 1 mol-’ cm-’ at X,,, 570 nm; VO(20Am)OH extracts partially into chloroform. However, in the presence of phenols there is quantitative recovery into chloroform and marked synergistic enhancement into organic solvents. The extracting species is found to be VO(20Am)OH. PhOH, having h max in the region 590 - 625 nm with E = 5100 - 7200 1 mol-’ cm-‘. Synergism in the extraction of vanadium(V) is explained on the basis of the formation and hyperchromic and bathochromic shifts of hydrophobic species in chloroform solution. A simple rapid sensitive and highly selective method has been developed for the extraction and photometric determination of vanadium(V) at microgram levels and has been applied to standard steel samples. Fe3+, Cu’+, Mn2+, Cr3+, Ti*+, Zr*+, Mo6+ and W6+ did not interfere.

1. Introduction A number of monobasic and bidentate chelating agents [l - 51 have been used for the extraction and photometric determination of vanadium(V). These reagents form 1:2 complexes having a basic V=O and an acidic V-OH group in the same molecule. The basic V=O group reacts with acidic substances (carboxylic acids, phenols, hydrogen chloride etc.) to give hyperchromic and bathochromic shifts of the adduct formed in the organic phase. N-hydroxy-N,N’-diarylbenzamidines, monobasic and bidentate chelating agents(I), have been used for the determination of various metal ions [ 6 - lo] . __C-N_

-N---OH (I)

156

N-hydroxy-N-p-tolyl-N’-(3-chloro-4-methylphenyl)-p-toluamidine (abbreviated as HTCMPTA), a newly synthesized reagent, reacts with vanadium(V) forming a complex which extracts into chloroform. The basic V=O group of this complex reacts with various phenols to give a highly sensitive and stable colour reaction in chloroform. This permits the extraction and photometric determination of vanadium(V) in complex materials. On the basis of sensitivity and selectivity the HTCMPTA method may be compared to the established PBHA method [ll - 141. The present paper reports the extraction and photometric determination of vanadium(V) with N-hydroxy-N-p-tolyl-N’-( 3-chloro-4-methylphenyl)-ptoluamidine in the presence of 11 phenols, and the various optimization constants.

2. Experimental 2.1. Apparatus and reagents An ECIL UV-VIS spectrophotometer Model 865 with matched 1 cm cells, and a Systronic pH meter Type 322 were used. All the reagents and chemicals used were of BDH Analar grade. A stock solution of vanadium(V) was prepared by dissolving BDH Analar grade ammonium metavanadate in doubly distilled water; the solution was standardized volumetrically [ 151. N-hydroxy-N-p-tolyl-N’-( 3-chloro-4-methylphenyl)p-toluamidine was prepared by condensation of an equimolar ratio of N-(3-chloro-4-methylphenyl)-p-toluimidoyl chloride and N-p-tolylphenylhydroxylamine in ether [6, 161. The resulting hydrochloride was treated with dilute ammonia to liberate the corresponding free base (m.p. 149”, yield 80%). Analysis showed: C, 71.54; H, 5.82; N, 7.69%. CzzH,,NzOCl requires: C, 71.65; H, 5.92; N, 7.89%. Alcohol-free chloroform was used for the preparation of reagent solutions and for the experimental procedures. 0.015 M reagent solution and 0.2 M phenol in chloroform were used.

2.2.

Procedure

An aliquot of vanadium(V) solution containing 100 pg of metal was placed in a 100 ml separating funnel. 10 ml glacial acetic acid was added and the total aqueous volume was made up to 25 ml. 5 ml each of chloroform solutions of the reagent and of phenol were added and the mixture was equilibrated for 1 min. The organic phase was dried over anhydrous sodium sulphate in a 50 ml beaker and was washed with 2 X 4 ml chloroform. The chloroform extracts were transferred into 25 ml volumetric flasks and were made up to a known volume with chloroform. The absorbance at h,,, was read against chloroform as a blank.

157

3. Results and discussion 3.1. Absorption spectra The absorption spectra of the reagent and the vanadium(V)-HTCMPTA complex in the absence and presence of phenols are shown in Fig. 1. The reagent showed negligible absorption in the region 450 - 700 nm. The vanadium-HTCMPTA complex in the absence of phenols at pH 3.0 showed a flat h,,, in the region 560 - 580 nm with E = 1600 1 mol-’ cm-‘. In the presence of 0.03 M phenols a strong hyperchromic and bathochromic effect of the adduct in chloroform solution is observed, as shown in Table 1. 3.2. Effect of phenols The wavelength of maximum absorption and the molar absorptivity depend on the nature of the phenols used. The effect of the conjugation of phenol on h,,, and E of the adduct is shown in Table 1. An increase in the absorbance and a shift of h,,, to longer wavelength occur as the conjugation is increased from phenol to 2-naphthol. The degree and position of substituents in phenol would be expected to have some effect. The difference in the absorbance of adducts in l- and 2-naphthol may be considered to be due to

\

.. \ *_,

600

500

3 7c)O

WAVELENGTH,~~

Fig. 1. Absorption spectra: ---o---o---o--, 6.28 X 10P5M Cv+ reagent + 2-naphthol; .-.-a-.-.o-.-.o-.-, 6.28 x 1O-5M Cv + reagent + p-chlorophenol; P, 6.28 x 10--5M Cv + reagent + phenol; -...-...~----a----n--, 7.85 x 10v5M Cv + reagent + 0.003 M reagent acetic acid; ----, 7.85 x 10A5M Cv + reagent; uy--, in chloroform.

158 TABLE

1

Spectral

data for the vanadium-HTCMPTA

Phenol

_ Phenol p-chlorophenol 2naphthol I-naphthol m cresol o-cresol p-cresol o-nitrophenol 2 :4-dinitrophenol m-aminophenol Resorcinol aBV, blue-violet; LB, light blue.

complex

Optimum acetic acid range (M)

Coloura

l-10.0 0 - 6.8 0 - 6.5 O-5.0 0 - 8.0 0 - 4.5 0 - 6.0 0 - 5.0 0.8 - 8.0 0.8 - 6.5 0.5 - 8.0 0.8 - 6.0

BV DB DB BG BG G GB B LB B LB LB

h,,, (nm)

580 595 595 625 625 605 590 595 590 595 590 590

in the presence

of phenols Sendell’s

mole1 cm-‘)

4400 5900 6700 7200 5100 5800 6250 6000 5200 5600 5200 5200

0.0115 0.0086 0.0076 0.0071 0.0100 0.0087 0.0081 0.0085 0.0098 0.0091 0.0098 0.0098

DB, deep blue; BG, bluish green; G, green; B, blue; GB greenish

blue;

steric hindrance; in monohydric and dihydric phenols the difference may be due to complexation of the vanadium(V) species. An approximately 250-fold molar excess of phenol was sufficient for the complete extraction of vanadium(V). Excess phenol up to a 2000-fold molar excess caused no adverse effect but in some cases if phenol was added in greater than 2000-fold excess, the h,,, shifted to shorter wavelength. 3.3. Effect of variables Chloroform was found to be the best solvent, as the reagent and the ternary complexes show a high distribution ratio in it. The acidity was maintained with glacial acetic acid and optimum acidity ranges are shown in Table 1. A three-fold molar excess of HTCMPTA was adequate for the complete extraction of vanadium. Addition of more reagent (up to a 200-fold molar excess) increases the extraction rate. The order of addition of the reagents was not critical. A period of 1 min was sufficient for the complete extraction of vanadium(V). The chloroform extract was stable for at least 30 h at 27 f 2 “C. Variation in temperature from 20 to 35 “C did not affect the h,,, and E values of the coloured system. No effect of electrolytes on the extraction of vanadium(V) was observed. 3.4. Beer’s law, optimum concentration range and precision Beer’s law was obeyed in the range 0.6 - 9.0 ppm of vanadium(V). The optimum concentration ranges on the basis of a Ringbom plot [17] lie between 1.0 and 8.5 ppm of metal. The relative standard deviation of systems is kO.6 - 0.9% (ten measurements were made each containing 4 ppm of vanadium in 25 ml).

159

3.5, Composition The stoichiometry of the vanadium(V)-HTCMPTA-PhOH complex was determined by various methods. Job’s method of continuous variation [ 181 and the molar ratio method [ 191 showed a 1:2 ratio of metal to reagent. The curve fitting method [ZO] showed a 1:l ratio of metal to phenol. Thus a 1:2:1 (me~l:reagent:phenol) complex was formed. 3.6, Extraction equilibrium The extraction equilibrium of the vanadium-HTCMPTA tween chloroform and water in the presence and absence,of expressed as follows [ 1, 21: VO; + 2HOAm, It can be written

G====== VO(2OAm)OH*

PhOH + H+

(I)

as

VO; + 2HOAm, In the presence

+ PhOH,

complex bephenol may be

G===+ V0(20Am)OH,

+ H+

(2)

of phenol a 1:l adduct is extracted:

V0(20Am)OH,

f PhOH,

G==== VO( 20Am)OH*

PhOH,

(3)

Then p = [VO(2OAm)OH.PhOH]

0 [H+] (4)

[VO;] [HOAm] 2 [PhOH] 0

(5)

P = P1,2.oP1.2.1

The distribution

ratio is given by

D,,,,, = P1,2,0[HOAm

? (1 + PI,Z,IPhOHl

1WI - ’

(6)

The subscript o, HOAm and PhOH denote organic phase, N-hydroxyamidine and phenol, respectively. D 1s2,1is a function of the concentrations of reagent, phenol and H+. Reaction (1) was appreciable in the presence of a three-fold molar excess of reagent. Thus phenol may be coordinated to the VO(20Am)OH complex through the basic V=O group and may enhance the distribution coefficient of the metal in the chloroform phase. 3.7. Effect of other ions The effect of other ions was studied with 4 ppm of vanadium(V) as described in the earlier procedure. Molybdenum(V1) forms a yellow complex and does not absorb at 590 - 625 nm. The interference due to molybdenum(VI) could be eliminated by the addition of more reagent. Iron(II1) did not interfere above 6 M acetic acid up to 600 ppm of metal. Below 6 M acetic acid, the interference due to ~on(II1) was removed by masking with trisodium phosphate. Chloride, bromide, nitrate, sulphate, ammonium, triethanolamine, urea, thiourea, alkali metals, alkaline earths and lanthanide elements had no interfering effect up to 1500 ppm. The tolerance limits for other ions are given in Table 2.

160

TABLE 2 Tolerance limits for foreign ions in the determination of vanadium(V) in the presence of p-chlorophenol at 6.0 M acetic acid Ion

Tolerated amounta

Tolerated amount*

Ion

(ppm)

(ppm) Fe3+ ;::

80 300 80

Ti4+ Mo6+ Zr4+

600 700 300

60 800 1000 800 800 600

co2+ “0; + Mn Cr3+ A13+ Pb2+

700 800 800 700 1000 1000

W6+ ;$+

;$z Hg2+

1000 800

Tartrate Arsenate Ag+

Bi3+ Sb3+ Citrate

600 800

aAmount causing an error of less than 2%.

3.8. Application in steel The reliability of the method was tested in two vanadium-tungsten steels (64a and 241/l) and a tungsten-free steel 252 obtained from the Bureau of Analysed Samples Ltd., Middlesbrough, Yorks., England. The results are shown in Table 3. A weighed quantity of sample was dissolved in dilute nitric acid. Tungsten was removed as tungstic oxide by filtration because its presence in excess interferes with the method. The vanadium content was evaluated as described earlier.

TABLE 3 Determination of vanadium in BCS’ steel with HTCMPTA in the presence of p-chlorophenol BCS no. and name of steel

Vanadium found (a)

Certified value (%)

Sb

64a alloy steel 241/l high speed steel 252 low alloy steel

1.552 1.546 0.444

1.57 1.57 0.46

*0.01009 +0.01193 + 0.00798

aBCS, British Chemical Standard. bAverage of 6 determinations.

161

References 1 2 3 4 5 6 7 8 9 10 11 12 13

I. Kojima and Yuko Miwa, Anal. Chim. Acta, 83 (1976) 329. I. Kojima and M. Tanaka, Anal. Chim. Acta, 75 (1975) 367. 0. Menis and C. S. P. Iyer, Anal. Chim. Acta, 55 (1971) 89. H. Kohara, N. Ishibashi and Y. Ito, Bunseki Kagaku, 16 (1967) 315. E. M. Donaldson, Talanta, 17 (1970) 583. K. Satyanarayana and R. K. Mishra, Anal. Chem., 46 (1974) 1609. K. Satyanarayana and R. K. Mishra, Indian J. Chem., 13 (1975) 295. K. K. Deb and R. K. Mishra, Curr. Sci., 45 (1974) 1609. K. K. Deb and R. K. Mishra, Indian J. Chem., 16A (1978) 727. K. Satyanarayana and R. K. Mishra, J. Indian Chem. Sot., 53 (1976) U. Priyadarshini and S. G. Tandon, Anal. Chem., 35 (1961) 435. D. E. Ryan, Analyst, 85 (1960) 569. A. K. Majumdar, N-Benzoylphenylhydroxylamine and its Analogues, Oxford, 1972.

14 15

A. D. Shendrikar, Talanta, G. Gharlot and D. Bezier, York, 1957.

16 17 18 19 20

K. A. P. J. L.

16 (1969) Quantitative

51. Inorganic

K. Deb and R. K. Mishra, J. Indian Chem. Sot., Ringbom, Z. Anal. Chem., 115 (1938) 332. Job, Ann. Chim. (Paris), 9 (1928) 113. H. Yoe and A. L. Jones, Ind. Eng. Chem., Anal. G. Sillen, Acta Chem. Stand., 10 (1956) 185.

Analysis,

Pergamon

Wiley-Interscience,

53 (1976)

Ed.,

63,469,928.

178.

16 (1944)

111.

Press,

New