494 A.nalyst, August, 1968, Vol. 93 ,$$. 494-497 Application of l=Phenyl=4=phenylamino=l,2,4=triazolium Chloride to the Determination of Cobalt(I1) BY C. CALZOLARI AND L. FAVRETTO (Istituto di Merceologia, Universitij di Trieste, Italy) A new reagent, l-phenyl-4-phenylamino-l,2,4-triazolium chloride, is proposed for the determination of cobalt (11) by extraction into 1,2-dichloro- ethane and spectrophotometric determination a t 626 nm of the ion-association compound formed in the presence of an excess of ammonium thiocyanate. The composition of the species extracted has been determined by applying the continuous variation method to the aqueous - organic phase system, and by determining the chemical composition and molecular weight of the compound precipitated from the aqueous phase.TERNARY complexes and ion-association compounds formed in the aqueous phase between a transition-metal thiocyanate and an organic base or organic cation have often been used for the extraction of the metal into an organic solvent and its spectrophotometric deter- mination. Among the organic substances proposed as reagents for cobalt( 11), tri-iso-octyl- amine,l di(4-antipyry1)methane and its derivatives,2~~ tetraphenylarsonium4.6,g and triphenyl- methylarsonium salts7 have been reported. Recently a derivative of 1 ,2,4-triazoleJ nitron, already well known as a precipitation reagent for nitrate ions,* has also been proposed for the extraction of various metals from aqueous solutions containing an excess of thiocyanate ions.9J0111J2 In the present paper, the results obtained in the study of a new 1,2,4-triazole derivative, 1-phenyl-4-phenylamino-lJ2 ,4-triazolium chloride (Cl4Hl3N,C1), as a reagent for cobalt (11) , are briefly reported.EXPERIMENTAL REAGENTS AND APPARATUS- 1-Phenyl-4-Phe~ylamino-lJ2 ,4-triazolium chloride-Prepare by the method of Runti and Nisi.ls The thiocyanate was obtained from a concentrated aqueous solution of 1-phenyl- 4-phenylamino-l,2,4-triazolium chloride by precipitation with ammonium thiocyanate. Both of the triazolium salts were purified by repeated crystallisation from ethanol - diethyl ether Standard solutions of the triazolium salts were prepared by direct weighing of the compounds previously dried at 60' C under vacuum. Stock aqueous solution of cobalt(ll), 1.00 x 10-2 F-Prepare from cobalt(I1) sulphate heptahydrate, CoS0,.7H20, and standardise complexometrically. By using this solution, prepare freshly with de-aerated water more dilute standard solutions as required.All of the solutions were adjusted to pH 3 by the addition of hydrochloric acid. Other solutions used were prepared with analytical-grade reagents [Erba (Milan Italy)]. Spectrophotometric results were obtained by using spectrophotometric-grade solvents (Erba) and a Unicam SP500 instrument. The pH of the aqueous phase was determined with a Beckman C pH meter, and the molecular weight with a Hewlett - Packard Mechrolab 302 vapour-pressure osmometer. (2 + 1, v/v). 0 SAC and the authors.CALZOLARI AND FAVRETTO PROPERTIES AND STABILITY OF THE TRIAZOLIUM SALTS- The melting-points and solubilities of the triazolium salts are given below.496 Solubility at 20" C (g per 100 g of solvent) Melting-poin t, I A -i Compound "C Water Chloroform 1,2-Dichloroethane 1 -Phenyl-4-phenylamino- l,B,Ptriazo- lium chloride .. .. . . 206, 21013 4-3 0.45 0.032 l-Phenyl-4-phenylamino-l,2,4-triazo- lium thiocyanate . . .. .. 136 0-046 1.5 0.28 The absorption spectra of the triazolium salts in chloroform solution show a maximum at wavelength 246 nm (for l-phenyl-4-phenylamino-l,2,Ptriazoliurn chloride, E = 1.15 x litres per cm per mole). In water and 1,2-&chloroethane, only an inflection is observed at 235 nm. The absorption spectrum does not change with varying pH in hydrochloric acid or Britton - Robinson buffer solutions. Buffered solutions of both salts are stable for at least 100 hours in the pH range 0.5 to 6-0.When adjusted with hydrochloric acid to pH 3, the solutions are stable for 2 weeks. Above pH 6-0, the salts are not stable and the hydrolytic oxidative degradation leads to the formation of diphenylformazane as the final product.13 SPECTROPHOTOMETRIC DETERMINATION OF COBALT( 11)- Conditions for maximzlm extraction-The absorption spectrum of the species extracted with lJ2-dichloroethane from an aqueous phase containing 1.0 x lo-* F cobalt(II), 0.6 F am- monium thiocyanate and 5.0 x F 1-phenyl-Pphenylamino-1,2,4-triazoliurn chloride is shown in Fig. 1 (broken-line curve). The spectrum is characterised by a maximum at wave- length 626 nm. Blank tests indicate that the strong ultraviolet absorption is mainly caused by the 1-phenyl-4-phenylamino-I ,2,4-triazolium thiocyanate formed with excess of thiocyanate and extracted into the organic layer.Extracts separated from the aqueous phase are stable for several days. 0 1 200 300 400 500 600 700 Wavelength, nm Fig. 1. Broken-line curve: absorption spectrum of the complex extracted with 1,2-dichloroethane (10.0 ml) from an aqueous phase (40.0 ml) containing 1.0 X 10-4~ cobalt (II), 0.5 F ammonium thio- cyanate and 5.0 x 1 0 - 3 ~ 1-phenyl-4-phenylamino- 1,2,4-triazolium chloride. Continuous-line curves : absorption spectra of the complex in 1,2-dichloroethane: curve A, at concentration 4-0 x 10-4~; curve B, at 5.0 x 10-5~; and curve C, at 2.0 x 10-6~. Optical path length 1 cm The shapes of the absorption spectra are not changed by varying the concentration of reactants in the aqueous phase, only their intensity changes.At a concentration of 1.0 x F in the aqueous phase, the extraction of cobalt(I1) is at a maximum when the concentration of the reagents reaches minimum values of 0.5 F for thiocyanate and 5-0 x F for l-phenyl-496 CALZOLARI AND FAVRETTO APPLICATION OF 1-PHENYL-4-PHENYLAMINO- [Analyst, VOl. 93 4-phenylamino-l,2,Ptriazolium chloride. Under these conditions, the variation of the pH in the range 0.3 to 4.0 does not affect the absorbance values and, at 626 nm, Beer's law is followed, at least for cobalt(I1) in the concentration range 5 x to 1 x 10"~. At 20" C the apparent specific absorption coefficient is 79.2 0.6 litres per cm per g [with an organic phase-to-aqueous phase (v/v) ratio of 4 : 13. This value has been calculated from the regression line of 12 pairs of observations. Irtterferertces-Only a few interferences have been tested as examples. With the condi- tions of maximum extraction, copper(I1) and iron(II1) give coloured extracts, which are orange - brown and red and interfere at concentrations higher than 1 x lo4 and 5 x F, respectively.Iron(I1) does not interfere. The interference of iron(II1) can be eliminated by using an excess of ammonium fl~oride.~ Manganese(I1) and nickel(I1) do not give visible absorbing extracts at levels of 1 x 10-3~, and the absorbance at 626nm caused by the cobalt( 11) is practically unaffected. Among the most common anions considered (fluorides, chlorides, bromides, iodides, sulphates and nitrates), nitrates interfere at concentrations higher than 1 x 1 0 - 3 ~ by causing the precipitation of the sparingly soluble salt, l-phenyl- 4-phen ylamino - 1,2,4- t riazolium nit rate .PROCEDURE- A slightly acidic aliquot (less than 10 ml), containing up to 40 pg per ml of cobalt(II), is transferred into a 50-ml calibrated flask, together with 5.0 ml of 4 F ammonium thiocyanate and 20.0 ml of 1.0 x F l-phenyl-Pphenylamin0-1,2,4-triazolium chloride. In the presence of up to 500 pg per ml of iron(III), 2 g of solid ammonium fluoride are added. After diluting the solution to about 38 ml, gently mixing and allowing it to stand for 5 minutes, 10-0 ml of 1,2-dichloroethane are added, the aqueous phase is diluted to the mark and the mixture shaken vigorously for not less than 3 minutes.The contents of the flask are then transferred into a 100-ml separating funnel and, after it has separated, the organic layer is run, dropwise, directly into the spectrophotometric cell. The absorbance is measured at 626 nm against the solvent and corrected for a reagent blank. For an optical path of 1 cm, the working curve lies in the concentration range of 1 to 6 pg per ml of cobalt(I1) in the aqueous phase and 1 pug of cobalt(I1) per ml is determined, with a standard error of 2 per cent. CONSTITUTION OF THE EXTRACTED SPECIES- The method of continuous variations,14 when applied to the measurement of the extracted compound in 1,2-dichloroethane at 626 nm, shows that the compound contains cobalt(I1) : thiocyanate:triazolium in the molar ratios 1:2:4, and it probably has the formula Co(SCN), (C14H13N4)2.The 600-fold excess of thiocyanate necessary for maximum extraction is about that required for the almost complete formation16 of the complex Co(SCN)i-. When a solution of cobaltothiocyanate (1 x 10" F cobalt(I1) in 2 F ammonium thio- cyanate) is added to a saturated solution of 1-phenyl-4-phenylamino-1,2,4-triazolium thio- cyanate in 2 F ammonium thiocyanate, a blue precipitate of waxy appearance is formed, which is purified by re-precipitation with carbon tetrachloride from 1,2-dichloroethane solution and dried under vacuum. Its elemental composition was found to be as follows: C , 50.22 per cent.; H, 3.53 per cent.; N, 22.35 per cent.; S, 16.65 per cent. and Co, 7-72 per cent.(total 100-40 per cent.), which agrees with that calculated for the formula Co(SCN),(CI4H,,N4),: C, 50-18 per cent.; H, 3.42 per cent.; N, 21-95 per cent.; S, 16.75 per cent.; and Co, 7.70 per cent. and, in the concentration range 0.05 to 0.3 F in 1,2-dichloroethane, the molecular weight was found to be 752 g per mole, which is in agreement with the value of 765.8 calculated for the proposed formula. The absorption spectrum in the same solvent presents two maxima, at 626 and 322 nm (see Fig. 1, continuous-line curves), and in the visible region it is identical with that observed for the organic extracts. Beer's law is obeyed, with the following molar absorption coefficients: at wavelength 626 nm, E = (1.256 -I 0.013) x lo3 litres per cm per mole (1 x 10-4 to 1 x 10-3 F) ; and at wavelength 322 nm, E = (8.82 0.26) x 103 litres per cm per mole (1 x 10-5 to 1 x 1 0 4 ~ ) (the concentration ranges used in this check are given in brackets).From the difference of absorbance at 626 nm between a 1,2-dichloroethane solution and an extract obtained from an aqueous solution containing an equivalent amount of metal, 95 per cent. of the metal is calculated to be extracted under the conditions specified by the proposed method.August, 19681 1,2,4-TRIAZOLIUM CHLORIDE TO THE DETERMINATION OF COBALT(I1) 497 CONCLUSIONS The reagent proposed for the determination of cobalt(I1) may be included among those which increase the sensitivity of the classical reaction with thiocyanate by extracting the ion-association compound formed with cobaltothiocyanate into an organic solvent.When compared with those already in use, the procedure suggested is simpler as it involves only one high-efficiency extraction. The sensitivity of the reagent is higher than that given for the tetraphenylarsonium salts6 The reagent can be used in media of uncontrolled acidity and no problems arise from instability. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. REFERENCES Selmer-Olsen, A. R., Analytica Chim. Acta, 1964, 31, 33. Zhivopistsev, B. P., Zav. Lab., 1952, 18, 649. Sokolova, E. V., Pesis, A. C . , and Panova, N. I., Zh. Analit. Klziiiz., 1957, 12, 489. Potratz, H. A., and Rosen, S. M., Analyt. Chem., 1949, 21, 1276. Affsprung, H. E., Barnes, N. A., and Potratz, H. A., Ibid., 1951, 23, 1680. Pepkowitz, L. P., and Marley, J. L., Ibid., 1955, 27, 1330. Ellis, K. W., and Gibson, N. A., Analytica Chim. Acta, 1953, 9, 275. Busch, M., Ber. dt. chem. Ges., 1906, 38, N 861. Babenko, A. S., and Tolmachev, V. N., Ukr. Khim. Zh., 1961, 27, 732. -- , Dopov. Akad. Nauk. Ukr. SSR, 1962, 394. Tolmachev, V. N., and Babenko, A. S., Ibid., 1962, 616. Babenko, A. S., and Tolmachev, V. N., Ukr. Khim. Zh., 1962, 28, 26 and 287. Runti, C., and Nisi, C., J . Med. Chem., 1964, 7, 814. Vosburgh, C., and Cooper, G., J . Amer. Chem. SOC., 1941, 63, 437. Lehn6, M., Bull. SOC. Chim. Fr., 1961, 76. Received October 30th, 1967