reagent was proposed for the detection of Ierri-cyanide-, peroxides- and gold(IIIt . .

Some reducing agents can be tltra.ted III alkalinemedium against terricyanide s~lutlOn: The .endpoint is usually detected. potent.lOmetncally, sm~eno indicator proved quite satisfactory for th.IStitration. The high sensitivity of phenolphthalinsuggested the possibility of using it as indicatorin the above-mentioned titrations. It was foundsatisfactory in the titration of hydroxylamineand hydrazine. The titrimetric reactions involvedare:

2 NHpH + 4[Fe(CN)613-+ 4 OH- = NP + 4[Fe(CN)6]4- +5 HP

N.H. + 4[Fe(CN)s]3- +4 OH- = N2 + 4[Fe(CN)614- +4 H20

Preparation of phenolphthalin - The indicator wasprepared by mixing phenolphthalein (2 g), sodiumhydroxide (10 g), zinc dust (5 g) and water(20 ml) and heating for 2 hr under reflux. Aftercooling, the liquid was passed through a hardenedfilter paper and the colourless filtrate made up to50 ml with distilled water. This indicator was keptin a dark bottle containing a few granules of zinc.Under this condition it remains colourless for atleast one week.

Determination oj hydroxylamine - For each 5 mlof the hydroxylamine test solution (,....",0·05211'), 6-7 mlof 5% NaOH solution was added followed by 3drops of the indicator. This solution was titratedwith standard O·IN potassium ferricyanide until thesolution became red.

NH20Ha= 2Ka[Fe(CN)6JHydroxylamine = VN.16·51 mg

where V and N are the volume and normalityof the ferricyanide solution respectively.

Determination oj hydrazine - For each 5 ml of thehydrazine test solution (,....",0·02M), 3-4 ml of 5%NaOH solution was added and heated to 50-60°.Indicator solution (3 drops) was added and titratedslowly with O'IN potassium ferricyanide with vigo-rous shaking till the solution became red.

N2H4= 4K3[Fe(CN)61Hydrazine = V N.8·01 mg

where V and N are as above.The above procedures were tested on dried analar

hydroxylamine hydrochloride and hydrazine sul-phate, and were found to be reproducible at mglevels with a coefficient of variation of about± 0'6%. The standard potential of the indicatoris -0·75 V in O·lM sodium hydroxide. Theindicator was found to change from colour less todeep red at -0·7 V. The method requires noblank, since one drop of O'lN ferricyanide gives adistinct red colour with the indicator. It is notnecessary to conduct the titration in an inertatmosphere since the effect of air on both indicatorand titrant is very slow. Trials to apply thepresent method to the determination of sulphite,sulphide and thiosulphate were not successful. Theend points were not sharp.

NOTES

References

1. KNIGA, A. G., Chem. Abstr., 31 (1937), 7000.2. SCHALES, 0., Bey. dt. chem, Ges., 71 (1938), 447.3. SHAHINE, S. & MAHMOUD, R., Mikrochim. Acta, (1976),

89.

N-Hydroxy -N -p-chlorophenyl- N' -(2,6-dimethyl-phenyl)benzamidine Hydrochloride as a

Gravimetric Reagent for Cu(II)

KANAK KANT! DEB & RAJENDRA K. MISHRA

Department of Chemistry, Ra vishankar UniversityRaipur 492001

Received 16 A ugwst 1977; accepted 3 March 1978

N - Hydroxy - N -P - chlorophenyt- N' • (2,6- dimethyl-phenyl)benzamidine hydrochloride has been success-fully employed as a highly sensitive and selectivegravimetric reagent for copper(II) in the pH range2·9-11·0. The buff'-coloured copper chelate having thecomposition, Cu(C.1H1.N.OCI)., is thermally stableup to 1800

, and insoluble in many common organicsolvents. Almost all common ions including Fe(III),Ni(II), Mn(II) and Co(II) and rare earths do not inter-fere with the procedure. Copper content of threeBCS alloys has been accurately determined using thisreagent.

THE N-hydroxy-N,N'-diarylbenzamidines havebeen found to be versatile reagents for the

gravimetric and photometric determination of tran-sition metal ions>", In the present communicationN-hydroxy-N -p-chlorophenyl-N' - (2,6-dimethylphe-nyl) benzamidine hydrochloride has been employedas a new, highly selective precipitant for the gravi-metric determination of Cu(II). The buff-colouredcomplex corresponding to the composition CU(C21H1SNPCI)2 is quantitatively precipitated overthe PH range 2·9-11·0, showing an initial turbidityat 2·2. Because of the low conversion factor(0,08329, copper/copper complex) amounts of copperdown to 2 mg could be determined with ease andaccuracy. The complex being insoluble in ethanol,the reagent excess is easily washed out. The highselectivity of the reagent permits the direct estima-tion of copper in several alloys such as brass,gunmetal and white metal.

All the chemicals used were of AR grade.Copper stock solution was prepared by dissolvingthe metal in dilute nitric acid and the solutionboiled to expel nitrogen oxides. The metal contentof the solution was determined gravimetricallyusing salicylaldoxime-. The reagent was preparedby condensing N-(2,6-dimethyl)phenylbenzimidoylchloride and N-p-chlorophenylhydroxylamine inequimolar amounts in ether as mentioned earlier",A 1% solution of the reagent in ethanol wasused for precipitation purposes. The pH's of thesolutions were adjusted with acetate buffersand ammonia. A single pan semi-micro balanceSAHM-68 (Veb-Analytic, DDR) was used forweighing.

727

INDIAN J. CHEM., VOL. 16A, AUGUST 1978

Recommended procedure - An aliquot of coppersolution containing 4-20 mg of the metal was dilutedto 100 ml, the pH adjusted to 2·9-11·0 and heatedto about 60°. To this, reagent solution (15 mlll0mg copper) was added dropwise with stirring. Thebuff-coloured precipitate was digested on a water-bath for 20 min and filtered through a preweighedG-3 sintered crucible. The complex was washedwith hot water followed by 60% aq. ethanol tillthe washings gave no red-purple colour with ferricchloride. It was dried at 120° to constant weightand weighed as CU(C21H18N20Cl)2 (Found: C, 65·98;H, 4·36; N, 7·50; Cu, 8·33. Calc.: C, 66·12; H, 4·72;N, 7·34; Cu, 8·33%). The copper chelate is in-soluble in ethanol, sparingly soluble in acetone, car-bon tetrachloride, chloroform and many other organicsolvents but has appreciable solubility in glacialacetic acid. The complex is thermally stable upto 180° and melts at 243°. The relative standarddeviation for 20 determinations of Cu (15 mg) was± 0·10%.

Influence of diverse i01~S- Following the proceduredescribed above a known amount of copper (12·5mg) was accurately determined at pH 2·9-5·0 inthe presence of alkali metals, alkaline earths, TI(III),Se(IV) and Te(IV) (8-fold); Pb(II), Zn(II), Cd(II),Hg(II), Ni(II), Co(II), ~1n(II), Al(III), Cr(III),Bi(III), Sb(III), La(III), Gd(III), Sm(III), Dy(III),Nd(III), Pr(III), U02(II), Zr(IV), and Th(IV) (four-fold); Ti(IV), Nb(V) and Ta(V) (two-fold); molybdateand tungstate (four-fold); citrate and tartrate (400-fold) and reasonable amounts of fluoride, chloride,bromide, nitrate, oxalate, sulphate, arsenate andthiourea. However, to determine copper in thepresence of Fe(III) (four-fold), vanadate (two-fold)and phosphate (80-fold) ions, the addition of tartaricacid (2 g) was necessary. Pd(II) and EDTA seriouslyinterfered with the determination.

Application to the analysis of alloys - A knownamount of the alloy selected to provide 10-15 mgof copper in a 25 ml aliquot of the final solutionwas accurately weighed, and dissolved in 40%nitric acid. The solution was evaporated to neardryness to remove oxides of nitrogen. It was dilutedto 100 ml and the precipitated tin and antimonyoxides were filtered and washed with hot diluteacetic acid and the solution diluted to 250 ml. A25 ml aliquot was pipetted and after adjusting thepH to 3 copper was determined by the recommendedprocedure. It is evident from the results summa-rized in Table 1 that the amount of copper in itsalloys could be determined accurately and precisely.

The displacement of \lC=N (1610 cm-1)6,7 and\IN-0 (940 cm-1)8.9 to 1575 and 970 cm! respec-

+tively and the disappearance of the =N - H fre-

728

TABLE 1 - DETERMINATION OF COPPER IN BeS* AI.LOYS

Copper found%

Certifiedvalue

%

Standarddeviation

Sf BRASS

70·73, 70·70, 70·76,70'73, 70·83average value, 70'75

70·8 ±0'050

6f GUN METAL

81-82, 87·86, 87·92,87-92, 87·78average value, 87·86

87·9 ±0'061

8c 'WHITE METAL

4·06, 4·09, 4·08,4·06, 4·09average value, 4·066

4·10 ±0·015

*BCS = British Chemical Standards.

quency (2525 cm-lpO .•l of the free ligand! in thecomplex suggests the formation of M -0 bond,deprotonation of the azomethine nitrogen atom+

(C=N-H) and its coordination to metal by formingC=N ... M type of bond.

Our sincere thanks are due to Prof. S. G. Tandonfor facilities and the CSIR, New Delhi, for fheaward of a junior research fellowship to one of us(K.K.D.).

References

1. SATYANARAYANA, K. & :'.IISHRA, RA]ENDRA K., IndianJ. Chem., 13 (1975), 295.

2. SATYANARAYANA, K. & MISHRA, RAJENDRA K., Analyt.Chem.,46 (1974), 1609.

3. DEB, K. K. & :'.fISHRA, RAJENDRA K., Curro Sci., 45(1976), 134.

4. VOGEL, A. 1., A textbook of quantitative inorganic analysis(Longmans, Green. London), 1964, 498.

5. DEB, K. K. & MISHRA, RAJENDRA K., J. Indian chem,Soc.,53 (1976), 178.

6. RAO, C. N. R., Chemical applications of infraredspectroscopy (Academic Press, ::\ew York), 1963,267. .

7. WITKOP, B. & BEILER, T. '0.'., J. Am. chem, Soc., 76(1954), 5589.

8. GIGURE. P. A. & LIU, 1. D., Can. J. Chem., 30 (1952),498.

9. PILLIPENKO, A. T., SHPAK, E. A. & SHEV'CHENKO, L. L.,Zhur. neorg. xu«; 121 (1967), 463.

10. WITKOP, B., J. Am. chem, Soc., 76 (1954), 5597.11. STONE, P. J., CRAIG, J. C. & THOMPSON, H. W., J. chem:

. Soc., (1958), 52.