Indian Journal of Chemistry Vol. 14A, February 1976, pp. 115-117

Interhalogens as Oxidimetric Titrants: Part VI* - Oxidimetric Determinations with Monochloride

C. G. R. NAIR & (Miss) R. LALITHA KUMARI Department of Chemistry, University of Kerala, Trivandrum 695001

Received 17 February 1975; accepted 16 April 1975

New analytical methods, employing bromine monochloride as an oxidimetrfc titrant, are described for the determination of isonicotinic acid hydrazide, triphenylphosphine, phosphore- thioate, trithionate, xanthate, dithiocarbamate, reineckate, oxine and oxlnates of Mg, AI, Mn, Fe, Co, Ni, Cu and Zn.

N our previous communicationsi-s we had acid was added. The solution was shaken well with described some convenient excess-back (2 X 10 ml), in order to remove Ititration oxidimetric methods for the deter- free bromine. Finally cone. (400 mination of several technologically important com- ml) was added and the solution diluted to one litre. pounds using in 5N HCI The solution was stored in contact with a layer of medium as the oxidant. In the present paper, a carbon tetrachloride which served to extr e.ct any more reactive inter , viz. bromine mono- trace of bromine produced in the aqueous phase. , is suggested as an oxidimetric reagent. It Before use, the solution was shaken well and allowed has been shown that, in general, bromine mono- to settle and the aqueous layer standardized by chloride effects a more extensive oxidation than adding, to measured aliquots (20 ml), 10 mi 10% iodine monochloride, giving larger equivalent con- aqueous KI, diluting to 200 ml and titrating the sumption of the oxidant and therefore leading to liberated iodine with standard thiosulphate. It has an improved accuracy. Analytical methods using been noted that under these conditions bromine bromine monochloride are described for the deter- monochloride exists as a complex-". mination of the following: isonicotinic acid hydrazide The formation of BrCI in the above preparation triphenylphosphine, phosphorothioate, trithionates, may be represented as: xanthates, dithiocarbamates, reineckates, oxine and 2Br-+BrO:i+6HCI-l>-3BrCl+3Cl-+3H20 metallic oxinates. The excess HCI taken serves to stabilize the BrCI, Pioneer work on the use of bromine monochlo- possibly by complex formation-s. It may be noted ride as an analytical reagent has been done by that stock solutions of bromine mono chloride are Schulek and coworkers". Schulek and Burger used reasonably stable and undergo no change in titre even bromine monochloride as a halogenating agent in for periods up to two weeks. the determination of antipyrine, phenol, p-nitro- Stock solutions of various compounds to be estimated phenol and fluorescein. Other compounds which - Solutions of potassium trithionate (prepared by have been determined with bromine mono chloride the method of Goehringw), potassium ethyl xanthate are hypophosphite", hydroxylamine", maleic and (USSR), sodium die thy I dithiocarbamate (BDH), fumaric acids", formic acid!", hydrazine!', hexo- sodium phosphorothioate (prepared by the method barbital= and thiocyanate, urea and thiourea-e. It of Kubierschky-P}, isonicotinic acid hydrazide (Koch- is hoped that the present studies would extend the Light) and Reinecke salt (E. Merck) were prepared scope of BrCI as a versatile and convenient oxidi- in distilled water while that of triphenylphosphine metric titrant. (Koch-Light) was prepared in carbon tetrachloride. All these solutions were standardized by procedures Materials and Methods involving oxidation with chloramine-T17-20 or iodine Preparation of stock solutions of bromine mono- monochloridet+. Cadmium thiourea reineckate was chloride - Preliminary studies showed that the prepared by the procedure of Rulf et aI.21 and was presence of even small amounts of bromate in used as such; the purity of the sample was checked BrCl solution causes complications. Therefore, the by the chloramine-T procedure". Oxine (Riedel) method described in literature was slightly modified was dissolved in 2N HCI and the solution stan- as follows, in order to ensure absence of any free dardized by the bromate- method. The bromate. (3·976 g) and potassium oxinates of magnesium, aluminium, manganese, bromate (2·7835 g) (molar ratio bromide/bromate iron, cobalt, nickel, copper and zinc were prepared = slightly more than 2) were dissolved together in by standard methods involving the addition of a water (125 ml). To this 100 ml of cone. hydrochloric solution of oxine in 2N acetic acid to the hot aqueous solutions of the respective metal sulphates under *For Parts I to V, see references 1 to 5. specified conditions of pH24. The precipitates were

115 INDIAN J. CHEM., VOL. 14A, FEBRUARY 1976 dried as recommended. Solutions of these oxinates cases the bromine mono chloride method has no were prepared in 2N HCI and were standardized using specific advantage over the iodine monochloride the bromate-bromide method. method and it is simply a useful alternative method. General procedure - All the experiments were But, with the remaining compounds, viz. xanthate, carried out at room temperature (28 ± 2°C). (It dithiocarbamate, reinecke salt and cadmium thiourea may be noted that, unlike solutions of iodine reineckate, bromine monochloride effects a more monochloride- in 5M hydrochloric acid, solutions extensive oxidation than iodine monochloride. The of bromine mono chloride in 5M hydrochloric acid numbers of equivalents of iodine monochloride con- decompose on heating). To measured volumes sumed for the above compounds are respectively (20-40 ml) of the bromine monochloride solution 14, 14, 24 and 64 whereas, with bromine monochlo- taken in stoppered conical flasks, measured aliquots ride, the values are 16, 16, 32 and 80 respectively. (5 to 12 ml) of the reductant solutions or a known This increased consumption of BrCI here may be weight of the reductant (in the case of cadmium traced to the ability of this oxidant to oxidize the thiourea reineckate) were introduced. The contents formate ion to carbonate (in the case of oxidations were shaken and were allowed to stand, in separate of xanthate and dithiocarbamate) and the cyanide experiments, for different time intervals (5 min to ion to cyanate (in the case of reinecke salt and cad- 24 hr) at the end of which the unconsumed bromine mium thiourea reineckate). For the above-mentioned monochloride was determined by adding 20 ml 10% compounds the bromine monochloride method aqueous potassium iodide and titrating the liberated is therefore intrinsically more accurate than the iodine with standard thiosulphate. A standing time iodine monochloride method. of 10 min is recommended for the oxidation of all I t is noteworthy in this context that in many the reductants studied, except for oxinates (15 min) other oxidimetric methods for the determination and cadmium thiourea reineckate (30 min). A of xanthates and dithiocarbarnates, the number (n) longer standing time (up to 12 hr) did not lead to of equivalents of oxidant consumed per mole of the any increased consumption of the oxidant in any reductant is <16. Thus for xanthate, n = 14 with case. Blanks were done concurrently for each chloramine-T!? and potassium iodate'" and n = 1 experiment. Blank corrections were negligible (less with iodine'". For dithiocarbamate, n = 14 with than 0·1 ml) even on keeping for 24 hr. chloramine-T?" and potassium iodate=, n = 1 with iodine'", ICN29 and BrCN29. On this basis, it would Results and Discussion appear that BrG should find preference over these Typical results are presented in Tables 1 and 2. For convenience, these results could be evaluated under two categories: TABLE 1 - OXlDIYETRIC DETERMINATIONS WITH BROMINE (a) Oxidations - It may be seen from the data MONOCHLORlDE in Tables 1 and 2 that the number of equivalents of bromine monochloride consumed per mole of the Substance No. of Eq. BrCI % rela- reductant is 4 for isonicotinic acid hydrazide, 2 for deterrnina- consumed! tive tions mole mean triphenylphosphine, 8 for trithionate and phosphoro- reductant error thioate, 16 for xanthate and dithiocarbamate, 32 (mean for reinecke salt and 80 for cadmium thiourea value) reineckate. These values agree with the following oxidation reactions. Isoriicotinic acid hydrazide 6 4'009 +0·23 Triphen ylphosphine 5 2·002 +0'12 BrCI+2e---+Bc+CI- Sodium phosphorot hioate 6 7'992 -0'10 Potassium trit hionate 5 7'993 -0'09 CsH,NCONH - NH2 + HzO--+C.H(NCOOH + NzH, Potassium ethyl xant hate 7 16'02 +0'15 Sodium diet hyl dit hiocarba- 6 16·08 +0'48 N2H,--+Nz+4Hf. +4e- mate Reinecke salt 5 32'05 +0'19 Ph3P+H20--+Ph3PO+2H+ +2e- Cadmium thiourea rei- 6 80'27 +0'32 SlIOi-+6H:P --+3S0:'+ 12H++8e- neckate POSS3- +5HzO--+PO~-+SOi" + tOH+ +8e" ROCSS-+ 10H O--+2S0i-+ROH+CO + 19H+ + 16e- z z TABLE 2 - DETERMI~ATlON OF OXINE AND METALLIC R2NCSS-+ tOHzO--+2S0i-+RzNH+COz+ 19H+ + 16e- OXINATES WITH BROMINE MONOCHLORlDE

CNS-+5H20--+CNO-+ lOH+ +SO!-+8e- Compound TO. of Ell' BrCI % relative [Cd (NHz-CS- NHz)z] 2+[Cr(CNS)( (NH3) Z]2 + 52H O--+ detcr minations consumed! mean error z mole reductant 2 > Cd .,. +2Crl +8NH~ +92H+ +2C02+8CNO-+ (mean value) lOSO~- + 80e- Oxine X 4'022 +0·55 Mg (oxinc}, 7 7'993 -0,10 On comparing these results with the results of Al (exine); 7 11'980 -0,17 iodine monochloride oxidation it may be noted that Mn (oxinej, 6 7-991 -0'12 in the case of four of the compounds in this study, Fe (exine}, 6 11·010 +0'07 Co (exine), 6 8-036 +0·45 i.e, triphenylphosphine, phosphorothioate, trithio- Ni (oxinej, 4 8'031 +0·38 nate and isonicotinic acid hydrazide, the number Cu (oxine), 6 6·972 -0·40 of equivalents of oxidant consumed per mole of Zn (OX;EC). 5 8·024 +0'29 reductant is the same for both the reagents. In these

116 KAIR & LALITHA KUMARI.: OXIDIMETRIC DETERMINATIONS WiTH BrCI oxidants for the determination of xanthates and 4. NAMBISAN, P. N. K. & NAIR, C. G. R., Anal. chi m, acta, 60 (1972), 462. dithiocarbamates. S. NAMBISAN, P. N. K., LALITHAKUMARI, R., KUMARAN, (b) Halogenations (brominations) - It was found C. N. & NAIR, C. G. R., Indian ]. Chem., 11 (1973), that in dil. hydrochloric acid medium oxine reacts 964. with b~omine monochloride to give dibromooxine, 6. SCHULEK, E. & BURGER, K., Talanta, 1 (1958), 147. consummg 2 moles (4 equivalents) of BrCI per mole 7. BURGER, K. & LADANYI, LASZLO, Acta pharm, Hung., 30 (1960), SO. of oxine. S. BURGER, K., GAIZER, F. & SCHULEK, E., Talanta, 5 (1960), C9H70N +2 BrCI-i>-CgH 0NBr +2HCl 97. 5 2 9. BURGER, K. & SCHULEK, E., Mug . Kem. Folyoirat, 67 It may be seen from Table 2 that the number of (1961), 33. eq~ivalents of BrCI consumed per mole of the 10. SCHULEK, E., BURGER, K. & GAIZER, FERENE, Acta ?xmates of Mg(II), Mn(II), Co(II), Ni(II) Zn(II) etc. pharm, Hu ng., 31 (1961), 241. . . 11. BURGER, K. & SCHULEK, E., Ann. Untv. sa. Budapest, IS = 8 and that for AI(III) n 12; for copper oxinate 2 (1960), 133. n = 7 and for iron oxinate n = 11. The apparent 12. BURGER, K., SCHULEK, E. & LADANYI, L., Acta ph arm. deviations in the case of Cu(II) and Fe (III) are due Hung., 29 (1959), 241. to the fact that during subsequent addition of KI 13. SHARMA, R. C. & TANDON, J. P., Indian]. appl. Chem., 34 (1971), 193. (for estimating the unconsumed BrCl) , there is a 14. BURGER, K. & SCHULEK, E., Ann. Univ. Sci. Budapest, concomitant reduction of Cu(II) to Cu(I) and Fe(III) 2 (1960), 133. to Fe(II). 15. STAMM, H. & BEEKE-GOEHRING, ::VI., Z. anorg, allgem; Oxine and metallic oxinates have been determined cs-«, 250 (1942), 226. by Cihaliks'' using iodine monochloride as the 16. BRAUER, G., Handbook of preparative inorganic chemistry (Academic Press, New York), 1963. oxidant, in a medium whose acidity is carefully 17. RAO, V. R. S. & MURTHY, A. R. V., T'alanta, 4 (1960),206. controlled by the addition of ammonia in suitable IS. NAMBISAN, P. N. K. & NAIR, C. G. R., Indian]. Chem., amounts. If excess ammonia is added, oxine is 8 (1970), 847. thrown out. Further, increase of acidity was reported 19. JACOB, T. J. & NAIR, C. G. R., Indian]. Chem., 4 (1966), 501. to slow down the rate of this reaction considerably. 20. NAIR, V. R. & NAIR, C. G. R., Anal. chim . Acta, 57 (1971), In the present investigation, it is found that the 429. reaction of oxine with bromine monochloride takes 21. RULFS, C. L., PRZYBYLOWICZ, E. P. & SKINNER, C. E., place very quickly in the acidic media employed. Analyt . Chem., 26 (1954), 40S. 22. NAMBISAN, P. N. K. & NAIR, C. G. R., 1vlikrochim. Acta Increase of acidity does not decrease the rate of the (Wien), (1973), 331. reaction. The present method is also superior to 23. KOLTHOFF, 1. M. & BELCHER, R., Volumetric analysis, the conventional bromate-bromide method, in which Vol. III (Intersciencc, New York), 1957. . special precautions have to be taken to preclude loss 24. VOGEL, A. 1., A textbook of quantitative inorganic analysis (Longmar s, London). 1964. of bromine. 25. NAIR, B. G. K. & NAIR, C. G. R., Curro Sci., 39 (1970), 209. 26. MATUSZAK, M. P., Ind. Engng Chem. (Anal.), 4 (1932)' 9S. References 27. NAIR, C. G. R., JOSEPH, T. & JOSEPH, P. T., cue«. A nalyst (Ba.~er), 54 (1965), 111. 1. NAMBISAN, P. x. K. & NAIR, c. G. R., Curro Sci., 39 2S. SHANKARANARAYANA, M. L. & PATEL, C. c., Z. anal. (1970), 34S. Chem., 179 (1961), 263. 2. NAMBISAN, P. N. K. & NAIR, C. G. R., Anal. chim, acta, 52 29. PAUL, R. C., SHARMA, N. c.. CHAUHAN, R. K. & PRAKASH. (1970), 475. R., Indian ]. Cheni., 10 (1972), 227. 3. NAMBlSAN, P. N. K. & NAIR, c. G. R., Indian ]. Chon., 30. CIHALIK, J. & TEREBOVA, K., Coltn Czech. chem . Commun-, 10 (19i2), 665. 23 (1958), 110.

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