Kumari, (Miss) R. Lalitha

Nair, C. G. R.

English

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Indian Journal of ChemistryVol. 14A, February 1976, pp. 115-117Interhalogens as Oxidimetric Titrants: Part VI* - OxidimetricDeterminations with Bromine MonochlorideC. G. R. NAIR & (Miss) R. LALITHA KUMARIDepartment of Chemistry, University of Kerala, Trivandrum 695001Received 17 February 1975; accepted 16 April 1975New analytical methods, employing bromine monochloride as an oxidimetrfc titrant, aredescribed 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.IN our previous communicationsi-s we haddescribed some convenient excess-backtitration oxidimetric methods for the deter-mination of several technologically important com-pounds using iodine monochloride in 5N HCImedium as the oxidant. In the present paper, amore reactive inter halogen , viz. bromine mono-chloride, is suggested as an oxidimetric reagent. Ithas been shown that, in general, bromine mono-chloride effects a more extensive oxidation thaniodine monochloride, giving larger equivalent con-sumption of the oxidant and therefore leading toan improved accuracy. Analytical methods usingbromine monochloride are described for the deter-mination of the following: isonicotinic acid hydrazidetriphenylphosphine, phosphorothioate, trithionates,xanthates, dithiocarbamates, reineckates, oxine andmetallic oxinates.Pioneer work on the use of bromine monochlo-ride as an analytical reagent has been done bySchulek and coworkers". Schulek and Burger usedbromine monochloride as a halogenating agent inthe determination of antipyrine, phenol, p-nitro-phenol and fluorescein. Other compounds whichhave been determined with bromine mono chlorideare hypophosphite", hydroxylamine", maleic andfumaric acids", formic acid!", hydrazine!', hexo-barbital= and thiocyanate, urea and thiourea-e. Itis hoped that the present studies would extend thescope of BrCI as a versatile and convenient oxidi-metric titrant.Materials and MethodsPreparation of stock solutions of bromine mono-chloride - Preliminary studies showed that thepresence of even small amounts of bromate inBrCl solution causes complications. Therefore, themethod described in literature was slightly modifiedas follows, in order to ensure absence of any freebromate. Potassium bromide (3·976 g) and potassiumbromate (2·7835 g) (molar ratio bromide/bromate= slightly more than 2) were dissolved together inwater (125 ml). To this 100 ml of cone. hydrochloric*For Parts I to V, see references 1 to 5.acid was added. The solution was shaken well withcarbon tetrachloride (2X 10 ml), in order to removefree bromine. Finally cone. hydrochloric acid (400ml) was added and the solution diluted to one litre.The solution was stored in contact with a layer ofcarbon tetrachloride which served to extr e.ct anytrace of bromine produced in the aqueous phase.Before use, the solution was shaken well and allowedto settle and the aqueous layer standardized byadding, to measured aliquots (20 ml), 10 mi 10%aqueous KI, diluting to 200 ml and titrating theliberated iodine with standard thiosulphate. It hasbeen noted that under these conditions brominemonochloride exists as a complex-".The formation of BrCI in the above preparationmay be represented as:2Br-+BrO:i+6HCI-l>-3BrCl+3Cl-+3H20The excess HCI taken serves to stabilize the BrCI,possibly by complex formation-s. It may be notedthat stock solutions of bromine mono chloride arereasonably stable and undergo no change in titre evenfor periods up to two weeks.Stock solutions of various compounds to be estimated- Solutions of potassium trithionate (prepared bythe method of Goehringw), potassium ethyl xanthate(USSR), sodium die thy I dithiocarbamate (BDH),sodium phosphorothioate (prepared by the methodof Kubierschky-P}, isonicotinic acid hydrazide (Koch-Light) and Reinecke salt (E. Merck) were preparedin distilled water while that of triphenylphosphine(Koch-Light) was prepared in carbon tetrachloride.All these solutions were standardized by proceduresinvolving oxidation with chloramine-T17-20 or iodinemonochloridet+. Cadmium thiourea reineckate wasprepared by the procedure of Rulf et aI.21 and wasused as such; the purity of the sample was checkedby the chloramine-T procedure". Oxine (Riedel)was dissolved in 2N HCI and the solution stan-dardized by the bromate-bromide method. Theoxinates of magnesium, aluminium, manganese,iron, cobalt, nickel, copper and zinc were preparedby standard methods involving the addition of asolution of oxine in 2N acetic acid to the hot aqueoussolutions of the respective metal sulphates underspecified conditions of pH24. The precipitates were115INDIAN J. CHEM., VOL. 14A, FEBRUARY 1976dried as recommended. Solutions of these oxinateswere prepared in 2N HCI and were standardized usingthe bromate-bromide method.General procedure - All the experiments werecarried out at room temperature (28 ± 2°C). (Itmay be noted that, unlike solutions of iodinemonochloride- in 5M hydrochloric acid, solutionsof bromine mono chloride in 5M hydrochloric aciddecompose on heating). To measured volumes(20-40 ml) of the bromine monochloride solutiontaken in stoppered conical flasks, measured aliquots(5 to 12 ml) of the reductant solutions or a knownweight of the reductant (in the case of cadmiumthiourea reineckate) were introduced. The contentswere shaken and were allowed to stand, in separateexperiments, for different time intervals (5 min to24 hr) at the end of which the unconsumed brominemonochloride was determined by adding 20 ml 10%aqueous potassium iodide and titrating the liberatediodine with standard thiosulphate. A standing timeof 10 min is recommended for the oxidation of allthe reductants studied, except for oxinates (15 min)and cadmium thiourea reineckate (30 min). Alonger standing time (up to 12 hr) did not lead toany increased consumption of the oxidant in anycase. Blanks were done concurrently for eachexperiment. Blank corrections were negligible (lessthan 0·1 ml) even on keeping for 24 hr.Results and DiscussionTypical results are presented in Tables 1 and 2.For convenience, these results could be evaluatedunder two categories:(a) Oxidations - It may be seen from the datain Tables 1 and 2 that the number of equivalentsof bromine monochloride consumed per mole of thereductant is 4 for isonicotinic acid hydrazide, 2 fortriphenylphosphine, 8 for trithionate and phosphoro-thioate, 16 for xanthate and dithiocarbamate, 32for reinecke salt and 80 for cadmium thioureareineckate. These values agree with the followingoxidation reactions.BrCI+2e---+Bc+CI-CsH,NCONH - NH2 + HzO--+C.H(NCOOH + NzH,N2H,--+Nz+4Hf. +4e-Ph3P+H20--+Ph3PO+2H+ +2e-SlIOi-+6H:P --+3S0:'+ 12H++8e-POSS3- +5HzO--+PO~-+SOi" + tOH++8e"ROCSS-+ 10HzO--+2S0i-+ROH+COz+ 19H+ + 16e-R2NCSS-+ tOHzO--+2S0i-+RzNH+COz+ 19H++ 16e-CNS-+5H20--+CNO-+ lOH+ +SO!-+8e-[Cd (NHz-CS- NHz)z] 2+[Cr(CNS)( (NH3) Z]2 + 52HzO--+Cd2.,. +2Crl > +8NH~ +92H+ +2C02+8CNO-+lOSO~- + 80e-On comparing these results with the results ofiodine monochloride oxidation it may be noted thatin the case of four of the compounds in this study,i.e, triphenylphosphine, phosphorothioate, trithio-nate and isonicotinic acid hydrazide, the numberof equivalents of oxidant consumed per mole ofreductant is the same for both the reagents. In these116cases the bromine mono chloride method has nospecific advantage over the iodine monochloridemethod and it is simply a useful alternative method.But, with the remaining compounds, viz. xanthate,dithiocarbamate, reinecke salt and cadmium thioureareineckate, bromine monochloride effects a moreextensive oxidation than iodine monochloride. Thenumbers of equivalents of iodine monochloride con-sumed for the above compounds are respectively14, 14, 24 and 64 whereas, with bromine monochlo-ride, the values are 16, 16, 32 and 80 respectively.This increased consumption of BrCI here may betraced to the ability of this oxidant to oxidize theformate ion to carbonate (in the case of oxidationsof xanthate and dithiocarbamate) and the cyanideion to cyanate (in the case of reinecke salt and cad-mium thiourea reineckate). For the above-mentionedcompounds the bromine monochloride methodis therefore intrinsically more accurate than theiodine monochloride method.I t is noteworthy in this context that in manyother oxidimetric methods for the determinationof xanthates and dithiocarbarnates, the number (n)of equivalents of oxidant consumed per mole of thereductant is <16. Thus for xanthate, n = 14 withchloramine-T!? and potassium iodate'" and n = 1with iodine'". For dithiocarbamate, n = 14 withchloramine-T?" and potassium iodate=, n = 1 withiodine'", ICN29 and BrCN29. On this basis, it wouldappear that BrG should find preference over theseTABLE 1 - OXlDIYETRIC DETERMINATIONS WITH BROMINEMONOCHLORlDESubstance No. of Eq. BrCIdeterrnina- consumed!tions molereductant(meanvalue)% rela-tivemeanerrorIsoriicotinic acid hydrazide 6 4'009 +0·23Triphen ylphosphine 5 2·002 +0'12Sodium phosphorot hioate 6 7'992 -0'10Potassium trit hionate 5 7'993 -0'09Potassium ethyl xant hate 7 16'02 +0'15Sodium diet hyl dit hiocarba- 6 16·08 +0'48mateReinecke salt 5 32'05 +0'19Cadmium thiourea rei- 6 80'27 +0'32neckateTABLE 2 - DETERMI~ATlON OF OXINE AND METALLICOXINATES WITH BROMINE MONOCHLORlDECompound TO. of Ell' BrCI % relativedetcr minations consumed! mean errormole reductant(mean value)Oxine X 4'022 +0·55Mg (oxinc}, 7 7'993 -0,10Al (exine); 7 11'980 -0,17Mn (oxinej, 6 7-991 -0'12Fe (exine}, 6 11·010 +0'07Co (exine), 6 8-036 +0·45Ni (oxinej, 4 8'031 +0·38Cu (oxine), 6 6·972 -0·40Zn (OX;EC). 5 8·024 +0'29KAIR & LALITHA KUMARI.: OXIDIMETRIC DETERMINATIONS WiTH BrCIoxidants for the determination of xanthates anddithiocarbamates.(b) Halogenations (brominations) - It was foundthat in dil. hydrochloric acid medium oxine reactswith b~omine monochloride to give dibromooxine,consummg 2 moles (4 equivalents) of BrCI per moleof oxine.C9H70N +2 BrCI-i>-CgH50NBr2+2HClIt may be seen from Table 2 that the number ofeq~ivalents of BrCI consumed per mole of the?xmates of Mg(II), Mn(II), Co(II), Ni(II) Zn(II) etc.IS 8 and that for AI(III) n = 12; for copper oxinaten = 7 and for iron oxinate n = 11. The apparentdeviations in the case of Cu(II) and Fe (III) are dueto the fact that during subsequent addition of KI(for estimating the unconsumed BrCl) , there is aconcomitant reduction of Cu(II) to Cu(I) and Fe(III)to Fe(II).Oxine and metallic oxinates have been determinedby Cihaliks'' using iodine monochloride as theoxidant, in a medium whose acidity is carefullycontrolled by the addition of ammonia in suitableamounts. If excess ammonia is added, oxine isthrown out. Further, increase of acidity was reportedto slow down the rate of this reaction considerably.In the present investigation, it is found that thereaction of oxine with bromine monochloride takesplace very quickly in the acidic media employed.Increase of acidity does not decrease the rate of thereaction. The present method is also superior tothe conventional bromate-bromide method, in whichspecial precautions have to be taken to preclude lossof bromine.References1. NAMBISAN, P. x. K. & NAIR, c. G. 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STAMM, H. & BEEKE-GOEHRING, ::VI., Z. anorg, allgem;cs-«, 250 (1942), 226.16. BRAUER, G., Handbook of preparative inorganic chemistry(Academic Press, New York), 1963.17. RAO, V. R. S. & MURTHY, A. R. V., T'alanta, 4 (1960),206.IS. NAMBISAN, P. N. K. & NAIR, C. G. R., Indian]. Chem.,8 (1970), 847.19. JACOB, T. J. & NAIR, C. G. R., Indian]. Chem., 4 (1966),501.20. NAIR, V. R. & NAIR, C. G. R., Anal. chim . Acta, 57 (1971),429.21. RULFS, C. L., PRZYBYLOWICZ, E. P. & SKINNER, C. E.,Analyt . Chem., 26 (1954), 40S.22. NAMBISAN, P. N. K. & NAIR, C. G. R., 1vlikrochim. Acta(Wien), (1973), 331.23. KOLTHOFF, 1. M. & BELCHER, R., Volumetric analysis,Vol. III (Intersciencc, New York), 1957. .24. VOGEL, A. 1., A textbook of quantitative inorganic analysis(Longmar s, London). 1964.25. NAIR, B. G. K. & NAIR, C. G. R., Curro Sci., 39 (1970), 209.26. MATUSZAK, M. P., Ind. Engng Chem. (Anal.), 4 (1932)' 9S.27. NAIR, C. G. R., JOSEPH, T. & JOSEPH, P. T., cue«.A nalyst (Ba.~er), 54 (1965), 111.2S. 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Interhalogens as Oxidimetric Titrants: Part VI* - Oxidimetric Determinations with Bromine Monochloride

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

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