Dhillon, D. S.

Konwer, D.

Paul, R. C.

Puri, J. K.

English

NOPR

IndianJournal of ChemistryVol. 15A,January1977,pp.23-26ChlorosulphuricAcid as a Non-aqueousSolvent:Part VI-Conductometric& SpectralStudiesof VariousInorganic&OrganicAcid Annydridesin ChlorosulphuricAcidR. C. PAUL*, D. S. DHILLON, D. KONWER & J. K. PURlDepartmentof Chemistry,PanjabUniversity,Chandigarh160014Received25 February 1976;accepted2 June 1976Conductometricandspectralstudiesof thesolutionsof acidanhydridesin chlorosulphuricacid indicatethat nitric and nitrousoxidesbehaveas non-electrolytes,whereasdinitro~entrioxide,dinitro~entetroxideanddinitro~enpentoxideform nitrosoniumandnitroniumions.Phosphorouspentoxide~ivesa mixtureof varioussulphuroxychlorideswhichbehaveas non-electrolytes.Arsenictrioxide,antimonytrioxideandbismuthtrioxide~etsolvolysedwhereasboricanhydrideformstetrachlorosulphatob ricacidwhendissolvedin chlorosulphuricacid.Or~anicacidanhydridesbehaveas bases.From theextentof protonationof thesesolutes,ithasbeeninferredthatchlorosulphuricacidis a stron~eracidthansulphuricacid.SYSTEMATIC physico-chemicalinvestigationsofthesolutionsof variousanhydridesof inorganicandorganicacidsin fluorosulphuricacid1haveshownthattheacidgetsdehydratedandhydronium(H;O) ions are formed. Such an investigationislacking in chlorosulphuricacid as a non-aqueoussolvent. As chlorosulphuricacid is weakerthandisulphuricandfluorosulphuricacids,investigations-on the solution behaviourof tlie inorganicand-organicacid anhydridesshallbe of greaterhelpindifferentiatingthebasicitiesof theseanhydrides.MaterialsandMethodsThe designof the conductivitycells used hasbeen described earlier2. Conductancemeasure-mentsweremadeasdescribedpreviouslys. Chloro-sulphuricacid(BDH technical)wasfirstfractionally<listilledaccordingto Robinson and Ciruna4 at151°/746mmpressureandredistilledundernitrogenatmospherebeforeuse.Nitrous oxide,nitric oxide,dinitrogentrioxide,<linitrogentetroxideanddinitrogenpentoxidewerepreparedand purified by the well establishedmethods5. Arsenic trioxide, antimony trioxide,antimonypentoxide,bismuthtrioxide,phosphorouspentoxideand boric anhydridewerecommerciallyavailablesamplesand wereusedwithout furtherpurification. Succinicanhydridewas washedwithdry etherand then dried over phosphorouspent-oxidefor 24hI. Commerciallyavailablesamplesofacetic anhydride (b.p. 140°/740 mm), isobutyricanhydride(b.p. 182°/745mm) and dichloroaceticanhydride(b.p. 101°/16 mm)weredistilledin aninert atmospherebeforeuse. Maleicanhydridewasrecrystallizedfrom chloroform and dried overphosphorouspentoxide. PotassiumchIorosulphatewas preparedby the literaturemethod'and used*Presentaddress:Vice-Chancellor,Panjab University,Chandigarh160014.as such. Antimonypentachloride(BDH) wasusedwithout furtherpurification.ResultsandDiscussionIt hasalreadybeenshownthat (SOaCI-)ionsareresponsiblefor the conductanceof thesesolutionsand(50aCl-)isthestrongestmonoacidbase'.Specificconductanceversus molality curves of varioussolutesin chlorosulphuricacid aregivenin Fig. 1.Theconductometricfactor,y (thenumberof SOaCl-bns producedpermoleof solute)hasbeenobtainedby comparingthe observedconductancecurveswith those of potassiumchlorosulphate(a fullyionizedbase). Acid-basetitrationcurvesin chIoro-sulphuricacidmediumaregivenin Fig. 2.Whensulphurtrioxideis addedto chlorosulphuricacid the conductanceof the solution decreases.This decreasein conductancemay be assignedtothe formationof higher chloropolysulphuricacidsofthetypeHS208CI,HSsOgCIandprobablyHS,01ICIandevenhigherpolyacidswhichfurtherbehaveasnon-electrolytesin chIorosulphuricacid. HigherpJlyacids of chlorosulphuricand disulphuricacidshave already been reported by Gillespie andRobinson8• Thenon-electrolyticbehaviourof thesehigheracidsin chlorosulphuricacid hasbeencon-firmedby thefactthat on additionof potassiumorsodium chloride there is always an increaseinconductance;at no stage there is any decrease.The reaction occurringcould be representedbyEq. (1) or (2).KCI + SOa---+KSOaCI--+K'"+ SOaCI- '" (1)KCI+HSOaCI-+HCI+KSOaCI-+K'"+SOaCI-+HCI'" (2)The sulphurtrioxide dissolvedin HSOaCImayconvertKCI to KSOsCI or KCI maybe solvolysedby chlorosulphuricacid to KSOaCl. In both thecasesSOsCI-ionsareproducedwhichareresponsibleINDIAN J. CHEM., VOL. I5A, JANUARY 1977Fig. I-Conductanceofvariousinorganicand organicacid anhydridesin chioro-sulphuricacidat 25°,--4.-..--.--'-_16 iBt148 '0 -z ,iMOLALITY XIO42o0.4,!I4.44.ol-o-O-NaOJ_~ Nl.04-4-4-HaOs8_._/(5°3'/3.6t __ -PHTHALLIC ANHYDRID£9--¢_ACETI ANHYDRID£fl__fIl-8ENZOI ANHYDRIDE-~-¢-SUCCINIC A Y RI E2 -t(-t{-"'N.EIC Y I___-)(- A¥'J4r Sb20)~-:-+-8"203\ 2.8- -,-PaOs- -l-B20], ~- -Sb20sE 1Il J8(- PI?OPlON/CANHYDRIQE~ .e 2:4 -"-" IS08UTYRICANHYOI?IOE'" 0- - (CI ~COz)20~ Cl-()-SeOzJC ~-4-TO.za 2.0~'.6'"'·20.83.6__ IV,~ VS SbCls~-A1z0+ VSSbCls_____ IVZ Os vs SbClse-e-- 8z~VSICSOJCI~ 8z03 V5 CHlCOOH~ 8a03 VS PVRIDINE0·80.4o ! 0.4 ()·B '·2 ,·6 2.0 2.4 -2·8 3.2 3.6MOLAR RATIOFig. 2+Conductometricacid-basetitrationsof differentanhydridesin chiorosulphuricacidat 25°for an increasein the conductance(HCI producedin the latter casebehavesas a very weakelectro-lyte4). Even the addition of potassiumchloro-sulphatedirectlydoesnot bring abouta fall in theconductanceof the solution which confirmstheobservationrecordedabove.In the caseof seleniumtrioxide,however,thereis no significantchangein the conductanceof thesolution indicatingtherebythat it behavesas anon-electrolyte,probably due to the formationof a compoundof thetypeHSeSOoCI,analogoustothe speciesHSeSOoFin fluorosulphuric7acidwhichbehavesas a non-electrolyte.Both seleniumandtellurium dioxides are highly soluble in chloro-sulphuricacidandgivehighlyconductingsolutions.From the conductometricfactor (Y), it is seenthatin the caseof seleniumdioxide monoprotonationtakesplacewhereasin thecaseof telluriumdioxideincompletediprotonationtakesplace. It seemstobequitereasonableto suggesthefollowingmodeofprotonation(Eq.3) in the caseof seleniumdioxide.+Se02+HS03CI.-+HO=Se=O+S03CI- ...(3)In the caseof tellurium dioxide the secondin-completeprotonationmay take placeat the otheroxygenatom.Both nitrousand nitric oxidesare quite solublein chlorosulphuricacid,but behaveas non-electro-lytes in it.24PAUL etal.: CHLOROSULPHURIC ACID AS A NON-AQUEOUS SOLVENTDinitrogen trioxide, dinitrogen tetroxide anddinitrogenpentoxideare readilysolublein chloro-sulphuricacid forminghighly conductingsolutions.At lowerconcentrationsthesesolutionsare colour-less but when the concentrationsare increasedyellow colour develops. From the conductancedataandtheY valuesobtained(Fig. 1),the follow-ing modesof reactions(4-6)mayberepresented:NzOa+3HSOaCI-+2NO++2S0aCl-+HzSO4+HCl••.(4)N20,+3HSOaCl-+NO~+NO++2S0aCl-+HZS04+HCl ...(5)NzO5+3HSOaCl-+2NO~+2S0aCl-+HZS04+HCl•..(6)The possibilityof the reaction(7)NzOa+3HSOaCl-+2NO·+H;0+3S0aCl- ...(7)has beenruled out as the Y value obtainedis 2.Chlorosulphuricacid is molecularlyself-dissociatedaccordingto Eq. (8)HSOaCl-+HCl+SOa ...(8)and the water formedduring the abovereactioncombineswith SOato producesulphuricacidratherthangettingprotonatedashydroniumions. Whenthe concentrationof theseanhydridesis increasedlight yellowsolids separateout. IR spectrumofthe solid obtainedfrom NZ05 in silver chlorideplatesshowa strongbandat 2310cm-1indicatingthe presenceof NO; ions. The other frequenciesof NO~ion andthosefor the anionscouldnot beresolvedas the solvent itself coversthe wholeregion. In the caseof solid obtainedfrom NzO"the bandsat 2280and2145cm-1maybe assignedto thespeciesNO+zandNO'"respectively.Similarlyin thecaseof the solidobtainedfromNzOaa sharppeakat 2165cm-1indicatesthe presenceof NO'"ion andsupportsthemodesof ionizationas shownin Eqs. (4-7).Further,to checkthevalidityof theabovemodesof ionization some acid-basetitrations betweenantimonypentachloride(astrongacidofthesystem)and the solutions of theseanhydridesin chloro-sulphuricacid have beencarriedout. Robinson8has reportedthat antimonypentachloridebehavesas strong Lewis acid in chlorosulphuricacid.When antimony pentachlorideis added to thesolutionsof these anhydridesin chlorosulphuricacidthereis a decreasein conductance(Fig. 2)andthisdecreasein conductanceis duetothereaction(9)H~SOaCl+SOaCI-~2HSOaCI ...(9)After completeremovalof the (SOaCI-)ionsfrom the solution,further addition of antimonypentachloridecausesan increasein the conduc-tance which is probablydue to the formationofanacid of the type H,[SbClz(SOaCI)aSOaCI]similarto H[SbFz(SOaF)aSOaF]already known in thecase of fhlOfOsulphuricacid system. From thepositionsof minimain the conductancecomposi-tion curves it is evident that all thesesolutesproducetwo moles of SOaCl-and behavein asimilarmanner.Engelbrechtand Stollehavereportedthat P205formsphosphorylfluoridewhendissolvedin fluoro-sulphuricacid. Paul and coworkers1o-ahavere-portedthat fluorosulphuric.acid is dehydratedbyphosphorouspentoxideto ,formdi$ulphuryldifluo-ride and trisulphurylfluoride whereasdisulphuricacid is dehydratedto form free sulphur trioxidewhichfurthergivestrisulphuricacid. Phosphorouspentoxidegivessolutionsof low conductanceinchlorosulphuricacid, accompaniedprobablywiththe formationof sulphuroxychlorideswhich areknown to behaveas non-electrolytes'.The pos-siblemodeof solvolyticreactioncanbe representedas shownin Eq. (to).PZ05+ 9HSOaCI-+2HaP04+ Sz05Clz+~SO,+HCI... (10}Arsenicpentoxideis extensivelysolublein chlqro-sulphuric acid on warmingto give conductingsolutions. It may be assumedthat when thissoluteis addedto chlorosulphuricacid solvolysistakesplaceand the solvolysedproductis slightlyionizedto producea significantchangein con-ductance.Arsenic trioxide has a very limitedsolubilityin chlorosulphuricacidyieldingsolutionsof low conductance(Fig. 1). The possiblemodesof reactionsoccurring.in these~olutionsmay berepresentedas in Eqs. (11)and (12).ASzOa+9HSOaCl-+2As(SOaCl)a+3H.SO,+3HCl...(ll}orAszOa+3HSOaCl-+2AsOSOaCl+HzSO,,+HCl••.(12}Onecan expectthepossibilityof the formationofthe 3peciesAs(SOaCI)a,analogousto As(SOaF)ainfluorosulphuricacid. If As(SOaCl)ais formeditmayfurthershowamphotericbehaviourin chloro-sulphuricacidaccordingto thereaction(13)As(SOaCl)a-+As(SOaCl)~+SOaCl- ...(13}and should give higher value of Y. As(SOaCI)smay further react with anotherSOaCl-ion fromchlorosulphuricacid to form the speciesof thetype As(SOaCl),(Eq. 14)As(SOaCl)a+SOaCl-~As(SOaCl)4 ...(14}whichwill furtherlowerthe Y value to a greaterextent. But as therewas no changeof conduc-tanceduring theseinvestigations,the possibilityof the Eq. (11) representingthe mode of reac-tion must be ruled out. The low conductancevaluesof the solutionsare eitherdueto the weakelectrolyticbehaviourof sulphuricandhydrochloricacidsor due to the slight ionizationof AsOSOaClwhichfurthersupportsthe modeof reactionrepre-sentedby Eq. (12).Bismuthtrioxideandantimonytrioxidedissolvein chlorosulphuricacid to give milky, stablesolt.·tiom. The possiblemodeof reactiomis showninEq. (15).SbzOa+3HSOaCl-+2SbO.SOaCI+HzSO,+HCl2SbO.SOaCl~2SbO"'+2S0aCl- ...(15)Eq. (15)requiresa valueof two for the conducti-vity factor(Y) but the low conductanceand milkyappearanceshow that SbO.SOaClspeciesformedare insoluble in chlorosulphuricacid possiblybecause of extensive polymerization.Similarobservationshavealreadybeenmadein the case25INDIAN J. CHEM., VOL. 15A, JANUARY 1977TABLE 1- DISSOCIATIONCONSTANTSOF ACID ANHYD1<W",SIN HS03Cl AT 25°HS03ClH2SO4H2S2O,S03FPhthalic anhydride19'8715'86Fully24·5ionizedMonochloroaceticanhy-23-650do3 ·8dride Maleic anhydride4 963 979,5 - 2Succinic anhydride4 46 78 08anhydrideandpropionicanhydrideformclearandhighly conductingsolutions when dissolved inchlorosulphuricacid. From the 'f valuesobtainedin thecaseof all thesesolutesit hasbeenobservedthat all of thembehaveas strongmonoacidbasesin it. But the solutions of succinic anhydride,maleicanhydride,phthalic anhydrideand mono-chloroaceticanhydridein chlorosulphuricacidhavelower conductancevalueswhich indica.tethat allthese anhydridesbehaveas weak basesin thissolvent.The dissClciationconstantsof these acid an-hydrides have also been determinedin chloro-sulphuricacidandwhenthesevaluesarecomparedwith thoseobtainedin thecaseof sulphuric,fluoro-sulphuricand disulphuricacids (Table 1), it hasbeeninferredthat chlorosulphuricacid is a weakerproton donor as comparedto fluorosulphuricanddisulphuricacids,but strongerthansulphuricacid.ReferencesKb X 102Compound1. PAUL, R. C., SHARMA,S. K., SHARMA,R. D., PAUL, K. K.& MALHOTRA,K C., J. inorg. nucl. Chern.,33 (1971),2905.2. GILLESPIE, R. J. & MALHOTRA,K. c., J. chern.Soc.,(1967),1994.3. PAUL, R. c., DHILLON, D. S. & PURl, J. K, Indian J.Chern.,13 (1975),1058.4. ROBINSON,E. A. & CIRUNA,J. A., Can. J. Chem.,(1968),1719.5. GEORGE BRAUER, Hand book of preparativeinorganicchemistry,Vol. 1 (AcademicPress,New York, London),1963,484.6. GILLESPIE, R. J. & ROBINSON,E. A., Can. J. Chem.,40(1962),645.7. PAUL, R. C., PAUL, K K & MALHOTRA,K C., J. inorg.nucl. Chern.,31 (1969),2614.8. ROBINSON,E. A., Paper presentedat the InternationalConferenceon Non-aqueous Solvent, Canada, June1967.9. ENGELBRECHT,A. & STOLL, B., Z. anorg. Chern.,292(1957),20.10. MALHOTRA,K C. & PURl, J. K, Indian J. Chem.,(inpress).11. PAUL, R. C., MALHOTRA.K. C. & VAIDYA, O. C., IndianJ. Chem.,3 (1965),1.12. PAUL, R. C., MALHOTRA,K. C. & KHANNA,K. C., IndianJ. Chem.,3 (1965),63.13. GILLESPIE, R. J., J. chem.Soc. (C), (1950),2542.14. BARR, J., GILLESPIE, R. J. & THOMPSON,R. C., Inorg.Chern.,3 (1964),1149.IIof ~orOSUIPhuriCand disulphuric acids. Thepossi ility of the reaction(16)Sb20+3HSOaCI...,..2SbO++HtO+3S0aCI-...(16)may eruledout asit requireshighervalueof 'f.In the caseof the solutionsof bismuthtrioxidin c~orOSUIPhuricacid alsosimilar typesof argu.-ment canbe put forward.Bo ic anhydride (B2,Os)is readily soluble inSll.lp ric and disulphuricacidsto givethespeciesof tw type B(HSO,), ions. But it dissolvesveryslowl in chlorosulphuricacid. However, thesolu ility can be increasedjust by warming. Thesolutonsarefoundto bequitestableandconduct-ing. I It is possiblethat it might get solvolysedwhe~ dissolvedin chlorosulphuricacid to formB(SlfsCI}a(Eq. 17)B20~+9HSOaCI"""2B(SOaCI)a+3H2S0,+3HCI '" (17)But when a strong baseKSOaCIor benzoicacidis a ed to the solutionthereis alwaysa decreasein c nductancewhich suggeststhat boron tri-chIoosulphatebehavesas an acid of this solventsystm and combineswith SOsCI- ions to formHB( 0sCI), accordingto the Eq. (18)B(S sCI)s+SOaCI-...,..B(SOaCI-), ...(18)So ~heoverall reaction may be representedassho nin Eq. (19)I .B20~+13HSOaCI...,..2B(SOaCI),+2H~SOaCli +3HCI+3H2SO, ...(19)At !igher concentrationB(SOaCI), ion has aten ncy to polymerize.A similar type of poly-mer'ation with B-O-B bond has alreadybeenrepoted by Gillespieand coworkers1a,l'fromtheRa~n spectroscopyof concentratedsolutionsofB20 in sulphuricacid.I orderto confirmfurtherthe natureof B20ain c lorosulphuricacid, someacid-baseconducto-metic titrations have also been carriedout be-twe1nthesolutionsof B20Sin chlorosulphuricacidandfhe strongbaseKSOaCIorbenzoicacid(Fig.2).Fro the shapeof the conductancecurveswhichhav sharpend points, it has beeninferredthatthe, acid HB(SOaCI),thus formedbehavesas astrotg acidin this solvent.T e behaviourof variousorganicacidanhydrideshas alreadybeen reportedin other strong acidswhee they are shownto behaveas weakbases.Ace ic anhydride undergoesself-dissociationasA~ ~Ac++OAc.A thoughit containsthreebasic oxygenatoms,yet 't is monoprotonatedin sulphuricand fluoro-sulp uric acids whereasit forms acyl ions in di-suI uric acid. But the solution of aceticanhy-dri in chlorosulphuricacidarehighlyconductingand quite stable. When its conductanceis com-par~dwith that of KSOsCI, it is found that itbeh~vesasa strongmonoacidbasein chIorosulphu-ric ~cid. Similarly benzoicanhydride,isobutyric26II.: I 1i' liP I

Chlorosulphuric Acid as a Non-aqueous Solvent: Part VI- Conductometric & Spectral Studies of Various Inorganic & Organic Acid Annydrides in Chlorosulphuric Acid

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Chlorosulphuric Acid as a Non-aqueous Solvent: Part VI- Conductometric & Spectral Studies of Various Inorganic & Organic Acid Annydrides in Chlorosulphuric Acid

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