Dellesalle, G.

Fischer, J. C.

Heubel, J.

Narula, S. P.

English

NOPR

Indian Journal of ChemIstryVol. 15A, August 1977. pp. 687-690Physico-chemical Studies in Non-aqueous Solvents: Part XV-Conductance Studies of Some Uni-univalent Electrolytes inNitromethane at 25°J. HEUBEL, J. C. FISCHER, G. DELLESALLE & S. P. NARULA*Laboratoire Chimie Minerale-l , Universite des Sciences et Technique de Lille 159650Ville neuve D'Ascq (France)andR. C. PAUL, S. P. JAUHAR & J. S. BANAITDepartment of Chemistry. Panjab University. Chandigarh 160014Received 3 December 1976; accepted 11 March 1977Conductances of tetraalkylammonium, tetraphenylphosphonium and tetraphenylarsoniumchlorides and chlorosulphates, pyridinium chlorosulphate and a few other similar salts ofimidobis(sulphuryl chloride) have been measured in nitromethane at 25°. The conductancedata have been analysed by the Fuoss-Onsager-Bjdnner equation for associated and dissociatedelectrolytes and limiting equivalent conductance (Ao)' ion-size parameter OJ) and associationconstant (KA) (where appropriate) have been calculated. All the salts (except pyridiniumchlorosulphate) are fully dissociated in this solvent. Ionic mobilities, solvated and correctedionic radii of the electrolytes have also been computed. The following order of increasingmobility of ions in nitromethane has been observed :Me.N+>Et,N+>HPy+>Bu,N+> Ph,As+>Ph,P+ ;Cl-> 803Cl-> [N(802Cl)2]->H80 •.NITROMETHANE is an important solventwhich has suitable physical properties(dielectric constant], 35·94; dipole moments,3·44 D; density", 1·1312 g ml": viscosity-, 0·627X 10-2P and specific conductance-, 0·5-2·0 X 10-8ohm? cm+: all at 25°) for studies of electrolytesolutions. Though a number of physico-chemicalstudies=" have been carried out in nitrornethaneyet a study of the behaviour of some salts of strongacids is lacking in this solvent. Presently, conduc-tances of tetraalkylammonium, tetraphenylphos-phonium and tetraphenylarsoniurn chlorides andchlorosulphates, pyridinium chlorosulphate and ofsimilar salts of imidobisisulphuryl chloride) havebeen measured and the data have been used for theestimation of limiting equivalent conductances,limiting ionic mobilities and effective ionic radii.Materials and MethodsNitromethane (Fluka] was purified by the methodalready reported' and stored over molecular sieves(4 A) in the dark. For each experimental run, thesolvent was passed through a column packed withdry alumina. distilled under vacuum; sp. cond.,2-5x10-a ohrrr+ crrr! at 25°; 't)25, 0·627 X 10-2 cpand d~5, 1-131 g ml".Tetraphenylphosphonium chloride and tetraethyl-ammonium hydrogen sulphate (AR, E. Merck) weredried in vacuum for 3-4 hr before use. Tetraphenyl-arsonium chloride monohydrate (AR, E. Merck)was heated in vacuum to 70° over phosphorous (V)oxide to render it anhydrous.*Correspondence may be made with the author at theDepartment of Chemistry. Panjab University. Chandigarh160014.Tetramethylammonium, tetrabutylammonium andtetraphenylarsonium salts of imidobis(sulphurylchloride) were prepared by the reaction of corres-ponding chlorides with imidobis(sulphuryl chloride)in equimolar quantities under dry nitrogen atmo-sphere and keeping the reaction temperature below80°. HCl was produced during the reaction. After thereaction, the products were washed with ether andrecrystallized from ether-dichloromethane. Thesewere finally dried in a current of dry nitrogen andwere characterized by their analysis and IR spectra-".Tetraethylammonium and pyridinium chlorosul-phates were prepared as follows: tetraethylammo-nium chloride and pyridine were taken in nitro-methane separately and equimolar quantities ofchlorosulphuric acid were added in each case. Thereaction mixture was kept for few hours and thenthe solvent removed under vacuum. The com-pounds obtained were washed with dry ether,recrystallized from dichloromethane ether mixtureand were then characterized by their analysis andIR spectra--.Conductance measurements - Conductances weremeasured at 25° ± 0·01 ° with the help of a precisionmeasuring bridge type WBR No. 108 with loga-rithmic indicator amplifier type TAV 1 KC No. 034(Wissenschaftlich Technishe Werkstatten Weilheim/Oby, Germany). The procedure for measuringconductances was essentially the same as reportedearlier-". The cell constant of a dip type cell wasdetermined by the standard methodt'' (0·1048 ±0·0002 cm+) and was periodically checked. Someof the measurements were rechecked with the helpof Flask type (Shedlovsky) conductance cell14 withcell constant = 1'3823 crrr-.687INDIAN J. CHEM., VOL. 15A, AUGUST 1977Results and DiscussionConductances of various electrolytes have beenmeasured in the concentration range 10xl0-'Mto 95 X 10-'M and the data are presented in Table 1.The conductance data have been analysed bythe Fuoss-Onsager-Skinner equation+ (1)A = Ao-S(CY)1/2+E'CY In(6E~CY}+LCY-KA CYf~A... (I)for associated electrolytes and by Eq. (2)A = Ao -SCI/2 +E'C In (6E; C}+(L-AAo)C ... (2)for dissociated electrolytes, in which the symbolshave the usual meanings; S = 0(. Ao+~ and E' =E~Ao-E~. The constants 0(., ~, E~ and E~, obtainedfrom the physical properties of the solvent, havethe values 0'7174, 125'8,2'25 and 57'80 respectively.All the calculations have been carried out on a IBM1620 computer using a programme in Fortran 1-The least-square method has been used for the eva-luation of the parameters Ao' Land KA (for associ-ated electrolyte) following the logarithm given byFuoss et a».The analysis of data by Eq. (I) gives negativevalues of association constants for all the electrolytes(except pyridinium chlorosulphate) suggesting therebycomplete dissociation of these electrolytes in thissolvent. The data have thus been analysed usingEq. (2). Schiff et al.4,5 have measured conductancesof some quaternary ammonium halides in nitro-methane and have shown that the tetramethyl saltsare slightly associated and the association decreaseswith the increase in the size of the cation. Coetzeeand Cunningham? have shown from conductancemeasurements that electrolytes having big ionssuch as tetraisoamylammonium, tetraisoamylboride,tetrabutylammonium, tetraphenylboride, etc., arecompletely dissociated in this solvent. Since mostof the electrolytes used here are constituted of re-latively big ions, their complete dissociation innitromethane is In agreement with the aboveobservations? However, positive association con-stant (22'9 ± 3'4) for pyridinium chlorosulphateshows it to be slightly associated in this solvent.All the relevant data along with standard deviationsare recorded in Table 2.It may further be pointed out that Eq. (I) givesthe best fit in all the cases, though it also givesnegative association constants (except forPyHS03CI). This is without any physical meaningand thus the parameters reported in Table 2 areobtained from Eq. (2). Monica et al.16 have alsoreported a similar observation in hexamethylphos-cxro-M13-63941-07747-54560'54915'77221·66422'83424'00029'87743-90318·67723·03026·24530·43133-60418'67820'32635·22336·95338'55541·74723·68255·31857·97961·95241·36947·15755·57761·09131·38238·15645·18563-60915-41329'89032-41937-270TABLE 1- CONDUCTANCEDATA FORNITROMETHANESOLUTIONSAT 25°±0·01°A Cx10'MA83-42380'98480'59279'743Ph,As[N (SO.CI) 2J73-524 46·29872-801 51·89472'646 58'58472-521 61·97471'963 65·25770'674 68·752Me,N[N(SO.CI).J96'678 34'58596·029 58·78295·503 63·04095·049 66·03394-61663'92492·22895'40379·44978·12677·81370·47670·11169·65869·37969·27568·94294·53492·29391·79291'603Bu,N[N (SO.ClhJ75·545 45·28975·332 61·75573'370 64·94973-193 71·40773·029 84'69372·722 94'669Ph,AsCI72'25070·95670·76570·20969·27168'69683·71381·11381-01480·91577·87781·99395'20079·98779·68379·029Et,NSOsCI90'617 66'80589·805 72'49789·030 78'60388·68388·00087'49086'514HPyS03CI84'679 74'68383·028 85'96281'306 97·44177-08475·59373-90572'513Et,NHSO.88·659 42·10585·298 51'91984·613 71·35283·72082'89481'36578·827ElectrolyteTABLE 2 - CONDUCTANCEPARAMETERSFOR NITROMETHANESOLUTIONSAT 25°+0,01 °Ph,PCIPh,AsCIPh,As[N (SO.CI).]Me,N[N(SO.CI)JBu,N[N(SO.CI)JEt,NSOsClEt.NHSO.HPySOaCI90·10±0·3592'57±0'1680·39±0·0910H3±0·0984·10±O·08102'87 ±0'249HO±0'0799·69±0·67L969·1±50·2968'3±33-9886·1 ±22'9874'7±21-5524'7±8'0637'5±4H218'2±16'9196'7±44'6688° crAa5-48±0·12 0·315-44±0'07 0·195·49±0·05 0'125·07±0·04 0·114·55±0·02 0'274-66±0'08 0'114·02±0·05 0·184'77±0'03 0·43HEUBEL et al.: PHYSICO-CHEMICAL STUDIES OF ELECTROLYTES IN NITROMETHANEphotriamide. Moreover, the standard deviations ofthe individual parameters in nitromethane areslightly larger than those in other solventsl6-l8. Thismay be attributed to slight instability of some ofthese salts in nitromethane. This is in accord withan earlier report '".Ion-size parameter - Ion-size parameter (a) offully dissociated electrolytes has been obtained usingEqs. (3) and (4):L-AAo = E~Ao H(b)-E~G(b)-6E'K(b)a = 567·4 (at 25°)bDwhere H(b), G(b) and K(b) have their usualmeanings and D is the dielectric constant of thesolvent. For pyridinium chlorosulphate, a hasbeen calculated from Eq. (5):L = 2E;Ao (1·603-ln 11) •.. (5)A perusal of results (Table 2) reveals that theion-size parameter for all the salts (except Et4-NHS04) is equal to 5·0 ± O'5 A in nitrornethane.These values compare favourably with those re-ported by Coetzee and Cunningham? for electrolytesconstituted of large ions in the same solvent.However, the values obtained for the electrolytesof relatively smaller ions in the solvent are lower"than the present values. This may be due toincomplete dissociation of these ions in nitro-methane--".Single ion conductances - Kay et al ", on thebasis of experimental transference number measure-ments, have computed the mobility of chloride ionto be 62·52 ohrrr+ cm2 mole>' in nitromethane. Thisvalue as well as that of Et4N+ ion (which in turnhas been obtained from chloride ion mobility fromEt4NCI) have been used to calculate ionic mobilitiesof the various ions studied here, employing Kohl-rausch's law of independent ion migration. Thoughthe mobilities of Me4N+ and BU4N+ ions obtainedhere differ by ± 0·33 ohrrr" cm2 mole? from theliterature values", yet in view of the slight instabilityof chlorosulphate-" and imidobis(sulphuryl chloride)anions in nitromethane-v, ionic mobility valuesreported here may be taken as the best approxima-tions. All the values are recorded in Table 3.The data in Table 3 give the following order ofdecreasing mobilities of ions: Me4N+ > Et4N+ >... (3)... (4)TABLE 3 - IONIC MOBILITIES (A'::'), STOKES (1'5) ANDCORRECTED (reorr) RADII OF VARIOUS UNIVALENT IONS INNITROMETHANE AT 250 ± 0.010Ion t"S (A)2·392·753'343·874·744·352'942·092'372·602'64reorr (A)3'474·004·524·945·705·354·163'473-683·873·92Me,N+Et.N+Pr.N+Bu.N+Ph.P+Ph.As+HPy+ci-S03Cl-[N(S02Cl).l-HSO.54·7946'62*39'14*33'7627'5830·0544'4362'5255'2650·3449'49*Values from ref. 6.6·0~--------------------------------~5·04·03·02·01.0~-;fn---------:!-::: ~ -L-.J2·0 3{) 40 5'0Fig. 1 - Nightingale calibration curve for determiningeffective ionic radii in nitromethane [Hollow circles (0)are the points for tetraalkylarnmonium ions and solidcircles (e) refer to effective ionic radii obtained from thecurve for various ions)PyH+ > n-Pr4N+ > n-Bu4N+ > Ph4As-+'> Ph4P+;ci- > S03Cl- > [N(S02Cl)2l > HS04·The mobilities of the ions decrease with increasein their size. However, Ph4P+ and HS04 areexceptions to this order. Although HS04 may beslightly solvated (probably through hydrogen bond-ing), the decrease in mobility of Ph4P+ is surprising.Stokes radii (r5) of various ions have been calcu-lated using Robinson-Stokes equation'",F2iX±!r. = 6reYfA,±N ... (6)In the Robinson and Stokes method the tetra-alkylammonium ions are assumed to be unsolvatedbecause of their low charge density. But it hasbeen found that the Stokes radii obtained fromEq. (6) are smaller in co~trast to the estimatedcrystallographic radii (rc) of these ions-". Thusthe Stokes radii obtained above have been correctedfollowing the suggestion of Nightingale-". Thecalibration curve (Fig. 1) has been constructed byplotting rc vs rs for tetraalkylarnrnonium ions insolution and the corrected radii (rcorr) of the ionsare obtained from the above plot corresponoing totheir respective r5 values. It is clear from Fig. 1that except for the tetramethylammonium ions,all other ions lie on a linear plot, indicating that thetetramethylammonium ion may be slightly solvatedin nitrornethane. A similar behaviour has beenobserved in dimethylsulphoxide'", hexarnethylphos-photriamide'"; N,N-dimethvlacetamide17 and tetra-methylurea'". "Table 3 records the solvated and corrected radiiof the various ions. A comparison of solvatedradii of monovalent anions in this and othersolvents= shows that the solvated radius decreaseswith the increase in size of anion in methanol andacetonitrile and is almost constant in formam ide,dimethylformamide and dimethylacetamide. How-ever, in nitromethane it increases with increase insize of anion and this behaviour is similar to oneobserved in sulpholane'", The conductance behaviour689INDIAN J. CHEM., VOL. 15A, AUGUST 1977of nitrornethane solutions of these uncommon elec-trolytes has also been found to show some resem-blance with sulpholane solutions'". A perusal of Table3 also reveals that the sum of the Stokes cationicand anionic radii for all the electrolytes is greaterthan the Fuoss-Onsager-Skinner ion size parameter(&) as has been observed in tetramethylurea'".AcknowledgementOne of the authors (S.P.N.) is grateful to MinistiereEducation Nationale, Government of France, fora visiting Associate Professorship (1974-75) andPanjab University for sabbatical leave.References1. JANZ, G. J. & TOMKINS, R. P. T., Non-aqueous electro-lytes handbook, Vol. I (Academic Press), 1972, 56.2. WISWALL, R. H. & SMYTH, C. P., J. chem. Phys., 9(1941), 314.3. WRIGHT, C. P., MURRAy-RUST, D. M. & HARTLEY, H.,J. chem. Soc., (1931), 199.4. UNI, A. K. R., ELIAS, L. & SCHIFF, H. I., J. pbys.Chem., 67 (1963), 1216.5. BLUM, S. & SCHIFF, H. I., J. pbys. Chem., 67 (1963),1220.6. KAY, R. L., BLUM, S. & SCHIFF, H. I., J. phys. Chem.,67 (1963), 1223.7. COETZEE, J. F. & CUNNINGHAM,G. P., J. Am. chem,Soc., 87 (1965), 2529.8. STREULI, C. A., Analyt. Chem., 32 (1960), 985.6909. KAUSHAL,R., Ph.D. thesis, Panjab University, Chandi-garh, 1970.10. NARULA,S. P., Inorg. nucl. Chem. Left. (communicated).'11. AUGER, Y., LEGRAND, P., PUSKARIC, E., WALLART,F. & NOEL,S., Spectrochim. Acta, 27A (1971), 1351.12. PAUL, R. C., GILL, D. S. & NARULA, S. P., Indian J.Chem., 8 (1970), 936.13. Fuoss, R. M. & ACCASCINA,F., Electrolytic conductances(Interscience Publishers, New York), 1959.14. SHEDLOVSKY,T. & SHEDLOVSKY,L., Physical methodsof chemistry, Part IIA, edited by A. Weissberger &B. W. Rossiter (Wiley, Interscience, New York), 1971.180.15. Fuoss, R. M., ONSAGER,L. & SKINNER, J. F., J. phys.Chem., 69 (1965), 2581.16. BRUNO, P., MONICA, M. D. & RIGHETTI, E., J. phys.Chem., 77 (1973), 1258.17. PAUL, R. C., BANAIT, J. S. & NARULA, S. P., Z. phys.Chem., 94 (1975), 199.18. PAUL, R. C., BANAIT, J. S. & NARULA, S. P., Aust. J.Chem., 28 (1975), 321.19. FISCHER, J. C., AUGER, Y. & WARTEL, M., c». hebd,Seanc. A cad. Sci. (Paris), 276 (1973), 1579.20. ROBINSON, R. A. & STOKES, R. H., Electrolyte solutions(Butterworths, London), 1959.21. NIGHTINGALEOr), E. R., J. phys. Chem., 63 (1959), 1381.22. GoPAL, R. & ]HA, ]. S., J. phys. Chem., 78 (1974), 2405.23. PAUL, R. C., ]OHAR, S. P., BANAIT, J. S. & NARULA,S. P., J. phys. Chem., 80 (1976), 351.24. MONICA, M. D. & LAMANNA, U., J. phys. Chem., 72(1968), 4329.25. J AUHAR,S. P. (unpublished work).26. BARKER, B. ]. & CARUSO,C. A., J. Am. chem. Soc., 93(1971), 1386.

Physico-chemical Studies in Non-aqueous Solvents: Part XV-Conductance Studies of Some Uni-univalent Electrolytes in Nitromethane at 25°

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Physico-chemical Studies in Non-aqueous Solvents: Part XV-Conductance Studies of Some Uni-univalent Electrolytes in Nitromethane at 25°

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