INDIAN 1. CHEM., VOL. 21A, APRIL 1982

literature'. The results in Table 1 show that theincrease of 80-D is much less than the decrease ofparallel vO-D. This is because the out-of-planebending frequencies (v-vibration) also increase atthe expense of the parallel vO-D. The effect ofhydrogen bonding on the 0- as well as y-vibrationsis to increase the restoring force tending to keepthe O-D bond in a fixed orientation.

References

1. HADZI. D. & BRATOZ,S., in The hydrogen bond. Vol. II,edited by P. Schuster, G. Zundel and C. Sandorfy,(North Holland) 1976, Chapter 12.

2. SREBRENJK,S., WEINSTEIN,H. & PA.UNCZ,R., Chern. Phys.Leu .• 20 (1973), 419.

3. SHEPPARDN., in Hydrogen bonding edited by D. Hadzi,(Pergamon Press, London), 1959, 85.

4. EVANS, 1. C., Spectrochim. Acta. 16 (1960), 1392.5. TAKAHASHI,H., MAMOLA,K. & PLYLER, E. K., J. mol.

Spectrosc. 21 (1965), 217.

Ion-Solvent Interaction in Sulpholane from ApparentMolal Volume Data

PANKAJ& RAM GOPAL·Chemistry Department, Lucknow University, Lucknow 226 007

Received 29 July 1981; revised and accepted 23 October 1981

Apparent molal volume (~v) values of some common andR.NI salts have been measured in sulpholane at different concen-trations and temperatures. The slopes of ~v versus ,Ie curves,in 40·60°C temperature range are positive in all the cases.The limiting apparent molal volume (~o) values of BujNl, Pen4NIand common salts increase with increase in temperature, passthrough a maxima and then decrease at higher temperatures;for Hex.NI and Hep.NI, no maxima are observed, althoughd.po/dt has a slight tendency to decrease with the rise in tempe-rature.

APPARENT molal volumes, ,pv of some commonand R4NI salts in solvents of medium dielectric

constants- like DMSO (f25° = 48.9), DMF (£260 =36.7) and propylene carbonate (£26° = 64.92) wereearlier found 2,3 to increase almost linearly with~ C, i..e. the slopes (S:) of the ,pv versus ~C curveswere positive. Positive slopes indicate strong electro-static ion-solvent and ion-ion interactions, theformer being predominant at lower concentrations.In the present study, which is an extension of ourearlier work, we have chosen sulpholane (f~oo = 43.3,p. = 4.81D) as solvent, which is a liquid at ordinarytemperatures (m.p. 2r) and without any hydrogenbonding". Due to poor solubilities of lower R4NIsalts, only the higher analogues of R4NI salts havebeen used in the present study,

Sulpholane (Fluka, puriss) was kept overnight onKOH pellets and then distilled twice under reducedpressure, middle fraction being collected each time.The fraction thus obtained was fractionally recrystal-lized and the final product, having m.p, 27" andd400 = 1.2515 glml (lit.d~60= 1.2613) was obtained,

404

312

300

286

27&

---'- J • • ! • + •

,Mal ~

iJ:g~~:::,--,~-~~.:~-::::-:;:~~-~~i:r:---:-:-:..--~ ::0·0 0-' 0';> 0·3 0'4 O·~ 0-6 0·7 0·8 009

.jC

Fig. 1 - Apparent molal volume (~,) versus '\fC curves forBu,NI and NaI in sulpholane,

33

31

Common and R,NI salts were purified as describedelsewheres-s, The experimental procedure was thesame as given earlier",

The ,pv versus 4c plots in all the cases (Fig. 1 as arepresentative figure) appear to fit well the empiricalMasson's equation namely,

,p., = ,po + s: ·reThe limiting apparent molal volume "'0 values,

were obtained by intrapolation of the ,pv versus ,,[Cplots to zero concentration. The ,po values thus ob-tained are only approximate in nature and hence notrecorded in the note. However, their qualitativedependence on temperature, on which our discussionwould be based, is expected to be unaffected and soonly the ,po versus t" curves given in Figs 2 and 3would be adequate.

It is evident from Fig. 1 that the slope (S:) valuesare positive similar to those reported in solvents ofmedium dielectric constants!". However, the S:values differ somewhat from those obtained in sol-vents of high dielectric constantst <! where the slopesare negative in some curves at significant concentra-tions, i.e. beyond the Debye-Huckel limiting concent-ration range. The ion-solvent interaction (electrostric-tion) decreases and ion-ion interaction increases withthe rise in concentration and both factors favour apositive slope.

The ¢o versus to plots for NaI, K£, RbI and CsI(Fig. 2) pass through a maximum around 50" as inthe case of aqueous and non-aqueous solvents ofhigh and medium dielectric constants. For Bu4NI andPen4NI, the maxima occur at slightly higher tempera-tures whereas for Hex4NI and Hep4NI, no maximaare seen (Fig. 3)within the temperature range studiedhere although the curves appear to approach, .very

Cst

•

r>;38

38

1.: "'~34

::1"~31

31~ N.(29

Fig. 2 - Limiting apparent molal volume (;0) versus tempo-ratUre curves for NaI, KI, RbI and CsI in suiphoJanc.

'>10Hqpl,-N(

S02

,.94

486

Hqx4 N I4'-18

•440

¢0'.12

•424376

368

160

Fig. 3 - Lim iting apparent molal volume (10) versus tempe--rature curves for Bu~NI, Pen~NI, Hex~NI and Hop,NI

in sulpholano.

NOTBS

slowly, the temperature axis at higher temperature,i.e. d;o/dt remains almost constant with a slight ten-dency to decrease. These results indicate that for thesalts containing smaller common ions, solute-solventinteraction is mainly electrostatic leading to solva-tion of ions (A-region of Frank) and resulting insomewhat break-down. to some extent, of the solventstructure (B-region of Frank) outside the solvation,sphere beyond which solvent structure is normal.This renders the solution more expandable than thepure solvent, as is the case in other solven ts, bothprotic and aprotic. At higher temperatures, B-regiondisappears and the solution becomes less expandablethan the pure solvent. These two factors give rise to ,maxima in t/lo versus t" curves. The occurrence ofmaxima at higher temperatures for BU4NI, Pen4NIand their apparent disappearance in Hex4NI and,Hep,NI needs explanation. In the absence of a strongelectrostatic interaction between R4N+ ions and sol-vent molecules, the B-region of Frank with break-down structure of the solvent, around the large cations(Hex4N+ and HeP4N+), would be more or less com-pletely missing. Of course, some solvent moleculeswould be favourably oriented towards the R4N+ ionson account of weak electrostatic forces and not avail-able for expansion; this would render the solutionto be less expandable than the pure solvent and thusdecrease the;o as to rises. On the other hand, coiledup R-chains of the cations would open up at highertemperatures and cause the solution to be more ex-pandable than the pure solvent. These two oppositeeffects would lead to a broad maximum in the ~oversusto curves of the larger R4N+ ions at higher tempera-tures. The longer the chain, the greater the expansionand the higher the temperature at which the maximumwould occur. This probably explains an almostcomplete disappearance of the maximum in Hex,NIand Hep,NI whereas its presence in the Bu,NIand Pen,NI at higher temperatures as compared tothat in the common salts.

The financial support from the UGC, New Delhifor the work is gratefully acknowledged.

References

1. Physical chemistry 0/ organic solvent systems. edited byA. K. Covington and T. Dickinson (plenum Press,London), 1973, 2.

2. GOPAL, R., AGARWAL. D. K. & KUMAR, R., Bull. chem.Soc. Japan, 46 (1973), 1973.

3. GOPAL, R., AGARWAL, D. K. & KUMAR, R., Z. phys.Chem. (N. F.), 84 (1973), 141.

4. PARKAR, A. I., Chern. Rev., 69 (1969), 1.S. CoNWAY, B. E., VERRALL, R. E. & DESNOYERS, I. E.,

Trans. Faraday Soc .• 62 (1966), 62.6. GoPAL, R. & IHA, I. S., Indian J. Chem., 12 (1974),618.7. GOPAL. R. & SIDDIQI, M. A., Z. phys. Chem. (N. F.),67

(1969), 122.8. WEN, N. Y. & NARA, K., J. phys. Chem .• 71 (1961),

3707.9. GOPAL, R. & SIDDIQI, M. A., J. phys. Chem .• 72 (196&),

1814. .10. MILLERO, F. I., J. phys. Chem .• 72 (1968), 3209.11. GOPAL, R., SIDDIQI, M. A. & SINGH, K., Z. phys. Chem,

(NF), 7S (1971), 7.

405