The isothermal compressibility of dimethylsulfoxide–water ...

The isothermal compressibility of dimethylsulfoxide-water mixtures at 35 O C

K. H. JUNGAND J. B. HYNE

Department of Cl~emistry,University of Calgary, Calgary, Alberta

Received February 4, 1970

Can. J. Chem. Downloaded from www.nrcresearchpress.com by 50.116.19.84 on 12/31/15 The isothermal compressibility of a series of dimethylsulfoxide-water mixtures passes through a
For personal use only. minimum near 0.4 mole fraction dimethylsulfoxide. This behavior is compared with that of other aqueous
binaries and provides further evidence of specific hydrogen bonded complexes in the dimethylsulfoxide-
water system.

Canadian Journal o f Chemistry, 48, 2423 (1970)

Introduction pressure for the various dimethylsulfoxide-water

In connection with our continuing study of the compositions have been filed.'- he pressure de-
effect of pressure on the rates of solvolytic
reactions in aaueous binarv solvent svstems we pendence of Vr,, was found to be adequately
have determined the isothermal compressibility, represented by the quadratic expression
KT, of dimethylsulfoxide-water mixtures from
pure water to 0.7 mole fraction cosolvent. These + +[11 In Vr,, = A Bp Cp2
results are presented here together with corre-
sponding compressibility or compression data within the limits of experimental error using a
for other aqueous binary systems. The extremum 'least mean square fit program and an IBM 360
behavior of KT as a function of solvent composi- computer. The values of the quadratic coefficients
tion is compared with the similar observed are given in Table 1. The need for a cubic ex-
behavior of the excess heat of mixing of the pression was checked and the value for the D
aqueous binaries to illustrate the parallelism in coefficient in a p3 term was found t o be insigni-
the dependence of these thermodynamic param- ficant, viz. 1 0 - l 6 atmP3.
eters on solvent composition and structure.
Since the isothermal compressibility is given by

Experimental

The compressibility determinations were made with a

Ruska motor driven, semi-automatic volumetric pump -By integration, rearrangement, and comparison

(Ruska Instrument Corp., Houston, Texas) capable of of coefficients of eqs. [ I . ] and [2] it can be show11

being read t o f 0.001 ml. Mercury was used both t o that, at 1 atm
KT - B
calibrate the apparatus and as the pressurizing fluid. The

DMSO-water sample was contained in a 270 ml stainless

steel compressibility cell mounted in a thermostatted

jacket maintained at 35.00 f 0.02 "C. The pressure TABLE 1
Coefficients A, B, and C of the quadratic equation
range employed for the compressibility determinations

was 34-680 atm and volumes were measured at approxi-

mately lOOatm intervals. The measured volume was

corrected for both mercury and cell expansion as pressure Mole c x lo9

was varied. fraction A x lo2 B x lo5
DMSO (atm-')
Triply distilled mercury was employed throughout the

apparatus and was redistilled after each DMSO-water

composition had been examined. Water was distilled in a

Pyrex apparatus after passage through an ion exchange

column. Conductivity was less than 1.7 x mhos

at 25 "C. Dimethylsulfoxide (Matheson, Coleman and

Bell) was dried over calcium hydride and vacuum distilled

at mm Hg. Batches were stored over molecular sieve

in air-tight bottles until required for use.

Results 'Photocopies of material may be obtained free of

The relative volumes, V,,, = V,/Vo, where Vo charge, upon request, from the Depository of Unpub-
is the volume of liquid a t 680 atm, as a function of lished Data, National Science Library, National Research
Council of Canada, Ottawa, Canada.

2424 CANADIAN JOURNAL OF CHEMISTRY. VOL. 48, 1970

TABLE 2 atm-' at 30 "C. Values have been reported over

Isothermal compressibility (KT) of the years varying from 30.9 x lop6 to 48.7 x

dimethylsulfoxide-water mixtures at atm-l, although more recent determina-

35 "C tions tend to have a narrower spread of values

--- -

Mole fraction between 39.2 x and 44.9 x l o p 6 atm-l.
DMSO
KT x lo6 (atm-l)

Can. J. Chem. Downloaded from www.nrcresearchpress.com by 50.116.19.84 on 12/31/15 Discussion
For personal use only.
It is immediately obvious from the data plotted
in Fig. 1 that the behavior of the compressibility
of dimethylsulfoxide-water mixtures as a function
of composition is significantly different from that
of the other aqueous organic binary mixtures
shown. Although it is true that the compressibility
data for most of the alcohols are adiabatic and
not isothermal, the difference between these two
forms of compressibility measurement is not large
enough to account for the large observed differ-
ence in DMSO-water behavior. The isothermal
(6) and adiabatic (8) compressibility behavior for
ethanol-water mixtures is shown in Fig. 1 to
illustrate this point.

The much deeper minimum at considerably
higher cosolvent mole fraction that characterizes
the KT behavior is also a pronounced feature of
the excess heat of mixing behavior of the dimethyl-
sulfoxide-water mixture as shown in Fig. 2.
Indeed, if the binary compositions at which the

FIG.1. Compressibilities of aqueous binary solvents

vs. solvent compositions: data from EtOH (adiabatic,
ref. 8; isothermal, ref. 5); acetone (ref. 7); i-PrOH
(ref. 7); t-BuOH (ref. 6); and MeOH (ref. 7).

within the limits of the accuracy of the experi-

mental data. The computed values of the iso-

thermal compressibilities of aqueous dimethyl-

sulfoxide mixtures are reported in Table 2.

It should be noted that the data for t-butyl-

alcohol shown in Fig. 1 are compression viz.

AV/V for a specific pressure interval and not

compressibility as defined above. II I I I I
0.0 0.1 0 . 2 0.3 0.4 0.5 0.6
+Our value for the isothermal compressibility
of water, 41.9 0.6 x atm-' at 35 "C, x2

is in reasonable agreement with the most recently FIG.2. Excess heats of mixing of aqueous binary

reported determinations of Whalley, 44.8 x l o p 6 solvents vs. solvent mole compositions: data from MeOH,
EtOH, acetone, i-PrOH, t-BuOH (ref. 1); DMSO (ref. 3).
atm-' at 25 "C, and Stutchbury, 41.8 x

J U N G AND HYNE: ISOTHERMAL COMPRESSIBILITY O F DMSO-H,O MIXTURES 2425

Can. J. Chem. Downloaded from www.nrcresearchpress.com by 50.116.19.84 on 12/31/15 I 0.2 0.3 0.4 water system. The extremum behavior observed
For personal use only. for many of the other aqueous organic binary
0.1 mixtures has been attributed to enhancement of
water structure by initial additions of cosolvent
Minima o f AH: in mole composition (1) followed by destruction of this structure as the
bulk composition increases in the organic com-
FIG.3. Minima of comoressibilities of aoueous ponent. In the case of dimethylsulfoxide, how-
binary mixtures vs. excess heat; ofmixing of the mix'tures: ever, it is difficult to envisage "water structure"
data from (i) compressibilities: MeOH, EtOH, i-PrOH, being maximized at such high cosolvent content.
and acetone (ref. 7); t-BuOH (ref. 6); DMSO (this work);
(ii) excess heats of mixing: MeOH, EtOH, i-PrOH; Parker (2) and Lindberg and Kenttamaa (3)
t-BuOH, and acetone (ref. 1); DMSO (ref. 3). have suggested that a specific hydrogen bonded
complex of composition D M S 0 . 2 H 2 0 may be
minimum in the parameters appears are predominant between 0.3 and 0.4 mole fraction
dimethylsulfoxide. The presence of a significant
plotted against each other, a smooth curve is amount of this compact complex in the mixture
obtained as shown in Fig. 3. There can be little would be expected to result in a reduction in the
compressibility. Other workers (4) have cited
doubt, therefore, that the extremum behavior specific dimethylsulfoxide-water complexes of
manifest in the dependence of these parameters on the type suggested above as being responsible
for the viscosity maximum in this binary system
solvent com~ositionarises from the Same Source, at 0.35 mole fraction dirnethylsulfoxide.

most likely the intermolecular force and solvent The authors wish to acknowledge the helpful sug-
structure variations as composition is changed. gestions of. and discussions with. Dr. D. D. MacDonald
i n d the financial support of the National Research
Our main interest here, however, is in the Council of Canada.

particular behavior of the dimethylsulfoxide- 1. F, FRANKSand D. J. G. IVES. Quart. Rev. XX, 1
(1966).

2. A. J. PARKER.Quart. Rev. XVI, 163 (1962).
3. J. J. LINDBERaGnd J. KENTTAMAAS. uomen Kemis-

tilehti, ~ 3 3 1,04 (1960).
4. 5. M. G. COWIEand P. M. TOPOROWSKIC. an. J.

Chern., 39, 2240 (1961).
5. K. H, JuNG. M , s ~ .thesis, universitoyf Calgary,

Calgary, Alberta. 1969.
6. J. E. STUTCHBURYA.ust. J. Cheni. 9,536 (1956).
7. B. JACOBSONA. rk. Kemi, 2, 177 (1951).
8. J. KORPELaAnd J. KOSHEKALLSIuSo,men Kemistilehti,

B39, 165 (1966).

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