J. Chem. Eng. Data 2001, 46, 851-857
851
Viscosities and Volumes of Dilute Solutions of Formamide in Water + Acetonitrile and for Formamide and N,N-Dimethylformamide in Methanol + Acetonitrile Mixed Solvents: Viscosity B-Coefficients, Activation Free Energies for Viscous Flow, and Partial Molar Volumes Kenneth Hickey and W. Earle Waghorne* Department of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland
The viscosity B-coefficients and partial molar volumes have been measured for N,N-dimethylformamide and formamide in methanol + acetonitrile solvent systems and for N,N-dimethylformamide in water + acetonitrile mixed solvents. These data are used to calculate the solute contribution to the activation free energy for viscous flow, ∆µ*13, for these systems. It is found that the ∆µ*13 values are simply related to the corresponding enthalpies of transfer.
Introduction The measurement of the viscosities of solutions formed the basis of some of the earliest studies of solute-solvent interactions. Jones and Dole1 showed that the viscosities of dilute solutions of strong electrolytes could be represented as
η13/η1 ) ηr ) 1 + Axc + Bc
(1)
where η13 and η1 are the viscosities of the solution and solvent, respectively, and c is the solute concentration. The A-coefficient takes account of ion-ion interactions and can be calculated2 and the B-coefficient reflects the effects of solute-solvent interactions on the solution viscosity. The viscosities of dilute solutions of nonassociated nonelectrolytes can be similarly represented as
η13/η1 ) ηr ) 1 + Bc
(2)
where the symbols have the obvious meanings. B-coefficients have been measured for a wide range of electrolytes in aqueous solutions and for a smaller number of electrolytes in organic and mixed aqueous-organic solvents.3 Nonelectrolytes have been less extensively studied although data are available for several solutes in water4,5 and for 2-methylpropan-2-ol (tert-butyl alcohol) in aqueous methanol solvent systems.6 In the present paper we present viscosity B-coefficients and partial molar volumes for formamide and N,N-dimethylformamide in methanol + acetonitrile mixed solvents at 298.2 and 308.2 K and for N,N-dimethylformamide in water + acetonitrile solvents at 288.2 and 298.2 K. We also report viscosity and volume data for the solvent mixtures at these temperatures. The values of the solute contribution to the free energy of activation for viscous flow, ∆µ*13, were calculated from the B-coefficients and molar volumes using the Feakins6,7 * To whom correspondence should be addressed.
relationship. It is found that the ∆µ*13 values are simply related to the enthalpies of transfer of the solutes in the same solvent systems. Experimental Section Viscosity. The viscosity measurements were made using a Schott-Gerate AVS/S measuring system and an Ubbelohde type suspended level capillary viscometer as described previously.8 The system was adapted to allow serial measurements to be made under computer control. The modification to the capillary viscometer involved replacing the lower reservoir by one with a volume of about 50 cm3. The viscometer was suspended in a specially constructed double water bath, which allowed the contents of the reservoir to be stirred using a magnetic stirrer. The temperature of the inner bath was stable to (0.001 K and was within (0.01 K of the reported temperature. The composition of the solution in the viscometer was altered by the addition of a stock solution, via a piston driven buret (Metrohm Dosimat 655, using a 1 cm3 buret), through the sidearm of the viscometer. The AVS was controlled and interrogated through its RS-232 port, and the stirrer and buret were activated using reed relays under computer control. Thus, in an experiment a known volume of solvent was placed in the viscometer and its flow time measured. Subsequently, known volumes of a stock solution were injected into the viscometer and mixed by stirring, and the flow times of the resulting solutions were measured. The weight of a 1 cm3 injection of the stock solution was measured before and after the experiment, and the density of the final solution was measured as a check on the final solution concentration. Typically B-coefficients were determined from measurements at nine solute concentrations (to 0.12 mol dm-3). The precisions of the B-coefficients, expressed as standard errors, are listed in the tables. Density. Densities were measured using a vibrating tube densitometer (Anton Paar DMA-60) with two cells (DMA-
10.1021/je0003647 CCC: $20.00 © 2001 American Chemical Society Published on Web 05/11/2001
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Journal of Chemical and Engineering Data, Vol. 46, No. 4, 2001
Table 1. Densities and Viscosities of Methanol (1) + Acetonitrile (2) Mixturesa x2 0.0000
0.0394 0.0798 0.1633 0.2064 0.2507 0.3423
0.0000
0.0799 0.1633 0.2506 0.3423 0.4384
density/ g cm-3 0.786635 0.78654g 0.78680h 0.78666i 0.786944 0.787085 0.786894 0.786592 0.786231 0.785318
0.777114 0.7772f 0.77718g 0.77771i 0.777322 0.776934 0.77617.. 0.775046 0.773763
viscosity/ mPa s
x2
298.15 K 0.5391 0.4383 0.5425e 0.545g 0.554i 0.5080 0.5393 0.4861 0.6455 0.4436 0.7574 0.4247 0.8754 0.4091 0.9368 0.3827 1.0000
308.15 K 0.4506 0.5393 0.474g 0.482i 0.4257 0.3905 0.3624 0.3400 0.3226
0.6451 0.7573 0.8755 0.9368 1
density/ g cm-3
viscosity/ mPa s
0.784162
0.3604
0.782845 0.781388 0.779846 0.778232 0.777420 0.776635 0.776549b 0.77614c 0.77645d 0.77686g 0.77690h 0.77622i
0.3460 0.3349 0.3285 0.3290 0.3334 0.3410 0.3405d 0.3409e 0.345g 0.341i
0.772266
0.3097
0.770685 0.769038 0.767340 0.766531 0.765765 0.7656f 0.76564g 0.76518i
0.3010 0.2970 0.2986 0.3024 0.3087 0.313g 0.306i
a Precisions are (0.000 005 in the densities and (0.2% in the viscosities; x2 represents the acetonitrile mole fraction. b Ref 11. c Ref 12. d Ref 16. e Ref 18. f Ref 13. g Ref 14. h Ref 15. i Ref 17.
Table 2. Densities and Viscosities of Water (1) + Acetonitrile (2) Mixturesa x2
density/ g cm-3
viscosity/ mPa s
0.0000 0.0225 0.0465 0.0718 0.0989 0.1278 0.1583 0.2264
0.997 043 0.989 45 0.981 07 0.971 53 0.961 30 0.950 08 0.938 63 0.914 81
298.15 K 0.8904 0.3050 0.9457 0.3969 0.9759 0.5060 0.9808 0.6371 0.9687 0.7980 0.9453 0.8929 0.9165 1.0000 0.8404
0.0000 0.0465 0.09887 0.29662
0.999 101 0.985 26 0.967 29 0.899 35
288.15 K 1.142 0.39695 1.272 0.50591 1.258 0.79795 1.0000
x2
density/ g cm-3
viscosity/ mPa s
0.890 84 0.867 15 0.843 84 0.820 82 0.797 95 0.786 90 0.776 635
0.7520 0.6535 0.5503 0.4572 0.3811 0.3537 0.3410
0.876 33 0.854 37 0.808 57 0.787 65
0.796 0.655 0.430 0.376
Figure 1. Excess molar volumes at 298.15 K for (a) water (1) + acetonitrile (2) mixtures [ref 11 (4), ref 12 (0), and the present results (b)] and (b) methanol (1) + acetonitrile (2) mixtures [ref 14 (4), ref 15 (O), ref 17 (0), ref 18 (3), and the present results (b)].
Chemicals. N,N-Dimethylformamide,9 formamide,9 and acetonitrile10 were purified as described previously. Water was distilled, passed through an ion exchange column, and then redistilled; the conductivity of the water was
