Communications to the Editor
2327
(4) (a) C. M. Huggins, G. C. Pimentel, and J. N. Shoolery, J. Phys. Chem., 60, 1311 (1956); (b) E. A. Allan and L. W. Reeves, ibid., 87, 591 (1963). (5)N. E. Vanderborgh, N. R. Armstrong, and W. D. Spell, J Phys. Chem., 74, 1734 (1970). (6) (a) R. Freeman, K. G. Pachler, and G. N. LaMar, J. Chem. Phys., 55, 4586 (1972); (b) 0. A. Gansow, A. R . Burke, and G. N. LaMar. Chem. Commun., 456 (1972); (c) 8. Barcza and N. Engstrorn, J. Am. Chem. Soc.. 94, 1762 (1972). (7) G. C. Levy, U. Edlund, and J. G. Hexem, J. Magn. Reson., in press. (8) Viewing these effects only as association between the phenols and the Cr(acac)s may be somewhat simpllstic since there is obviously a competition between phenol-phenol and phenol-chelate association. In spite of a significantly greater steric hindrance the carbonyl ligands of Cr(acac)s can compete favorably as hydrogen bond receptors. (9) (a) Alfred P. Sloan Fellow, 1975-1977. (b) On leave of absence from Jagiellonian University, Krakow, Poland. (c) Universitat Dusseldorf, Dusseldorf, West Germany.
George C. Levy"' Tadeusz Holakgb AIOIS steigelgC
Department of Chemistry The Florida State University Tallahassee, Florida 32306 Received March 24, 1975
CloMe6 and C6Me6 in water a t 25O extend to near saturation (1.8 and 2.1 M , respectively, according to Pearson2), and they support the low concentration results of Menger and Wrenn, and also those of Pearson2 obtained from dye uptake and bromide ion activity measurements. Our results for the behavior of 4, with c1/2 for CloMe6 and C6Me6 are shown in Figures 1and 2, respectively. Density measurements for the determination of 4, were made below 0.4 m with 34-cm3 capacity pycnometers to an accuracy of f 4 X g ~ m - and ~ , above this concentration with an automatic precision digital densimeter Model DMA 02C manufactured by Anton Paar KG, the accuracy in this case being f 5 X g ~ m - The ~ . calculated error in 4, at various concentrations is shown by the vertical barred lines on the graphs. The Debye-Huckel theoretical limiting slope (DHLL) is also shown on the graphs. This is given by S, where
s, = kw3/2 in which I
w = 0.5 C u ; z ; ~ and k has a value of 1.868 cm3 for water a t 25°.3 The number of i ions of valence z, formed from dissociation of 1 molecule of electrolyte is given by u,, and thus S , for these compounds is 9.706 cm3 mol-312 L1l2. On the Micellar Properties of Bolaform Electrolytes in Micellization is usually indicated in a &(c1I2) graph by a Aqueous Solution rapid increase in 4, with c ~ n c e n t r a t i o n There .~ is no evidence of this for the C&e6 and C6Me6 bolaforms and so the micellization conditions of Menger and Wrenn are conSir: Last year Menger and Wrennl reported surface tension firmed for n >- 10. However the 4, (c1/2) behavior of our and kinetic measurements on aqueous solutions of bolaU ~ by form electrolytes of general formula R 3 N ( C H 2 ) n N R ~ B r ~ compounds is quite different from that of C ~ B studied Broadwater and Evans.5 This shows a pronounced mini(abbreviated C,&$ R = Me, n-Bu; n = 4, 8, 12). Micellizamum a t about 0.6 M which suggests aggregate formation tion of the C&e6 and C12Bug compounds was inferred above this concentration. The exact concentration a t which from the sigmoidal surface tension vs. log concentration the $,(c~/~) graph for C&u6 deviates from the DHLL was curves for these compounds, and it was suggested that, up not determined by Broadwater and Evans, but, as would be to the highest concentration investigated (0.1 M ) , a miniexpected from the molecular structure, C ~ B Ushows G greatmum chain length of 12 methylene groups was required beer deviations from DHLL than C6Me6 or CloMe6 over the fore micellization occurs for C,Me6 bolaforms. entire concentration range. Our measurements of the apparent molal volumes (4,) of
~
0
0.2
0.4
e-
0.6
,,,ah ib
0.8
1.0
1.2
Figure 1. Variation of apparent molal volume with c"' a t 25' for hexamethonium bromide [ ( C H ~ ) ~ N ( C H ~ ) ~ N ( C H ~ ) ~ . B ~ Z ] . The Journal of Physical Chemistry, Vol. 79, No. 2 7, 1975
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Communications to the Editor
330
I
Figure 2. Variation of apparent molal volume with c112at 25’ for decamethonium bromide [(CH~)~N(CH*)~ON(CH~)~.B~~].
I t is interesting to note that significant deviations from DHLL occur a t about the same concentration (0.045 M) for both C&e6 and CloMe6. This observation recalls the report by Fuoss and Chu6 of the conductance of the CnMe3-12 (n = 3, 4, 5) bolaform electrolytes for which cation-anion association was indicated. The extent of association was found to be practically independent of methylene chain length. Thus i t was postulated that one of the cationic sites became associated with an anion and the other site would be attracted to this anion and cause the methylene chain to bend into a loop (cf. “wickets” of Menger and Wrennl). This phenomenon could account for the similarity in &(cI’~) behavior a t low concentrations for C6Mes and CloMes. At concentrations above ca. 0.16 M, C&e6 shows greater deviations from DHLL than C&e6, but neither compound shows evidence of micelli~ation.~ Evidently some effect associated with the longer methylene chain for the CloMe6 compound is responsible for this difference; it is possible that a hydrophobic interaction between the methylene chains, exposed by the curved configuration suggested above, could result in the observed reduction in QV.
The Journal of Physical Chemistry, Vol. 79, No. 2 7, 7975
I t appears that bolaform quaternary ammonium electrolytes exhibit considerable bending of the methylene chain in aqueous solution as well as a t the air-water interface. However, clarification of the exact nature of any higher aggregates requires further experimental data. References and Notes (1) (2) (3) (4) (5) (6)
F. M. Menger and S. Wrenn, J. Phys. Chem., 78, 1367 (1974). J. 1.Pearson, J. ColloidlnterfaceSci., 37, 509 (1971). F. J. Mlllero, Chern, Rev., 71, 147 (1971). J. E. Desnoyers and M. Arel, Can. J. Chem., 45, 359 (1967). T. L. Broadwater and D. F. Evans, J. Phys. Chern.,73, 164 (1969). R . M. Fuoss and V. F. H. Chu, J. Am. Chem. Soc.. 73,949 (1957).
Pharmaceutical Chemistry Department University of Strathclyde Glasgow, 07 IXW, Scotland The School of Pharmacy University of London London, WC 1N 2AX, England
Recelved March 20, 1975
J. R. Johnson.
R. Fleming
