1598
Communications to the Editor
Scheme 11: Mesomeric Forms of the 5-Halogeno-8hydroxyquinoline (A) and of the 7-Halogeno-8hydroxyquinoline (B).. :X:,
@
:x:
scribed by Leffler and Grunwald,24 with an interaction term proportional to the product of the two UI values, for the dihalogeno derivatives
log K,*
10.6Zlq
- 1 . 7 Z u ~ u-~ 215
(6) with axand UP inductive constants of the halogens X and Y, PI = 10.6, interaction constant qI = -1.7, and multiple correlation coefficient r = 0.998. The significantly different PI value compared with the PI value of 16.6 for the monohalogeno derivatives (eq 4) indicates a greater sensitivity of these last compounds to the inductive effect. =
(24) J. E. Leffler and E. Grunwald. “Rates and Equilibria of Organic Reactions,” Wiley, New York, N. Y., 1963, pp 192-194. (25) Present address, Carleton University, Ottawa, Ontario, Canada. (26) On leave from the Laboratoire de Chimie Organlque Physique, Paris, France.
Department of Chemistry University of Florida Gainesville, Florida 32601
M. P. BratzeIz5 J. J. Aaronz6 J. 0 . Winefordner*
College of Pharmacy University of Florida Gainesville, Florida 32607
S. G. Schulman
Boyce Thompson lnstitute for Plant Research, Inc., Yonkers, New York 10701
H. Gershon
Received November 3, 1972
Reply to the Comments of Desnoyers on the Paper, “lOniC Solvation Numbers from Compressibilities and Ionic Vibration Potentials Measurements” Publication costs assisted by The Flinders University
Sir: We wish to discuss the points in Desnoyers’ communicationl in order. The Journalof Physical Chemistry, Vol. 77, No. 12, 1973
(1) “It is better to use the apparent molar compressibility and apparent molal volumes to determine solvation numbers from compressibility data. In this way, one eliminates interionic effects.” This could be done; we think the advantage would be nugatory. Our work is aimed at models of the solvation shell at infinite dissolution. The changes with codcentration are better interpreted in terms of the interpenetration of solvation shells. (The correlations with this model are shown in our paper,2 Figure 10 and Table VIII.) A similar model has been used by Ramnathan and Friedman.3 ‘(2) “The partial molar expansivity can be related to hydration numbers and, in this case, certain assumptions give rise to a negative value for the hydration number.” We do think this relates to our paper, where we have used the relative compressibilities of solvent and solute to calculate solvation numbers. The assumption (we correct for the partial degree of its applicability in our calculation2) is that the water molecules are completely incompressible a t sufficiently high field. The assumption of Dr. Desnoyers’ equation relating expansivity to hydration numbers is that both the hydration number and the volume of the water molecules in the hydration sheath are independent of temperature. This assumption seems to have a different status from that which we have used. We suggest the contradiction in sign arises from the lack of applicability of the assumptions. Corresponding remarks may be applied to his comment on heat capacity data. (3) In respect to the heat capacity data for sodium chloride solutions in H20 and DzO, we cannot agree that they are relevant to the interpretations of the compressibility data. They tell us something about how the heat capacities of solutions and salts vary in these two solvents, and it seems likely that the effects of structural changes outside the solvation sheath may be different, for heat capacities than for compressibilities. Now let us move to the general thought behind the comments of Dr. Desnoyers, and provide a general answer. In the work of Bockris and Saluja,4 the ionic vibration potentials have been combined with compressibility measurements to give individual solvation numbers, because the first measurement gives the sum and the latter measurement the difference of solvation numbers. This is the essential new thing about the experimental approach of Bockris and Saluja and the essential new thing about the theoretical approach is to distinguish quantitatively for the difference between the coordination number of the ion in aqueous solution and the number of water molecules temporarily attached to it, while it moves in the soluti~n.~-? Dr. Desnoyers’ essential point is to suggest that the fact that we have assumed (for univalent ions) that the change of the solution compressibility can be given predominantly by the change in the layer which the solvation and coordination waters inhabit, and then one further struc(1) J. E. Desnoyers, J. Phys. Chern., 77, 567 (1973). (2) J. O’M. Eockris and P. P. S. Saluja, J. Phys. Chern., 76, 2140 (1972). (3) P. S. Ramnathan and H. L. Friedman, J. Chem. Phys., 54, 1086 (1971). (4) J. O’M. Bockris and P. P. S. Saluja, J. Phys. Chern., 76, 2298 (1972). (5) J. O’M. Bockris, Quart. Rev. Chem. SOC.,3, 173 (1949). (6) J. O’M. Eockris and A. K. N. Reddy, “Modern Electrochemistry.” Plenum Press, New York, N. Y.. 1970. (7) 0. Ya Samoilov, ”Structure of Electrolyte Solutions and Hydration of Ions,” Consultants Bureau, New York, N. Y., 1965; Discuss. FaradaySoc., 24, 141 (1957).
Communications to the Editor
1599
TABLE I : Comparison of the Results of Bockris and Saluja for Ionic Solvation Values with Results of Other Authors Ref 6a
(6methods)
Li +
Na+ K+ Rb+ FCI -
Br I-
5 5 4 3 4 I l l
f l h l f 2 1 1 f l f 1 f l f l
Ref 9 ( 7 methods)
Ref 2
4 f l 3 f 0.8 2 f 0.7 2 f 0.5 2 f 0.3 1 f 0.2 l f l l f l
4.5 4.5 3.8 3.0 4.0 2.2 1.8 1.5
a Results rounded off to nearest integers for solvation numbers.
TABLE 11: Results Quoted by Desnoyers and Jolicoeurn on the Solvation Number of Some Salts Compared with Those of Bockris and Salujab Salts
Ref 10
Ref 2
LiCl Lii
4 f l 3 f l 4 f l 5Xtl 3f1 6 f l 4 f l 2rtl
7 f l 6 f l 8 f l 7 f l 6 f l 71tl 6rtl 5 f l
NaF
NaCi Nal KF KCI RbCl
aReference 10. Mean of three methods, bReference 2. Results rounded off to nearest integers for solvation numbers.
ture-broken layer, might be too crude an approximation, so that the numerical results of a determination based on it would lose validity. If there were a substantial structural change outside the first two layers of water molecules around the ion, extending, say, to the first five layers, there might be point in what he claims. The broken down water structure would be less compressible than the structured water and our results would be too high. We do, however, have a basis for our approximation, and it has been developed in our second paper.4 Here, we have gone into detail in the structure breaking and have developed a model in which we have solvational (i. e., oriented) water molecules, and other water molecules, which make up the first layer around the ion, and then a second layer in which the water is regarded as broken down into freely rotating monomers. For univalent ions, we find that fits can be obtained to entropy and heat data only if we do not extend the break-down further. Thus, the model with which our attitude is consistent derives from that of Bockris,5 but is modified to resemble that of Frank and Wen,8 in respect to the structural assumptions, and that of Samoilov' in respect to the dynamic aspects. Finally, the degree of damage our approximation may cause can be probed. Let us compare our results with those of other authors who used methods which did not involve our assumption. In Table I we compare Bockris and Saluja's2 results with the summary given by Bockris and Reddy (1970) of the results of five methods, and the tabulation of Case,s who quoted seven methods (mostly different from those of Bockris and Reddy). It has not been claimed that solvation numbers have the same status as thermodynamic parameters, but there can be no doubt from Table I that
Bockris and Saluja's numbers do measure the same quantity, within an overall significance of about il,as is being measured (if rather roughly) by many other methods. It is also of intereSt to compare the values of Bockris and Saluja with those which Desnoyers and Jolicoeur quoted in 1969.10 These are shown in Table II. Thus, Desnoyers and Jolicoeurlo quoted values (three methods) which are distinctly less than those of the roughly consistent values of the other authors, but again (using Desnoyers' own results as a criterion) there is no doubt that the changes which are followed as one goes from ion to ion show that the results of Bockris and Saluja have not been overwhelmed by structural effects well outside the layers very near the ion. The possibility of coincidence in the agreement is negligible in the many correlations exhibited. Conversely, were we to try to take the determination of solvation numbers to, say a f 5 % degree of consistency among the methods, perhaps Dr. Desnoyers' point about a more far reaching correction for the effect of the ion on compressibility of the regions would have more punch. (8) H. S. Frank and W. Y. Wen, Discuss. Faraday SOC., 24, 133 (1957). (9) B, Case, "Molecules at Electrodes," N. Hush, Ed., New York, N. y., 1972. (10) J. E. Desnoyers and C. Jolicoeur, "Modern Aspects of Electrochemistry," B. E. Conway and J. O'M. Bockris, Ed., Vol. 5 , Plenum Press, New York. N. Y., 1969.
School of Physical Sciences The Flinders University Bedford Park, South Australia Department of Chemistry Cornell University Ithaca, New York 14850
J. O'M. Bockris*
P. P. S. Saluja
Received February 26, 1973
Gaseous Thallium(1) Metaborate and Thallium( I ) Aluminum Fluoride Publication costs assisted by the U. S. Atomic Energy Commission
Sir: While all the thallium(1) halides have been studied,l only two gaseous ternary compounds of monovalent thallium, thallium(1) nitrate2 and thallium(1) ~ u l f a t e ,have ~ been reported so far. The purpose of this work was to extend the range of known gaseous ternary compounds of thallium(1) and to compare their mass spectrometric behavior to that of the corresponding alkali compounds. We have therefore examined the vapors above thallium(1) metaborate and an equimolar mixture of thallium(1) fluoride and aluminum fluoride. Samples of thallium metaborate, thallium fluoride, and aluminum fluoride were obtained from Research Organic/ Inorganic Chemical Gorp. Mass spectra were run on an Atlas CH-4 mass spectrometer. The samples were contained (1) D. Cubicciotti, J. Pbys. Chem., 68, 1528, 3835 (1964); 69, 1410 (1965); F. J. Keneshea and D. Cubicciotti, ibid., 69, 4910 (1965); 71,1958 (1967). (2) D. Cubicciotti, High T'ernp. Sci., 2, 131 (1970). (3) D. Cubicciotti, High Temp. Sci.. 2, 389 (1970).
The Journal of Physical Chemistry, Voi. 77, No. 12, 1973
