Feb., 1954
EQUILIBRIUM STUDIES OF SOMEMONOVALENT IONS ON DOIVEX 50
183
EQUILIBRIUM STUDIES OF SOME MONOVALENT IONS ON DO\\'ES 50 BY OSCARD. BONNERAND WILLIAMH. PAYNE's~ Department of Chemistry of the University of South Carolina, Columbia,S. C'. Received July 17, 1953
Equilibrium studies involving lithium, hydrogen, sodium, ammonium, potassium and silver ions on a Dowex 50 resin of approximately 8% divinylbenzene content have been made while maintaining a constant ionic strength of approximately 0.1 M . A quantitative relationship between the selectivity and maximum water uptake of the resin is shown.
Introduction One of the principal limitations in any attempt to explain the ion-exchange process is a lack of data on characterized resins. The resin used for these exchange reactions was therefore characterized as to capacity in the dry hydrogen form (5.10 meq. per gram) and as to maximum water uptake in the various ionic forms. Equilibrium studies of the silver-sodium, silverhydrogen and sodium-hydrogen exchanges on several Dowex 50 resins have been reported previo~sly.~ Eight ~ ~ additional exchange reactions on approximately 8% DVB Dowex 50 involving six monovalent ions are now completed. These data make possible the establishment of quantitative selectivity scale for these ions on this resin. It appears, however, that a completely satisfactory theoretical interpretation of these results is not possible a t this time. Perhaps future studies of the osmotic properties of concentrated solutions of electrolytes in water or in mixed solvents will
furnish the information necessary for such an interpretation.
3k n
0
20 40 60 Mole per cent. silver resin. Fig. 2.
80
100
3.0
4 ' sj
.-
+;,
g 2.0 .r(
B .3
0
20 40 60 80 Mole per cent. ammonium resin. Fig. 1.
100
(I) Part of the work described herein was included in a thesis submitted by William H. Payne to the University of South Carolina in partial ful6llment of the requirements for the degree of Master of Science. (2) These results were developed under a project sponsored by the United States Atomic Energy Commission. (3) 0. D. Bonner, W. J. Argersinger and A. W. Davidson, J. A m . Chem. SOC.,74, 1044 (1952). (4) 0. D. Bonner and Vickers Rhett. THISJOURNAL, 57, 254 (1453).
w% 1.0
0
20 40 60 80 Mole per cent. potassium resin. Fig. 3.
100
184
OSCAR
D. R O N N E R
AND
WILLIAM H.
Vol. 58
PAYNE
TABLE I TABLE OF EQUILIBRIUM CONSTANTS Exchange system
1.50 +*
.-.e8
s
.*L3
6 1.25 .e
I
"
8
1.oo I 0
20
40
GO
80
100
Mole per cent. ammonium resin, Fig. 4
0
20 40 60 80 Mole per cent. hydrogen resin. Fig. 5.
100
Kexp
Koaled
Ammonium-hydrogen 1.76 1.72b 1.85' Hydrogen-lithium 1.26 1.23d 1.32' Ammonium-li thium 2.17 2.22' 2. 45g Ammonium-sodium 1.26 l.lSh 1.23' Potassium-ammonium 1.17 1.19' Silver-lithium 7.74 Silver-ammonium 3.16 Potassium-hy drogen 2.09 Silver-hydrogen' 5.84 Silver-sodium" 3.89 Sodium-hydrogen" 1.49 Previously r e p ~ r t e d . ~ From NH4-Li and H-Li exchanges. From Ag-NHr and Ag-H exchanges. From NHd-Li and NH,-H exchanges. a From Ag-Li and Ag-H exchanges. J From H-Li and NH4-H exchanges, From Ag-Li and AF-NHI exchanges. From "4-H and Na-H exchanges. From Ag-NH4 and Ag-Na exchanges. j From K-H and NH4-H exchanges.
It is of interest to note that for these exchanges there was no reversal of selectivity such as occurred in the sodium-hydrogen exchange4 on 16% DVB resin. It appears, however, that such a reversal might occur on a higher cross-linked resin in the ammonium-hydrogen or ammonium-lithium systems. The true thermodynamic equilibrium constants, calculated3 from the equation log K = J 1log k d N are given in Table I. I n these calculations it is assumed that the activity coefficients of these uniunivalent electrolytes in 0.1M aqueous solution are approximately equal. Hence IC is merely the equilibrium quotient at any resin composition. The reasonable agreement of the experimental equilibrium constants with those calculated from other exchanges appears to justify the application of the mass action law to ion-exchange equilibria. It may also be observed that there is a relationship between the affinity of the resin for each of these ions, relative to the affinity for the lithium ion taken as unity, and the maximum water uptake of the resin in that ionic form. This semi-logarithmic relationship is shown in Fig. 6. This relative affin10
Experimental and Results The methods of equilibration, separation and analysis used in this work were identical with those reported previously.4 Hydrogen, ammonium and silver ion concentrations were determined volumetrically, and lithium, sodium and potassium ion concentrations were determined spectrophotometrically with a Beckman DU flame photometer except when radioactive methods of analysis were used. The aqueous solution concentration was approximately constant a t about O.lM, and the samples were maintained at a temperature of 25 f 0.5" during the equilibration period. The results of these exchanges are presented graphically in Figs. 1-5. The complexities of ionexchange equilibria are illustrated by the slopes of equilibrium quotient-resin composition curves. No explanation is a t present forthcoming for the different types of behavior which are exhibited.
5
a
1 120
140
160
180
Maximum water uptake. Fig. 6.
200
%
1
ity of the resin for these ions in effect establishes a quantitative selectivity scale for these monovalent ions on a resin of this cross-liiikage. The selcctivity will, of course, be different for resins of varying divinylbenzene content. It has been s h o ~ v nhow,~
ever, for the sodium-hydrogen system, that the selectivity may be calculated when the maximum water uptake is known, and it is expected that similar calculations will be possible for other systems.
STTJDTES I N MOLECULAR ORBITAL THEORY OF VALENCE. MULTIPLE I30NDS INVOLVING d-OItBITALS’
ITP.
BY H. H. J A F F ~ Venereal Disease Experimental Laboratory, U.S. Public Health Service, School of Public Health, University of North Carolina, Chapel Hill, North Carolina Received August 6, 1065
Multiple bonding involving both valence and penultimate electron shell d-orbitals has long been postulated. This paper discusses the construction of molecular orbitals for such multiple bonds from combination of d r - and hybrid dpr-orbitals with pa- and dr-orbitals, and from d6- with d&orbitnls, and illustrates the resulting MO’s graphically. The symmetry and directional properties of d-orbitals are used to discuss conjugation by such multiple bonds of several radicals attached to a central atom in several geometric arrangements. Square planar and octahedral central atoms are found to permit conjugation of four and six radicals, respectively. Tetrahedral central atoms on the other hand are seen to permit conjugation only a t the espense of appreciable multiple bonding energy. Hence it is concluded that unequal radicals will enter into effective competition for the d-orbitals of the central atom. This conclusion explains the apparently contradictory findings in attempts to demonstrate conjugation in compounds such as sulfones. Finally it is concluded that multiple bonding involving valence shell d-orbitals can be important only if the central atom carries a positive charge in the single bonded structures.
Introduction Double bonds involving d-orbitals have long been p o ~ t u l a t e d . ~I n~ ~the complex compounds and ions of the transition metals, double bonded structures involving the partially filled d-orbitals of the penultimate electron shell4 have been suggested.2J Furthermore, expansion of the valence shell beyond the octet, with formation of multiple bonds, has been proposed for the oxy-compounds and halides of sulfur, oxygen and silicon.2 For the complexes of platinum(I1) chlorides with the trihalides and trialkyls of phosphorus, Chatt has recently postulated double bonds formed by use of penultimate d-orbitals of platinum and nd-orbitals4 of phosphorus.5 Resonance with structures having double bonds involving d-orbitals also occurs in aromatic metalloorganic compounds,6 and probably in heterocyclic compounds of s u l f ~ r . ~ . ~ Originally double bonds using d-orbitals were proposed in order to explain abnormally short bond distance^,^^^ and further evidence for the existence (1) Presented before the Division of Physical and Inorganic Chemistry, a t the 123nd Meeting of the American Chemical Society, Atlantic City, N. J., September, 1952. For paper I1 of this series see J . Chem. Phys., 21, 1618 (1953). (2) L. Pauling, “The Nature of the Chemical Bond,” 2nd ed., Corne11 University Press, Ithaca, N. y., 1944, Chapter V I I . (3) Y. IC. Syrkin and M. E. Dyatkina, “Structure of Molecules and the Cliemical Bond,” translated and revised by M. A. Partridge and D. 0. Jordan, Interscience Publishers, Inc., New York. 1950, Chapter 14. (4) For convenience we shall denote the orbitals of the valence shell
by ns, np. nd and the d-orbitals of the penultimate electron shell by fn 1)d. (5) J. Chatt and A. A. Williams, J . Chem. SOC.,3061 (1951); J. Chatt and R. G. Wilkins, ibid., 273 (1952). (6) A detailed investigation of the importance of such resonance in metallotirganic compounds will be the subject of a later paper. (7) H. C. Longuet-Higgins, Tram. Faradau SOC.,45, 173 (1949). ( 8 ) V. Rchomaker and 1,. Pauling, J . A m . Chem. Soe., 6 1 , 1700 (1939).
-
of bonds involving (n - 1)d-orbitals4is plentiful.5~9 However, the existence of double bonds involving nd-orbitals has been subject to controversy.lOnl‘ Kimball has derived, from group theory, the number of d-orbitals of correct symmetry for multiple bond formation for most common states of hybridization.12 However, he has considered neither the directional properties of the orbitals involved, nor the possibilities of conjugation of several groups. Multiple bonding and conjugation have been considered on the basis of non-localized molecular orbitals for a few specificc o m p ~ u n d s ~ ~ J ~ J ~ ; however, such arguments are difficult to generalize, since they depend strongly on the symmetry properties of the specific compounds involved. The present paper is concerned with an examination of the symmetry and directional properties of d-orbitals, and their relation to multiple bond formation and conjugation. The discussion mill be based on molecular orbital (MO) theory. In the framework of this theory a multiple bond is described as arising from the superposition of a single bond (u-bond) having local cylindrical symmetry around the bond axis, and one or more r-bonds arising from the interaction of ?r-orbitals of the bonded atoms. The r-bonding MO’s are characterized by nodal planes which contain the a-bond axis. In ztlmost all cases previously treated by MO theory the (9) See e a , H. H. Coerver, P. A. McCusker and C. Curran, Abstracts 121st ACS Meetinz, Buffalo, N. Y..March 19.52, p. 7N; E. 0. Brimm and M. A. Lynch, Jr., ibid., p. 38N; J. Owen a n d R. W. H. Stevens, Nature, 171, 836 (19.53). (10) Ea.,A. F. Wells, J . Ckem. Soc., 55 (I949), and references cited there. ( 1 1 ) For sulfur-oxygen bonds, c/. also W. Moffitt, Proc. R a y . Soc. (London), A200, 409 (1950). (12) G . E. Kimball, J . Chem. Phys.. 8 , 188 (1940). (13) H. P. Koch and W. Moffitt, Trans. Farodall Soc., 47, 7 (1951). (14) RQ. Wolfsbera and I,. Heltnhola. J . Clrem. Phys., 20, 837 (10.52).
