NOTES
organic ions on the phase boundary is most probably a kind of thermodynamic requirement arising from the high energy of absorption. The slight ionization of water has been neglected for convenience. ncl- in eq 6 represents the actual concentration of C1- ions within the interfacial double layer. The neglected term ncl-dkcl- of eq 1 represents the negative surface excess value. The consideration of the Gibbs equation on the basis of Stern’s model of a double layer requires no special treatment. Here, the fixed part of the double layer which is similar to that of Helmholtz does not contain any chloride ions. However, both chloride and sodium ions will be present in the diffuse part of the double layer so that m’ will be given by eq 11 with replacement of $ by $d, which is the potential of the diffuse double layer in Stern’s model. In the recent model of the penetration double layer proposed by Haydon and Taylor5 for the oil-water interface, the possibility of distributing only counterions in the space between the plane containing charged head groups and the phase boundary plane has been considered. For such a model, m’will be same as that for Stern’s model. I n fact, the K T coefficient occuring in the bracketed expression of eq 8 and containing the term, ncl-/nNa+is quite general in form. For the Helmholtz model, this ratio is zero, and for the Gouy and Stern models this is dependent on and +d, respectively.
+
Crystallographic Data for Some New Type I1 Clathrate Hydrates’
by D. F. Sargent2 and L. D. Calvert Division of Applied Chemistry, National Research Council, Ottawa, Canada (Received February 83, 1966)
The present paper establishes the structure of and presents lattice parameter measurements for five clathrate hydrates not previously characterized by Xray examination. The work was undertaken in an attempt to explain the anomalies described below. Davidson and c o - ~ o r k e r s ~have - ~ recently reported dielectric absorption studies of the clathrate hydrates of tetrahydrofuran (THF), 2,s-dihydrofuran (DHF), propylene oxide (PO), 1,3-dioxolan (DO), cyclobutanone (CB), trimethylene oxide (TMO), and ethanol (E). It was known’ that the hydrate of T H F was Type I1 (8M.136H20, a = 17.0-17.5 A, Fd3m) and the others were thought to be Type I1 from their
2689
dielectric behavior and approximate stoichiometry. Davidson, et u Z . , ~ suggested that the vhf absorption regions were associated with “hindered” rotation of the guest molecule in the cavities of the clathrate structure. Free rotation of the T H F molecule was deduced by Maks for the THF-H2S double hydrate. Hindered rotation of the ethylene oxide molecule was described by McMullan and Jeffreys for the Type I ethylene oxide hydrate. Davidson and his eo-workers observed certain differences between the results for trimethylene oxide and ethanol hydrates and the results for the other hydrates. It was tentatively suggested that these two might have a structure different from the normal Type I1 hydrate, either a new kind, one with modified hydrogen bonding, or one of those described by Jeffrey and co-w~rkers.~The present work was undertaken to investigate this possibility and to see if the observed lattice parameters might be correlated with the size of the guest moleculelo or with the frequencies of the dielectric absorption.
Experimental Section Powder specimens were prepared in thin-walled glass capillaries containing mixtures of the compound and distilled water in the approximate mole ratio M.17Hz0. These were frozen in liquid nitrogen. The best composition, usually slightly rich in the organic compound, was found by trial and error. For the compounds with an incongruent melting point, samples were annealed for a suitable time in an appropriate freezing bath. Both dihydrofuran and cyclobutanone were immiscible with water in the concentrations used. Samples were taken after thorough shaking. To obtain lattice parameters, further specimens were prepared containing- silicon as internal standard. This-silicon (99.9%, -325 mesh) had a = 5.4304 A at 25” in good agreement with a = 5.4305 A found for a specimen of the IUCr lattice parameter (1) N.R.C. No. 9107. (2) N.R.C. Summer Student. (3) D. W. Davidson and G. J. Wilson, Can. J . Chem., 41, 1424 (1963). (4) D. W. Davidson, M. M. Davies, and K. Williams, J. Chem. Phys., 40, 3449 (1964). ( 5 ) D. W. Davidson and R. E. Hawkins, J . Phgs. Chem., 70, 1889 (1965). (6) A. D. Potts and D. W. Davidson, ibid., 69, 996 (1965). (7) M. yon Stackelberg and B. Meuthen, Z . Elektrochem., 62, 130 (1958). (8) T. C. W. Mak and R. K. McMullan, J . Chem. Phys., 42, 2732 (1965). (9) R. K. McMullan and G . A. Jeffrey, ibid., 42, 2725 (1965). See also earlier papers in this valuable series. (10) M. von Stackelberg and W. Jahns, Z . Elektrochem., 58, 162 (1954).
Volume 70, Number 8 August 1966
2690
NOTES
~~
Table I: Collected Data for Type I1 Clathrate Hydrates Front reflexion at llO°K a, A a, A
Name of gueat FormuIa
Tetrahydrofuran CH~CH~CHZCHZO
17.13"
2,bDihydrofuran CHzCH=CHCH20
17.p
Cyclobutanone C&CH&HzC=O
17.09
I
-
L
0.03
J
0.1b 0.07
J
0,
Back reflexion a t 13K°K A st A
0
0
17,170 17.162
0.004 0.007
C
17.166d 17.162
0,004
-1.3
0.007
C
17.161' 17.155
0.006
5
0.004
0
Source and punty treatment
5.9
Eastman, 99.9+% Refluxed, fractionated
6.1
Aldrich, 99.7f "0
6.5
Aldrich Vacuum distilled
C
~
Propylene oxide CHaCHCHiO
17.10
1. SDioxolan CHzCHzOCHzO
17.10
0.06
17.124
0.005
-4.4
6.5
Matheson 99.9+%
5.6
Kodak, 99.9+% Refluxed, fractionated
5.5
Kodak, 99.9+%
C
L-J
L
Estd diam, A
MP.
0.05
17.118'
0.004
-5 C
A
Trimethylene oxide CHpCHzCHzO
17.1'
0. lb
17.095
0.006
-13.1 i
I J _
" Compare the value of 17.18 A found by von Stackelberg at 273'K. * Spotty photographs, accuracy low. c = congruent melting point; i = incongruent melting point. The value 17.22 A, u = 0.01 A was found at 233 10°K. a The value 17.23 A, u = 0.01 A, was found at 233 f 10'K. The value 17.099 A, u = 0.005 A was found at 100°K.
'
*
silicon" in the same 114.6-mm Debye-Schemer camera. and CB to obtain an estimate of the possible effects The lattice parameter of silicon was assumed to be of nonstoichiometry. If present, this effect does not 5.4297 A at 110°K and 5.4298 A at 135°K12 (factor appear to be appreciable. __ __ kX to A taken as 1.00202). Powder photographs were Results and Discussion taken at 110°K in a 6-cm flat plate camera in an apThe patterns of THF, DHF, CB, PO, DO, and TMO paratus previously describedI3 (Mo Kal = 0.70926 A) agreed closely with that obtained from tetrahydrofuran and the measurements corrected for shrinkage (fiducial already known to be Type II7p8and these hydrates dots) and geometrical errors (internal standard). are therefore Type 11, a t least within the sensitivity At least sixteen lines of the clathrate hydrate were of the powder method. In the TMO-H20 system measurable. The average lattice parameter and its there is a second hydrate. I n the ethanol-HzO standard deviation for random errors are given in system the hydrate is not Type 11. In both cases the Table I. The complete measurements are being subso far obtained are not adequate to charpowder data mitted to the ASTM Powder Data File. Flat-plate acterize them completely and work will be continued back reflexion photographs were also obtained at 135OK using modified techniques. in a specially constructed apparatus (Ni filtered Cu The hexakaidecahedral hole in Type I1 hydrates radiation, X Cu Ka1 = 1,54050 A). Six to ten a1a2 is almost spherical with a free diameter of about 6.6 hydrate doublets were observable but usually only A and it had been anticipated that the larger guest eight lines were measurable. These measurements molecules might expand the host lattice, perhaps were corrected for errors using the internal ~tandard.1~ rather abruptly at some critical value of their van der The results are listed in Table I together with a few Waals radius as suggested by von Stackelberg and measurements at other temperatures. Cobalt and chromium radiation were also tried but gave less satisfactory results. Temperatures were measured (11)w- Parri*h* Acta cry st.^ 838 (lQ6O). (12) D. N. Batchelder and R. 0. Simmons, J. Chem. Phys., 41, 2334 using a No.40 B & S gauge copperconstantan thenno(1964). couple touching the specimen and held Parallel to the (13) J. E. Bertie, L. D. Calvert, and E. Whalley, ibid., 38, 840 gas stream. The absolute values are believed to be (1963). (14) W. Parrish and A. J. C. Wilson, "International Tables for accurate to * 50 but were to within 2"* X-ray Crystallography," Vol. 11, Kynoch Press, Birmingham, 1969 Separate specimens were prepared for THF, DHF, p220. 133
Y
The Journal of Physical c h m & t r y
NOTES
Jahns'O for the Type I1 double hydrates. No such correlation was observed with the front reflexion data but it was possible that a small effect had been masked by the error of measurement (u = 0.03 to 0.10 A). Accordingly, more precise lattice parameters were obtained by taking back-reflexion photographs of new samples. A linear trend was observed when the lattice parameters were plotted against melting points, an observation interesting in itself. Once again there is no marked correlation with van der Waals diameters although it is probably significant that TMO and E, the hydrates of which differ from the others have, respectively, the smallest and largest diameters. The two sets of measurements at 110 and 135°K yield rough values for the mean coefficient of expansion a = AU/UAT. The values lie in the range 30-150 X 10-6 with an average value of 80 as compared to (/IC) and 32 X lov6 ( I C ) for values of 23 X ice at l10"K.15 The variation in values is probably due to the low accuracy of the values at 110°K. Using an average value of 17.34 A for clathrate hydrates at for the range 110273"K,' one derives a = 75 X 273°K.
Conclusions The hydrates of THF, DHF, CB, PO, DO, and TMO are all Type 11. In the TMO-H20 system there is a second hydrate. In the E-H20 system the hydrate is not Type 11. These differences between TMO and E and the other hydrates studied probably account for the differences in dielectric behavior observed by Da~idson.~-~ Acknowledgments. We are grateful to Dr. D. W. Davidson for bringing this problem to our attention and for supplying samples of the organic compounds which he used. (15) S LaPlaca and B. Post, Acta Cryst. 13, 503 (1960)
Hydration of Benzoic Acid in Diphenylmethane
by Gerry 0. Wood, Delbert D. Mueller, Sherril D. Christian, and Harold E. Affsprung Department of Chemistry, The University of Oklahoma, Norman, Oklahoma (Received February 68,1966)
I n previous communications from this laboratory, it has been reported that carboxylic acid molecules interact with water to form hydrated species in nonpolar solvents and in the vapor phase.'-* Partition and water
2691
solubility data have been analyzed to show that monomers of acetic and benzoic acids form hydrates in dilute solutions in benzene, but that the dimers of the acids show less tendency to associate with water. In order to obtain additional information about the stoichiometry and stability of hydrates of carboxylic acid species, we decided to investigate the interaction of water with a nonvolatile acid dissolved in a nonvolatile solvent; the solute chosen was benzoic acid and the solvent was diphenylmethane, which is quite similar in solvent properties to benzene and toluene. We report here water solubilities, partial pressures, and partition data for solutions of benzoic acid in diphenylmethane at 25".
Experimental Section Technical grade diphenylmethane was vacuum distilled through a 12-plate Oldershaw column. A constant-boiling fraction amounting to about the middle half of the sample was collected. The compound had a melting point of 24.6" under a vacuum and a refractive index of 1.5756 at 25". The vapor pressure apparatus and technique have been described previ~usly.~Approximately 100 ml of a solution of benzoic acid in diphenylmethane was added initially to the 250-ml Florence flask serving as the solvent reservoir. Successive 0.010-ml samples of pure water were introduced through the mercurycovered sintered-glass disk inlet valve into the evacuated system, using a 0.2000-ml precision microburet (manufactured by Roger Gilmont Industries, Inc.), which was found to deliver 0.0100 ml to within =k0.0002ml. After equilibrium was established (within 4 to 12 hr), the pressure indicated on the closed-end mercury manometer was measured with a cathetometer. Formal concentrations of benzoic acid in the reservoir were varied from 0 to approximately 0.3 M ; the entire apparatus was immersed in the constant temperature water bath at 25.0 i 0.1". In addition, the solubility of benzoic acid in diphenylmethane at 25" was determined at both zero and unit water activity. Samples of the solid acid were equilibrated with diphenylmethane in isopiestic cells of the type described previ~usly.~Distilled water or solid (1) S. D. Christian, H. E. Affsprung, and S. A. Taylor, J. Phys. Chem., 67, 1871 (1963). (2) S. D. Christian, H. E. Affsprung, and C. Ling, J. Chem. Soc., 2378 (1965). (3) S. A. Taylor, Ph.D. Dissertation, The University of Oklahoma, Norman, Okla., 1965. (4) A. A. Taha, R. D. Grigsby, J. R. Johnson, S. D. Christian, and H. E. Affsprung, J. Chem. Educ., in press. (5) S. D. Christian, H. E. Affsprung, J. R. Johnson, and J. D. Worley, ibid., 40,419 (1963).
Volume 70,Number 8
August 1066
