DONALD W. RICEAND N. W. GREGORY
4524 This result allows us to calculate a tentative value for the rate constant, kat of reaction 2. We find, using the kl and k2/k3 averages tabulated for the water-sodium reaction in Table 11, a value of k3 = (4 i 2) X lo6 M-l sec-' at -33.9' in liquid ammonia. We may compare this result with the results found for the comparable reaction of the hydrated electron, eaq-, with the ammonium ion in water at zero ionic strength, as summarized by Rabani.zO The rate constants reported vary from 1.1 X lo6 to 1.8 X lo6 M-' sec-' a t ambient (presumably) temperature. Our estimate of kl appears to be in agreement with the work in the aqueous systemz0 and is also consistent with the rate of the reaction between cesium and ethylenediammonium ions in ethylenediamine.21 Our kinetic data for the reaction of the two weak acids with sodium in liquid ammonia support the conclusion that the mechanism for reaction 4 is reactions 1 and 2.22 The average values of kl and k2/k3 determined in the present work are in generally poor agreement with the comparable constants deduced from the data of Kelly, et aL,6 by Jolly.8J We feel that this
discrepancy may be due to unavoidable precipitation occurring when ethyl alcohol and sodium react at the concentrations employed by the former workers. We are now reinvestigating the kinetics of the reaction of ethyl alcohol with sodium in liquid ammonia. Also, the value reported in this work for the rate constant of the ammonium ion-solvated electron reaction is within the range of the stopped-flow method, and an effort is now being made in this laboratory to measure this constant directly.
Acknowledgment. This research was supported by the National Science Foundation under Grant No. GP 6239. (19) D. R. Clutter and T. J. Swift, J . Amer. Chem. Soc., 90, 601 (1968). (20) J. Rabani, Advances in Chemistry Series, No. 50, American Chemical Society, Washington, D. C., 1965,p 242. (21) L. H. Feldman, R. R. Dewald, and J. L. Dye, Advances in Chemistry Series, No. 50, American Chemical Society, Washington, D. C., 1905,p 163. (22) R. R. Dewald and R. V. Tsina, Chem. Commun., 647 (1967).
Vaporization Equilibria in the Sodium Chloride-Zinc Chloride System by Donald W. Rice and N. W. Gregory Department of Chemistry, Universityof Washington,Seattle, Washington 98106
(Received June 6 , 1068)
Partial pressures of ainc chloride and of species of the form Na,ZnClz+, in equilibrium with condensed mixtures of NaCl and ZnClz, and with pure NaCl(s), have been derived from effusion and transpiration data. Evidence is found cor the existence of the solid-state compound NazZnClr, for which values of AH{' = -299 f 3 kcal mol-' and So = 95 f 4.5 cal de$-' mol-' at 625°K are derived. I n the presence of NaCl(s), partial pressures of the complex in the vapor phase, assumed to be NaZnCla(g), are only ca. 1% of those of ZnClz a t 600'.
Relatively little is known about the zinc chloridesodium chloride binary system. A melting point study by Nikonowa, Pawlenko, and Bergman indicates the existence of only one solid-state intermediate compound, NasZnCl4, with an incongruent melting point around 41OO.l Its crystal structure has not been determined. Dijkhuis and Ketelaar studied NaC1-ZnClz melts by emf methods at GOO" and found that deviations from the ideal Temkin model appeared to be a maximum around X N ~ C=I 0.59; they suggested that this dissymmetry may be due to complex ion formation.z Ellis reported evidence from Raman studies for ZnCl3and ZnC12- in KC1-ZnC12 meltsa3 Markov and Volkov observed that the volume change on mixing liquid NaCl The Journal of Physical Chemistry
and ZnClz is negative for mole fractions of NaC1 less than 0.5 and suggested the formation of complex ions.4 We now report a thermodynamic study of this system in which vaporization characteristics between 300 and GOO" have been determined by effusion and transportation experiments. Experimental Section The torsion effusion and Knudsen effusion apparatus, (1). N. Nikonowa, S. P. Pawlenko, and A. G. Bergman, Bull. Acad. Scz. URSS Classe Sei. Chim., 391 (1941).
(2) C. Dijkhuis and J. A. Ketelaar, Electrochim. Acta, 12, 795 (1967). (3) R.B.Ellis, J. Electroehem. SOC.,113, 485 (1966). (4) B. F. Markov and S. V. Volkov, Ukr. Khim. Zh., 29, 946 (1963).
VAPORIZATION EQUILIBRIA IN THE SODIUM CHLORIDE-ZINC CHLORIDE SYSTEM cells and calibration procedures,6.6 and the quartz transpiration apparatus and methode!' have been described previously; only features unique to the present application will be mentioned here. Argon, at ca. 1000 torr and at flow rates between 10 and 50 cm3 min-l, served as the carrier gas in transpiration studies; partial pressures of the various components of the equilibrium vapor were independent of flow rate over this range. Argon was made to flow either directly over heated NaCl-ZnCl2 mixtures or first over a sample of pure ZnCl2, in a compartment adjacent to the main reactor and heated by a separate furnace to introduce the desired partial pressure of ZnCl2, and then over a sample of pure NaC1. Ideal gas partial pressures in the equilibrium vapor were deduced from the relative numbers of moles of Zn, Na, and Ar in the condensed sample. The total zinc transported was determined by EDTA complexiometric analysis;* sodium was determined with a Beckman DU flame photometer. Because solutions to be analyzed contained only 0.1-3.0 ppm of sodium, considerable care was necessary to prevent contamination. The pressure of argon was measured manometrically; the number of moles of argon flowing through the reactor was determined by measuring the pressure of the quantity collected (in a liquid nitrogen cooled trap) after expansion into a calibrated volume. Samples of Baker's Analyzed reagent grade ZnClz and Mallinckrodt analytical reagent NaCl were vacuum dried, and the ZnClz was vacuum sublimed prior to use. Mixtures were first melted under vacuum and then cooled slowly; the composition was verified by analysis for zinc and chloride (Mohr method). The solidified melts were ground and transferred to the transpiration reactor or to effusion cells in a drybox. X-Ray powder photographs were taken of samples in Pyrex or Lindemann glass capillary tubes, using a Debye-Scherrer camera and Cu K a radiation.
Results and Discussion The vapor pressures of zinc chloride above the prepared solid mixtures were derived from independent Knudsen and torsion effusion experiments between 315 and 400". At a given temperature pressures were considerably less than the equilibrium vapor pressure of pure zinc chloride5 and did not change as XNacl(bulk) was varied between 0.7 and 0.92. The torsion effusion and Knudsen data gave the same values (within experimental uncertainty, see Figure 1) for the pressure when it was assumed that the zinc effused as monomeric zinc chloride. Results showed no systematic dependence on cell orifice areas, which ranged between 2X and 90 X cm2. A least-squares treatment of all effusion data gave the equation log Pl;,cll(torr) = -(8195
f
275)T-'
+ 10.57
f
0.40 (1)
-2
-
4525
-
c
E E
N
5;
d0
-6 0
-3-
-4
'
,
1.45
I
1.50
I
Ih5
1.60
I
1.65
270
IOOO/T(OK) Figure 1. ZnClz pressures above solid mixtures of NaCl and ZnClz (eq 1 gives the solid line): Knudsen: cell 1, 14.07 X - cm* orifice area; cell 2, 2.24 X lo-* - cm2 orifice om* total orifice area; area; torsion: cell 1, 7.18 X 10-8 cell 2, 90.9 X - om2 total orifice area. For the data points, X N ~ C and I cell, respectively: Knudsen: 0 , 0.92, 1; 8 , 0.83, 1; 0, 0.73, 1; A, 0.74, 1 and 2; torsion: w , 0.92, 1; 0.74, 1; X, 0.70, 2.
-
+,
The data points and least-squares line are shown in Figure 1. The observations are consistent with the conclusion, reached in the melting point study,*that the solid material in the cells was a mixture of NanZnClr and NaC1. On this basis the mixtures had bulk mole fractions of NazZnCl, between 0.24 and 0.90. Since ZnClz pressures were independent of the relative amounts of the two phases, the composition of these phases must have been the same in the different mixtures. Evidence for the composition of the complex solid was obtained from the following effusion experiment. An equimolar mixture of NaCl and ZnCl2 was placed in a torsion cell (5) D. W. Rice and N. W. Gregory, J. Phys. Chem., 72, 3361 (1968). (6) Bee the Ph.D. thesis of D. W. Rice, University of Washington, Seattle, Wash., 1968. (7) R. R. Richards and N. W. Gregory, J. Phy.3. Chem., 68, 3089 (1964). (8) H. A. Flaschka, "EDTA Titrations," Pergamon Press Inc., New York,N. Y., 1959,p 75. Volume 78,Number IS December 1065
DONALD W. RICEAND N. W. GREGORY
4526 and brought to 288". At this temperature the melting point diagram' indicates the presence of a liquid phase ~ (XZnc12= 0.55) in equilibrium with with X N ~ =C 0.45 NazZnCL(s). The effusion pressure of ZnClz was observed to be much higher than values represented by eq 1 and to remain constant at 2.36 X torr for some time, as expected when both liquid and solid phases are present. When the pressure began to fall rapidly (the value predicted by eq 1 was just below the limit of reliable measurement), it was assumed that the liquid phase had disappeared. The apparatus was then cooled; analysis of the solid remaining in the cell gave XNacl = 0.654, which, within experimental error, is that expected for NazZnC14, 0.666. X-Ray powder patterns of samples of the various mixtures with X N ~ ChI 0.7 (Xznc125 0.3) showed the presence of at least one phase in addition to NaC1; NaCl lines were at spacings expected for pure sodium chloride. The pattern characteristic of ZnClz(s) was not observed. The 52 lines (Table I) not attributable to NaCl were the same in all samples and are believed characteristic of YazZnCl4. The pattern was too complex to permit an unambiguous assignment of crystal class and unit cell. An orthorhombic cell with a. = 5.68 8, bo = 10.0 8, and co = 14.1 A gave a reasonable correlation of the spacings.
1.2 and 35.2 f 1.3 cal deg-l mol-', respectively; these results, together with standard values for ZnClz(g)s and NaCl(s),g give (at 625°K) a standard entropy for NazZnCld(s) of 95 f 4.5 cal deg-' mol-' and AHr" = -299 i 3 kcal mol-'. Association of Sodium Chloride and Zinc Chloride in the Vapor Phase. I n Ihudsen experiments amounts of sodium in the condensates were detected which exceeded that expected from the sublimation of sodium chloride. Correction for the contribution of the sodium-containing species, which were only 0.1-1 mol % of the zinc, in the derivation of eq 1 was not necessary. To obtain sufficient amounts of sodium for an accurate determination, it was necessary to raise the temperature; effusion experiments above the melting point were unsuccessful because the liquid crept through the orifice. Transpiration experiments between 500 and 600" led to transport of sufficient quantities of sodium to permit determination by flame photometric methods with good precision. The transpiration data are presented in Table 11. The contribution (w 10% maximum) from vaporization of sodium chloride was subtracted from the total amount of sodium co1lected;'Ot'l the remainder was attributed to species such as NaZnCL(g). The specific
/
Table 1: NazZnCll X-Ray Powder Pattern t/d2
8, deg
6.45 7.65 8.45 8.85 9.43 10.98 11.95 13.15 14.68 15.38 17.13 17.88 19.13 20.05 20.68 21.30 24.30
A -2
0.0213 0.0300 0.0366 0.0401 0.0455 0.0614 0.0726 0.0876 0,1088 0.1191 0.1469 0.1596 0.1818 0.1989 0.2111 0.2234 0.2866
25.03 25.83 26.25 27.38 27.73 28.20 28.75 29.30 30.11 30.60 31.28 31.85 32.48 32.85 33.63 34.12 34.75
0.3031 0.3214 0.3311 0.3579 0.3666 0.3780 0.3915 0,4053 0.4261 0.4385 0.4564 0.4713 0.4882 0.4979 0.5192 0.5328 0.5498
35.10 37.50 39.03 41.85 42.20 51.05 52.08 52.68 58.05 63.20 63.90 67.13 69.13 72.03 73.28 75.38 76.80 82.50
/
0.5595 0.6273 0.6713 0.7534 0.7636 1.0236 1,0532 1.0704 1,2184 1.3483 1.3647 1.4368 1.4776 1,5312 1.5522 1,5844 1.6042 1.6633
From these observations we conclude that eq 1 characterizes the equilibrium NazZnC14(s)+2NaCl(s)
+ ZnC12(g)
(2)
The standard enthalpy and standard entropy changes (standard states chosen as pure solids and the perfect gas state at 1 atm, respectively) for reaction 2 at 625"K, obtained by the van't Hoff method (eq l ) , are 37.5 The Journal of Physical Chemistry
/
/
-
10-
0
8-
E
4
E
852OK
n
Y
-
n
V
c N 6-
' a 4-
0
.s
.4
.6
1.0
Figure 2. The apparent pressure of Na,ZnCla us. the pressure of and 5 represent ZnClz(g), in equilibrium with NaCl(s). the upper limit "saturation" values, obtained when both a melt and NaCl(s) are present.
(9) K. K. Kelley and E. G. King, Bulletin 592, U. S. Bureau of Mines, U. S. Government Printing Office, Washington, D. C.,1961. (10) J. E. Mayer and I. H. Wintner, J . Chem. Phys., 6, 303 (1938). (11) T.A. Milne and H. M. Klein, ibid., 33, 1628 (1960).
VAPORIZATION EQUILIBRIA IN THE SODIUM CHLORIDE-ZINC CHLORIDE SYSTEM
4527
Table I1 : Transpiration Results Flow rate, cm'/min
Ar pressure, mm
847.2 850.2 851.1 800.0 799.0 773.7 770.4 799.2 767.9
51.0 52.8 21.5 15.3 16.1 15.3 15.8 50.6 47.8
973.4 944 * 7 993 * 7 1034.0 1033.0 1012.2 1019.0 990.0 974.0
852.2 851.7 852.7 852.9 853.4 799.0 800.4 798.7
55.0 52.5 53.9 54.0 54.8 49.0 49.5 50.1
968.4 964.0 965.1 941.0 960.5 955.0 951.0 891.0
Temp, OK
10*[Ar], mol
106[Zn], mol
10'[Na], mol
107INal (from NaCl), mol
PZnClz,
10apNsZnClzs
mm
mm
10'Ks
Argon Passed over NaC1-ZnClt(1) NaCl(s) Mixtures 12.35 9.92 16.0 0.572 11.10 9.45 15.7 0.592 5.473 4.54 7.33 0.287 2.95 3.18 8.110 0.056 3.69 4.10 10.94 0.074 1.28 1.08 5.205 0.012 2.33 0.025 2.81 12.86 7.75 0.149 7.98 21.09 5.69 4.20 26.00 0.045
0.780 0.805 0.820 0.376 0.348 0.249 0.222 0.374 0.213
12.1 12.8 12.8 3.98 3.80 2.07 1.82 3.57 1.56
15.5 15.9 15.6 10.6 10.9 8.31 8.20 9.54 7.32
Argon-ZnClt Mixture Passed over Pure NaCl(s) 18.55 10.3 19.3 1.01 25.47 12.2 22.4 1.40 1.00 17.89 7.78 14.1 25.70 8.18 15.3 1.50 15.93 4.20 8.00 0.930 36.41 2.21 2.45 0.267 23.22 2.29 2.70 0.171 15.34 1.27 1.43 0.117
0.539 0.463 0.420 0.299 0.253 0.0579 0.0940 0.0737
9.52 7.95 7.02 5.04 4.29 0.571 1.04 0.759
17.7 17.2 16.7 16.9 17.0 9.90 11.0 10.3
+
molecular form of the vapor complex has not been established. However, a series of experiments in which solid NaC1, a t a fixed temperature, was allowed to equilibrate with various partial pressures of ZnClz (all sufficiently small so no melt was formed) clearly demonstrated that the amount of sodium transported in complex molecules was proportional to the partial pressure of zinc chloride, Figure 2. This shows that complex molecular species containing more than one zinc atom per molecule were not present at significant concentrations. An effort to fix the sodium content of these molecules in a similar way was made by passing ZnClz(g) over solid solutions of AgCl and NaC1. The activity of NaCl in such mixtures has been derived from emf measurements.lZ However, at large mole fractions of AgC1, a liquid phase was formed a t temperatures needed to generate measurable amounts of the vapor-phase complex molecules; zinc chloride dissolved in this liquid and activities of sodium chloride were no longer known. At low mole fractions of AgC1, melt formation was avoided, but the activities of NaCl were not well enough established by the emf data to permit one to differentiate between, for example, a linear or square dependence of the pressure of the complex on the NaCl activity. Hence, the question as to whether the correct molecular form of the complex is NaZnCL, NazZnClr, or a mixture of these and/or perhaps molecules with even larger amounts of NaC1, cannot be answered at present. Forms corresponding to M'MXI have been reported for the KC1-PbC12 and RbC1-PbC12 systems, although in neither is a 1 : 1 solid compound observed.l* Evidence for this molecular form was based on vapor den-
sity experiments; however, the temperature (1345°K) was much higher than ours and these systems involve a different coordinating metal atom. Moss assumed without proof that the complex vapor molecules above KC1-ZnC12 mixtures have the form KZnC13.I4 Bloom and Hastie pointed out the general lack of evidence to suggest the formation of significant amounts of alkali
0
-
0
I20
I30
140
1.50
IOOO/T(%)
+
Figure 3. Apparent equilibrium constants for NaCl(s) ZnClz(g) + NaZnCla(g). Transpiration: 0 , argon over NaC1-ZnC12(l) NaCl(s); 0, argon-ZnClz(g) over NaCl(s). X N ~ (Knudsen C ~ effusion, cell 1): 0.92; X, 0.83; A, 0.73, 8 , 0.74.
+
+,
(12) M. B. Panish, F. F. Blankenship, W. R. Grimes, and R. F. Newton, J. Phys. Chem., 6 2 , 1325 (1958). (13) K. Hagemark, D. Hengstenberg, and M. Blander, ibid., 71, 1819 (1967). (14) H. I. Moss, Ph.D. Thesis, Indiana University, Bloomington, Ind., 1960. (16) H. Bloom and J. W. Hastie, Aust. J. Chem., 19, 1003 (1966).
Volume 78, Number 18 December 1968
J. J. DUVALLAND H. B. JENSEN
4528 halide-metal halide binary vapor complex molecules with more than one alkali metal atom.ls Table I1 includes equilibrium constants evaluated on the basis of an assumed reaction iYaCl(s)
+ ZnC12(g)+NaZnC13(g)
(3)
The temperature dependence of these constants is shown in Figure 3, together with values deduced from the effusion data. Considering the large uncertainty in the sodium determinations for small quantities obtained in the low-temperature effusion studies, the agreement between the two independent methods is quite good. Because the pressure of the complex is such a small fraction of the partial pressure of ZnClz, information concerning the molecular weight of the complex cannot be derived by comparison of effusion and transpiration data. The consistency of the two sets of data in no
way supports the assumption that NaZnCls is the dominant vapor form of the complex. A least-squares treatment of the transpiration data, based on reaction 3, leads to the equation logK3 = -(2593
f
250)T-'
+ 1.261
f
0.315 (4)
This relationship gives the line shown in Figure 3. Apparent thermodynamic properties of NaZnCls may be readily derived from eq 4; however, discussion of these values will be deferred until experimental evidence for the molecular form of the vapor is available. It may be noted that the association enthalpy of NaC1(g) and ZnClz(g) (-42 kcal) appears substantial, only ca. 6 kcal less, for example, than the dimerization enthalpy of NaCl(g) (-48 kcal). Acknowledgments. We acknowledge with thanks the financial support received from the National Science Foundation, GP-6608x.
Reactions in the Cobalt-60 Irradiation of Pyridine and Methylpyridines by J. J. Duvall and H. B. Jensen U.S. Department of the Interior, Bureau of Mines, Laramie Petroleum Research Center, Laramie, Wyoming 82070 (Received June 7 , 1968)
y Irradiation of nitrogen bases found in shale oil has been studied as a possible means of enhancing their value. Pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, and 2,6-dimethylpyridine were subjected to cobalt-60 irradiation with total dosages of 2 X lo7 to 2 X lo8 rads. G values for hydrogen, methane, acetylene, methylacetylene, and polymer, as determined by gas-liquid partition chromatography and mass spectroscopy, are reported. Products resulting from rupture of bonds external to the ring, rupture of ring bonds, aromatic substitution, and intramolecular rearrangement are reported. Respective examples of each of the above reactions on irradiation of 2-methylpyridine are the formation of methane, acetylene, 2,4-dimethylpyridine, and 3-methylpyridine. Possible reaction mechanisms are discussed. Dealkylation of methylpyridines occurred but not in significant amounts.
Introduction Shale oil contains relatively large amounts of nitrogen bases; thus, their investigation as a chemical source seems worthwhile. The nitrogen bases in naphtharange shale oil products have been shown to be mostly CZ-Cd alkylpyridines which have limited commercial value. Conversion of these alkyl-substituted pyridines to pyridine and methylpyridine would enhance the value of these nitrogen bases. One possible type of reaction for this conversion would be a yinduced dealkylation. The obvious first step in such a study is to determine the effects of Y irradiation on pure cornpounds. This paper reports the action of y irradiation from upon pyridine' the three monomethy'pyridines, and one dimethylpyridine. The Journal of Physical Chemistry
Pyridine has been the subject of several y-irradiation studies, but there is no mention of the y irradiation of alkylpyridines. Pearce1g2found that the main product of the y irradiation of pyridine was a polymer (G(po1ymer) = 3.14)3 that was about one-third bipyridines (G(bipyridine) = 1.06). Pearce also found small amounts of hydrogen (G(H2) = 0.018) and acetylene (no yield reported). In later work, Pearce and Ellison4 (1) C. K. Pearce, U. 8. Department of Commerce, Clearinghouse for Federal Science and Technical Information, A D 286,058,Ft. Monmouth, N. J., 1962. (2) C. K. Pearce, Department of Commerce, Clearinghouse for Federal Science and Technical Information, AD 605,430,Ft. Monmouth, N. J., 1964. (3) The G value is the number of molecules changed per 100 eV of energy absorbed.
