NOTES
4374 This mode of decomposition is analogous to that suggested for the HClO4 decomposition6 and observed in the pulsed laser decomposition of NH4C104.7 Although the presence of OH from this source would be masked by NH3 in the mass spectrometer, the "3+/"2+ ratio was greater than the normal ratio observed for NH, alone (after correcting for HzO). This could indicate possible additional contribution from the OH radical. The results of the Knudsen experiments compared to those of free-evaporation seem to indicate that very little reaction occurred between the sublimed products of NH4ClOs dissociation.
Conclusion The dissociation of ammonium chlorate appears to proceed via a proton-transfer mechanism : NH4C103-
+
(c) -+ KH3 HC103, with subsequent decomposition of the acid to produce ClOz as the major product. The gaseous products of the dissociation process do riot show any tendency to undergo further reaction. The energy of activation for the dissociation process has been determined as 17 kcal/mol. No evidence was obtained for the existence of an NH4C103 vapor phase species.
Acknowledgments. This work was funded under the Foundation Research Program of the Naval Ordnance Systems Command. The authors would also like to express their appreciation to Dr. George Wilinot for reading the manuscript and making valuable suggestions. (6) J. B. Levy, J. Phys. Chem., 66,1092 (1962). (7) G. L. Pellet and A. R. Saunders, AIAA Sixth Aerospace Sciences Meeting, New York, N. Y., 1968.
NOTES
Ion-Solvent Interactions.
Conductance
and Nuclear Magnetic Resonance Studies of Sodium Tetrabutylaluminate in the
Presence of Benzene and Toluene by C. K. Hammonds, T. D. Westmoreland, and 11'.C. Day1 Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 'YO805 (Received May 98, 1989)
The importance of solvent interactions on the behavior of ionic solutions is well recognized. Their effects on ionic conductance and extent of ion-pair formation were clearly pointed out by Gilkerson2 and have been extensively studied by several research More recently there has been considerable interest in the effects of such interactions on the rates of anionic polymerizatjon reactions in the presence of various alkali metal counterions.8 Although these studies have generally been carried out in ethereal solvents such as tetrahydrofuran (THF) and dimethoxyethane (DME), some studies have been made in the nonpolar solvents c y c l o h e ~ a n eand ~ ~ ben2ene.l' ~~ There can be no question that specific complexation occurs between the smaller alkali metal cations and basic solvents such as T H F and DME and that this The Journal of Physical Chemistry
affects the rates of anionic polymerization reactions, but the possibility of specific complexation of alkali metal cations with aromatic solvents such as benzene has not been determined although the effect of benzene on anionic polymerization rates has been studied and the possibility of such complexation has been proposed. Using cyclohexane as an inert solvent and sodium tetrabutylaluminate (NaAIBu4) as a source of the sodium ion, we have recently shown that it is possible to study the specific solvation of the sodium ion by bases such as T H F using nmrlZand conductance13techniques. We report here the use of these techniques in the study (1) Reprint requests should be sent to M. C. Day.
(2) W. R. Giikerson, J. Chem. Phys., 25,1199 (1956). (3) R. M. Fuoss, et al., J. Phys. Chem., 69, 2676 (1965), and many others in the series. (4) C. A. Kraus, J. Chern. Educ., 35,324 (1968). (6) W. R. Gilkerson and J. B. Ezell, J. Amer. Chem. SOC.,89, 808 (1967). (6) T. E. Hogen-Esch and J. Smid,!ibid.,'88,318 (1966). (7) A. D'Aprano and R. Triolo, J. Phys. Chem., 71, 3474 (1967). (8) T. Shimomura, J. Smid, and AT, Szwarc, J. Amer. Chem. SOC.,89, 5743 (1967). (9) J. E. L. Roovers and 5.Bywater, Can. J . Chem. 46, 2711 (1968). (10) F. S. Dainton, et al., Makromol. Chem., 89,257 (1966). (11) J. E. L. Roovers and S. Bywater, Trans. Faraday SOC.,62, 701 (1966). (12) E. Schaschel and M. C. Day, J . Amer. Chern. SOC.,90, 503 (1968). (13) C. N. Hammonds and M. C. Day, J. Phys. Chem., 73, 1161 (1969).
NOTES
4375
of the system NaAlBu4-cyclohexane with both benzene and toluene.
Experimental Section The nmr and conductance measurements and the preparation of SaAlBu4 have been previously reported.12,13The proton magnetic resonance spectra were obtained at -37" and the conductance measurements were made at 25.00 0.05". All solvents were purchased as reagent or higher grade chemicals. Cyclohexane, benzene, and toluene were refluxed over sodium-potassium alloy and distilled under a dry nitrogen atmosphere with an 80% return to the distillation column. All solvents were stored over sodium chips in vacuum-tight flasks in a nitrogen drybox. Standard solutions of XaAIBu4 were prepared by dissolving the salt in the bulk solvent cyclohexane. Aliquot portions of this solution were withdrawn and added to a series of 100-ml volumetric flasks which were fitted with outer caps to prevent contamination by the ground-glass joint lubricant, Coordinating agents were added by weiglht to the flasks to give the appropriate mole ratio of coordinating agent to salt, and the solutions were diluted with the bulk solvent at 25.00 =t 0.05" in a constant temperature bath by means of a closed dilution apparatus fitted to the flask.
*
Results and Discussion In a solvent of low dielectric constant such as cyclohexane, KaA1BIu4can be considered to exist as an ionpair or higher aggregate. On the addition of a complexing agent such as tetrahydrofuran, a complex with the sodium ion is formed. Based on the distinctive nmr and conductance behavior observed in earlier studies, we have proposed the equilibrium
+ 3THF = Na,4THF+, X-
Na.THF+, X-
1
0
I
2
3
4
5
6
7
8
9
IO
Ratio Base :NaAIBu,
Figure 1. Chemical shifts in the benzene and toluene proton signals as a function of the mole ratio, base:NaA41Buc. Solid line represents the corresponding signals in the absence of salt.
in which the 1: 1 complex is assumed to be totally in the complexed form. A summary of the application of these methods to the study of possible complexation of the sodium ion by benzene and toluene is shown in Figures 1 and 2. In Figure 1, the chemical shifts of the indicated protons are shown for both toluene and benzene as a function of the mole ratio of base to NaAlBu4 using cyclohexane as a solvent with a salt concentration of 0.20 M . The corresponding chemical shifts in the absence of the salt are seen to be very nearly coincident with those in the presence of the salt, indicating that concentration effects are responsible for the chemical shifts. The absence of any inflection points along with the fact that there is no significant change in the chemical shift in the presence cr absence of NaAlBu4 indicates that no specific complex exists between the sodium ion and benzene or toluene.
c
r'l
1
2
Ratio
3
4
5
6
Base : N a A I B u 4
Figure 2. Equivalent conductance of NaAIBul in cyclohexane-base mixtures as a function of mole ratio, base: salt; salt concentration (benzene): 0 , 0.2023 M ; .,0.1032 M ; A, 0.04776 M ; salt concentration (toluene) = 0.1994 M .
The analogous conductance data are shown in Figure 2 where the equivalent conductance of NaA1Bu4 in cyclohexane as a function of base to salt ratio is given, respectively, for benzene and toluene. I n contrast to the behavior observed in the presence of a coordinating solvent such as THF,I3no inflection points are noted in these curves. Rather, the regular increase in equivalent conductance is most reasonably attributed to an increase in solvent dielectric constant. Thus, the conductance data substantiate the nmr studies, and we conclude that the sodium ion does not form a specific complex with either benzene or toluene at 25". Based on general observations of ion-solvent interactions and cation size, it can reasonably be assumed that complexation also does not occur with the larger alkali metal cations. Attempts to carry out analogous studies on the lithium ion were unsuccessful because of Volume 73, Number 12 December 1969
4376 the inability to find a lithium salt that is soluble in a saturated hydrocarbon solvent.
NOTES
I
I
I
I
I
I
Acknowledgment. Support of this work by National Science Foundation Grant Gp6421 and a National Science Foundation Science Faculty Fellowship for C. N. Hammonds is gratefully acknowledged.
Negative Ions Produced by Electron Capture in Phosphine by M. Halmann and I. Plataner Isotope Department, The Weizmann Institute of Science, Rehovot, Israel (Received January 8,1969)
n’egative ions, PH2-, PH-, P-, and H - had been produced by electron impact on phosphine in the mass spectrometer. Their appearance potentials were measured by the retarding potential difference method, but only in the resonance electron capture region, below 10 eV.2 I n the present work, measurements have been extended up to electron energies of 75 eV, covering also the region of ion pair formation. The new data, together with previous results on positive primarya and secondary4ions, enable a more complete description of the various processes of electron capture and ionization.
Experimental Section Experiments were performed with an Atlas CH-4 mass spectrometer, using the normal electron impact ionization chamber (Type AK4). The highest ion curA. rents a t the ion collector were about Appearance potentials were calculated from the observed ionization efficiency curves by linear extrapolation to zero ion current, using the steepest section of the increasing curve for each process. Each curve was measured at least twice, and a t three different gas pressures (2, 5 , and about 10 Torr in the inlet reservoir). The electron energy was measured with a HewlettPackard Model 3440 A digital voltmeter connected between the filament and the ion chamber. For calibration of the electron energy scale the appearance potentials of 0- by electron capture and ion pair formation in carbon monoxide (9.60 and 20.9 eV) were used. Results given in Table I include the average of the observed appearance potentials and their probable errors. Phosphine was prepared by thermal decomposition of phosphorous acid.4b
Results and Discussion Ionization efficiency curves for the ions H-, PH2-, PH-, and P- in the mass spectrum of phosphine are The Journal of Physical Chemistry
E l e c t r o n Energy-eV(corrected1 Figure 1. Ion current (in arbitrary units) as a function of electron energy (in eV) for the negative ions in the mass spectrum of phosphine.
shown in Figure 1. The curves show both the sharp maxima due to resonant electron capture, as well as the gradual onset of ion pair formation. Appearance potentials derived from these curves for resonant capture and ion pair formation are presented in Table I, and are compared with previously reported results on the resonant capture. On the basis of the observed appearance potentials we are able to propose some conclusions on the reactions of phosphine in the ion source (see Table I). The conclusions are based on the following values for the ionization potentials I , electron affinities EA, and bond dissocia(1) 0. Rosenbaum and H. Neuert, Z. Naturforsch., 9a, 990 (1954). (2) H. Ebinghaus, K. Kraus, W. Muller-Duysing, and H. Neuert, ibid., 19a, 732 (1964). (3) H. Neuert and H. Clasen, ibid., 7a, 410 (1952); M. Halmann, J. C h m . SOC.,3270 (1962); J. Fischler and M. Halmann, ibid., 31 (1964); F. E. Saalfeld and H. Svec, Inorg. Chem., 2, 46 (1963): Y. Wada and R. W. K. Kiser, ibid., 3, 174 (1964): A. A. Sandoval, H. C. Moser and R. W. Kiser, J.Phus. Chem., 67,126 (1963); T. P. Fehlner and R. B. Callen, in “Mass Spectrometry in Inorganic Chemistry,” J. L. Margrave Ed., Advances in Chemistry Series, No. 72, American Chemical Society, Washington, D. C., 1968, p. 181. (4) (a) A. Giardini-Guidoni and G. G. Volpi, Nuovo Cimento, 17, 919 (1960); (b) M. Halmann and I. Platzner, J . Phys. Chem., 71, 4522 (1967).
