764
YOTES
to be a surface reaction, makes a temperature-dependent and M-MX3, where JrT represents alkali, alkaline earth contribution to the product ratio below 150". At and rare earth metals, and X represents halide ions. higher temperatures, this process is apparently overThis report on the phase equilibria in the KzS-K system deals with an extension of the work to the first whelmed, for the acetone to isopropyl nitrite ratio representative of systems hrT-nIzY, where Y is a doubly becomes temperature independent above about 160". This constancy together with independence of the ratio charged chalcogenide ion, and where the anion-toof the other variables suggests the ratio be identified cation ratio is as much as a factor of 6 smaller than with kl/kz. The value thus obtained, 0.17, is the same in the previous other extreme, the I\rT-,lIXa systems. as the grand average of low-temperature results (26The significance of the stoichiometry for the electrical conductivity, i e . , for the mobility of the metal elec79") , 1 The disproportionation :combination ratio may therefore be taken as 0.17 over the range 26-180". trons, was discussed earlier.3 The isopropoxy-nitric oxide pair is evidently similar to The KzS was prepared by slowly adding triply subalkyl-alkyl reactions in showing an inappreciable diflimed, carbon-free sulfur to excess potassium in an ference in activation energies between the two procinert atmosphere at a controlled temperature of 180esses. 200". The excess potassium was then removed by As has been pointed out,2 a value of 0.17 for k l / k 2 a t distillation at 300-350" under high vacuum. The final 120" would fit well with a correlation showing the disproduct was analyzed for K, S, and 0 and found to be proportionation to combination ratios for alkoxy better than 99% IGS with the major impurities being radicals and nitric oxide to be proportional to the I< and KzO. The potassium contained less than 0.02% number of available hydrogen atoms, in contrast to of other cations. All handling operations were perresults on alkyl-alkyl reactions. Such a correlation formed under helium in a drybox. would not be expected from data on reactions of alkoxy The phase diagram was determined by thermal radicals with methyl radicals, which indicate that analysis (cooling curves). Inconel capsules with isopropoxy disproportionates with methyl about twice thermocouple wells were used as cor tainers and a Ptas fast relative to combination as does m e t h ~ x y . ~ Pt-lO% Rh thermocouple was used in conjunction Furthermore, a referee has pointed out that the corwith a Rubicon potentiometer acd a Brown recorder relation would be significant only if all the alkoxyto measure temperatures. The Inconel capsules were nitric oxide disproportionation :combination ratios were sealed under helium in a welding drybox. A rocking furnace permitted mixing of the components before temperature independent, and this must be considered questionable in view of the apparent absence of diseach cooling curve was run. proportionation at 25" in the reaction of methoxy and The K-KzS phase diagram is shown in Figure 1. ethoxy radicals with nitric oxide The melting point T , of 948" is considerably higher Acknowledgment. Grateful acknowledgment is made than the value of 912" reported in the l i t e r a t ~ r e . ~ of support of this work by the Div'sion of Air Pollution, However, the latter value mas determined with KzS Bureau of State Services, U. S. Public Health Service. which contained at least 5% impurity. The critical solution temperature T , lies at about goo", or about 50" (4) Summarized in G. R. McMillan and J. G. Calvert, "Oxidation below the melting point of the KzS. The monotectic and Combustion Reviews," Vol. I, C. F. H. Tipper, Ed., Elsevier T,,, is 883" and the monotectic concentratemperature Publishing Co., Amsterdam, 1965,p 123. ( 5 ) A. R. Knight and H. E. Gunning, Can. J . Chem., 39, 1231,2466 tion is 21 mole % K. The K2S-K system thus resembles (1961). the KBr-K system except that T , for the former lies about 180" higher. The end of the miscibility gap at 63 mole % K is somewhat uncertain due to the very rapid increase in Miscibility of Metals with Salts. VII. The the sulfide solubility in the liquid metal just below the Potassium-Potassium Sulfide System' monotectic temperature. This rapid increase is, of by A. S. Dworkin and M. A. Bredig Oak Ridge National Laboratory, Oak Ridge, Tennessee (Received September 8, 1966)
so1utions2 Our previous studies Of have dealt with systems of the type M-RIX, M-RIIX2, The Journal of Physical Chemistry
(1) Research sponsored by the U. S. Atomic Energy Commission under contract with the Union Carbide Corp. (2) M. A. Bredig, "Mixtures of Metals with Molten Salts," in "Molten Salt Chemistry," 11.Blander, Ed., Interscience Publishers, Inc., New York, N. Y.,1964. (3) M. A. Bredig, J . Chem. Phys., 37, 914 (1962). (4) J. Goubeau, H. Kolb, and H. G. Krall, 2. Anorg. Allgem. Chem., m , 4 5 (1938).
NOTES
765
i
95.L
800
1
Y-1
course, connected with the fact that immiscibility in this system is close to being suppressed altogether. The liquid-liquid equilibrium curve was drawn as shown, namely, above rather than through the point at 51 mole % K, for two reasons: (1) to avoid having to accept an even more rapid, namely, infinitely steep increase in the K2S solubility in liquid K near the monotectic temperature, which would be in disagreement with the existence of a finite, even though very small, region of immiscibility, and (2) because the appearance of the first cooling halt at 51 mole % K indicated some supercooling. An attempt to interpret the liquidus near the melting point of K2S in terms of solute species leads to the following results. From the experimental entropy of a melting point depression of fusion of
AT nNK
RT, 2 X 1220 -- __AS, 3.16 x 100
=
3.1°/mole % K. This case is supported by the straightness of the liquidus which is in disagreement with curvature due to positive deviation from Raoult's law as expected in a system with only partial miscibility of the components and as actually observed in the potassium-potassium halide systems. This is the case implied in Figure 1, where the curved solidus (dotted line) was drawn to reflect the assumed increasing positive deviation from Raoult's law, ie., a faster- NK(') with inthan-linear increase of ANK = NK(*) creasing N K . 2. If pairs of electrons would occupy S2- positions in the K2Smelt and if at the same time the assumption of a rapidly increasing positive deviation from Raoult's law with increasing metal concentration were to be maintained, a comparatively much smaller solubility of K in solid K2S would have to be assumed, perhaps of the order of 1mole % at the monotectic temperature. Direct experimental determination of the solid solubility or, still better, of the activity of potassium metal through measurement of the potassium vapor pressure of the solutions will be required in order to support better any assumption about the molecular structure of these solutions. ~
( 5 ) A.
S. Dworkin and M. A. Bredig, submitted for publication.
(The entropy of fusion, 3.2 eu/mole, compares to the similarly low entropies of fusion of 4.2 and 3.4 for the anti-isomorphous substances CaFz and SrC12, respectively.) ( 6 ) This possibility is suggested by the large cation-to-anion ratio and should be of sufficient interest also to be investigated in additively colored K2S crystals.
7.7"/mole % K
is expected, if one assumes n = 1, for F-center-like or anion-like electrons singly occupying S2- ion positions in the K2S melt. If, however, the potassium metal electrons would pair up6 in the sulfide melt to substitute for S2-, ATINKwould be '/2 X 7.7 = 3.85" per mole % of K. Observed is T, -- TmOn 65 - 3.1°/mole NK(rnon) 21
%K
The Nitrogen-14 Nuclear Quadrupole and Spin-Rotation Coupling Constants in Methyl Isocyanide and Methyl Cyanide
by R4. E(. Kemp,'& J. RiI. Pochan,'b and W. H. FlygarelG Nooyes Chemical Laboratory, University of Illinois, Urbana, Illinois (Received August 18, 1966)
Although this experimental result appears at first glance to favor the second case, it actually cannot Until recently, the quadrupole coupling constant of at this stage of the study be interpreted unambiguously, methyl isocyanide has proven to be too small to measbut rather in either one of two ways. ure by microwave spectroscopy. The upper limit on 1. Electrons may occupy anion positions singly. the coupling constant has been lowered progressively in I n this case, a relatively large solubility of potassium recent years. I n 1947, Ring and co-workers2 predicted metal in solid potassium sulfide near its melting point similar to that found for calcium in the anti-isomor(1) (a) University of Illinois Fellow and National Science Foundaphous calcium fluoride could explain the difference tion Summer Fellow; (b) National Science Foundation Summer between (AT/NK)theoret= 7.7 and ( A T / N K ) ~=~ ~ ~ Fellow; I (e) Alfred P. Sloan Fellow. ~
~~
Volume 71, Number 3 February 1967
