SOTEB
1380
Vol. 67
A fraction of these radical ions would be protonated by the alcohol to give a neutral radical. The splitting of such a proton would probably be lost in the line width.l4 The photoradical probably arises from a side reaction to the conversion of the nitro group to a nitroso group since the low radical yield indicates conclusively that it is not an intermediate of the rearrangement to give nitrosobenzoic acid. In the absence of single crystal studies it is not possible to say whether the photoradical in the solid state is the same as that seen in solution. The low temperatures necessary to stabilize the photoradical in the solid state indicate that the two radicals are probably different species.
. 10
10
‘0
20
30
40
(13) G. Porter, “The Fifth International Symposium on Free Radicals,” Stockholm 1961. (14) T. J. Stone and W . A. Waters, Proc. Chem. Soc., 253 (1962).
VOLUME % ETHYL ALCOHOL.
Fig. 2.-The effect on the nitrogen splitting constant of the negative ion of o-nitrobenzaldehyde of altering the solventcomposition by adding ethyl alcohol t o the acetonitrile.
siderable solvent effect, the spectruni increasing in length as more ethyl alcohol is added, while a t the same time the radical becomes less stable. The increase in length is caused mainly by a change in the nitrogen splitting constant the variation of which is given in Fig. 2 . We attribute this change in the nitrogen splitting constant to a redistribution of the electron density in the nitro group due to increasing hydrogen bonding by the alcohol molecules. Comparison of Fig. l a and b indicates that even after the solvent effect is eliminated the photoradical spectrum is very different from that of the negative ion and since the spectrum of the positive ion should be similar to that of the negative ion,12we may say that the photoradical corresponds to neither of these ions. The 5- and 6-chloro-substituted o-nitrobenzaldehydes are photosensitive and the comparison of the negative ions and photoradicals for 5-chloro compounds showed a large proton splitting of about 11 gauss in the photoradical but this is not present in the negative ion. Thus the 5-chloro compound behaves in the same way as o-nitrobenzaldehyde. The 6-chloro compound did not give a measurable photoradical, owing presumably to steric factors. Very few examples of such a large proton splitting in aromatic compounds have been reported in the literature. Porter13 has reported a proton splitting of 11.9 gauss attributed to the hydrogen on the nitrogen in a 2,4,6-tri-t-butylanilino radical (-%-H). Similar splitting constants for the proton attached to the nitrogen atom have been found by Stone and Waters14 for the p-aminobenzoic acid radical (-N-H). Thus it would seem that the proton causing the large splitting in the photoradical is located directly on the nitrogen. We propose one of the following structures for the radical
7
.N
0
I
.N-H
(12) R . Bersohn, “Determination of Organic Structures by Physical Methods,” Vol. 11, Academic Prses, Kew P o r k , S . Y., 1962, p. 579.
THE THIRD VIRIAL COEFFICIENT OF POTASSIUNI AS ESTIMATED FROM ITS V,4POR PRESSURE1 BYJ. F. WALLING Battelle Nemorzal Instztute, Columbus, Ohio Recezved November 16, 1962
The importance of dimers (or alternatively the second virial coefficient) has long been recognized in connection with all of the alkali metals. Simple thermodynamics predicts increasing complexity of saturated vapors of alkali metals with increasing temperature. The vapor pressure data discussed here are the first for potassium2 that corroborate this prediction by displaying the effect of trimers. The vapor pressure of carefully purified potassium was determined in a modified boiling point experiment. I n brief, purified helium was maintained at constant pressure over a small sample of potassium contained in a test tube. Data were collected using a stainless steel test tube up to about 1100’K. At higher temperatures a container of 99% niobium-l% zirconium alloy was employed to avoid bothersome reactions. The imposed slow temperature rise of the metal, measured by means of a sheathed Pt us. Pt-10% R h thermocouple immersed in the liquid, was recorded as a function of time. It was possible, with the application of some corrections in the case of the stainless steel apparatus, to identify the estimated break in the curve with the onset of boiling. Pressures below two atmospheres were measured using a large (2.5-em. diameter legs) mercury manometer back lighted and read with a cathetometer. h conventional barometer was used t o determine atmospheric pressure in all measurements exceeding one atmosphere. Gravitational and mercury temperature corrections were applied. Pressures exceeding two atmospheres were measured using dead weight calibrated Bourdon-type gages. Data, in order of collection, are shown in Table I. An apparent third law heat of sublimation to the monomer at absolute zero (AHoo)was calculated from each datum by using recently published free energy (1) Based on research for the National Aeronautics and Space Administiation under Contract S A S 5-584. (2) The only other published potassium data a h i c h extend t o sufficiently elevated temperatures seem to be in serloua error. K. S.Grachev and P. L. Kirillov, Inzhenerno-Fzzicheskzy Zhurnal, 3 161, 62 (1960).
NOTES
June, 1963
1381 I
I
I
-
21,80(
A
A A 21,701
-
--!--A
8
Legend
21,601
\
Data taken in stainless steel apparatus A Datci taken in Nb-IZr apparatus 0
8
0 0
I
4 21,508
21,408
i----i
21,341
1200
Fig. 1.-Apparent
Temp., =]
