NOTES
nonmetallic elements. I n view of the comparatively lower ionization potentials of the metallic elements, this is a rather unexpected result worthy of further investigation.
Studies on Solutions of High Dielectric Constant.
VIII. The Cationic Transport Numbers of Potassium Bromide in N-Methylformamide at Different Temperatures and Concentrations
by Ram Gopal and 0. N. Bhatnaga? Department of Chemistry, Lucknow University, Lucknow, I n d i a (Received February 7, 1066)
I n view of the lack of the transport number data of ions in N-methylformamide, it was considered desirable to extend the previous work3v4on the determination of the transport numbers to solutions in N-methylformamide (NAIF) in order to evaluate the limiting ionic mobilities from the existing electrolytic conductance data and also throw some light on the ion-solvent interaction in this solvent of very high dielectric constant (e 182.4 at 25").4a With this aim in view, the cationic transport numbers of KBr in NMF, a t different temperatures and concentrations, have been determined and are reported in the present communication.
Experimental Section Potassium bromide was found to be an appropriate electrolyte on account of its appreciable solubility in NAIF so that the transport numbers could be determined at the significantly different concentrations. The A.R. grade KBr was recrystallized from conductivity water, thoroughly dried in an electric oven at 110", and was used for preparing the solutions. The N M F of specific conductance 10-4 mho was dried over freshly ignited quicklime and distilled twice under reduced pressure. The process of drying, distilling, and collecting the middle fraction for redistillation was repeated until the conductance of the sample was reduced to about mho. The sample of NMF thus obtained was kept in an amber bottle and stored in the dry nitrogen box. The sample was used for preparing the solutions soon afterward as the solvent appeared to be slightly more unstable than the other solvents of this family used However, the variation of conductance with time was found to be very little and was not expected to affect the results on
3007
the transport numbers a t ordinary temperatures. All of the solvent transfers were made in the dry nitrogen box. The transport number cell was similar to that used in formamide3 and N-methyla~etarnide~solutions. The cathode of the cell was a silver bromide electrode and was prepared as described el~ewhere.~The anode was a silver wire wound in the form of a spiral of about 4-5-mm diameter and 7-8 cm in length. The solution of any desired concentration was prepared in the manner described earlier and all possible precautions, given in detail in the previous comm~nications,~~4 to keep away the atmospheric moisture while preparing the solutions and during the course of experiments, were taken. The experimental results are summarized in Table I.
Table I : Cationic Transport Numbers of Potassium Bromide in N-Methylformamide Concn, M
0.00 0.05 0.10 0.20 0.25
0.30 a
15'
0.4945 0.4909 0.4881 0.4804 0.4765 0.4723
Transport number, t, 25' 359
0.5080 0.5048 0.5037 0,4980 0.4953 0.4931
0,5210 0.5184 0.5169 0.5119 0.5097 0.5084
450
-.
0.5290" 0.5288 0.5257 0.5210 0.5148 0.5130
From t h e graph by interpolation.
From the transport numbers given in Table I, the limiting transport numbers, t+O, of potassium ion at different temperatures were evaluated by using the Longsworth p r o ~ e d u r e . ~The values of the various terms involved in calculating the Longsworth function were as follows. Limiting equivalent conductivities of KBr at 15 and 25" were 36.51 and 43.69, as given by French and Glover,'j while those at 35 and 45" were 53.00 and 60.75 and were determined experimen(1) Work supported by the Council of Scientific and Industrial Research (India). (2) CSIR Junior Research Fellow. (3) R. Gopal and 0. N. Bhatnagar, J. Phys. Chem., 68, 3892 (1964). (4) R. Copal and 0. N. Bhatnngar, ibid., 69, 2382 (1965). (4a) NOTEADDEDIN PROOF.G. P. Johari and P. H. Tewari [ibid., 70, 197 (196S)l have published the cationic transport numbers of KCl in formamide and in NMA without discussing and referring to the data given in ref 3 and 4. It is interesting to note that t h e "ever-vigilant" refereeing staff of the Journal of Physicd Chemistry appears to have failed to draw the authors' attention to the already existing detailed investigations',' of such a recent publication. ( 5 ) L. G. Longsworth, J . Am. Chem. Soc., 54, 2741 (1932). (6) C. M .French and K. H. Glover, Trans. Faraday SOC.,51, 1418 (1955).
Volume 70,Number 9 September 1066
NOTES
3008
tally by the usual procedure. The dielectric constants were €150 200.1, €250 182.4, €350 174.3, and €450 167.1 a t the temperatures indicated and were those reported by Leader and Gormley.' The values of viscosities a t the different temperatures were 7160 = 0.0199, 7250 = 0.0165, 7350 = 0.0142, and 7450 = 0.0123 The values of the limiting transport numbers, t+O, of K+, at various temperatures, obtained from the plot of the Longsworth function against concentration, are also given in Table I under the concentration heading 0.00 M .
Table 11: Mobilities of Some Ions in N-Methylformamide a t Different Temperatures Ionic mobility at-------
Ion
Na + K+ CS
+
(Cz&)aN
+
Picrate-
c1-
BrI-
Results and Discussion As can be seen from Table I, the variations in the transport number, t+, of K ion in N-methylformamide are very much similar to those in formamide3 and in K-methyla~etamide;~i.e., t+ decreases with increase in concentration and increases with increase in teniperature. The limiting transport number of potassium ion, i.e., t+*(K+)! increases from 0.4945 at 15" to 5290 at 45". This behavior is opposite to that in aqueous solutions in which t+"(K+)decreases slightly with rise in temperature. Recently, Gill9 has reported similar behavior of the cationic transport number of KN03 in liquid ammonia in which t+"(K+)has been found to decrease with rise in temperature in the range -65 to -45", although t + ' ( ~ ~ + )t +, " ( L i + ) , and ~ + " ( N H , + ) increase with rise in temperature as t + " ( ~ + )(KBr) does in K-methylformamide. It may be noted that t + " ( ~ +increases ) beyond 0.5 with rise in temperature. This is a little unusual although such values of the transport number have been reported in the literature.1°
Ionic Mobilities The limiting cationic transport numbers at different temperatures can be used to calculate the ionic mobilities from the available electrolytic conductance data6 in this solvent and making use of the usual Kohlrausch law of the independent migration of ions. The ionic conductivities at infinite dilution of some ions thus obtained are given in Table 11. Since no ionic conductance data are available jn the literature, it is not possible to verify the values given in Table 11. However, they seem to be reasonable if they are compared with the corresponding values in formaniide and in K-methylacetamide. Since the tetrahedral structure present in water is missing in these solvents, the structure-breaking effect of the larger ions like K + is also missing in these solvents and SO all the ions behave normally. I n view of the lack of sufficient and appropriate electrolytic, and hence the ionic, conductance data in this solvent, it is not possible The Journal o j Physical Chemistry
150
25'
17.59 18.05 19.90 21.52 11.28 16.88 18.46 19.38
21.56 22.13 24.39 26.20 13.08 19.70 21.56 22.76
350
450
...
...
27.62
32.15
. . I
...
... . . I
... ...
... ...
25.38
28.60
...
...
to make a reasonable estimate of the solvation of ions as was done in NMA.4 This aspect will be examined later when the required data are available.
Acknowledgnient. A grant from the Society of Sigma Xi and RESA Research Fund of the United Stat,es of America for the purchase of the solvents (NMA, NAIF, and NJIP) is very much appreciated. ~
~~~
~~~~~
~
~
(7) G . R. Leader and J. F. Gormley, J . Am. Chem. SOC.,73, 5731 (1951). (8) R. Gopal and S.A. Rizvi, J . I n d i a n Chem. SOC.,43, 179 (1966). (9) J. B. Gill, J . Chem. Soc., 5730 (1965). (10) B. E. Conway, "Electrochemical Data," Elsevier Publishing Co., London, 1952, p 166.
Photooxidation of Perfluoroethyl Iodide and Perfluoro-n-propyl Iodide'"
by Dana Marsh and Julian Heicklen'b Aerospace Corporation, El Segundo, California (Received February 15, 1966)
In earlier reports, the oxidation of CF? and CFClz3 radicals was examined. In the former case, the only carbon-containing product was CF20, whereas in the latter case only CFClO was found. In the presence of HI, the results were unchanged. In this work, we extend the oxidation studies to C2Fs and n-C3F7 radicals in order to determine the products of reaction and the nature of the intermediates. In both cases, the major product is CF20. (1) (a) This work was supported by the U. S.Air Force under Contract No. AF 04(695)-669. (b) To whom requests for reprints should he sent. (2) J. Heicklen, J . Phys. Chem., 70, 112 (1966). (3) D.G, Marsh and J. Heicklen, ibid., 69, 4410 (1965).
