NOTES
4070
Further studies, on the cyclization of the open-chain quinone of adrenalin, have also yielded encouraging results. Ball and Chen have measured, by means of a flow technique and chemical oxidation, the cyclization rate constant of the adrenalin quinone as being independent of pH at pH >6 and equal to approximately 10 sec-'." The values of k measured by the RDE at pH 6.3 and 7.15 are 19 f 6 sec-1 and 20 f 4 sec-', respectively. ( ~ L I N / w % " ~ ) ~ = o was obtained from runs at pH 2.75, where k is effectively zero. In the electrochemical study of Hawley, et aZ.,12 IC's at pH > 5 were too fast to be measured by the chronoamperometric terhnique since this technique and the others mentioned previously are not easily applied for IC >1.0 sec-I. The rotating disk electrode appears to be a very valuable tool in studying the kinetics of homogeneous chemical reactions of electrochemically generated intermediates. Using the limits of w as 5 and 300 radians/ see, first-order rate constants jn the range of 0.3-100 sec-' may easily be measured. Studies are now in progress with the RDE on the kinetics of other homogeneous chemical reactions coupled to electrochemical charge transfer. The effects of such chemical reactions on diffusion coefficient measurements and on correlations of electrochemical parameters with molecular orbital theory are also under investigation using the RDE. Acknowledgments. This work was supported by the National Science Foundation through Grant GP-5079 and this support is gratefully acknowledged. The authors wish t o express their appreciation to the University of Kansas Computation Center and to Donald W. Leedy for technical assistance. (11) E. G. Ball and T. Chen, J . Biol. Chem., 102, 691 (1933). (12) Sf. D. Hawley, S. Tatwawadi, S. Piekarski, and R. N. Adams, submitted for publication.
Studies on Solutions of High Dielectric Constant. IX. Cationic Transport Numbers of KBr in N-Methylpropionamide at Different
Temperatures and Concentrations'
by Ram Gopal and 0. N. Bhatnagar* Chemistry Dewrtment, Lucknow Unieersity, Lucknow, India (Receited J u n e 94,1966)
In ContiIluation with our previous work on the cationic transport numbers in solvents of high dielectric T h e Journal of Physical Chemistry
constant like formamide, N-methyla~etamide~ (NMA), and N-methylformamides (NMF), studies have now been extended to N-methylpropionamide (NMP), which has a dielectric constant of 164.36at 30". Despite its stability, it does not appear to have received adequate attention from the workers in this field. Dawson and co-workers7have reported the limiting equivalent conductivities of the halides of sodium and potassium from 30 to 60", at 10" intervals. Hoove9 reported the limiting equivalent conductance of KC1 in this solvent from 20 to 40". However, in the absence of limiting ionic conductance data, our understanding of the ion-solvent interaction in this solvent would be more limited. It is, therefore, desirable to have accurate ionic transport number data in order to evaluate the ionic mobilities. Strangely enough, no one appears to have attempted even the usual indirect method, used by Dawson and co-workersg for evaluating the ionic conductances in some solvents in which the transport number data have not been available. The present note reports the measurements of the cationic transport numbers of potassium bromide in NRIP at 30, 40, and 50", at different concentrations by the Hittorf method. From the data obtained, the limiting ionic conductivities have been evaluated from the available electrolytic conductance data at infinite dilution. Experimental Section Eastman Kodak N-methylpropionamide (specific conductivity = mho) was first dried over freshly ignited quicklime and the supernatant liquid was distilled under reduced pressure. The process was repeated until the distillate was found to have a specific conductivity of (6-8) X lo-' mho. It was stored in dark amber bottles in the drybox. The conductivity of the purified samples was checked from time to time. Changes in conductivity were found to (1) Work supported by the Council of Scientific and Industrial Research (CSIII), India. (2) Junior Research Fellow, CSIR, India. (3) R. Gopal and 0. N. Bhatnagar, J. Phys. Chem., 68, 3892 (1964). (4) (a) R. Gopal and 0. N. Bhatnagar, ibid., 69, 2382 (1965); (b) Tewari and Jauhari ( J . Phys. Chem., 70, 197 (1966)) have recently reported transport numbers-of KC1 in formamide (25') and in Nmethylacetamide at 40" without referring to our work already published in this journal. There appears t o be a deliberate attempt to suppress information already available in the literature. (5) R. Gopal and 0. N. Bhatnagar, ibid., 70, 3007 (1966). (6) G. R. Leader and J. I. Gormley, J. Am. Chem. SOC.,73, 5731 (1951). (7) L. R . Dawson, et al., ibid., 79, 298 (1957). (8) T. B. Hoover, J . Phys. Chem., 68,876 (1964). (9) L. R. Dawson, et al., J . Am. Chem. SOC.,79, 3004, 5906 (1957).
NOTES
407 1
be negligible and the solvent appeared to be quite stable. AR grade potassium bromide was recrystallized from conductivity water, thoroughly dried, and stored in a vacuum desiccator. It was subsequently used for preparing solutions. The transport number cell and the electrodes, used in the experiments, were similar to those used for solutions in NMA.4* Solutions of KBr were prepared in freshly distilled samples of NMP. The experimental procedure, including the precautions to avoid atmospheric moisture while preparing solutions and during the course of experiments, were the same as described previously. The transport numbers, thus obtained at different temperatures and concentrations, are summarized in Table I.
Table I: Transport Numbers of K + in KBr, Dissolved in NMP, at Different Temperatures and Concentrations Concn, M
--_---
0.000 0.075 0,100 0.150 0.200 0.250
30'
0.4320 0,4200 0.4182 0.4132 0.4104 0.4076
Transport number at-----40°
0.4370 0.4249 0.4221 0.4195 0.4143 0.4113
50'
0.4425' 0.4313 0.4286 0.4236 0.4202 0.4179
' From the graph.
From the values of transport numbers, given in Table I, the limiting transport numbers, t+O, of K+, a t different temperatures, have been obtained by the Longsworth procedure,1° as followed in the cases of the solutions in f~rmarnide,~ NMF,5 and reported earlier. The values of viscosity, dielectric constant, and the limiting equivalent conductance at different temperatures needed to calculate the Longsworth function were as follows: viscosity (in poise): vN0 = 0.04568, 9400 = 0.03451, 9 5 0 0 = 0.02825; dielectric constant: €300 = 164.3, €400 = 148.9, €500 = 133.4; limiting conductance: X'NO = 12.40, Xoa0 = 15.90, = 19.80 (as given by Dawson and coworkers"). The values of the limiting transport numbers of K+, thus obtained, are also given in Table
I. Results and Discussion It is evident from Table I that the cationic transport number, t+, at any temperature, decreases with increase in concentration, C , and increases with increase in temperature, a behavior similar to that found in
f ~ r m a m i d e ,N-methylf~rmamide,~ ~ and in N-methyla ~ e t a m i d e . ~Potassium ~ ion, K+, with a transport number less than 0.5, has a positive temperature coefficient for t+. The ion-solvent interaction in NMP should, therefore, be similar to that in formamide, NMF, and NMA. It is not possible to calculate the solvation of ions in NMP since the conductance of tetraalkylammonium ions, needed for this purpo~e,~a are not available in this solvent. Ionic MobiEities. The values of the limiting transport numbers, t + O , at 30, 40, and 50', have been used to calculate the ionic conductivities from the appropriate available electrolytic conductance data a t infinite dilution.' In order to evaluate the ionic conductance at 60°, at which some electrolytic conductance data are available in the literature, the required limiting transport number, t+', was obtained from the extrapolation of the t+' vs. t (temperature) curve to 60'. The curve was found to be almost a straight line. The value of t+', corresponding to go', was found to be 0.4475. The ionic mobilities of some ions, thus obtained, are given in Table 11.
Table 11: Mobilities of Some Ions at Different Temperatures Ion
Na
+
Kf c1Br-
I-
__--
Ionic mobility at-
30°
40'
50'
60"
5.06 5.36 6.24 7.06 8.34
6.45 6.95 7.95 8.95 10.45
8.06 8.76 9.94 11.04 12,94
10.01 10.91 11.99 13.49 15.69
It may be noticed from Table I1 that the ionic mobilities are very low indeed and are similar to those in formamide, NMF, and NMA. The temperature coefficient of conductance is about 2.70joldeg which appears to be slightly higher than those in formamide, NAIF, and NMA. The conductivities of Na+ and K+ are almost the same, as in the other solvents of this family, indicating no abnormal ion-solvent interaction which occurs in water in which the structurebreaking effect of K+ enhances its mobility abnormally. Acknowledgment. The authors' thanks are due to the Council of Scientific and Industrial Research, India, and to the American Society of Sigma Xi, for financial assistance. (IO) L. G . Longsworth, J . Am. Chem. Sac., 57, 1185 (1935). (11) L. R. Dawson, et al., ibid., 79, 298 (1957).
Volume 70,Number 12 December 1966
