3 2-1
I
in
31.2
0
WSERVED
0
PREDICTED PROPANE RESONANCES
60
PROPANE RESONANCES
I
t
70
00
i
-
5
"F CHEMICAL SHIFT (p.p.rn. Upfield from CFCIS)
I 9 F CHEMICAL SHIFT (p.p.rn. Upfield from CFCII)
Figure 1 . Variation of fluorine chemical shift for internal -CF2group of perhalopropanes
Figure 2. Variation of fluorine chemical shift for the terminal CF groups of perhalopropanes
electronegativity (9, 11); however, the magnitude of the J values found here reflect their dependency upon the orbital overlap ( 4 , 7') for near neighbors as well as fluorine-to-fluorine dihedral angle. lT7henthere is but one fluorine atom on a given end of the molecule, it reacts with the central pair to give a J value of greater than 1 C.P.S. However, when there are two or three terminal fluorine atoms, their interaction with the central pair is weak and the J value is only 1 c.p.s. Strong four-bond interactions are displayed in this series by the 13.6, 8.9, and 7.3-c.p.s. couplings of compounds with fluorines on both terminal carbon atoms.
ACKNOWLEDGMENT
The author thanks J. W. Clark and L. 0. Moore for preparing these compounds and V. A. Yarborough and J. F. Haskin for interest and support on preparation of the manuscript. LITERATURE CITED
(6) RIahacsi, E., J . Chem. Educ. 41, 38 (1964). (7) McConnell, H. RI., J . Chem. Phys. 24, 764 (1956). ( 8 ) Meyer, L. H., Gutowsky, H. S., J . Phys. Chem. 57, 481 (1953). (9) Ng, S., Sederholm, C. H., J. Chem. Phus. 40. 2090 (1964). (10) ivhite', H. F.~, AN.4L. CHEM. 36, 1291 (1964). \ - - - - I
(1) ~, Arnold. J. T.. Packard. M. E.. J . I
-
Chem. Phys. 19,'1608 (1951). (2) Brame, E. G., Jr., ANAL.CHEM.34, 591 (1962). (3) Dietrich, &I.W., Keller, R. E., Zbid., 36, 258 (1964). (4) Eaton, D. R., Josey, A. D., Sheppard, W. A., J . Am. Chem. Sac. 8 5 , 2689 (1963I. j-.__,.
(5) Filipovich, G., Tiers, G. 5'. D., J . Phys. Chem. 63,761 (1959).
(11) Zbid., 37,403 (1965). HORACE F. WHITE^ Research and Development Dept. Chemicals Division Union Carbide Corp. South Charleston] W. F'a. Present address, Dept. of Chemistry, Portland State College, P.O. Box 751, Portland, Ore. 97207.
Polarography of Salicylate Complexes of Cadmium in Aqueous Mixtures of Formamide SIR: The use of polarographic data for the study of complexation is well known (6). DeFord and Hume ( 1 ) first derived equations for the calculation of successive stability constants from polarographic values; subsequently, a number of workers have utilized the technique and have modified some of the details to obtain more precise results. I n particular, Irving (2) has reviewed the approach very thoroughly. Polarography of cadmium complexes in nonaqueous media has been studied primarily by Migal and his coworkers (6-10) and by Khotsyanovskii and Kudra (3, 4). During the polarographic study of cadmium in various complexing agents, it was found that cadmium reduces reversibly in salicylate solution, and the reduction was diffusion-controlled. The present paper deals with the composition and stability of the formation of salicylate complexes of cadmium in aqueous and aqueous mixtures of f ormamide. 626
ANALYTICAL CHEMISTRY
EXPERIMENTAL
An L.P. 55 Heyrovsky system polarograph was used manually for obtaining the current-potential curves. The capillary characteristics for the open circuit
I
?
were m = 1.745 mg. per second and t = 4.2 seconds. A constant temperature of 30' 5 0.01' C. was maintained by means of a Haake type ultra thermostat. Purified hydrogen was used for removing dissolved oxygen from the solutions. ,411 the half-wave potentials refer to saturated calomel electrode. Reagent grade chemicals were used. Solutions containing 0.75mN cadmium and different concentrations of sodium salicylate (0.1M to 1.0M) were prepared and a requisite amount of potassium nitrate was added to keep constant ionic strength ( p = 1). Triton-XIW supplied by Rohm and Haas Co. was used as maximum suppressor. The above sets were also carried out in 20, 40, and 60% formamide (by volume). Above 60% of formamide, the experiments could not be performed because of the insolubility of potassium nitrate. RESULTS A N D DISCUSSION
0.4
0.8
0
Log c x
Figure 1 .
Plot of
€I/,
vs.
log C,
I n each case, a single well defined reduction wave appeared. The plots of log i / i d - i us. E d . e . were found to be
i
loo
16 I
5
B 60
i 3
19
U
t X
Y
t'8
0.8
0.6
0.4
0.9
0
Log cx +
Figure 3. Percentage distribution of various species in cadmium-salicylate system 4
Cd
+2
A (Cd CoHjOH COO)' Cd (CeHbOH COO)*
r Figure 2.
I
I
I
0.4 0.6 Cx (Salicylate concn., M ) *
0.2
I
1
0.8
1 .o
F j ( X ) plots for cadmium-salicylate system e o:! [XI A FI Fz
[XI [XI
linear with a slope of 32 i 2 mv., showing the reversibility of the reduction (n = 2 ) . A plot of Eliz US. log C x (Figure 1) was found to be a smooth curve , indicating the presence of more than one complex. The classical method of Lingane ( 5 ) cannot be applied here. As such, the DeFord and Hume method (1) as modified by Irving (2) has been used. The overall stabilities were calculated by the graphical extrapolation method. The results have been recorded in Table I. The plots of F,( [ X I ) L'S. C, are shown in Figure 2 . The stability constants of cadmium salicylate complexes in aqueous and aqueous formamide mixtures are tabulated in Table 11. The percentage dis-
tribution of cadmium present in various forms as a function of salicylate concentration in aqueous medium has been presented in Figure 3 . It is clear from Table I1 that cadmium fonns two complexes with salicylate ion in aqueous mixtures. I n aqueous formamide mixtures, the number of complexes also remains a t two, but the overall stability constants increase. I n 20% formamide, PI and P 2 have the same values as in water. However, as the percentage of formamide is increased, the stability increases. I n 60% fonnamide the overall formation constants are twice as large as those in water. This increase in stability constants may be attributed t o the following two
factors: (a) solvat'ion effect, and (11) dielectric constant. Recently Zolotukhin and Galanets (11) have reported t'he complex fonnation of Cd+2with salicylate ion in which they reported only one complex having a stability constant of 9 in aqueous medium. We have obtained two coniplexes with PI = 4 and Pz = 16. The discrepancy is due to the study a t the low concentrations of ligand (0.16X to 0.5N) by these workers, and the different method of calculation. We have studied the comples formation between 0.1 and 1Jf ligand concentration and have calculated t'he overall formation constants hy the DeFord and Hume method for calculating successive format'ion constants. Since the reduction is diffusion-controlled, cadmium can be determined polarographically in salicylate solution. ACKNOWLEDGMENl
The authors express their t'hanks to R. C. Nehrotra for providing facilities. LITERATURE CITED
(1) DeFord, D. D., Hume, D. Chetn. Soc. 73, 5321 (1951).
Table I.
cx (moles) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
1.0
Analysis of the F j ( [ X I ) Function for the Cadmium Salicylate System in Aqueous Medium
(-V
El 12 S.C.E.)
US.
0.5828 0.5872 0.5927 0.5965 0.6008 0.6042 0.6080 0.6105 0.614 0.6172
id
( divisions)
63.0 61.0 58.0 55.0 53.0 51.5 49.5 48.0 46.5 45.5
FO ( [XI
FI ( [XI)
...
1'.4'69 2.355 3.221 4.793 6.431 8.884 11.14 13.39 20.31
4.69 6.77 7.73 9.48 10.86 13.14 14.5 16.16 19.31
Fz ( [XI )
...
14.9 17.8 15.1 15.7 15.5 16.5 16.4 16.2 16.1
Table II. Values of Stability Constants of Formation for Cadmium Complexes of Salicylate
Stability constant PI
Pz
Aqueous medium 4 ,0 16.0
20% 4.0 15.5
Formamide 40% 6.0
18.5
60 % 8.0
30.0
K.,J . Am.
(2) Irving,,, H., "Advances in Polarography, Proc. Second International Congress on Polarography, Cambridge, 1959, 1-olume I, p. 42. (3) Khotsyanovskii, 0. I., Kudra, 0. K., C.A. 54, 196087: (l(358). (4) Khotsyanovskii, 0. I., Kudra, 0. K., Khim. i Khim. Tekhnol. 1, 43 (1958). (5) Lingan:: J., Kolthoff, I. AI., "Polarography, J701. 1, p. 214, Interscience, hew York, 1955. (6) Migal, P. K., Pushnyak, A. S., Russian J . Inorg. Chetn. 5 , 293 (1960). (7) Migal, P. K., Grinberg, N., Ibid., 6 , 369 (1961). (8) Ibid., p. 675. (9) Ibid., 5 , 70 (1960). (10) Rligal, P. K., Serova, G. E'., Ibid., 7.827 (1962). (llj Zolotukhin, Y. K., Galaneta, Z. G., C.A. 62, 4909a (1965). J. N. GAUR N. K. Gosw.im D. S.Jam Chemical Laboratories University of Rajastham Jaipur, India Junior' Research Fellowships granted to D.S.J. and N.K.G. by C.S.I.R. VOL 38, NO. 4, APRIL 1966
627
