sublimed salicylic acid within the sensitivity of the method was, on the 100 P . P . ~of. hydroxyb benzoic acid. On rare occasions p-hydroxyisophthalic acid was observed a t the limit of detection. The possibility does exist that an impurity may have been overlooked in this analysis. However, from examination of salicylic acid mother liquors, it concluded that no other impurities Of significant ?Oncentration were present.
LITERATURE CITED
( 1 ) Bailey, R. w., AKAL.cHEM. 36, 2021 (1965). ( 2 ) Lederer, AI., Australian J . Sci. 11, (3)208 Marvel, ( 1949).C. S.,Rands, R. D. Jr., Chem. sot, 72, 2642 (1950). J. (4)Pastuska, G., Z. Anal. Chem. 179, 355 (1961). ( 5 ) Shcherbachev, K. D., Khim. Form. Prom. 1934 ( 5 ) , 37. ( 6 ) Sinton, F. C., J . Assoc. Oflc. Agr. Chemists 13, 344 (1930).
(7) Skelly, N. E., ANAL. CHEM.33, 271 (1961). (8) Skelly, N . E., Crummett, W. B., Ibid., 35, 1680 (1963). (9) Van Oame, H. C., J . Assoc. Oj'ic. Agr. Chemzsts 43, 593 (1960).
NORMAN E. SKELLY Special Services Laboratory The Dow Chemical Co. Midland, Mich. Division of Analytical Chemistry, Winter Meeting, ACS, Phoenix, January 1966.
Stability Constants of Some Dihydrazide Complexes of Cadmium SIR: A recent polarographic investigation of the complexation of cadmium by alkyl and aryl carboxylic acid hydrazides (6) led to the conclusion that the complesing moiety was the neutral hydrazide rather than the anion, as had been found for other metal ions such as copper (1, 3 ) . At least three soluble cadmium complexes were found, and distinct differences in stability between the alkyl and aryl comple.;es were noted. Therefore, it a1)peared that, in the case of cadmium, the coniplexing hydrazide ligand was behaving like an amine. I n a manner analogous to the situation with organic mono- and diamine complexes, it was felt that the complelation of metal ions by dicarboxylic dihydrazides might be significantly different from that found with monohydrazides. Therefore, a study of the behavior of cadmium in the presence of some dihydrazides was undertaken. The success obtained with the polarographic approach for the determination of complexity constants in the previous study (6) led to its use in the present case. The method of DeFord and Hume
( 2 ) was utilized to calculate stability constants from the polarographic data obtained. EXPERIMENTAL
Chemicals. Carbohydrazide, succinic dihydrazide, and adipic dihydrazide (Olin Mathieson Chemical Corp.) were recrystallized twice from water, dried a t 100" C., and stored under dry nitrogen. All other chemicals were reagent grade and were used without further purification. Apparatus and Procedure. Detailed descriptions of the apparatus and procedure have been given previously (6). RESULTS AND DISCUSSION
Previous studies on the complexation of cupric ion by isonicotinic acid hydrazide established that the over-all reaction involves release of protons (1, 3 ) . Titration of the hydrazide with copper solution lowered the pH about 0.6 unit below that for the corresponding copper alone. The reaction of monohydrazides with cadmium, however, did
not seem to be of the same type; no release of protons was found (6). I n the present instance, titration of the dihydrazides with C d f 2 produced the data shown in Figure 1. The p H of the solutions did not drop below that for Cd+2 itself. Therefore, any reaction of the dihydrazides with cadmium must occur without release of protons and, again, through a neutral hydrazide species. Polarographic studies of complexation are well established ( 5 ) . If single, strong complexes are involved, a simple plot of Elidus. log ligand concentration can give sufficient information for elucidation of the complex. With successive eomplexes, more elaborate calculations are required. DeFord and Hume ( 2 ) first derived the necessary equations for calculation of the stability constants of consecutive complexes. For a reversible reduction of a complexed metal ion to the amalgam, they have defined functions, F J ( X ) , such that
-+
EH,V.
Carbohydrazide t
Carbohydrazide
I
Cd++Blank
I
I
I
I
-
1.5
I -1.1
I
- 8.8
I 0
lag [Hydrarid4
Figure 2. Half-wave potential of cadmium as a function of log hydrazide concentration
936
ANALYTICAL CHEMISTRY
fJXl x
19
[Succinic Dihydraxid.]
Figure 4. Values of F&X), Fl(X), and Fz(X) for cadmium in succinic dihydrazide solutions Figure 3. Values of F d X ) , Fl(X), and Fz(X) for cadmium in carbohydrazide solutions
and
ficients may be equated to unity (4, were assumed to fit a linear regression with the general form, and the stability constant thus obtained will include any activity coefficient F J ( X ) = K J m(Cxfx) (5) factor. Figure 2 shows the plot of Eli2 US. where m is the slope of the line. Calculations, using this technique, gave log hydrazide concentration for the systems studied, In all cases, a curved formation constants of K3 = 408,453 line, representative of the formation and K 4 = 182,002. From the plots of successive complexes, was found. prepared, a definite slope was noticed Plots of Fo ( X ) ,F 1 ( X ) ,and F&Y) for with the F 3 ( X ) data, while the F 4 ( X ) carbohydrazide are shown in Figure 3, plot was essentially horizontal, indicatWhen these curves were expanded in ing that the 4 : 1 complex probably is the scale and extrapolated to C X ~ X = 0, highest complex present under the conditions of the study (2). formation constants for the first two consecutive complexes were found to be In the case of carbohydrazide, the K1 = 500and K z = 4,500. value for K4was found to be of the same Curves also were prepared for F3(X) order of magnitude as that for K s , and F4(X),but these showed a large although the latter was approximately amount of scatter. Graphical extratwice that of the former. I n addition, polation of these curves was difficult; the slopes of the two curves were difbut when expanded scales were used, ferent; the F,(X) plot had a definite formation constants of K3 = 420,000 slope, while F 4 ( X ) was horizontal. and K4 = 240,000 were estimated. In These data led credence to the presence order to obtain better values, a least of a 4: 1 complex, which may not be as squares method ( 7 ) was used to evaluate strong as the 3 :1. the F 3 ( X ) and F 4 ( X ) data; the data When the dihydrazide molecule is
+
and
Fz(X)
=
F,(X) -
The values, (E1,Jaand (El/z)c, are the half-wave potentials for the unconiplexed and complexed metal ions, respectively; and I , and I , are the diffusion current constants for the same species. The formation constant of the zero complex, KO,is defined as one. Terms, fs and fz, are the activity coefficients of the uncomplexed metal and the ligand; and C, is the concentration of the latter. K 1 is the stability constant of the 1: 1 complex, and fmz, the activity coefficient of the complex. The intercept of a plot of F J ( X ) us. C,fz, when extrapolated to C, = 0, is equal to KJ/~,,,.. The activity coef-
VOL. 30, NO. 7, JUNE 1966
937
FJ(X) x lo* 300.-
I
0
1
0.2
1
I
0.4 0.6 buccinic Dihydrarid.]
I
I
0.6
10
938
ANALYTICAL CHEMISTRY
-
100
-
I
0.2
Figure 5. Values of &(X) and F4(X) for cadmium in succinic dihydrazide solutions
expanded by inserting an alkyl chain between the hydrazide groups, the results are somewhat different. Plots of F o ( X ) , F I ( X ) , and F 2 ( X )for succinic hydrazide are shown in Figure 4. Extrapolation of these curves on an expanded scale gave values of K1 = 80 and K z = 4,500. These are very similar to the corresponding acetic hydrazide values (6). Figure 5 shows the F 3 ( X ) and F4(X) plots for succinic dihydrazide. Closer examination of these plots gave stability constants of K 3 = 98,000 and K 4 = 90,000, with the K ( X ) curve horizontal. Comparison of the K S value with the corresponding acetic hydrazide value disclosed a 4-fold increase in stability with the succinic dihydrazide. Furthermore, the K4 value for succinic dihydrazide was the same as the K 3 value , which again adds support (within for a 4 : 1 complex with this dihydrazide. Further expansion of the chain of the dihydrazide to adipic dihydrazide gave enhanced stabilities. Figure 6 shows the F o ( X ) and Fl(X), while Figure 7, the F 2 ( X ) ,F 3 ( X ) , and F4(X) plots for adipic dihydrazide. Values for the stability constants were found to be K1 = 230, Kz = 16,500, K3 = 160,000, and K 4 = 395,000. From all these data, i t appears that, as one increases the molecular weight of the alkyl dihydrazide, the stability of the complexes formed is increased and the likelihood of forming higher complexes also increases. The case of carbohydrazide is somewhat different in that it is possible to postulate formation of a six-membered ring with both hydrazide functional groups entering into the complexation reaction.
200
0.4 [Adipic Dihydraride]
I
1
0.6
0.6
Figure 6. Values of Fo(X) and F l ( X ) for cadmium in adipic dihydrazide solutions
I/
/
[Adipic Dihydraridd
Figure 7. Values of Fz(X), F3(X), and F4(X) for cadmium in adipic dihydrazide solutions LITERATURE CITED
(1) Albert, A., Ezperientiu 9, 370 (1953). (2) DeFord, D. D., Hume, D. N., J . Am. Chem. SOC.73, 5321 (1951). (3) Fallab, S., Erlenmeyer, H., Helv. Chim. A’ctu 36, 6 (1953): (4) Hume, D. N., DeFord, D. D., Cave, G. C. B.. J . Am. Chem. SOC.73. 5323 (1951). ( 5 ) Kolthoff, I. M., Lingane, J: J.,
“Polarography,” 2nd ed., Interscience, New York, 1952.
( 6 ) Krivis, A. F., Supp, G. R., Doerr, R. L., ANAL.CHEM.37, 52 (1965). ( 7 ) Snedecor, G. W., “Statistical
Methods,” 4th ed., Iowa State College Press, Ames, Iowa, 1946.
ALANF. KRIVIS GEORGER. SUPP RICHARD L. DOERR Chemicals Division Research Olin Mathieson Chemical Cow. New Haven, Conn.
