Polarographic Study of Some Hydrazide Complexes of Cadmium ALAN F. KRIVIS, GEORGE R. SUPP, and RICHARD L. DOERR Chemicals Division Research, Olin Mathieson Chemical Corp., New Haven, Conn. The complexation of Cd+' by acetic and isonicotinic hydrazides and diacetyl hydrazine has been studied polarographically. Diacetyl hydrazine did not form a detectable complex, while the other hydrazides each formed at least three consecutive, soluble complexes. The stability constants of the various complexes were calculated from the data. The Cdf2-hydrazide complexes appeared to involve the neutral hydrazide molecule as the complexing species. This behavior is distinctly different from the previous reports of some metal-isonicotinic hydrazide systems which have shown that the anionic form is involved.
C
hydrazides have a \vide variety of applications varying from biological-ljhariiiaceutical activity to heavy cheniical uses and, therefore, the importance of this group of compounds has grown. During an analytical study to develop a universal method for carbosylic acid hydrazides (8),complexation of metal ions by hydrazides appeared likely. Since the formation of metal hydrazide complexes would be important in many of the applications for the materials, a study of some hydrazide complexes was undertaken. The only literature references to hydrazide complexes which could be found were the work of ;Ilbert' ( I ) , and of Fallab and Erlenmeyer (3) on the coniplexes of isonicotinic acid hydrazide. -4lbert used a potentiometric method to determine t,he stability constant? for Co+?, Cu+2, Xi+2, and Zn+*complexes. I n each case, a 1 : l coniples was found with the log of the stability constants as follows: C o t 2 , 4.8; Cu+*,8.0; Sit2, 5 . 5 ; Zn+2, 5.4. Fallab and Erlenmeyer determined the copper conii)les stabilit'y constant sl)ectrol)hotometrically, using Job's method of continuow variations; a 2 : 1 comples was found with a constant a t 1.7 X lo5. The use of polarographic data for the study of complexation is well known (6). ; I siiiilile plot of the shift in EllP2)s. log ligand concentration suffices for strong, single complexes, while more elaborate calculations are necessary for multiple coniplese..j. DeFord and Huiiie ( 2 ) first derived equations for the cal52
ARBOKPLIC ACID
0
ANALYTICAL CHEMISTRY
culation of succesqive stability constants from polarokraphic values. Subsequently, a number of workers have utilized the technique and have modified some of the details to obtain more precise results: in particular, Irving (5)has reviewed the approach vel y thoroughly. The polarographic technique seemed to produce excellent iesults and, therefore, a polarographic investigation of the possible complexation of cadiilium by some simple hydrazides was undertaken. EXPERIMENTAL
Chemicals. =111 inorganic chemicals were reagent grade and were used without further purification. .icetic hydiazide (Olin Xathieson Chemical Corp.) r\ ab redistilled under vacuum and stored under dry nitrogen. Diacetylhydrazine (I) (Olin Xathie-on Chemical Corp.),
[CH3CSHSHCCH3] (1) was recrystallized ta ice from water, dried a t 100" C., and also itored under dry nitrogen. Isonicotinic hydrazide (Eaqtnian Khite Label) was u.ed without further 1)urification. Gelatin (Fizher Scientific Co.) was used as a maximum suppre>sor, and purified and equilibrated nitrogen v a s used t o remove oxygen from the solutiom. Apparatus. X Sargent Model XXI polarograph was u>ed in conjunction with a therrnostated H-cell (25' i. 0.1" C.) containing a qaturated calo-
me1 reference electrode ( 7 ) . The agar salt bridge connecting the reference and sample cells was prepared with sodium chloride, as was the reference cell, to avoid precipitation of perchlorate salts from the test solution. The resistances of the two cells and electrode used were 138 and 175 ohms, as measured by a General Radio 1650-d impedance bridge. -411 polarogranis were run with the damping control in the "off" position and the current sensitivity a t the 0.04 pa./inni. setting. The capillary used had a constant of 1.98 mg.2t3 second1i6a t 25 em. of Hg, in 1.11SaC104 at -0.562 volt. Procedure. A series of I n i M cadmium perchlorate solut'ions containing varying concentrations of hydrazide and 0.005% gelatin were prepared. Sodium perchlorate was added t o maintain the ionic strength at 1111. The thoroughly mived solutions were transferred to the cell and deoxygenated for 10 minutes with nitrogen. The mercury head was adjusted to 25 em. and the polarograms were run. -411 polaroqrams were started at an initial voltage of 0.4 volt, which was measured accurately with a Rubicon Portable Precision potentiometer. The span used wa5 0.5 volt, and the final voltape was meawred with the potentiometer. The maxima of the recorder traces were u\ed to measure currentz. Halfwave potential. were obtained from plots of E vs. log %,'(id - i), and a correction for the iR drop wa4 applied. .ill of' the plot4 of the log term us. voltage ere ,traight lines with slopes which agreed with the theoretical value: the mean .lope for the qeries was 0.0301 =k 0.0006.
PA 8
Figure 1. Half-wave potential of cadmium as a function of log hydrazide concentration
0.65-
A.
Acetic h y d r a z i d e Isonicotinic h y d r a z i d e C. Diacetylhydrazine 8.
I -1
0
i
i
-0 5
0.0
Log H y d r a z i d e Concentration
i
*8,5
15000
Fi(XI
12000
Figure 2. Values ‘of Fo(X) and FI(X) for cadmium in acetic hydrazide s o b tions
forniation constant of the zero complex, is defined as unity. f a and f z are the activity coefficients of the uncomplexed metal ion and the coniplexing ligand, respectively, and C, is the concentration of ligand. K1 is the formation constant of the 1:1 complex and the activity coefficient of the complex. When a plot is made of F , ( X ) us. CIfz and extrapolated to C, = 0, the intercept is equal to K,/ fmz. The values of the activity coefficients are usually not known, but since the ionic strength is maintained constant, they should remain constant; and one may equate them to unity (4) and remove them from the equations. The formation constants thus obtained will not be the true thermodynamic constants, but will include an activity coefficient factor. Figure 2 shows the plots of F , ( X ) and F1(X) and Figure 3, the plots of F 2 ( X ) and F 3 ( X ) us. acetic hydrazide concentration. E\;trapolation of es-
F
I RESULTS AND DISCUSSION
The plot of Ellzas a function of log hydrazide concentration for the three hydrazides under study is s h o m in Figure 1. Essentially, no change in El12for Cd+2 could be found when the diacetyl hydrazine concentration was varied over the range of 0.1 to 1.0-If; these data indicate no measurable complexation by diacetyl hydrazine. =icetic and isonicotinic hydrazides, however, showed the curvature expected + w e comfrom the formation of succei,’ plexes. KO precipitate was noticed in any of the solutions during or after the measurements. DeFord and Hunie ( 2 ) have derived a series of equations to relate polarographic data t o complexity conqtants. For the reversible polarographic reduction of a compleyed metal ion to the metal amalgam,
+
L1fXYl+(n-i*)ne ++ M(Hg)
+ jX-b
0
metal ion must occur through the primary nitrogen. The primary hydrazide formed three complexes, while the symmetrically disubstituted hydrazine did not appear to form any. .In the latter compound, only secondary nitrogens are present and, since no coniplexation could be detected, complex formation must require the presence of the primary nitrogen. The effect of resonance factors on the complexation was studied also. -icetic hydrazide is a small alkyl hydrazide, and it was felt that an aromatic hydrazide ligand might give different results. Isonicotinic acid hydrazide was chosen as a good example of this latter type of hydrazide. The discrepancy between the results of dlbert ( I ) and Fallab and Erlenmeyer (3) concerning the formula of the coniple.;(es) formed was of interest, particularly in comparison with the results obtained with acetic hydrazide. Figures 4 and 5 show the F ( X ) values for cadmium-isonicotinic hydrazide systems. Again, a t least three complexes were found, lvith the F 3 ( X ) plot being almost horizontal. The constants for the first three complexes were: K1 = 16, Kz = 278, and K 3 = 1950, with estimated errors of 1 2 , 1 4 0 , 1 3 0 0 , respectively. I n attempt to calculate and plot an F4(S) us. isonicotinic hydrazide gave a $ot with a large amount of scatter and a number of missing points, which had essentially the same slope a5 the F 3 ( X ) plot. The constant obtained from the plot was K4 = 340. On the basis of these data, it is questionable whether a complex with four ligands actually is present ; the missing points, same slope as the previous function, and the K value almost an order of magnitude smaller than the previous one, all throw doubt on the presence of a fourth complex.
0.2
0.4
0.6
0.8
1.0
(Acetic Hydrazide)
Figure 3. Values of Fz(X) and F3(X) for cadmium in acetic hydrazide solutions
panded curves gave values for the three formation constants as follows: (1)
they have defined functions, F ( X ) , such that
(E1,2)sand (E1/2>c are the half-wave potentials for the uncomplexed and coniplexed metal ions, respectively; and I , and I , are the diffusion current constants for these species. KO, the
K1
=
85, Kz = 4380, K3
=
24,300
The plot of F 3 ( X )showed a horizontal line and indicated that only three coinplexes were involved ( 2 ) . .Is a check on the values for K z and Ka, the limiting slopes of the Fl(S) and E’?(X) plots were obtained; the limiting slopes approsimate the K value for the next higher complex ( 2 ) , The limiting slope for the F 1 ( X ) curve was 4369 (K2 = 4380) and for the F 2 ( X ) curve was 23,459 ( K 3 = 24,300). The estimated errors for the three formation constants were: K1, + 9; K2, + 350; K3, + 1900. The data obtained on the Cd+2diacetyl hydrazine and -acetic hydrazide systems indicated that bonding t o the
(Isonltotinir Hydrazid.1
Figure 4. Values of FdX) and F1(X) for cadmium in isonicotinic hydrazide solutions VOL. 37, NO. 1, JANUARY 1965
53
former were beyond a n order of magnitude greater than the corresponding values for the latter complexes. The results obtained for the cadmium-hydrazide compleses were distinctly different from those reported by ;ilbert (1) and Fallab and Erlenmeyer (3) for the various metal ion-isonicotinic hydrazide systems. Fallab and Erlenmeyer (8) found that the copperisonicotinic hydrazide comples constant was dependent on pH. Titration of isonicotinic hydrazide with C U + ~ gave a solution which had a p H value 0.6 unit lower than the corresponding concentration of Cu+2 alone. Therefore, they proposed that the complexation reaction was (Isonicotinic Hydrazide)
Figure 5. Values of F*(X), F3(X), and Fd(X) for cadmium in isonicotinic hydrazide solutions
Comparison of the complex constants of the acetic and isonicotinic hydrazides shows the effect which might be expected on the basis of resonance stabilization. The values for the acetic hydrazide constants all were much higher than the isonicotinic hydrazide constants. I n fact, the values for the second and third constants of the
2RH
+ C U +e ~ RzCu f
2Hf
(5)
with the release of two protons in the over-all reaction. .Ilbert ( I ) calculated stability constants based on the anion as the complesing agent. I n the present study, a t least three complexes were formed with cadmium, instead of the two found with copper. Furthermore, no measurable release of protons was noted on titration of the hydrazides with Cd+2. -1pproxiniately one millimole of each hydrazide was titrated with ca. 0.1X Cd+2 solution to a point well beyond the equivalence point-Le., the mole ratio of Cd+2 : hydrazide was greater than 1,
but no detectable proton release occurred. I n all cases, the p H of the “blank” CdA2titration was lower than the titration of the hydrazide. Comparable titration\ with Cu+2 did sholv the loiverinq in p H reported by Fallab and Erlenmeyer ( 3 ) . Therefore, based on thePe data, complesation of cadmium appears to involve the neutral hydrazide qpecies rather than the anion. ACKNOWLEDGMENT
The authors thank D. X. Hume and M. -1. Robinson for many helpful discussions. LITERATURE CITED
(1) Albert, A, Eiperientiu 9, 370 (1953). ( 2 ) IIeFord, I). D., Hume, 1). V., J . d m . Chem. SOC.73, 5321 (1951). (3) Fallab, S., Erlenmever, H., Helv. Chim. A C ~36, U 6 (i963j. (4) Hume, 11. S., DeFord, I). I)., Cave, G. C. B., J . A m . Chem. Sac. 73, 5323 i1951). ( 5 ) Irving, H., “Advances in Polarograph\r,” 2 , 42 (1960). (6) Kolthoff, I. ll., Lingane, J. J.,
“Polarography,” 2nd ed., Interscience, Xew York. 1952. ( 7 ) Komyathy, J. C., llalloy, F., Elving, P. J., ASAL. CHEM. 24, 431 (1952). (8) Krivis, A. F., Gazda, E. S., Supp, G. R . , Kippur, P., Zbid., 35, 1955 (1863). RECEITEDfor review August 24, 1964. Accepted Xovember 4, 1964.
Type Analysis of Nitrogen in Petroleum Using Nonaqueous Potentiometric Titration and Lithium AI uminum Hyd ride Reduction 1. OKUNO, D. R. LATHAM, and W. E. HAINES laramie Pefroleum Research Cenfer, Bureau of Mines, U . S. Deparfmenf of the Inferior, laramie, W y o . A procedure is described for classifying nitrogen in petroleum into five different types-strongly basic nitrogen, three types of weakly basic nitrogen, and nontitratable nitrogen. The five types of nitrogen are determined by titrating oils potentiometrically in acetic anhydride with perchloric acid before and after reduction with lithium aluminum hydride. This procedure has been applied to several crude oils and has shown wide variation in the types and distribution of nitrogen compounds in oils.
N
in petroleum have deleterious effects on cracking catalysts in refining operations and on the stability of petroleum products. Knowledge of the occurrence and types of nitrogen compounds in petroleum is 54
ITROGEN COMPOUNDS
ANALYTICAL CHEMISTRY
important in combating these undesirable effects. -1 procedure is described for classifying nitrogen in petroleum into five different types-strongly basic nitrogen, three types of weakly basic nitrogen, and nontitratable nitrogen. The procedure involves titrating oils potentioinetrically in acetic anhydride with perchloric acid before and after reduction with lithium aluminum hydride (L.1H). The nitrogen compounds that would be included in each of the types are inferred from tests on model compounds. I n contrast to older methods, which classify t,he nitrogen only as basic or nonbasic and suggest a marked similarity of the nitrogen types in crude oils ( I S ) , applicat’ion of t’his procedure to a number of crude oils shows wide variation in the types of nitrogen compounds present.
Titration of bases in acetic anhydride systems wit,h perchloric acid has been investigated by several workers (3, 5 , 15, 16). Kinier (16) and Streuli (15) have shown that when acetic anhydride is used as a solvent for potentiometric titrations, weakly basic compounds such as amides can be titrated quantitatively. K h e n crude oils are titrated by Winier’s method, two end Iioints can be observed on the titration curve of some oils. I‘nder the assumption that nitrogen coinpounds are being titrated, the first, end point can be attributed to nitrogen compounds that are strongly basic and the second end ljoint to more weakly basic nitrogen coinpounds. If the total nitrogen is known, it is po$sible from such a titration to group nitrogen in an oil into three broad types as strongly basic nitrogen, tveakly basic nitrogen, and nontitratable nitrogen.
