Polarographic Studies of Some Mono- and Di-Hydrazide Complexes of Zinc G . R. S u p p O h ,275 Winchester Ace., New Hacen 4 , Conn. THE GROWING commercial application for carboxylic acid hydrazides and their biological activity to bacteria has increased the importance of this class of compounds. In particular, the increased toxicity to bacteria in the presence of heavy metals is well known, Because information concerning the formation of metal complexes would aid in many of these applications, complexation studies for some of these hydrazides have been continued. Recently ( 1 , 2 ) , polarographic investigations of the complexation of cadmium by some monohydrazides and dihydrazides have been carried out. The complexes appeared to involve neutral hydrazide molecules with cadmium. Based on discrepancies between the formula of the complex(es) as reported by Albert (3) and Fallab and Erlenmeyer ( 4 ) and the nature of the complexes as reported by Krivis and co-workers ( I , 2), it seemed that further study on these systems may help clarify some of these problems. Therefore, a study of the behavior of zinc with some of these hydrazides was undertaken. As the polarographic approach has been successful for the determination of complexation reactions, the same technique was used for the present study. The method derived by DeFord and Hume (5) for the polarographic determination of successive, soluble complexes was used to calculate the formation constants. EXPERIMENTAL Chemicals. All inorganic chemicals were reagent grade and were used without further purification. Succinic dihydrazide, adipic dihydrazide, carbohydrazide, and diacetylhydrazine (Olin Mathieson Chemical Corp.) were recrystallized twice from water, dried at 100" C., and stored under nitrogen. Acetic hydrazide (Olin Mathieson Chemical Corp.) was redistilled under vacuum and stored under nitrogen while isonicotinic hydrazide (Eastman White Label) was used without further purification. Gelatin (Fisher Scientific Company) was used, without further purification, as a maximum suppressor. Purified and equilibrated nitrogen was used to remove oxygen from the solutions. Apparatus and Procedure. The apparatus and procedure followed have been given earlier ( I ) . RESULTS AND DISCUSSION
Figure 1 shows the plot of Eliz us. log hydrazide concentration for the hydrazides studied. Acetic hydrazide and succinic dihydrazide exhibit the curvature expected for successive complex formation while diacetyl hydrazine gave a horizontal line. No shifts in Elizwere noticed for zinc over the concen(1) A. F. Krivis, G. R. Supp, and R. L. Doerr, ANAL.CHEM., 37, 52 (1965). (2) A. F. Krivis, G. R. Supp, and R . L. Doerr, Zbid., 38,936 (1966). (3) A. Albert, Experientiu, 9, 370 (1953). (4) S. Fallab and H. Erlenmeyer, Helu. Chim. A c f a , 36, 6 (1953). ( 5 ) D. D. DeFord and D. N. Hume, J. Am. Chem. SOC.,73, 5321 (1951).
- 1 .1IC
-1.10-
-1.05
- 1.0-
-
+
I
I
tC
I
tration range studied for diacetyl hydrazine indicating the absence of measurable complex formation. The complexation behavior between zinc and isonicotinic hydrazide could not be studied by the polarographic approach. The Ellz for zinc was masked by the reduction wave for isonicotinic hydrazide. Liberti and coworkers (6) studied the polarographic behavior of isonicotinic hydrazide over a wide pH range and obtained a reduction wave for this compound at - 1.1 V at approximately pH 7.0. Attempts were made to study adipic dihydrazide and carbohydrazide. However, at concentrations of ligand greater than 0.4M, the zinc-adipic dihydrazide complex gave an irreversible reaction, whereas the carbohydrazide complex gave an irreversible response over the entire ligand concentration studied. The stability constants were determined by the method outlined by DeFord and Hume (5, 7 ) . The F ( X ) plots resembled the figures for the cadmium hydrazides studied earlier and will not be given here. The formation constants determined for acetic hydrazide were found to have the following values: Ki
=
300
Kl
=
4500
Ka
=
48,000
The limiting slopes gave values of 4385 for Kz (K2= 4500) and 48,415 for K 8 (K3 = 48,000). The formation constants found for succinic dihydrazide had the following values: (6) A. Liberti, E. Cervone, and C. Cattaneo, Giorn. Biochim., 1, 440 (1952). (7) D. N. Hume, D. D. DeFord, and G. C. B. Cave, J . Am. Chem. SOC.,73, 5323 (1951). VOL. 40, NO. 6, MAY 1960
981
KI = 180
Kz
= 21,900
KS = 126,500
Kq
=
43,000
A wide scatter in points was noticed for the F3(X) and F4(X) plots and the data were reanalyzed in the form of a linear regression (8). K3 was found to be 129,268 and K4, 51,264. In comparison to the corresponding cadmium-succinic dihydrazide complexes (2), the zinc complexes tended to be more stable. Comparison of the K3 complexes disclosed a 5fold increase in stability for the zinc compared to the cadmium complex. From the data obtained, it appears that the dihydrazide complexes of zinc are more stable than the monohydrazide (8) G. W. Snedecor, “Statistical Methods,” 4th ed., Iowa State
College Press, Ames, Iowa (1964).
complexes. Also, the possibility of forming higher complexes is increased for the dihydrazide as compared to the monohydrazide complexes. The results found by Albert (3) and Fallab and Erlenmeyer ( 4 ) for the complexation between copper and isonicotinic acid hydrazide indicated that the reaction involved release of protons. Titration of the hydrazide with copper lowered the pH approximately 0.6 unit below the pH for copper alone. Titrations of the hydrazides studied with zinc were carried out beyond the 1 :1 mole ratio, and, the pH of the solutions did not drop below that for zinc alone. Complexation of zinc by these hydrazides appeared to involve the neutral hydrazide molecule. RECEIVED for review November 22, 1967. Accepted February 26, 1968.
Titration of Amides by Chlorination and Equilibrium Constant Evaluation with Constant Current Potentiometry C. 0. Huber and K. E. Smith’ Department of Chemistry, University of Wisconsin-Milwaukee, Milwaukee, Wis. 53201 VARIOUS TITRATION methods for determination of amides have been proposed. These include potentiometric and photometric acid-base titration in acetic acid or acetic anhydride ( 1 , 2), formation and titration of the corresponding amines (3), and ion exchange hydrolysis to acids followed by titration (4). In 1965 Post and Reynolds ( 5 ) proposed an amperometric chlorination titration of certain aliphatic and aromatic amides in a water-dioxane solvent using readings well beyond the equivalence point of the reaction. The work reported here presents a constant current potentiometric titration using the chlorination reaction in aqueous solvent. Several sources of error are examined and a method for measurement of the equilibrium constant is given. In constant current potentiometry the polarizing current is produced by a relatively high dc voltage in series with appropriate value resistors and the titration cell electrodes (6). In the case for the titration studied here a platinum cathode serves as the indicator electrode. The potential shift near the equivalence point is caused by reduction of excess chlorine at potentials considerably more positive than those occurring at the cathode before the equivalence point is reached. Platinum is also used for the anode. It undergoes virtually no change in potential throughout the titration. 1 Present address, Dept. of Chemistry, University of Iowa, Iowa City, Iowa. ~~
(1) T. Higuchi, C. H. Barnstein, H. Ghassemi, and W. E. Perez, ANAL.CHEM., 34, 400 (1962). (2) D. C. Wirner, Zbid., 30, 77 (1958). (3) S. Siggia and C. R. Stahl, Zbid., 27, 550 (1955). (4) T. M. Bednarski and D. N. Hurne, Anal. Chim. Acta, 30, 1 (1964). (5) W. R. Post and C. A. Reynolds, ANAL.CHEM., 37, 1171 (1965). (6) C. N. Reilley, W. D. Cooke, and N. H.Furman, Zbid., 23, 1223 (1951). 982
ANALYTICAL CHEMISTRY
The constant current potentiometry technique, in contrast to the amperometric titration proposed by Post and Reynolds (5), permits direct reading of the end point signal-Le., does not require graphical extrapolations based on a linear indicator electrode signal. As is often the case, the superior end point technique results in helpful observations concerning the titration reaction itself. These observations result in elimination of several sources of error and in improvement of titration accuracy and convenience. In addition, the titration data show that the equilibrium constant for the titration reaction is relatively low. The constant current potentiometric data at 200 FA allows the determination of end points reproducibly far enough beyond the equivalence point to yield stoichiometric accuracy. The potentials at lower currents permit evaluation of concentrations of reactants and products to allow estimation of the equilibrium constant. A value for the equilibrium constant for the propionamide chlorination reaction is presented. EXPERIMENTAL
Apparatus. The constant current potentiometric apparatus used was similar tot hat described by Reilley, Cooke, and Furman (6). The vessel used to prevent loss of chlorine through evaporation was a 125-ml Erlenmeyer flask fitted with a ground glass neck joint into which fits a complementary joint sealed onto the tip of a 2-ml self-filling micro buret. The titration vessel was covered to shield the titration solution from light. Two 20-ga. platinum wires were sealed through the vessel walls. The cathode was 8 mm in length and the anode was 15 mm. A calomel or other nonpolarized electrode could just as well have been used for the anode, but would have been less convenient. Solutions were stirred magnetically with a synchronous motor. Constant current was supplied by a 90-V battery with appropriate resistors in series. A commercial direct reading pH meter on the 1400
