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C. R. BERTSCH, W. C. FERNELIUS AND B. P. BLOCK
Vol. 62
The value of An at 27" is a measure of the amount decomposition of the acetylacetonates was not of decomposition product still gaseous at room determined. In general the change in appearance temperature. The fact that An. at 27" is still of the chelates paralleled the extent of decompolarge, in many caees, indicates that at least some of sition, as indicated by An. Those acetylacetonates the decomposition products are of low molecular undergoing extensive decomposition generally gave weight. The nature of the volatile decomposition very dark colored, and frequently resinous, resiproducts for certain of these compounds is currently dues. It is planned to study t,he nature of some of being investigated. The results of this study will these materials. be reported in a later paper. Acknowledgment.-The authors are grateful to The nature of the solid residues obtained from the Miss M. I. Mistrik for certain of the analyses.
A THERMODYNAMIC STUDY OF SOME COMPLEXES OF METAL IONS WITH POLYAMINES' BY CHARLES R. BERTSCH, W. CONARDFERNELIUS AND B. P . BLOCK The Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania Received November 99, 1967
The dissociation constants of these several amines have been determined at 10, 20, 30 and 40": N,N,N',N'-tetramethylmethanediamine (I), 1,3-propanediamine (11),1,4butanediamine (111), cis- and truns-l,2-cyclohyexanediamines IV and V, resp.), 2,2',2J'-triaminotr~ethylamine(VI) and 1,3-diamino-2-pro anol (VII), and at 10' for truns(?)-l,2-cyclo eptanediamine (VIII). Formation constants and enthalpy and entro y cKanges have been determined for I1 with Ag+, Cu++ and Ni++; 111with Ag+; I V and V with Cu++, Ni++, Zn++ a n 8 Cd++; VI with Cu++; and VI1 with Ag+ and Ni++at the four temperatures. Formation constants have been determined for VI11 with CU++,Ni++, Zn++ and C d + +a t 10". These uantities are compared from one ligand to another with the same metal ion. The difference in stability for the formation of 8ifFerent sized rings is primarily an entro y effect which is related to the strain introduced in the ring and the loss of freedom of the diamine in the chelate. The cherates formed with the cyclic diamines are generally more stable because of a more favorable entro y effect. however, there appear to be exceptions when the metal ion is not the pro er size to fit a given diamine and weaier bonds result. An ion-exchange process for preparing diamine solutions directry from diamine salts is described.
L
Introduction The publication in 1941 of J. Bjerrum's thesis2 on equilibria involving metal ion-amine complexes initiated a series of investigations which have demonstrated the effect of (1) chelates us. monodentate ligands,s (2) ring size for bidentate amine8,d-s (3) number of points of attachment,a (4) C3s7-9 and Ns u b s t i t ~ t i o n , ~ *(5) ~ - ~d,Z-diamines ~ us. the meso forms,gb(6) cis- vs. trans-1,2-cyclohexanediamines'2 and (7) substitution of :NH by :SI3 and :O.'4 Many of the values for the equilibrium expressions given in the literature are not strictly comparable (1) From a dissertation presented by Charles R. Bertsch in partial fulfillment o f the requirements for the degree of Doctor of Philosophy, August, 1955. (2) J. Bjerrum, "Metal Ammine Formation in Aqueous Solution," P. Haase and Son, Copenhagen, 1941. (3) G. Schwarzenbach, Report No. BRL/146, May 1951. Presented at Discussion on Coordination Chemistry held b y Imperial Chemical Industries. Ltd. at Welwyn, Herts, September, 1950. (4) G. B. Hares, W, C. Fernelius and B. E. Douglas, J . A m . Chem. SOC.,78, 1816 (1956). 69, 1203 (1955). (5) F. A. Cotton and F. E. Harris, THISJOURNAL, (6) I. Poulsen and J. Bjerrum, Acta Chem. Scand., 9, 1407 (1955). (7) J. Bjerrum, Chsm. Revs., 46, 381 (1950). (8)R. J. Bruehlman and F. H. Verhoek, J . Am. Chem. Soc., 70,1401 (1948). (9) (a) F. Basolo and R. K. Murmann, ibid.. 74, 5243 (1952); (b) F. Basolo, Y. T. Chen and R. K. Rlurmann. i b i d . , 76, 956 (1954). (10) H. Irving, see ref. 3. (11) F. Basolo and R. K. Murmann, J . A m . Chem. Boc., 76, 211 (1954). (12) G. Schwaraenbach and R. Baur, Helv. Chim. Acto, 89, 722 (1956). (13) E. Gonick, W. C. Fernelius and E. E. Douglas, J . A m . Chsm. Soc., 7 6 , 4671 (1954); C. R. Bertsch. W. C. Fernelius and B. P. Block, T H I SJOURNAL, 60, 384 (1956). (14) J. R. Lotz, Ph.D. Thesis, The Pennsylvania State University, 1954.
k,
one to the other because the measurements were made in solutions of different ionic strength and at varying temperatures. Unfortunately, the measurements for any one system seldom include measurements at more than one temperature. Hence, although there is considerable information about approximate free energies of reaction, very little is known about enthalpies or entropies of reaction. With these equilibrium constants at hand for a range of temperatures, more satisfactory values for the enthalpies and entropies of reaction can be calculated. I n continuation of previous ~tudies'4.1~ there are presented here studies of N,N,N'N'-tetramethylmethanediamine, 1,3-propanediamine7 1,4-butanediamine, cis- and trans-l,2-cyclohexanediamine, trans(?)-1,2-cycloheptanediamine, 2,2',2"triaminotriethylamine and 1,3-diamino-2-propanol. Experimental Procedure.-The general procedure involved the titration of 100 ml. of solution 0.001 M in metal ion and 0.002 M in acid with ca. 10 ml. of 0.04 to 0.10 M amine under nitrogen a t 10, 20, 30 and 40". A Beckman Model G pH meter equyf ed with a saturated calomel electrode and a Beckman Mo e E No. 1190-80 glass electrode was used to follow the titrations. For the titrations involving silver ion a salt bridge containing saturated potassium nitrate solution (in contact with excess solid) was used to isolate the calomel electrode from the solution in the titrating flask. The method used to calculate the constants was reported earlier .le For these calculations concentrations were converted to activities by application of the Debye-Hiickel equation .I6 (15) R. M. Izatt, C. G. Haas, Jr., B. P. Block and W. C. Fernelius, THINJOURNAL,68, 1133 (1954). (16) B. P. Block and G. H. McIntyre, Jr., J . A m . Chem. Soc., 76.
6667 (1853).
April, 1958
THERMODYNAMIC STUDY OF COMPLEXES OF METALIONS WITH POLYAMINES 445 1.0 1
Reagents.-All metal perchlorate and perchloric acid solutions were prepared from G. F. Smith Chemical Co. reagent-grade materials. The concentrations of the solutions were determined by means of standard analytical methods. The amine solutions were prepared using freshly boiled, distilled water. The normality of each solution was determined by titration with a, standardized perchloric acid solution.
Results.-The log Kn values are given in Table I together with the calculated thermodynamic quantities AF,, AHn and AS,. The =tvalues are the 95% confidence intervals based on three or more (17) M.Picon, BULL soc. chim., [ 4 ] 33, 89 (1923). (18) We wish to express our appreciation to Dr. H. Kroll of Alrose Chemical Company for the gift of trans-I ,2-cyclohexanediamine SUIfate and cis-1.2-cyclohexanediamine (b.p. 70-73O at 12 mm.), and t o Mr. G . 8. Burah of Carbide and Carbon Chemicals Company for the gift of 2,2',2''-triarninotriethylamine. (19) R. W. Vander Ham, R. C. Voter and C. V. Banks, J . Org. Chem., 14,836 (1949). (20) L. D.Berg, unpublished observations in this Laboratory, (21) F. M. Jaeger and H. B. Blumendal, Z . anorg. Chem., 111, 161 (1928). (22) H. L. Riley, J. F. Morley and N. Friend, J . Chem. SOC.,1875 (1932). (23) Dutch Patent 58,279 (Sept. 16, 1946); C. A . , 41, 4807 (1947).
I
I
I
5.00
6.00
7.00
I
0.80
Amines.-N,N,N',N'-Tetramethylmethanediamine
(Peninsular ChemResearch, Inc .) was distilled over sodium through a 24"-column packed with glass helices, and the fraction boiling at 82.5" collected; Picon'' reports 82.5'. 1,3-Diamino-2-propanol (Distillation Products Industries) could not be distilled through a acked column because of its high viscosity and hence was Xstilled over barium oxide in a simple distillation flask: m.p. 38-40". The preparation of pure anhydrous polyamines usually involves lar e losses and presents difficulties in storage and handling. %'herefore, aqueous solutions of several amines were obtained by passing an aqueous solution of the purified hydrochloride or sulfate (twice recrystallized from an alcohol-water mixture) through a column filled with the hydroxide form of Amberlite IRA-400. 1,3-Propanediamine dihydrochloride (L. Light and Co.), 1,4-butanediamine dihydrochloride (Distillation Products Industries), 2,2',2"-triaminotriethylamine trihydrochloride, cis-1 ,%cyclohexanediamine dihydrochloride, tmms-l,2-cyclohexanediamine sulfate,'* and truns(?)-l,2-cycloheptanediamine hydrochloride were treated in this manner. Although the complete recovery of the amine from the column involves too great a dilution for most purposes, complete recovery can be obtained, and, when this is done, the equivalent weight of the amine agrees with that expected Cycloheptanone (Columbia Organic Chemicals Co .) was converted to the dione and dioxime by the method of Vander Haar.19 The dione was obtained in 75% yield and boiled at 116-117° a t 20 mm. (as compared to 85% and 107-109' a t 17 mm.): The dioxime was obtained in 50% yield and melted a t 182' as compared to 179-180".19 Onetenth mole of 1,Z-cycloheptanedionedioximewas added with stirring over a period of 4 hr. to a slurry of 31 g. of LiAlH4 in 500 ml. of anhydrous ether. The mixture was then refluxed for 48 hr. with constant stirring and hydrolyzed successively with wet ether and with water. The ether layer was decanted and extracted with dilute HC1. The white hydrolysis residue was treated with KOH and steam distilled into dilute HC1. The combined HC1 solutions were evaporated to dryness. The resulting amine dihydrochloride was purified by recrystallizing several times from an alcohol-water mixture. A 10% yield of 1,2-~ycloheptanediamine dihydrochloride was obtained. Anal. Calcd. for C7HI8Cl2N2:C1, 35.25;. N, 13.93. Fqund: Cl,, 35.31, N, 13.97. Presumably this is the trans isomer since similar 20 reactions produce truns-l,2-cyclohexanediamine. The preparation of trans-1,Z-cyclopentanediamine was tried unsuccessfully a number of times. 1,Z-Cyclopentanedione was made in 50% yield by the method of Jaeger and Blumendal,2I but not by oxidation of cyclopentanone with SeOs either a t 0' or 35',22 or by hydrolysis of 2-chlorocyclopentanone followed by oxidation with FeCla.23 Reduction of the dioxime of the dione with sodium and alcohol was unsuccessful.
I
0.60 la'
0.40
0.20
0.00
I
3.00
4.00
8.00
PWI. Fig. 1.-Formation curves of silver in titration a t 20': A, 1,3-propanediamine; B, l14-butanediamine; C, 1,3diamino-2-propanol; G, theoretical formation curves for the N = 1.
calculations for each constant. Plots of log Kn vs. 1/T were constructed in order t o determine AH,. The formation curves for the titrations at 20" involving silver ion are plotted in Fig. 1,together with the theoretical formation curve for the case N = 1. The log K z values for the chelation of Cu++ with l13-propanediamine are not reported since they varied when different data points were used in the calculation. I n the titrations run in the presence of cobalt(I1) ion, the pH of the solutions continually dropped with time after a small amount of amine was added. No precipitation was observed, and the color of the solutions indicated that coordination was taking place. A possible explanation is that the cobalt(I1) was being oxidized to cobalt(111). McIntyre reports a similar difficulty in attempts t o titrate cpbalt(I1) solutions with amines.24 Precipitation occurred during the titrations of Ag+, Cu++, Ni++, Zn++ and Cd++ with N,N,N',N' -tetramethylmethanediamine,of Cu ++, Ni ++, Zn++ and Cd++ with 1,4-butanediamine, of Zn++ and Cd++ with l13-propanediamine and of Zn++ with 1,3-diamino-2-propanol. Although no precipitation was noted during the titration of the latter amine and Cd++, the calculated constants were not consistent.
Discussion I n general 5-membered chelate rings are the most stable in syst8ems with saturated rings.26 The failure of N,N,N',N'-tetramethylmethanediamine to form stable chelates with the usual bivalent ions under conditions in which N,N,N',N'-tetramethyll12-ethanediamine does form stable chelates with both copper(I1) and silver ions26 is in agreement with this general observation. Another qualita(24) G. H. McIntyre, Jr., Ph.D. Thesis, The Pennsylvania State University. 1953. (25) A. E. Martell and M. Calvin, "Chemistry of the Metal Chelate Compounds," Prentice-Hall. Inc.. New York, N. Y..1952, p. 137. (26) B. P. Block, unpublished observations.
C. R. BERTSCH, W. C. FERNELIUS AND B. P. BLOCK
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VALUES FOR THE t,
oc.
H+
Vol. 62
TABLE I THERMODYNAMIC QUANTITIES LOG I
