Dee., 1960
FORMATION CONSTANTS OF METALDERIVATIVES OF @-TRIKETONES
1927
STUDIES ON COORDINATION COMPOUNDS. XIX. FORMATION CONSTANTS OF SOME METAL DERIVATIVES OF p,6-TRIKETONES'~2 BY HIDEHIKO KIDOAND W. CONARD FERNELIUS Department of Chemistry, The Pennsylvania State University, University Park, Penna. Recciued June $4, 1960
The dissociation constants of l-phenyl-l,3,Bhexrtnetrioneand 1,5-diphenyl-l,3,Bpentanetrionehave been measpred in 75 volume % ' dioxane at 30" as well as the formation constants of complexes with uranyl, copper(II), nickel, cobalt, zinc and cadmium ions The triketones are monobasic and function as bidentate ligands.
replaced by potassium in liquid ammonia, the pKz value is too great for dissociation in a partially aqueous medium. The most closely related compounds on which information is available are CHaCOCH2COCOCH2COCH8, pKi = 10.3; pKz = 13.0, and CeH5COCH2COCOCH2COC6H~, @I = 11.2; pKz = 14.0e8 Thus, the second proton is held more tightly when the first is removed from l-Phenyl-1,3,5-hexanetrione and 1,5-diphenyl-l,3,5-pen- I than when removed from 11. tanetrione were kindly supplied by Drs. R. J. Light and C.
The metal derivatives of a variety of p-diketones have been extensively studied. However, virtually nothing is known about the metal derivatives of @-triketones. The present study was undertaken to gain some insight into the behavior of such compounds. Experimental R. Hauser.'
H
Techniques.-The potentiometric titrations were perf ~ r m e dthe , ~ acid dissociation constants6 determined, and the calculations performed6 as described previously. Tetrameth lammonium hydroxide was used for all the titrations and tKe metal salts were perchlorates. Results.-The results of the determinations in 75 volume % dioxane at 30" are assembled in Table I. The color of the solutions was yellow becoming more intense in basic polution, except for the uranyl ion which wns definitely orange.
CpH&OCH&OCH&OCH,
1
H+
uoi++
Be++
log Kn
cu++
10.03 Ppt.
2
10.64
C~H,COCH~COCHLCOC~H, 1
10.03 Ppt.
Yellow
Ppt.
Ppt,
2
11.90 10.03
H
70IhOXANE AT 30""
Yellow
11 .62
H
I 11 I n the formation of metal derivatives the nsud
TABLE I FORMATION CONSTANTS I N 75 VOLUME n =
H
10.08 f0.05
Nl++
cot+
9.95 1 0 . 02 8.20 10.03 10.21 f0.03 8.86 10.05
9.37 10.04 7.88 10.05 9.62 &0.03 8.51 10.05
en++ 9.19 10.02 7.87 210.05 9.49 10.03 8.54 f0.06
Cd++
7.90 f O .03 6.46 f0.03 8.17 f0.03 7.84 10.03
The uncertainty in these values represents the 95% confidence limits.
Discussion It is interesting to note that the triketones are stronger acids (tenfold or more) than the corresponding P-diketones (CH3COCH2COCHa,12.70, CsHsCOCH2COCH3, 12.85 and CeH5COCHzCOCaH6, 13.75)' and that the dibenzoyl compound is the weaker acid just as dibenzoylmethane is a slightly weaker acid than benzoylacetone. Although the second proton in the triketones can be (1) This investigation w a oarried ~ out under contract AT(30-1)-907 between The Pennsylvania State University and the U. S. Atomic Energy Commission. (2) For XVIII of this aeries eee H. Kido and W. C. Ferneliua, Anal. Clrim. Acta, %3,116 (1960). (3) For preparation, etc., see C. R. Hauser and T. M. Harria, J . A m . Chem. Soc.. 80,6360 (1958). (4) L. G . Van Uitert, et al., J . A m . Chem. Soc., 7 8 , 451, 457 (1953). (5) (a) L. G . Van Uitert, et d., ibid., TO, 455 (1953); (b) 76, 5887 (1954). (6) B. P. Block and G. H. McIntyre, Jr., ibid., TO, 5667 (1953). (7) L. G. Van Uitert and W. C. Ferneliue, ibid.. 75, 2736 (1953).
order of stabilities is found: (a) the order of metals is UOz++>Cu+ +>Ni ++>Co + +>Zn ++>Cd ++ ' ~ 9 9 and (b) the weaker acid forms the more stable derivatives.9-11 However, the complexes of CsH6COCH2COCH2COCH3 are more stable than those of CH3COCH2COCH3but somewhat less stable than the corresponding ones of benzoylacetone. Similarly those of (CoH6COCHz)zC0are more stable than those of beneoylacetone but less stable than those of dibenzoylmethane. There is no indication that the triketones behave as other than bidentate ligands. (8) E. H. Holst, Ph.D. Thesis, The Pennsylvania State University, September, 1955. (9) H. Irving and H. Rossotti, Acta Chem. Scand.. 10, 72 (1956). (10) W. C. Fernelius, Boldtln del Colegio Qulmacos de Pusrfo Rieo, l S , 3 (1956). (11) M. Calvin and K. W. Wilson, J . Am. Chem. Sac., 61, 2003 (1945).
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