[ CCINTRIBUTION
F R O Y THE
LABORATORIES OF THE NEW YORK,N. Y.1
LfOUXT
SINAI HOSPITAL,
CHOLEIC ACIDS. VI. ISOMERISM AND COORDINATIVE VALENCE; COLORED CHOLEIC ACIDS WALTER MARX*
AND
HARRY SOBOTKA
Receiced July BO, 1936
the coordination compounds of In the preceding papers of this desoxycholic acid with a number of organic substances were studied. The influence of structural and steric isomerism on the molecular ratio and stability of coordination compounds was discussed. The coordinative affinity for desoxycholic acid was found to vary for optical antipodes, thus affording a means for the resolution of certain racemate^.^ The tendency of enol forms to combine with the bile acid led to complete enolization of tautomeric substances when they formed choleic acids.4 In the present investigation these studies were extended to the choleic acids of cis-trans isomers. We prepared the choleic acids of the pairs, oleic-elaidic and erucic-brassidic acids, and determined the coordination number, which was invariably eight. This was the value previously found for the corresponding saturated acids. The acholic components could be recovered unaltered, no cis-trans rearrangements occurring. The effect of angular as against straight annulation was tested in the case of phenanthrene and anthracene. Phenanthrene combines with three molecules of desoxycholic acid, as has also been observed by Fieser and Newman,6 while the isomeric, but longer, anthracene molecule forms a tetra-choleic acid. This finding parallels the observation that normalchain aliphatic acids possess higher coordinative valence than their less symmetrical isomers.3~7 1 ,2-Benzanthrene, with a coordination number of three,6 behaves, therefore, like phenanthrene of which it is the 2,3benao derivative. The question as to the stability of organic coordination compounds in
* Isidore Hernsheim Research Fellow. H. SOBOTKA AND A. GOLDBERG, Biochem. J . , 26, 555 (1932). H. SOBOTKA AND A. GOLDBERQ, ibid., 26, 557 (1932). 3 H:. SOBOTKA AND A. GOLDBERQ, i b i d . , 28, 566 (1932). 4 HI. SOBOTEA AND J. KAHN,ibid., 26, 898 (1932). 5 H. SOBOTEA AND A. GOLDBERQ, ibid., 26, 905 (1932). 6 L. F . FIESERAND M.S. NEWMAN, J . Am. C h e m . Soc., 67, 1602 (1935). 7 E. CHARQAFF AND G. ABEL,Biochem. J . , 28, 1901 (1934). 275 1 2
276
WALTER MARX AND HARRY SOBOTKA
solution, especially of choleic acids, is still open and the answer will have a bearing on the physiological significance of the choleic acid principle. Molecular weight determinations8 and enol titrations4 indicate practically complete dissociation upon solution. However, confirmation of these results is desirable by methods, preferably optical, which do not affect association when the coordination compound is dissolved. The color of certain diketones, such as di-(3-methoxy-4-hydroxycinnamoyl)methane (curcumin), is known to deepen when the second carbonyl group becomes enolized with an excess of alkali. The progress of enolization during formation of choleic acids, and their degree of association in various solvents, may be observed directly with the choleic acids of such colored diketones. At the same time, the formation of such colored choleic acids, as slightly soluble as the related colorless benzoylacetone-choleic acid,4 might be put to analytical use. Thus, choleic acids of the following compounds were prepared : dibenzoylmethane, cinnamoylacetone, dicinnamoylacetone and dicinnamoylmethane. The coordination number of dibenzoylmethane was three, of the monocinnamoyl derivative four, whereas six molecules of desoxycholic acid were found associated with each molecule of the dicinnamoyl compounds. The crystals of the two latter choleic acids are greenish yellow, yet lighter in appearance than the dark yellow crystals of their acholic components. Nevertheless, when compared to physical mixtures of their respective components in proportionate amounts, the colors of the choleic acids are decidedly deeper in the solid state. These differences, however, disappear in solution, where corresponding concentrations of choleic acids and acholic components cannot be distinguished by colorimetric or spectroscopic observation thus indicating practically complete dissociation in solution. 8 g
EXPERIMENTAL
Preparation of Substances.-Desoxycholic acid was prepared and purified according to Sobotka and Go1dberg;z m.p. 176". (All melting points corrected.) Oleic acid, free of linolic acid, was redistilled i n V ~ C U Ounder NZand recrystallized from alcohol. Elaidic acid was obtained from oleic acid10 and recrystallized from alcohol and ether; m.p. 45-46", Erucic acid was recrystallized from alcohol and petroleum ether; m.p. 34-35'. Brassidic acid was prepared from erucic acid,10 and recrystallized from alcoholpetroleum ether solution, then from alcohol; m.p. 58-5-59.5;. Phenanthrene and anthracene were recrystallized from benzene-alcohol (1 :1) ; m.p. 99" and 217-217.5", respectively. * H . SOBOTKA, Chem. Rev., 16, 311, 364 (1934). H. SOBOTKA AND J. KAHN,Ber., 65, 227 (1932). l o A. GRWEN, "Analyse der Fette und Wachse," J. Springer, Berlin, 1926, vol. I, p. 240.
277
CHOLEIC ACIDS
Chnamoylacetone (1-phenyl-1-hexene-3,5-dione)was obtained from methyl cinnaniate plus acetone according to Ryan and Dunlea," as the preparation from cinriamoyl acetoacetate proved unsatisfactory;12 m.p. 84-85'. Dicinnamoylacetone (1 ,9-diphenyl-1 ,8-nonadEene-3,5,7-trione)was derived from the monocinnamoyl compound by condensation with sodium amide;12 m.p. 112.5113.5'. Dicinnamoylmethane (1,7-dipheny1-1,6-heptadiene-3,5-dione), in turn, from the preceding substance by boiling with 50 per cent. acetic acid;'* m.p. 143".
TABLE I CHOLEICACIDSOF Cis-Trans
AND
STRUCTURAL ISOMERS
ANALYSIS
COORDICHOIBIC ACID FROM:
]Cc. N/lOAlbliUsed
M.P. (CORR.)
--
DWXYcholic Acid
Found
?:$-
NATION NUMBER
n
--
Oleic acid*
188"
440.2
1.505
10.41
8.50t
8.25$
8
Elaidic acid
187-1 88'
433.4 441.3
-
10.16 10.35
8.04 8.02
8.25 8.25
8 8
Erucic acid
193.5-194.5"
421.6 452.7
1.267 1.273
9.82 10.32
9.411 10.12t
9.73.' 9.73
8 8
193-194"
415.3 433.0
-
9.59
1.16
9.52 9.07
9.73 9.73
8 8
Brassidic acid
-
?:%-Found
Phenanthrene
186-187"
219.7 221.4
193"
314.9 194.6
Anthracene
-
-
4.85 4.95
453 448
451 451
3 3
7.24 4.45
435 437
437 437
4 4
* Cf. reference 12.
t Mean value of both determinations.
3 Percentage for n = 7: 9.32; n = 9: 7.40. ** Percentage for n = 7: 10.96; n = 9: 8.74.
A11 three cinnamoyl derivatives, as well as dibenzoylmethane (1,3-diphenylpropane-1 ,3-dione), m.p. 79", were purified by recrystallization from alcohol. Choleic Acids.-When desoxycholic acid and a small excess of the fatty acid were dissolved in hot methyl alcohol under nitrogen, the coordination compounds of the 11. 1'2
H. RYANAND I. M. DUNLEA,Proc. Roy. Irish Acad., S2B, 1 (1913). V. LAMPEAND J. MILOBEDZKA, Ber., 46,2235 (1913).
278
WALTER MARX A N D HARRY SOBOTKA
fatty acids crystallized readily upon cooling. I n the case of phenanthrene and anthracene, the low solubility in alcohol of the acholic component necessitated the addition of benzene. The choleic acids of the three yellow cinnamoyl derivatives and of dibenzoylmethane were synthesized in concentrated hot methyl alcoholic solution, yielding well-formed prismatic crystals. Dibenzoylmethane-choleic acid is distinguished by its very slight solubility. Recrystallization of choleic acid from alcohol, especially from ethyl alcohol, always entails the danger of dissociation and subsequent contamination of the choleic acid with ethyl alcohol-choleic acid, as indicated by lower and less sharply defined melting points. This should be taken into account in any study of the physical or chemical properties of these compounds (see, e.g., footnote 13). The analysis of the fatty acid-choleic acids was done by the xylene method of Wieland and Serge" under nitrogen. The xylene was removed by steam distillation TABLE I1 COLOREDCHOLEICACIDS ANALYBIB
CXOLmIC ACID FROM:
c c . N/10 Alkali Mg. Sub- Used for
Y.P. (CORR.)
ACID EQUIVALENT
CO~RDINATION NUMBER
stance
Desoxycholic Acid
Found
Calculated
259.7 191.8
5.65 4.15
467 470
467 467
3 3
Dibeneoylmethane
199.5-200.5
Cinnamoylacetone
190.5-191.5'
97.8 170.3
2.22 3.88
441 439
439 439
4 4
Dicinnamoylacetone
191.5"
166.4 175.0
3.73 3.93
446 445
442 442
6 6
Dicinnamoylmethane
195-196"
95.5 163.4
2.15 3.72
444 439
438 438
6 6
O
in a nitrogen atmosphere under reduced pressure. The titrations of the separated desoxycholic acid and fatty acid- were carried out with N/10 alcoholic alkali and naphtholphthalein as indicator. The presence of desoxycholic acid interfered with the determination of the iodine number of the unsaturated acid. The coordination numbers of anthracene, phenanthrene and of dibenzoylmethane were determined by direct titration of the choleic acids in hot alcohol with N/10 alcoholic alkali and naphtholphthalein as indicator. The acidity of the enol group of the diketone was negligible. The colored cinnamoyl derivatives were analysed by the xylene method, as the color and the enolic character of the acholic components prevented direct titration. Is 1'
Y . Go AND 0. KRATKY,2. phys. Chem., B26, 439 (1934). H. WIELANDAND H. SORQE, 2. physiol. Chem., 97, 1, (1916).
CHOLEIC ACIDS
279
SUMMARY
1. The choleic acids of cis-trans isomers of unsaturated aliphatic acids have coordination numbers equal to each other and to that of their corresponding saturated acids. 2. Phenanthrene combines with three molecules, anthracene with four molecules of desoxycholic acid. 3. Various aromatic diketones form colored, slightly soluble coordinat i m compounds with desoxycholic acid. These choleic acids are apparently completely dissociated when dissolved.
