COMMUNICATIONS TO THE EDITOR
a c t . 5: 1959 activity coefficients
where the bar marks the stronger solution. Equation l takes account of the fact that the solutions are mixtures of two electrolytes, utilizing Br@nsted's rule. The ratio of the activity coefficients in the dilute solution equals about unity. Hence In (1
+
e) N
E
(In 77
- In 78)
(2)
Glueckauf2has shown that the hydration parameters which largely determine the trends of the activity coefficients are a function of the Pauling radius of the cation. Equally-without making use of the hydration concept-the activity coefficients of the aqueous solutions of alkali salts of the same halogen can be directly expressed as functions of the Pauling radii ( r , in hgstrom). The activity coefficients of all alkali chlorides a t 25" for m > 1 are adequately expressed by the equation3
5263
the Li-isotopes, this being the square of the inverse ratio of the masses. If this principle applies generally, the outlook for enriching isotopes of higher mass by pure ion exchange is very dim indeed. One would expect for the exchange on Dowex 50 K39-K4'
A/, = 2 X
lWhA&
and
t
=
1.8 X 10 -5
and for Rbs6-Rbs7 & = 5 X 1 0 - - 6 kand e = 3.5 X ATOMIC ESERGYRESEARCH ESTABLISHMEST HARTVELL, ENCLAXD E. GLUECKAUF RECEIVED JULY 13, 1959
T-CYCLOPENTADIENYL-TCYCLOHEPTATRIENYL VANADIUM
Sir :
The chemical literature contains several examples of the preparation of cyclopentadienyl-metal carbonyl compounds by heating together a metal carbonyl and cyclopentadiene or dicyclopentaIn -/ = 0.60;/% + km (3) diene. However, when molybdenum hexacarwhere k = 0.270 ((l/r) - 0.38) bony1 or iron pentacarbonyl is heated with cyclo(4) heptatriene, there is no loss of hydrogen to form The differences of the Pauling radii for Li6 and Lij are known from Thewlis' measurement4 of the tropylium compounds. Instead the complexes ) ~ ~produced. lattice constants of LiaF and Li'F. These data CjHsMo(C0)32 and C ; K B F ~ ( C Oare The only tropylium sandwich compound so far give reported is the ionic compound [ C ~ H ~ M O ( C O ) ~ ] B F ~ , ( T ) L ] ~- ( I ) L , ~= 0.0004 zt 0.00007 ingstrom (5) prepared by a different method. From equations 2, 3, 4, 5 follows Using a different approach to tropylium-sand0.270 % wich chemistry, the reaction between cyclopentam X A r = X r7) = 3 x 10-4% (r~i)* dienyl vanadium tetracarbony15 and cycloheptatriene was investigated. A mixture of CsH5V(C0)d (0.01 mole) and 30 ml. of commercial cycloTABLE I heptatriene was refluxed under nitrogen a t 120' Approx. 103 calculated for for 9 hours. After removal of excess cycloheptaexchanger I O 3 observed LiCl solutions (E) % DVB molality (Z) (ref. 1) from eqn. 6 triene a black residue remained. Sublimation a t 80" yielded oily material which was discarded. 4 3 1.0 0.9 Further sublimation a t 100" afforded 0.82 g. 8 5.5 1.6 1.7 (yield 40%) of purple crystals, C5HjVC7H7, spar12 7.5 2.7 2.3 ingly soluble in organic solvents to give purple 16 9 3.7 2.7 solutions which in air begin to deposit a brown 24 12.5 3.8 3.8 precipitate after a few minutes. Table I shows the agreement between the sepaAnal. Calcd. for C12H13V: C, 69.6; H, 5.8; ration factors E observed,' when the isotopes were separated on various exchanger types of different V, 24.6; mol. wt., 207. Found: C, 69.7, 69.8; crosslinking (divinyl benzene content) by elution H, 5.8, 5.8; V, 24.6; mol. wt., 229 (cryoscopic in with dilute hydrochloric acid solution, and those benzene). calculated for the equilibria between a dilute and The analytical results are in less accord with a a concentrated lithium chloride solution of the composition C5H5VCjHs (C, 69.2; H , 6.25) than same molal concentration as the exchanger. for C5HbVCjHj. However, a clearer demonstraEquation 6 can be used also for the reverse tion of the nature of the new vanadium compound process of calculating the differences in ionic is provided by its magnetic properties. It is radius from observed isotopic separation factors, paramagnetic with X2sp,"I", = 1055 X cm3e.g., for the case of the isotopes NaZ2and Na24.5 mole-l, corresponding to 1.69 B.M., which is On Dowex 50 (Z 6) this gave E = 1.4 X 10-4 equivalent t o one unpaired electron. This cona t 25". Hence from eq. 6 firms the composition as CjHjVCjH; rather than L
-
8 X 10-6 ingstrom
The radii of two adjoining h'a-isotopes would thus differ by only a tenth of the difference between (2) E. Glueckauf, T r a m . Favoday SOL.,SI, 1235 (1955). (3) J. C. Gosh, J. Chem. S o c . , 113, 449 (1918). (4) J. Thewlis, Acta. Crysl., 8, 36 (1955). (5) R. H. Betts. W. E. Harris and M. D. Stevenson, Con. J . of Chem., 34, 65 (1956).
( 1 ) For a recent review of compounds wherein an aromatic ring system and carbon monoxide groups are simultaneously bonded t o metal atoms, see E. 0. Fischer and H. P. Fritz, "Advances in Inorganic and Radiochemistry" (Eds. H. J. Emeleus and A. G. Sharpe) 1, 55 (1959),Academic Press, Inc., Kew York, N. Y. (2) E. W. Abel, M. A . Bennett, R. Burton and G. Wilkinson, J . Chcm. Soc., 4559 (1058). (3) R.Burton, M. L. H. Green, E. W. Abel and G. Wilkinson, Chcm. I d . , 1892 (1958). (4) H. J. Dauben and L. P. Honnen, THISJOCRNAL, 80, 5570 (1958). ( 5 ) E. 0. Fischer and S . Vigoureux, B e y . , 91, 2205 (1958).
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COMMUNICATIONS TO THE EDITOR
VOl. 81
tribution of 29 transfers with the upper phase moving in a system of ethyl acetate:heptane:water in a 1:1:2 ratio. Tubes 7 to 22 were combined and taken to dryness in vacuo. The residue was dissolved in benzene and put on a silicic acid column. With 0.75% methanol in benzene, I was eluted, evaporated t o dryness, and the residue rerun through the countercurrent distribution and the silicic acid column. The final product was sublimed a t 75” for three hours in vacuo to give 400 p g . of I. Ultraviolet light absorption maximum of I w5s a t 2760 A. with shoulders a t 2960 and 3080 A. No appreciable acid-base shift of the maximum occurred. Maximum fluorescence was a t 338 mp and maximum activation a t 304 m p . Infrared examination showed a broad carbonyl absorption a t 1710 ern.-' and the possible presence of a methoxy1 group. A strong blue violet color was obtained with Ehrlich reagent. Electrophoretic studies showed that the compound migrated as if it had a free carboxyl group. Ultraviolet absorption and fluorescence proper(6) E. 0. Fischer and H. P. Kogler, Be?., 90, 250 (1957). ties and the reaction with Ehrlich reagent indicated (7) T. A. Manuel and F. G. A. Stone, Proc. C h e m . Soc., 90 (1959); that the compound was a 5-hydroxyindole derivaTHIS JOURNAL, in press. (8) Because of the possibility of occurrence of this type of resonance tive. The lack of a significant acid-base shift of designation of the 7-CiH7 group in CsHavCiHi as “cycloheptatrienyl” the ultraviolet absorption maximum signified rather than “tropylium” seems preferable. According to conventions that the hydroxy group was blocked. The Ehrlich now in use it is also difficult, or even perhaps unwise, t o assign a definite reaction indicated that positions 1 and 2 probably oxidation state to the vanadium. (9) National Science Foundation predoctoral fellow 1968-1960. were free. Ultraviolet and infrared data showed DEPARTMENT OF CHEMISTRY that the carboxyl, detected by electrophoretic HARVARD UNIVERSITY R. B. KING9 studies, was not conjugated with the ring. CAMBRIDGE 38, MASS. F. G. A, STONE Because extremely small amounts of material RECEIVED AUGUST6, 1959 were available, final evidence for the structure of I was obtained by mass spectrometry. The ISOLATION OF 5-METHOXYINDOLE3-ACETIC ACID methyl ester, prepared by treating I with dinzoFROM BOVINE PINEAL GLANDS’ methane, had a mass of 219. A strong peak a t mass 160 indicated the structure of a fragment as Sir : CH30-Cs&N-CH2-. These data suggested that During the isolation and characterization of the structure for I was 5-methoxyindole-3-acetic melatonin,2 a substituted 5-hydroxyindole deriva- acid. I was synthesized from 5-methoxyindole-3tive in the pineal gland that can lighten pigment a c e t ~ n i t r i l e . ~ -The ~ J synthetic and natural comcells, we found a chemically related but biologically pounds were found to have identical chemical and inactive compound. The latter, now identified physical properties as determined by reaction with as 5-methoxyindole-3-acetic acid (I), is the first Ehrlich reagent; infrared, ultraviolet absorption demonstration of 0-methylation of a 5-hydroxy- and fluorescence curves; countercurrent distriindole. This compound had not been known to bution; silicic acid column; and paper chromaexist in biologic tissue although it had been isolated tography with acidic, basic and neutral solvents. as a urinary excretion product in rats after admin- Mass spectrometry of the methyl esters of both istration of 5-methoxytryptamine. synthetic and natural I revealed the same proOne hundred grams of trimmed lyophilized bovine portion of 219 and 160 masses. pineal glands4 was powdered in a blender and deO F DERMATOLOGY fatted with petroleum ether in a soxhlet extracter. SECTION DEPARTMENT OF MEDICINE AARONB. LERNER The powder was mixed with 1700 ml. water in a YALEUNIVERSITY SCHOOL OF MEDICINE blender for two minutes and the mixture centri- NEWHAVEN11, CONNECTICUT JAMES D. CASE K. BIEMANN OF CHEMISTRY fuged a t 16,000 X g for 30 minutes. The supernate DEPARTMENT IXSTITUTE OF TECHKOLOGY was passed through glass wool and extracted twice -MASSACHUSETTS 39, MASSACHUSETTS with equal volumes of ethyl acetate. The ethyl CAMBRIDGE RICHARD V. HEINZELMAN acetate layers were taken to dryness in vacuo. RESEARCH DIVISION JACOB SZMUSZKOVICZ W. C. ANTHOSY The residue was subjected to countercurrent dis- THE UPJOHNCOMPANY CSHgVC7H8, since the latter would be a cycloheptatriene derivative of vanadium1 with two unpaired electrons. The vanadium compound should most probably be formulated as C7H;+V°C5H5-(I). However, in the solid state it is stable in air a t room temperature, only beginning to decompose a t about 130°, in distinct contrast to the isoelectronic (C6H6)2V.6 Perhaps it is possible to explain the increased stability of C ~ H S V C ~over H ~ (C6H6)2V by regarding the former as a resonance hybrid of I and C7H7-VIIC5H6-(II). Although the cycloheptatriene anion, isoelectronic with a “planar” cyclooctatetraene molecule with eight a-electrons, is not normally stable, the existence of C8HsFe(CO)a and C8H8[Fe(C0)3]27indicates that stable sandwich compounds can be formed by 8 T electron systems, suggesting that the canonical form (11) might have some importance.8 IVe thank the Milton Fund for support of this work, the Shell Chemical Corporation for a gift of cycloheptatriene, and Union Carbide Metals Company for a gift of vanadium halides.
(1) This investigation was supported hy grants from the American Cancer Society and the United States Public Health Service. (2) A. B. Lerner, J. D. Case, Y.Takahashi, T. H. Lee and W.hlori, THISJOURIAL, 80, 2587 (1958). (3) V. Erspamer, J. Physiol., 127, 118 (1965). (4) W e are grateful t o the Armour Laboratories for supplying us with many kilograms of bovine pineal glands.
KALAMAZOO, MICHIGAN RECEIVED JULY 29, 1959
;1
KRIVIS
( 5 ) T. Hoshino and K. Shimodaira, Bull. Chem. S o r . Jnp,a,t. 11, 221 (1936); C. A . , SO, 59829 (1936). (6) S. P. Findlay and G. Dougherty, J . Oig. Chem., 13, X O (ISIS). (7) B. Asero. V. A. Colo and A. Vercillone, I1 Pharinaco (Pn73,n). E d . s c i . , ii, 219 (1956); C. A , , 80, 138700 (1956).
