.no
FRANCIS 1'. DKYRR,FRANCIS 1,.
simple nialonate ion in the potassium salt. This band has been assigned to the OCO antisymrnetric stretching vibration. '1 previous investigation6 showed that thc 11'~ture of the metal-to-ligand bond (h4-0) niay be detcrmined indirertly from the values of the CO stretching frequencies, without determining the low frequencies characteristic of the 34-0 stretching vibration. The in-phase OCO frequency in inalonato metal complexes is lower than the correspmding OCO syinniCtriC freclucncy of the iiniplc
[ CION~RIIIIJI.IOS
RROX
r m I~PARTMRST
I K V A K .4ND :II,I3ERT
SIIUI.\IAN
Vol. 81
malonate ion, and the out-of-phase frequency is higher than the corresponding antisymmetric frequency. However, these cliff erences are less than thvse observed for the osalato metal complexes. Consequently we may conclude that the metal-toligand bond of the malonato metal complexes is more ionic than that of the oxalato metal complexes. Although the OCO bending vibrations are also affected by coordination, the observed frequencies can reasonably be assigned ns shown in Tnhle TI. Y O l K r r>AMC, I \ I ) I " i Y \
OD INORGANIC CIIEBIISTRY, JOIIN CIJRII C Scrrncii, AuSI.R:\I.IAS S A T I O S A I , cNIVERSI'I.Y]
or; MRMCAI. RESBARCII,
Stereospecific Influences in Metal Complexes Containing Optically Active Ligands. Part I. Some of the Optical Isomers of Tris-(propylenediamine)-cobalt(II1) Ion BY
FRANCIS
P.
DWYER, FR.4NCIS
L. GiZRV.4N
AND ilLI3ERT SI1ULMAN
RECEIVED JULY 21, 1935 Oxidatiuii of a misturc of a cobalt( 11) salt and levo-propylenediamiiie in the prcsericc of some acid gave two isomeric The optical antipodes were prepared from dextro-propylenedjamine. tris-compounds for which [ a ] -24' ~ aiid +214'. The base recovered from each isomer was optically pure, [ a ](in~ dry Imizene) 3~31.4".The isomers for which [ a ]~ t~2 1 4 O are believed to be the ~ l i and l ~ - d d disomers. For the reaction D-111 2 all u.;iiig charcoal as catalyst the equilibrium constant was found to be 5.ic5whence LIP= - 1.02 zk 0.03 kcal./g. mole. The preparation of optically pure d- and l-propylenetliatnine is dcscrilictl ant1 also the resolution of DI. [Co(dl-p11)3]3+ion.
to occur in the synthesis of complexes with Introduction The introduction of asymmetric groups or mole- three asymmetric ligands. Two forms only, descules into metal complexes, that themselves are ignated L-ddd and D-111, have been obtained for ]~+ [ P t ( ~ n ) ~ ] ~ + , capable of existence in enantiomeric forms, in- [Co(cptdin)3]3 f , [ R h ( ~ p t d i n ) ~and creases very considerably the number of theo- when the racemic base was used for the synthesis. retically possible optical isomers. The bis- (ethyl- Since propylenediamine, (pn), is unsymmetrical as enediamine)-(d,l-propylenediamine)-cobalt(111) ion well, each of the optical isomers can exist in cis and may exist in four possible optical forms designated trans forms, making a total of twenty-fourtheoretical simply D - d , D-I, L-1, ~ - d , while l eight isomers are isomers. Frequently, in order to simplify the system possible for the tris-(d,l-tuans-l,2-cyclopentane-in the tris-complexes, one optical form only of the diamine)-cobalt(II1) ion, ([ Co(cptdin),I3+). How- ligand has been used. The number of theoretical ever, in practice it is believed that the interaction isomers is reduced thereby to two (D-ddd and L-ddd) of the ligands with themselves and with the asym- with symmetrical ligands. With one exception, one metrical field of the whole complex provide a isomer only has been isolated. Three forms of the stereospecific limiting factor that excludes many of possible four have been obtained of tris-(&alanine)the isomers. It is believed that a single asym- cobalt(lII), of which one presumably is the unusual. metric ligand occasions but partial stereospeci- thermodynamically unstable form.5 Detailed discussions of the principle of stereoficity and certain forms (usually D-d and L-L), predominate in the mixture of More specificity will be found in recent revie.ws and text pronounced stereospecificity appears to be en- hook^.^-^ It: is unfortunate that the evidence for the countered in the synthesis of complexes with two asymmetric donor groups, and isomers containing principle of stereospecificity is largely negative and both optical forms of the donor groups, such as that this aspect of the theory has not been sufD-dl and L-dl, have not been Very ficiently emphasized. Critical evaluation of the great liniitation causing the exclusion of most of the experimental detail of much of the work shows that theroretically possible isomers has been claimed little quantitative information is available and, as Bailar and Johnsonlo have pointed out in relation (1) T h e symbol D o r I. specifies the theoretical configuration of t h e to the tris-(propylenediamine)-platinum(1V) comwhole complex which is not necessarily related t o t h e sign of t h e rotation in a convenient wave length o f light. As t h e absolute conplex, that much of the chemical material is unfiguration neither oi t h e optical forms of propylenediamine nor o f any of its metal complexes is known. t h e arbitrary designation sugrested b y Jaeger a n d used constantly h y all authors subsequently has been used in t h i s paper. T h e capitals refer t o t h e sign o f the rota. tion of t h e whole complex and the sinall letters t o t h a t of the ligand, usually at t h e D-line of sodium. ( 2 ) F. h l . Jaeger a n d 11. R . Plumenrlal, 2 . n n o i g . Cheni., 175, l G l , 198, 200, 220 (192s). ( 3 ) J. C. Hailar. 11. n. Jmiassen and E , IT. IInffnian, T r ~ r JsO I ~ R N A I . . 70, 7.56 (1!)1R). (4) 37 3l:irLiiirtlp :!nil J . 0.J h i l a r , ~ h i i l . 1, 4 , 111.51 (lR,-)Z),
(.?I
J . Lifschitz, 2.$ i z y ~ i k .C h e m . , 114, 44.3 (1925). ( 6 ) F. Basolo. Chein. Revs., 52, 512 (1953). (7) A. E. AIartell and bl. Calvin, "The Chemistry oi t h e Metal Chelate Compounds," Prentice-Hall, Inc., Iiew York, N. Y . , 1952, p. :307. ( 8 ) F, Hasolo and R. G. Pearson, "1Iechanisms of Inorganic Reactions." John Wiley and Sons, Inc., New York. K. Y . , 1958, p. 289. (9) J . C . Railar ( E d ) , "The Chemistry of t h e Coordination Compounds," Reinhold Publ. Corp., S e w York, N. Y . , 1956, p. 313. (111) R . D. .Johnsou, l h e s i s , Tinivers1t.y of Illinois, 1948.
Jan. 20, 1959
OPTIC.4L
ISOXERS O F TRIS-(PROPYLENEDIAMINE)-COBA4LT(III) ION
291
The synthesis of tris-(propylenediamine)-cobalt(111) salts was carried out by Pfeiffer and Gassman16 using the racemic base and later by Tschugaeff and Sokoloff l7 and Smirnoff l8 using the optical forms of the base. The salts isolated1* were D[C0(d-pn)~]Br~.2H~O from the d-base and L[ C ~ ( l - p n )Br3.2Hz0 ~] from the I-base.19 No other forms were detected and comparison of the rotatory dispersion curves1* with the optical forms of tris-(ethylenediamine)-cobalt(II1) bromide confirmed the configurational assignment and the absence of other isomers. In this investigation, before repeating Smirnoff’s work, the preparation of optically pure d-and 1propylenediamine and its recovery from the cobalt complexes have been studied. The true specific 2 ~ - [ R h21lI3+ + D - [ R h 3 ~ - [ R hlZdI3’ rotation of propylenediamine and a reproducible This reaction which necessitates dismutation and method of measurement are essential for the valid reformation of the complex from the fragments is characterization of the metal complexes, especially a t variance with the known robustness of the those containing more than one optical form of the rhodium(II1) complexes which characteristically base. do not undergo this kind of rearrangement. CoThe resolution was reported originally by Baubalt(II1) complexes are also robust but the syn- rnannZowho recrystallized the hydrogen d-tartrate thetic conditions usually employed to prepare ten times to give [Ly]D - 20.96’. Exactly the tris-(diamine) complexes can permit equilibrium same procedure used by Tschugaeff and Sokoloff 2 1 to be attained between various species by electron gave a product for which [ C X ~ D -28.04”. Laterz2 transfer with the labile Co(I1) intermediates. For these workers carried out fifteen recrystallizations the latter reason the suggestion that the isolation and also used 1-tartaric acid to obtain the d-isomer. of the L-ddd and D-ddd isomers of tris-(d-alanine)- The highest specific rotations were +29.70 and cobalt(II1) depended upon greater strength of the -29.78‘. Recent workers have not used the chelate ringsl1,lZis unlikely. More feasible rea- specific rotation of the “anhydrous” base as the sons are that the free energy difference between criterion of optical purity but have quoted the the D-ddd and L-ddd isomers is smaller than in the rotation of the dihydrochlorideZ3(+3.99’ to tris- (diamine) complexes or that the solubility 4.10°,from I-pn) or the melting point of the hyrelationships are more favorable. drogen d-tartrateZ4(142’). The small rotation of The analogy between the internal diastereo- the hydrochloride is a practical objection, and the isomeric complexes and organic substances with melting point of the diastereoisomer is unreliable more than one optical center is obvious. Where because of decomposition near the melting point, purely steric factors are not involved, the free besides giving no indication of the relative amounts energy difference anticipated from the kind of of the optical isomers present. It is not clear from physicochemical forces likely to exist should be of the published descriptions how the recrystallizathe same order. From measurements of the tions of the diastereoisomer should be performed, equilibrium of organic diastereoisomeric salts in how many are necessary, nor in fact whether the non-ionizing solvents and consideration of the data optically pure isomers ever have been obtained, on sugars and esters with a t least two optical The variation in the specific rotation obviously centers, Kacser and U b b e l ~ h d econcluded ~ ~ , ~ ~ that depends on the hygroscopic nature of the subthe free energy difference between optical isomers stance and the change in sign that accompanies was of the order nRT where n is a small number, protonation. Fowles, McGregor and SymonsZ5 ( K = - l S ) . From the equilibrium between d- have shown that the preparation of anhydrous and l-tris-(l,l0-phenanthro1ine)-nickel(I1)ion in ethylenediamine and propylenediamine requires the presence of d-a-bromocamphor-n-sulfonate ion drastic and elaborate procedures involving several the free energy difference between diastereoisomeric distillations over sodium and potassium. The anhyion pairs was found15 to be 70 cal./g.mole. This drous bases are reported to be blue. would suggest that when the interacting groups are (16) P. Pfeiffer and T. Gassman, Liebig’s Ann. C h o n . , 346, 45 held by covalent bonds rather than van der Waals (1906). association, free energy differences similar to the (17) L. Tsehugaeff and W. Sokoloff, Be?., 42, 55 (1909). organic isomers can be expected, and appreciable (18) A . P. Smirnoff, H e l v . Chim. Acta, 3, 177, 194 (1920). (19) Some confusion has arisen in the literature because Tschugaeff amounts of most of the theoretical isomers should and Sokoloff have stated (presumably in error) t h a t [Co(pn)a]la~ZH~O be present in the synthetic mixtures. +23.63O (cf. [.ID - 2 4 O reported in derived from the 1-base had DI.[
accounted for in the total amount of isomer finally isolated. Similarly, i t is not certain that some of the complexes from which stereospecific conclusions have been adduced have in fact ever been prepared. As we shall show later the synthetic reaction [CoAZClz]+ B-t[CoAzBI3+ 2C1-, (A and B are diamines), used frequently, does not proceed as a formal displacement and yields with some bases, at least, a difficultly separable mixture of products containing both [CoA3I3+and [CoB3I3+ions. In order to account for the failure to isolate some of the optical isomers of the tris-(diamine) coniplexes of Co(II1) and Rh(III), i t has been proposed3 that while they may be formed initially, they undergo disproportionation
+
+
+
(11) F. M. Jaeger, “Optical Activity and High Temperature Meas. urements,” McGraw-Hill Book Co., New York, N. Y.,1930. (12) J. C. Bailar, Rer. Chem. P y o g y . (Kresge-Hooker Sci. L i b , ) , 10, 17 (1949). (13) H. Kacser and A. R. Ubbelohde, J . Chem. Soc., 2152 (1950). (14) M. M. Harris, “Progress in Stereochemistry,” Butterworth London, 1958, p. 164. (15) N. R. Davies and Ti. 1’. Dwyer, Tvans. F u r a d u y Soc., SO, 24 (lY5l).
this work), suggesting t h a t i t was the D-111 isomer. (20) G. Baumann, B e y . , 28, 1176 (1895). (21) L. Tschugaeff and W. Sokoloff, ibid., 40, 3461 (1907). (22) L. Tschugaeff and W. Sokoloff,ibid., 42, 56 (1909). (23) J. C. Bailar, H. B. Jonassen and A. D. Gott, THIS JOURNAL, 74, 3131 (1952). (24) T. D. O’Brien and R. C. Toole. ibid., 75, 6009 (1954). (25) G. W. A . Fowles, W. R . McGregor and M. C. R. Symons, J . Chen7. Soc., 332!i (1957).
FRANCIS P. DWYER, FRANCIS L. GARVAN A N D ALBERT SHULMAN
292
i t has been found that the partly dried base can he extracted into benzene and dried therein with caustic potash t o give consistent values of the specific rotation. Resolution is best effected by the use of a mixture of tartaric acid and acetic acid. Ten recrystallizations from dilute acetic acid sufiice fur all pmctical purposes, [ a ] -34.2' ~ in benzene. The rotation only rises to -34.8" after twenty-three recrystallizations. The preparation of the d-isomer from ~ - [ C o ( d - p n ) ~ ]has ~+ been proposed by Johnson and Bailar'O who obtained indications for the resolution of DL-[Co( d l - ~ n )3 ~ f lion through the chloride d-tartrate by extraction of the gummy mixture of the diastereoisomers with methanol] following the failure of Lifschitz and Rosenbohm,26who used the tartrate and the a-bromocamphor-r-sulfonate. Resolution can be effected through the chloride d-tartrate by the use of ethylene glycol as a solvent, and then recrystallization from aqueous ethanol. The cobalt complex after distillation with caustic potash and potassium rnetabisulfite gave the pure d isonier in good yield. The cobalt(II1) complexes prepared from either optical form of the base can be separated into two isomers of opposite sign but greatly different rotatory power. These have been assigned the configurations D-ddd, L-ddd and L-111, D-112. The propylenediamine, recovered from each isomer by fusion with sodium suIfide in the presence of sodium hydroxide and extraction with benzene, was optically pure. No evidence was obtained, despite repeated fractionation of the stable isomer, of cis and trans forms. For all of the fractions of the D-ddd-r.,-ddd mixture (Table I) the composition calculated from the observed [ a ]and ~ the specific rotations of the pure components agreed well with the composition calculated from the observed [aI5461. It is probable that in the Co(II1) complexes the geometrical isomers have similar solubilities or form solid solutions. The visible absorption curves of the D-ddd and D-111 isomers appear to be identical with an absorption maximum a t 466 r n p . From measurements a t 589.3 and 546.1 rnp it is concluded that the rotatory dispersion curves are quite different. The thermodynamically stable isomer can be isomerized on charcoal a t 20' in 0.5 hr to yield the equilibrium mixture in which the D-111 isomer is present to the extent of 14.8 =t 0.7OjoO.The same percentage has been found when the Co(II1) complex is synthesized from the base in the presence of charcoal. From the value K = 5.75 we calculate AF* -- - 1.02 + 0.05 kcal./g. mole. The adjoining table summarizes the optical properties of the substances isolated : [.ID Compound
[ab
~ - [ C o ( d - p n ) , ] I ~ . H &-k 24" rd- [ Co ( d - p n ) ~13.H20 ] 2 14O ~-(Co(l-pn),]I~.H:0 24' u-[Co(l-pn)3]Is.H20 + 2 1 4 O
-
(in beuzene) of recovered propylenediamine
[alsasi
+184O
-404" -184'
+404O
+34.2" f34.4O -34 8" -34 3"
Recently it has been proposed from a study of the dispersion ratio of various colorless tris-(propyl(20) J. Lifschitz aiid E. Rosenbohm, Z 19, 10s (lQI'3)
ginphtr
wrssenschafLlzche
Vol. SI
enediamine) metal complexes a t 470.5 and 5SS.O m p , that the induced asymmetry inherent in the concept of stereospecificity is spurious and that the optical activity of the complex arises only froin the ligand.24p27The present work shows that while the ligand may make some contribution to the activity the induced asymmetry is the predoniinating factor. Substantial support is afforded by the isolation of the corresponding isomers of the colorless tris-(propylenediamine)-platinum(1V) ion to be described in Part (11). It should be emphasized that we have not obtained completely exclusive evidence that the optical isomers isolated are not simply the cis and trans isomers. However, the specificity of the resolving agent toward one isomer (e.g., d-tartrate and the D - d d d isomer), the coprecipitation of the D-ddd and D-111 isomers as C1-d-tartrate, and the differences in rotatory power of opposite sign suggest strongly that the configurations are as designated. By using Courtauld models it can be shown that there is no steric interference in isomers such as ~-ddl or L-lld nor in the cis and trans geometrical isomers. The methyl groups of the asymmetric carbon atoms are directed away from each other and from the metal atom. The separation of isomers containing two optical forms of the base is being pursued b y fractionation of the mixture of isomers produced when dl-propylenediamine or 80% d or 1-base is used in the synthesis of the complex. The use of partly resolved base might be expected to simplify the separation of some of the isomers. The isolation of an isomer believed to be L-lld for which ID -78', [cx]5461 -2244' and from which the recovered propylenediamine had [ a ]-~11.5' (in benzene) will be described later. Experimental Rotations were measured a t 20' in a one-dm. polarimeter tube unless otherwise stated. Resolution of dl-Propylenediamine, (1,2-Propanediamine) levo-Isomer.-Technical propylenediamine (260 g., 325 ml.) was added slowly with stirring to a solution of dtartaric acid (700 g.) in cold water (750 rnl.). The mixture: which had almost boiled, was allowed to cool slowly to 40 and then cooled rapidly in ice t o 5' and kept a t that temperature for 0.75 hr. The crystalline diastereoisomer was filtered through a large buchner funnel, sucked very dry and washed with ice-water (230 ml.). The yield of airdried material (fraction 1) was 420 g. A further crop of crystals (200 g. Fraction 1A) was obtained by the addition of glacial acetic acid (150 ml.) to the hot filtrate and washings and allowing to c o d overnight. Recrystallization was effected by dissolution in boiling water (850 nil.) followed by glacial acetic acid (50 ml.) and cooling to 10'. For each additional crystallization the volume of water was reduced by 50 ml. and the acetic acid by 3 ml. Ice-water (100 ml.) was used for washing the crystals. A t the end of each recrystallization a sample was reserved for recovery of the base. After 10 recrystallizations a portion of the product (100 9.) was recrystallized a further 13 times from 20% acetic acid. The base from each sample (8 g.) in water (40 ml.) containing sodium hydroxide (22 g.) was extracted by boiling benzene (50 ml.) for 0.75 hr. in an extraction tube. The extract was dried over solid potassium hydroxide (5 g.) for three days. The rotation was measured in a well dried polarimeter tube (2 dm.) and the concentration of the base determined, after extraction into water, by titration with 0.1 V. acid to the methyl orange end-point. ((YD average = -0.8", titer average, 10 ml. benzene = 30 m1.1. The specific rotation [a]Din dry benzene was -25.2
Photo(27) T.D. O'Brien and IC. C. Toole, THISJ O U R N A L . 7 7 , 1808 ( 1 9 6 5 ) .
OPTICALISOMERS OF TRIS-(PROPYLENEDIAMINE)-COBALT(~~~) TON 293
Jan. 20, 1959
and -26.5' for fractions 1 and l A , rising t o -34.2' after ten recrystallizations and -34.8 f 0.4" after twenty-three. The specific rotation was independent of the concentration in dry benzene in the range 0.53 to 2.84%. The separation of propylenediamine from benzene is impracticable because of codistillation in the boiling range 82 to 119'. In all subsequent work ten recrystallizations were considered sufficient and yielded 430 g. of the diastereoisomer, which was converted to the hydrochloride by the method of Bailar, Jonassen and Gott.*3 The best yield cf the base was obtained by cautious distillation from the hydrochloride (dried for 15 hr. a t go"), mixed intimately with sodium hydroxide flakes (200 g.). This gave 110 g. of aqueous Ipropylenediamine, equivalent to 74 g. of the pure base. dextro-Isomer.-The filtrate after the separation of the second crop of crystals (Fraction 1A) was evaporated in a large dish on a steam-bath in a strong current of air. In this way much of the acetic acid evaporated leaving a thick sirup which was transferred t o a 2-1. flask. Sodium hydroxide flakes were added until alkaline and then 200 g. more. The mixture was distilled using a current of air for agitation, until the base was removed and frothing commenced. The distillate contained 130 g. of the base in aqueous solution, ( [ a ] ~ in dry benzene $25'). This was partly neutralized with 10 N hydrochloric acid (58.3 ml.) and added t o a solution of cobalt(I1) sulfate 7-hydrate (163 g.) in water (1000 ml.). After the addition of charcoal (50 g.), a brisk current of air was passed for 24 hr. through the solution. The charcoal was filtered from the resulting tris-(propylenediamine)-cobalt(III) chloride sulfate and washed with hot water (300 ml.). Barium d-tartrate l-hydrate (178 9.) was stirred in and the mixture kept a t 90" for 2 hr. with mechanical stirring. After removal of the barium sulfate, the filtrate was evaporated to about a liter on the steam-bath and then cooled and an equal volume of ethanol added. The re: oil that separated, crystallized on The solid was recrystallized by standing overnight a t 4 dissolution in 500 ml. of water (45') and addition of ethanol (400 ml.) with cooling in ice. The yield of yellow D[Co(d-pn)a]Cl-d-CaH~06~3H~O was 163 g. (d-pn recovered gave [ a ]$31.3", ~ in benzene). It was recrystallized twice from water (400 ml.) by the addition of methanol (250 ml.) and cooling in ice for 0.5 hr. (yield 132 g.). The diastereoisomer, f i s t air-dried and then heated a t 90" for 1 hr. was ground with a finely powdered mixture of potassium metabisulfite (20 g.) and sodium hydroxide Bakes (200 9.) and distilled cautiously with a large free flame. The yellowish distillate was redistilled from solid potassium hydroxide (10 g.); yield 53 g. of 737, (w.[w.) aqueous d-propylenediamine, [ a ]in~ benzene $32-33 Purer d-propylenediamine, but in lower yield, could be obtained by evaporation of the original solution of the chloride d-tartrate to a thick sirup, stirring in ethylene glycol (360 ml.) and then adding cold methanol (360 ml.) The solid that separated was recrystallized by dissolution in water (600 ml.) adding an equal volume of methanol and cooling in ice (yield 104 g.). This gaze 42 g. of 737, (w./ w.) d-propylenediamne, [ a ] ~ +34 0 small portion (20 9.) of this purer diastereoisomer was recrystallized another five times The pn. was extracted into benzene giving [ a ] D $34.8 f 0.6. Recovery of Propylenediamine from Small Samples of the Co(1II) Complexes.-Sodium sulfide 9-hydrate (2 9.) and potassium hydroxide (0.4 9.) were just fused in a test-tube with a ground glass joint. The cobalt compound (0.5 to 0.8 g.) was poured onto the fused mass, which immediately became black. Sodium hydroxide pellets (5 g.) were added, a reflux condenser attached and the mixture heated for a few minutes t o complete the decomposition. Benzene (10 ml.) was added through the condenser and the mixture refluxed for 20 min. After cooling, the benzene was filtered on to solid potassium hydroxide (4 8.) and the extraction repeated with a fresh portion (10 ml.) of benzene. After drying for 24 hr. the rotation of the benzene solution was measured in a 2 dm. tube and the concentration of the base determined as before by titration with acid. For pure isomers containing only one optical form of the base the average rotation measured was 0.6 to 0.7'. Resolution of n , ~ - [ C o ( d , 1 - p n ) ~ ] I ~ .to H~ Yield o the Isomers ~-[Co(d-pn)~]I~.H and ~ o ~-[C~(l-pn)a]Ia .H2O.-A solution (1 1.) of D,L-[CO(d,l-pn)a]~(SOl)awas prepared by the aerial oxidation of cobalt(I1) sulfate 7-hydrate (45 g.), technical propylenediamine (48 ml.), sulfuric acid (16.4 ml. 10 N)
.
.
.
and charcoal (10 g.). The charcoal was removed after 10 hr., the solution heated to 90' and barium iodide 2-hydrate (100 9.) added. After digestion, the barium sulfate was removed and the filtrate evaporated to 500 ml. on the steam-bath. The orange-yellow iodide separated on cooling and was recrystallized three times from the minimum volume of water a t 90" followed by cooling to 20'. This substance was substantially the racemic form of the D-ddd and E-111 isomers. The other isomers remained in solution. dextro-Isomer.-The racemate (22.5 9 . ) in water (200 ml.) was transformed to the chloride by shaking with silver chloride. After filtration and washing of the silver halide precipitate, silver d-tartrate (12.10g.) was added to the filThe silver halide was trate and vigorously shaken a t 80 removed, washed with hot water and the filtrate and wash liquid evaporated to a thick sirup. Acetone (500 ml.) was added whereupon the mixed chloride d-tartrates crystallized. The solid was washed with acetone and dried in the oven a t 70'. I t then was dissolved in ethylene glycol (100 ml.) by warming and stirring. On cooling and scratching the sides of the vessel the D-diastereoisomer crystallized in very fine yellow needles. The crystals were washed with 507, methanol-ethylene glycol, then with methanol and acetone. After separation of most of the D-diastereoisomer in this way, the substance could be crystallized easily from water by the addition of half the volume of methanol. Anal. Calcd. for [CO(C~HI~NZ)I]C~.C~HIOB.~H~O: C, 30.08; H , 7.77. Found: C , 30.22; H , 7.67. The diastereoisomer (5 g.) in warm water (20 ml.) was treated with concentrated ammonia solution (0.2 ml.) and 25% sodium iodide solution added. On scratching the sides of the vessel and cooling in ice the dextro-iodide crystallized. The fine orange powder was washed with cold 25% sodium iodide and recrystallized three times by dissolution in hot water, followed by the addition of a little solid sodium iodide. The crystals were washed with acetone and air-dried. A 1.00% aqueous solution gave a~ 0.24", whence [ a ] ~ $24'; and a 0.507, solution gave 05~61 +0.92', whence [a15461 f184' (dispersion ratio, 7.66). The recovered dpropylenediamine gave [ a ] f34.2 ~ f 0.7". Anal. Calcd. for [Co(C3Hlon'2)3]Is.H20: C, 15.9; H, 4.74; N, 12.40. Found: C, 16.12; H, 4.75; N, 12.47. Zao-Isomer.-The same procedure as above, using silver 1-tartrate, was employed. The iodide had [ a ] ~ -24O, [a16461 - 184", and the recovered I-propylenediamine gave i a. l ~-34.8 f 0.7". . Anal. for [Co(CaH:oT\'p)a]C1.CHaOa.3H20. Found: C, 30.30; H, 7.34.. Anal. for [ C O ( C ~ H ~ ~ N ~ ) ~ ] I ~ Found: . H Z O .C, 16.16; H , 4.50; N, 12.54. L-Tris-(d-propylenediamine)-cobalt(111) Iodide I-Hydrate, ~-ddd.-dextro-Propylenediamine (28.4 g., [ a ]$33") ~ was used to prepare the sulfate of the Co(II1) complex as described previously. This was transformed to the iodide with the required weight of barium iodide 2-hydrate in aqueous solution, and crystallization effected fractionally by evaporation on a steam-bath in a current of air (theoretical yield 87.0 g.), The results are shown in Table I. The most soluble fraction A6 was separated as the sparingly soluble salt of the anion 1 3 - by addition of hydrogen peroxide, sodium iodide and acetic acid. After air-drying it was suspended in absolute ethanol and converted to the iodide by passage of sulfur dioxide.
.
+
TABLE I Fraction
Vol. of s o h . , mi.
Ai
700
A2
400 150 80 30
A8
A,
As A6
Total
..
wt. of fraction, g.
3G.0 23.3 12.6 2.3 2.7 0.4 77.3
lalu
[alntcl
- 3" - 122' - 136"
+l76" $182' 160' $110' - 188' -216"
+ 21" + 22O + 15"
+
Fractions Ai,A2, As, A, were combined, dissolved in water (500 rnl.), activated charcoal (10 g.) added and the mixture refluxed for 1 hr. The solution then was cooled and the small amount of Co(I1) complex formed during the isomerization reaction re-oxidized by the passage of air for 2 hr.
The slightly alkaline solution was neutralized with a few drops of dilute sulfuric acid, the charcoal removed and wnsfied with a little liot water. The solution was evaporated on a stcani-bath in n current of air until the sulitl wliich separated was.still wet. After cooling in ice, tlic solid w:is separated and the isomerization repeated as before. The filtrate (average volume 10 ml.) rich in the ~ - d d disomer was added to fractions .q6 and As and retained. The isomerization with charcoal was repeated ten times. The combined solutions containing the L-ddd isomer were evapoThis was rated to dryness (yield 22.6 g . , [?ID -110'). converted to the chloride by sliaking the aqueous solution ( 8 0 " ) with freshly precipitated silver chloride (20 g.) a17d then to the chloride d-tartrate with silver d-tartrate (12.1 g.). This was evaporated to dryness and the semi-solid residue treated with acetone (100 inl.), Crystallization ensued overnight, a n 3 the solid was collected and dried at 110' for 20 minutes. It was then dissolved in ethylene glycol (60 ml. at 50°), the solution seeded with the chloride dtartrate of the D-ddd isomer and allowed to er)-stallize in a desiccator for three days. The crystalline diastereoi was collected arid the filtrate reserved. The diastereoi after washing with 30% eth3-lenc glycol/etlinnol and then ethanol was recrystallized from water by the addition of ethanol. T h e iodide obtained as described previously was the optically pure D-ddd isomer, [ a ] D f24'. T h e diastereoisomer remaining in tlie ethyleiie glycol solution above was precipitated by a large volunie of acetone and transformed in aqueous solution to the iodide (yield 8.1 g:, [ a ] D -162'). It was agaiii resolved through the chloride d-tartrate as before and suficient acetone added to the ethylene glycol solution to cause separation of about 25%; of the diastereoisomer. The latter, which crystallized slowly, was rejected and the inore soluble diastereoisomer transformed t o the iodide. Separation ;if the iodide into two fractions gave [ a ] D -194' nnd -810 . Thelesssolublr (bigger) fraction was recrystallized from water by the addition of sodium iodide and the fractioii that remained iri solution separated as the salt of the 1 3 - anion. After drying and passsage of sulfur dioxide in absolute ethanol, the latter gave a yellow powder having [ m ] D -214' and [ Q ] S ~ G I -404' (dispersion ratio, 1.89j. The rotation of the substance was unchanged after recrystallization from 20y0 aqueous methanol by the addition of ether. The recovered propylenediamine had [ a ]in~benzene 4 3 4 . 4 ==! 0.7". So change in rotation occurred when a 0.4yc aqueous solution was allowed t o stand for six months. 0 1 1 rrfluring this soluti
