A STUDY OF SYNTHESIS AND STEREOISOMERISM

OF SOME COMPLEX COBALT COMPOUNDS

APPROVED:

iajor Professor Major

Minor Professor

Stoi^of^ theD epartm^t^ f^h emi s t ry

Dean of the Graduate School

A STUDY OP SYNTHESIS AID STEREOISOMERISM

OP SOME COMPLEX COBALT COMPOUNDS

THESIS

Presented to the Graduate Council of the

North Texas Stat® University in Partial

Fulfillment of the Requirements

For the Degree of

MISTER OF SCIENCE

By

Daniel T. N. Yuan, B, E,

Denton, Texas

January, 1965

TABLE OF CONTENTS

Page

ACKNOWLEDGMENT iv

LIST OF TABLES v

LIST OF ILLUSTRATIONS . vi

Chapter

X, INTRODUCTION 1

Historical Development Definition of Terms The Problem and Its Purpoaes

II. EXPERIMENTAL 5

Reagents 0 Synthesis of [CoCenJofk-amino-acid)JI2 Reactions of and Separation of

Diastereoisomers

ttical Activity «ibl® Spectra

Infrared Spectra

III. DISCUSSION 22

BIBLIOGRAPHY 26

iii

Acknowledgment. The financial support of this

investigation by the Robert A. Welch Foundation is grate-

fully acknowledged*

iv

LIST OF TABLES

Table Page

I. Summary of Synthetic Data 9

II, Comparison of the Specific Rotation of Certain Amino Acids with Their Corresponding Complexes 24

LIST OF ILLUSTRATIONS

Figure Fag®

1. Infrared Spectrum of L~l@uein@ . 16

2. Infrared Spectrum of L-yaline . . 17

3. Infrared Spectrum of L-aianine 18

4. Infrared Spectrum of L-leucine Complex 19

5. Infrared Spectrum of L-valine Complex 20

6. Infrared Spectrum of L-alanine Coaplex . . . . . . 21

vi

CHAPTER I

INTRODUCTION

It was demonstrated that some complex compounds with

the same chemical composition had different properties.

Numerous theories were proposed in aw attempt to explain it.

The fact that the compound M(AA)j yields two, and only

two, forms of opposite optical rotation confirms the belief

that it exists as two optical isomers by an octahedral

arrangement, and it is now realized that this is the correct

structure for almost all compounds containing atoms which

are hexacovalent ."*•

Optically-active bidentate molecules or ions have been

made to coordinate with hexacovalent metals and the stereo-

chemistry of some of these complex compounds has been

investigated. When one aolecule of the optically-active

base is present in the coordination sphere, there is some

tendency toward the formation of preferred configuration.

For example, d-tartaric acid reacts readily with

jCo(en)2C03)+ t 0 give the two diastereoisoaiers D~ and

L-jCo(en}2(d-tart)]+, which differ strikingly in stability,

1A. Werner, Ber., XLVII (1914), 3067.

reactivity and solubility.2 By heating to 150°, the two

diastereoisomers change to L- (co (d-tart)} +.

The optical activity found in coordination compounds

is not always caused by the presence of an asymmetric atom.

Coordination compounds possessing only axial symmetry may

exist in enantiomorphously related forms and have high

optical activity, i.e. |Co (ei^Br^, (m]d = t 602®.^ The

optical activity results from the dissymmetrical spatial

disposition of these identical substituents. If optically

active bidentate molecules, as d-tartaric acid, are incor-

porated into the coordination sphere, they exert an influence

on the configuration and change the optical properties as

well.

Optically active inorganic complex compounds are often

optically unstable and can easily be racemized. Thus care

in the resolution of isomers is necessary in order to sepa-

rate the enantiomorphs. Many processes have been used, as

the spontaneous crystallization method by Pasteur,^ the

preferential crystallization method by Werner and Basshart,^

% . B. Jonassen, J. C. Bailar, and E. H. Huffman, J. Am. Cham. Soc., LIZ (194#), 756.

^J. C. Bailar, Chemistry of the Coordination Compounds (New York, 1956), p. 308.

^1. Pasteur, Ann. Chin. Phys., 37, XXIV (1$48), 442.

^A. Werner and J. Basshart, Ber., XLVII {1914)» 2171.

the conversion to diastereoisomers method^ which is most

widely used, the equilibrium method'*' of resolution which is

widely used for organic compounds and preferential absorption

on optically-active quartzetc.

However, there is another process which produces

optically-active compounds from symmetrically constituted

molecules by the intermediate use of optically-active

reagents, but without the use of any of the methods of

resolution. This is called the asymmetric synthesis. Up to

now only two examples of asymmetric synthesis in the field

©f inorganic complex compounds have been published, 9,10 o n e

of which is represented as follows:

BL-£bo (eq^CO^J4 d-H2-tart. DL- [Co (er^d-tart] * 9n>D- [Co (er^]

It is believed that these results are achieved because of the

difference in stability of the D and L forma of dextro-

tartrato-bls-ethylenediaminecobalt (III Hon, £bo (en)L, (d-tart +«

The less stable D form reacts more readily with ethylenediamine

to form the dextro rotatory tris-ethylenediamlneeobalt(III)ion.

^F, M, Jaeger, Rec. trav. chim., XXXVIII (1919), 1&5.

^H. J. S. King, Ann. Repts• Chem. Soc., London, XXX (1933), 261.

d M. Aimi, H. Kuroya, and R. Tsuchida, J. Chem. Soc.

Japan. LXIV (1943), 995.

% . B. Jonassen, J. C. Bailar, and E. H. Huffman, J. Am. Chem. Soc.. LXX (1946), 756,

"^J. C. Bailar, Jr. and B. Das Sanaa, J. Am. Chem. Soc.. LXXVII (1955), 54SO.

The purpose of this investigation is two-fold. Some

new complex compounds > where on© of the bldentate molecules

is an optically active amino acid, were prepared, and

attempts to separate those complex isomers by different

methods were made. The replacement of the amino acid© by

optically inactive ligands was studied*

CHAPTER IX

EXPERIMENTAL

Reagents

The amino acids used were purchased from the Aldrioh

Chemical Company and used without further purification.

The trans-dichloro-bis-ethvlenediaminecobalt(III)chloride

used was prepared by the standard procedure1 with a Mod-

ification where 100 mis, of 30 per cent hydrogen peroxide

was used as oxidant rather than air. The material was

purified by washing thoroughly with alcohol and acetone

followed by a reerystallization. In recrystallissation, the

material was dissolved in a minimum volume of water at room

temperature, an equal volume of hydrochloric acid was added

and the solution chilled to ice temperature. The hydrogen

chloride was driven off the filtered precipitate by heating

at 110°C.

Synthesis of (Co(en)2(L-amino-acid))l2

Preparation of f Cotenl^d'-alapinato)]

Procedure A.—A solution of 14.25-g. {0.05 moles) of

trana-dichloro-bis-ethylenediaminecobalt(III) chloride and

"̂ J. C. Bailar, Jr., Inorg. Syn., II (1946) t 222.

6

4.90-g. {0,05 soles) of L~alanine were slurried in 40 mla.

©f water, and approximately 1.5-g.(12 pellets) of solid

potassium hydroxide was dissolved is the slurry. The deep

purple solution was heated on the steam bath until a clear,

reddish-brown solution was obtained {usually less than

thirty minutes). Then 15~g. of solid sodium iodide was

added to the clear solution. After the sodium iodide had

dissolved, cooling and scratching induced crystallization.

After recrystaliizat ion from minimum water, rotations of

toCjjj ~ - 3 0 - 4 0 ° were found.

Procedure B.—A solution of 14.25-g. (0.05 moles) of

trans-dichloro-bis-ethylenediaminecobalt(III) chloride and

4.90-g. (0.05) moles of L-alanine were mixed with 40 mis, of

water and approximately 2-g. (16 pellets) of solid, potassium

hydroxide was dissolved in the slurry. The deep purple

solution was heated on a hot plate with magnetic stirring

at a temperature of sixty degrees until it turned red

(usually from forty-five minutes to one hour). After cooling,

10-g. of solid sodium iodide was added. Further cooling and

scratching usually induced a greenish-brown precipitate.

This first precipitate was discarded and 5-g. to 20-g* more

sodium iodide was dissolved in the solution. Cooling and

scratching induced precipitation of the red crystalline

Cco(en) 2(L-alaninato)JAfter recrystallisation a .

specific rotation of [ « -200°~- -337° was found.

Preparation of fCo(en)g (L-vallnato)I12

Procedure A.—A solution of 14.25-g. (0.05 moles) of

trans-dichloro-bis-ethylenediamlnecobalt(III) chloride and

5.35-g (0.05 moles) of L-valine In 50 mis. of water was

refluxed for 20 minutes. The solution was filtered and then

evaporated at 110°C. The solid residue was dissolved in

40 mis. of water and 15-g. of solid sodium iodide was dis-

solved in the solution. The solution was stored in a

refrigerator for one day. Then the brick-red solid was

filtered and boiled with 50 mis. of ethanol. The solid was

recrystallized from a minimum quantity of boiling water.

The product showed a specific rotation (flClg « -93°.

Procedure B.—To a solution of 14»25~g. (0.05 moles) of

trans-dichloro-bis-ethylenediaminecobalt(III) chloride ana

5.^5-g. (0.05 moles) of L-valine in 40 to 45 oils, of water

was added approximately 3.0-g. (25 pellets) of solid potassium

hydroxide. The deep purple solution was heated on a hot plate

with magnetic stirring at a temperature of 110-120°C until a

clear, reddish-brown solution was obtained (about fifteen

minutes)* After adding 12-g. of solid sodium iodide, cool-

ing and scratching induced crystallization. The product

showed a specific rotation of teLlj} « -104°. This procedure

was more satisfactory.

a

Preparation of (Co(en)2(L-leucinato)J I2

Procedar# A.—A solution of 14.25-g. (0.05 moles) of

trans-dichloro-bis-ethrlenediaminecobalt(III) chloride and

6.55-g. CO.05 moles) of L-leucine in 50 mis. of water was

refluxed for twenty minutes. The solution was filtered and

then evaporated at 110°C. The solid residue was pulverized,

and 16-g. of the powder was dissolved in 50 als. of water

and 16-g. of solid sodium iodide was dissolved in the

solution. The solution was stored in a refrigerator for

two days, then the brick-red solid was filtered and boiled

with 50 mis. of ethanol. The solid waa recrystaliized from

a minimum quantity of boiling water. The product showed a

specific rotation of (i.lD - -58".

Procedure B.—To a solution of 5.7-g. (0.02 moles) of

trans-dichloro-bls-ethylenediaminecobalt(III) chloride and

2.62-g. (0.02 moles) of L-leucine in 20 mis. of water was

added approximately 1.5-g. (12 pellets) of solid potassium

hydroxide. The deep purple solution was heated on the steam

bath until a clear, reddish-brown solution was obtained

(usually less than one hour). The solution was filtered and

10-g. of solid iodide was added. After the sodium iodide

had dissolved, cooling and scratching induced crystallization.

A rotation of IJLJp » -60° was observed. This procedure was

more satisfactory.

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Reactions of and Separation of Diastereoisomers

f Co(en)2(L-alaninato))Ig

A sample of the alanine complex whose specific rotation

was -336° was dissolved in 50 mis. of wator. The observed

rotation of this solution was -1.170°. k portion of the

sample was refluxed with 0.5 g» of activated charcoal for

five minutes, then filtered and cooled. The observed rota-

tion of the solution was then found to be -0.113®, corre-

sponding to CXIq ® -32.5°.

A sample of the alanine complex whose specific rotation

was -359 was dissolved in water and refluxed with activated

charcoal• No significant change in specific rotation was

found for this solution.

A mixture of high and low rotation L-alanine complex

samples was charged onto a filter paper strip. Elution with

50 per cent ethanol solution resulted in no separation.

Two grams of the alanine complex with^] D « -3300 was

placed in a 50 ml. volumetric flask with 5 mis. of water

and 10 mis. of 50 per cent ethylenediamine. This solution

was placed on a shaker for two days at room temperature.

The reaction products were transferred to a 150-ml. beaker,

chilled in an ice bath, and treated with an excess of solid

sodium iodide. The (Co (en)^]was filtered from the

solution, recrystallized from water and washed with ethanol,

acetone and finally ether. A 0.5 per cent solution of the

XI

purified salt had a negligible rotation at the sodium

D-line.

Two grams of the alanine complex with («Mjj » -330° was

placed in a 50 ml. volumetric flask with 10 mis. of water.

This solution was placed on a shaker for more than three

days. Then the solution was treated with an excess of

solid sodium iodide. Red crystals of (Co(en)2(L-alanine)]I2

were filtered from the solution. After washing with ethanol,

acetone and ether, a specific rotation of U-1d = -327° was

observed.

Two grams of the alanine complex with [£]D » -36° was

dissolved in water and placed on a shaker for more than

three days. Ho change of rotation was observed.

Two grams of the alanine complex with l«UD « -360 was

placed in a 50 mis. volumetric flask with 5 mis. of water and

10 mis. of 50# ethylenediamine. This solution was placed on

a shaker for two days at room temperature. The reaction

products were chilled in ice and treated with an excess of

solid Nal. The (Co(en)^Jformed was filtered from the

solution, r©crystallised from water, and washed with ethanol,

acetone and ether. A solution of the purified salt had a

negligible rotation.

Four grams of the L-alanine salt was mixed with 6 mis.

of acetylacetone and put on a shaker for one week. lo

reaction was observed.

12

Five grams of the L-alaniae complex was mixed with a

saturated solution of sodium carbonate, then put on a

shaker for out week, No reactions were observed.

Five grams of the L-alanine complex was treated with

5 mis. ©f saturated sodium hydrogen oxalate solution and

put on a shaker. Ho reaction was observed after one week.

r C o ( e n ) o ( L - v a l i n a t o ) ] 12

A small amount of the valine complex sample was charged

onto a filter paper strip. Elution with 50 per cent ethanol

solution resulted in no separation.

A small amount of the valine complex was treated

with a saturated solution of sodium tetraphenylborate; some

pink precipitate formed but the product had indefinite

chemical composition.

Five grams of the valine complex was mixed with a small

amount of saturated carbonate solution, then put on a shaker

over one week. No reaction was observed.

Five grams of the valine complex was mixed with 10 mis.

of saturated sodium hydrogen oxalate solution and put on a

shaker over one week. No reaction was observed.

Four grams of the valine complex was mixed with 5 mis.

of acetylacetone and put on a shaker for one week. No

reaction was observed.

Four grams of the valine complex was mixed with 10 mis.

of water and 10 mis. of 50 per cent ethylenediamine in a

13

50 ml. volumetric flask and placed on a shaker for three

days at room temperature. Then the solution was transferred

to a 50 ml. beaker, cooled and treated with an excess of

solid sodium iodide. Orange crystals of [Co(en)^)1^ were

filtered from the solution, reerystallized from water, and

washed with ethanol, acetone and ether. Optical rotation

at the sodium B-line was observed to be negligible.

fCo(en)2(^-leuciaatofllg

Five grams of the leucine complex was dissolved in just

enough water to effect solution and then added to 15 mis.

of 50 per cent ethylenediamine. This solution was placed

on a shaker for two days. The resulting solution was cooled

t© 0°C and an excess of solid sodium iodide added to praeip-

it.te (Co(en)3)I3. The product showed negligible optical

rotation.

Pour grams of (Co (en) 2 (L-leucinato) ] I 2 was dissolved in

a minimum amount of water and to it was added a saturated

sodium cyanide which contained about 2 grams of sodium

cyanide. After mixing, the solution was placed on a shaker

in room temperature. After four days, crystals of

(0o(en)2(CM)2)X started to precipitate. The [Co(«)2(CS)jJ I

was filtered and washed with alcohol and acetone.. A® the

yellow-orange colored [Co(en)2(CN)2")I is quite insoluble, it

was crushed in a mortar with a saturated silver nitrate

solution. After filtering off the silver iodide, the clear

14

yellow solution of (Cofen^CCNyNO^ was observed to have

negligible rotation.

Five grams of the leucine complex was dissolved in a

minimum amount of water* Four grams of acetylacetone was

added and the mixture was placed on a shaker. After two

weeks a precipitate was obtained by adding solid sodiua

iodide. By the results of nitrogen analysis (11.35$) and

rotation {[jL]g » -29°), it is supposed some of the leucine

complex (N, 12.4$> l<Uj) ~ -53°) reacted to form an optical

inactive [Cofen^f&cetylacetoneJllg (N, 10,6%). An attempt

to separate them was unsuccessful*

Five grams of the leucine complex was mixed with

saturated sodium carbonate solution and then put on a shaker

for one week. No reaction was observed.

Five grams of the leucine complex was mixed with satu-

rated sodium hydrogen oxalate solution and put on a shaker

for one week. No reaction was observed.

A wall amount of L-leucine complex was charged onto a

filter paper strip and elution with 50 per cent ethanol

resulted in no separation.

Five grams of the leucine complex was dissolved in water.

Two grams of sodium tetraphenylborate was dissolved in water

and added into the complex solution. A reddish-pink solid

precipitated. The solution was stirred on a magnetic stirrer

overnight)then the product was filtered off. A rotation of

15

-49® was observed for the product. To the filtrate

another two grains of tetraphenylborate in solution was

added. A second quantity of precipitate formed. After

stirring o m day, the precipitate was filtered and a

rotation of [<C]Q = -50.fl° was observed. A third time two

grans of sodium tetraphenylborate in solution was added into

the remaining filtrate and after one day's stirring a rota-

tion of [<UD » -45® was observed.

Optical Activity

All measurements were made on a Rudolph Model 60 Pre-

cision Polarimeter using a sodium vapor lamp as the light

source. A determination was made on a water blank before

m d after each measurement. All reported rotations were the

average of several readings.

Visible Spectra

Visible spectra were determined on a Beekmen Model DK-1

Recording Spectrophotometer. Samples were solutions of

1 par cent concentration of the complexes. A peak at 4$0 m/<

was shown for all the three complexes.

Infrared Spectra

Infrared spectra were determined on a Perkin-Elmer Model

237 Grating Infrared Spectrophotometer. Samples were mounted

as Nujol mulls between rock salt plates. Results are shown

in the following figures.

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CHAPTER III

DISCUSSION

la many of the reactions of synthesis, m quantity of

the tyris-ethylenediaminecobalt (III) halide contaminates the

first precipitate despite extreme care in purifying the

cobalt complex used as a starting material. It is presumed

that this compound is formed in the reaction by some type

of rearrangement. After the amino acid complexes have been

isolated and purified, no tendency to form the tris-ethylene-

diaminecobalt(III} ion is observed.

The infrared spectra of all the three complexes are

quite similar in the 2.5-7,f>M region, with characteristic

absorption in the 6.05-6.20 region*

Spectra of amino acids in the zwitter ion form show a

broad absorption band in the region 6.2~6.4/<while the

hydrochlorides show two peaks, one at about 5.&M and

the other at about 6.4x» Apparently the $.6 absorption

is a C-0 vibration. The shift from 5,Bm to about 6.1m is

presumably due to the coordination of the carboxyl group.

The spectra of L-alanine, L-valine and L-leucine acids all

show an absorption peak at 6.3>n which corresponds to a

frequency of 1590 cm.""1, which is exactly the carboxyl fre-

quency shown by their sodium salts investigated by

22

23

1

Rosenberg* The corresponding peaks of carboxyl group for

the complexes are 6.15X (1630/cm) for L-alanine complex,

6.1IM (1620/cm) for L-valine complex, and 6.1M(1640/cm)

for L-leucine complex. Rosenberg also examined the spectra

of several metal complexes of amino acids and discussed

these bands. He suggested that the 6.4M band is an NH

bending absorption. Powell and Sheppard2 examined the

spectra of a number of tris-ethvlenediamine complexes and

found strong absorption in this region for all the hydrated

complexes. This band was absent, however, in an anhydrous

complex. The 6.4M band appears prominently in the speetrum

of the alanine complex whose C«Ud = -64°, but is missing in

the spectra of materials of high optical rotation. Since

these spectra vary from strong absorption to none at all in

this region, it is felt that this band is indicative of

residual or lattice water in the complexes.

Ho pure ftona of those complexes has ever been reported

in the literature. A comparison of the specific rotation

of the complexes with their corresponding amino acid are

shown in Table IX.

XA. Roaenberg, Acta Cheta. Scand.. X (1956), £40.

2D. B. Powell and N. Sheppard, J. Cheat. Soc. (1959), 791-5.

24

TABLE II

COMPARISON OF THE SPECIFIC ROTATION OF CERTAIN AMINO ACIDS WITH THEIR CORRESPONDING COM-PLEXES OP THE TYPE (CoUn^Ucid)] 4 4

Free Acid Coi^lex r ^ ) D2 5

L-alanine + 2.7° [Co(en) 2(L-alanato }J Ig -30^-337®

L-ieu line -10.2° [Co(en)2(L-leucinato)) I2 -60°

L~valine + 6.42* [Co(en)2(L-valinato)]l2 -104®

As the preparations of those complexes were carried

out in alkaline solution , it is conceivable that no replace-

ment results in treating the complexes with Na2C0^,

NaHCgO^.etc. due to their basic properties, but only very

strong Uganda such as cyanide ion and ethylendiaraine can

react•

All of the complexes investigated gave rise to an

optically inactive tris-(ethylenediaaine}cobalt(III} iodide

when treated with an excess of ethylenediauine and precip-

itated with potassium or sodium iodide and reacted very

slowly at room temperature {usually two to three days}.

These examples serve to illustrate that those compounds

prepared are relatively stable and that asymmetric syntheses

are not successful.

3? 'Handbook of CI (Cleveland, 195§7, pp.

ISl Physics« 40th edition *53.

25

Prom the result of the alanine complex reflux with

activated charcoal and the well-known ability of activated

charcoal to induce racemization,^ it is concluded that those

preparations yielding the material for which 35°

represent separation of the equilibrium mixture of isomers,

while in other cases predominantly a single isomer was

obtained. Similar experiments using the leuaine and valine

complexes both resulted in a change in observed rotation of

less than +0,015°> which is too slight to be considered sig-

nificant , It is then assumed that the leucine and valine

complexes isolated are the equilibrium mixture.

In preparing the L~alanine complex, the only significant

difference between procedures A and B is the temperature. It

sews that one isomer is more stable at a temperature of 60°C;

however, further investigation is required. Reacting the

high rotational Isomer with ethylenediamine still produced

<m inactive [Oo(en!3]I3. It is assumed that the reaction

between the complex and ethylene-diamine involves soae type

of rearrangement vahich induces racesii nation.

E. Douglas, J. Am. Chesu Soc., IX5CVI (1954), 1020.

BIBLIOGRAPHY

Books

Bailar, John C., Jr., Inorganic Syntheses, II, New York, McGraw-Hill, 1953. '

Baaolo, Fred, "Stereoisomerism of Hexacoyalent Atoms," Chemistry of the Coordination Compounds. edited by John C, BalXar» Jr., New tork, fteinhold, 1956,

Handbook of Chemistry and Physics. 40th edition, Cleveland, Chemical Rubber Publishing Company, 1959•

Articles

Aimi, M., H. Kuroya, and R. Tsuchida, Journal of the Chemical Society of Japan, LXIV (1943), 995-1001,

Bailar, J, C., Jr. and B, Das Sanaa, Journal of the American Chemical Society. LXXVII (1955),$&£'5435.

Bailar, J, C., Jr., E, H. Huffman, and H. B. Jonas sen, Journal of the American Chemical Society, M X amy* 736=750: - — •

Basshart, J, and A. Werner, Berichte der Deutschen Chemischen Pesellschaft. XLVII (19H), W l ^ K S T " ~

Douglas, B. E., Journal of the American Chemical Society, LXXYI (1954TTTS5M&2T:

Jaeger, P, M», Recueil des travaux cheoiques des Pays-bas, m v x n (191977135^137;

King, H. J. S., Annual Reports of the Chemical Society, London. xu (1933), 25I-263T ~

Pasteur, L., Annalen Der Ch®aie Physics, 37. H I I (1343). 442-446. ' ' ~~

Powell, D» B. and N. Sheppard, Journal of the Chemical ~ " (1959), 791-795• "

26

21

Rosenberg, A., Acta Cheraica Scandinavica, 1 (1956). 840-851. ~

Warner, A . , B e r i c h t e tier Deutschea Cheiaigchen G e s e l l s c h a f t . XLVII (1914), 30&7-3094..