Metal Chelates

Metal Chelates

MARTIN KNELL

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch003

Geigy Chemical Corp., Ardsley, Ν. Y

Metal chelates, in which an organic molecule bonds a metal cation covalently or ionically, are discussed. There are both synthetic chelates such as the phthalocyanines and natural chelates such as the porphyrins. The formation, stability, and commercial importance of these are summarized. The major uses of metal chelates are in agriculture and the dye and pigment industries.

A metal chelate is a compound in which a metal cation is bound by a molecule con taining two or more sites for bond formation. The word chelate is derived from the Greek word chela, meaning claw, because of the structure of the molecules. A great variety of organic and inorganic molecules can participate in chelation. Only those chelates in which the chelating agent, or ligand, is organic are discussed here. In metal chelates, the metal is bonded either ionically or covalently with the strongly nonmetallic elements of Groups V and V I , whereas in other organometallics the metal is bonded covalently directly to carbon. Most of the metal chelates produced in industry today are formed in situ and never isolated. By chelating metals in solution, undesirable properties such as precipitation of heavy metal soaps and hydroxides and catalysis by metallic ions can be avoided. The use of (ethylenedinitrilo)tetraacetic acid (EDTA) in the textile industry is well HOOCCH

CHCOOH

2

2

NCH CH N 2

2

HOOCCH/

CH C00H 2

known. Several million pounds are used each year in such operations as dyeing, kier boiling, and bleaching. In the latter operation, the chelating agent has a stabilizing effect on hydrogen peroxide, the decomposition of which is catalyzed by trace quantities of such metals as iron, copper, and manganese. Another chelating agent that has reached commercial importance as a result of its deactivating effect on trace quantities of a metal is iV, A '-disalicylidine-1,2-propanediamine. This compound is sold r

OH

^

OH

CH=NCHCHN=CH(l

|

2

at the rate of about a million pounds per year and is added to gasoline to counteract the oxidative effect of trace quantities of copper which may be present in the gasoline. 37

In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

38

ADVANCES IN CHEMISTRY SERIES

Formation An EDTA

example of m e t a l chelate f o r m a t i o n is t h e reaction of E D T A

with

with

corresponding

four

carboxyl

groups

ionizes

i n four

steps,

with

four

calcium.

ionization constants: HY

=F

4

H Y"

+

3

[Η1[Η ΥΊ 3

H

[H Y] 4

k =

3


[Hl[H Y- ] 2

2

H Y'

9

[Η3ΥΊ [H+][HY- ] 3

HY'

H Y" 2

+

H

*3 =

+

[H Y- ] 2

2

[Hl[Y- ] 4

HY"

+

H

+

[HY" ] 3

where Y represents t h e (ethylenedinitrilo)tetraacetate anion. T h e s e i o n i z a t i o n c o n s t a n t s h a v e been d e t e r m i n e d

(4), a n d e x p r e s s e d i n t e r m s o f

p k ( l o g k) a r e p k = 1.99, p k = 2.67, p k = 6.16, a n d p k = 10.26. x

EDTA

2

3

I

Figure 1.

2

T h e t i t r a t i o n of

4

w i t h a n a l k a l i i s s h o w n b y c u r v e A , F i g u r e 1.

T h e first t w o d i s s o c i a t i o n c o n -

3

4

NaOH Equivalents

Titration of (ethylenedinitrilo) tetraacetic acid

A. No calcium ions present β. Excess calcium ions present s t a n t s c o r r e s p o n d t o s t r o n g a c i d s , a n d a single s h a r p b r e a k i s o b t a i n e d a f t e r t h e a d d i t i o n o f t w o e q u i v a l e n t s of a l k a l i . t h i r d equivalent of alkali.

A second break occurs after t h e a d d i t i o n of t h e

A s p k corresponds t o a v e r y weak acid, n o further break 4

is o b t a i n e d o n f u r t h e r a d d i t i o n o f a l k a l i . I n t h e presence o f a n excess o f c a l c i u m i o n s , t i t r a t i o n w i t h a l k a l i gives c u r v e B, Figure

1: T h e presence of c a l c i u m ions causes a l l f o u r

r e a d i l y , g i v i n g i n effect a s t r o n g t e t r a b a s i c a c i d . takes place

according

protons

t o be dissociated

T h e f o r m a t i o n of t h e c a l c i u m chelate

t o t h e following reactions

starting with

the zwitterion

form

of H Y ~ : 2

2

"OOCCH

2

H

H

CH COCf 2

NCH CH N^ 2

"OOCCH

2

CH COO" 2

C H

2

Co"

2

*0 OOCCH \ H / 2 -(X NCH CH N —*>Ca

—

2

2

C

V

"OOCCH ^0

"00CCH

CH x

c

CH C00"

H

2

2

+

2

/

CH

/ c

£

7


+

Η

39

KNELL-METAL CHELATES

T h e exact n a t u r e o f C a H Y ~ chelate i s n o t k n o w n , b u t i t i s s h o w n i n t h e t w o m o s t likely forms.

A s more alkali is added, t h e calcium coordinates

forming C a Y ~

2

with both

nitrogens

a n d releasing another p r o t o n : ~OOCCH

CQHY

CH CH

2

2

CH C00"

2

2

CH Ca CH \ / \ / C—O 0—C // V

>-

2

+

2

H

v


0

0 CaY~*

T h e successive d i s p l a c e m e n t o f t h e t w o n i t r o g e n - b o u n d p r o t o n s i s s u m m a r i z e d i n the following equations : CQ

+

+2

Co"

2

+

H Y~ 2

HY"

2

=^=^=

CQHY"

3

=^=±:

CQHY"

^==^

CaY'

CQHY"

+ H

+ H

2

+

+

T h e s h a p e o f c u r v e B, w i t h o n l y o n e b r e a k a t f o u r e q u i v a l e n t s o f a l k a l i , shows t h a t all four protons are t i t r a t e d together.

T h u s , i n t h e presence of c a l c i u m ions, t h e four

acid groups of E D T A have about equal a c i d i t y a n d the intermediate C a H Y a t r a n s i e n t existence w h e n a l k a l i i s c o n t i n u o u s l y a d d e d . CaY-

has only

T h e stability constant f o r

i s d e f i n e d b y K.

2

_

+ 2

Ca

+2

+

γ

4

4

_ 5^=55:

. CQY

[CQY~ ] ' __ [CQ ][Y ] 2

Κ =

2

Γ

4

+2

Stability

4

Constants

T h e s t a b i l i t y c o n s t a n t s o f a l a r g e n u m b e r o f m e t a l chelates o f E D T A h a v e determined. I

been

T h e p K ' s ( l o g K) f o r some o f t h e c o m m o n e r m e t a l s a r e g i v e n i n T a b l e

(6,7).

Table

I.

Ion Li Na Mg Ca Sr Ba Zn++ Fe +

+

+ +

+ +

+ +

+ +

+ +

Stability Constants of Metal Chelate of EDTA pK 2.79 1.66 8.69 10.59 8.63 7.76 16.58 14.22

Ion Mn Co Cu Ni Cd Pb La Fe Cr+ +

+ 1

"

+ +

+ +

+ +

+ +

+ +

+ +

+

+ +

+

+

F o r a g i v e n c h e l a t i n g agent, t h e b o n d s t r e n g t h b e t w e e n vary widely

pK 13.47 16.10 18.38 18.54 16.48 18.20 15.4 25 24

metal and ligandm a y

( T a b l e I ) . P r o p e r t i e s o f t h e m e t a l s s u c h as a t o m i c n u m b e r ,

i o n i z a t i o n p o t e n t i a l , i o n i c r a d i u s , a n d c?-orbitals a l l c o n t r i b u t e t o c h e l a t e

valence, stability.

T h e u n i v a l e n t metals f o r m v e r y w e a k chelates a n d t h e m u l t i v a l e n t metals f o r m t h e stronger chelates.

T h e o r d e r o f s t a b i l i t y o f chelates o f v a r i o u s m e t a l s i s a p p r o x i m a t e l y

t h e same f o r a l a r g e n u m b e r o f c h e l a t i n g agents. EDTA

T h e order of chelate s t a b i l i t y f o r

a n d t h e a l k a l i n e e a r t h series i s b a r i u m < s t r o n t i u m < m a g n e s i u m < c a l c i u m .

M a g n e s i u m o c c u p i e s a v a r i a b l e p o s i t i o n ; w i t h s o m e c h e l a t i n g agents i t f o r m s

more

stable complexes t h a n c a l c i u m , a l t h o u g h f o r the p o l y a m i n o c a r b o x y l i c acids t h e c a l c i u m chelate i s m o r e stable.

T h e stabilities of some of t h e b i v a l e n t t r a n s i t i o n metals w i t h

chelating agents generally follow t h e following o r d e r :

manganese < i r o n < cobalt
zinc. F o r a g i v e n m e t a l , t h e s t r u c t u r e o f t h e c h e l a t i n g agent i s i m p o r t a n t i n d e t e r m i n ing t h e chelate stability, t h e t w o most i m p o r t a n t factors being t h e n u m b e r of atoms



40

i n t h e chelate r i n g a n d t h e n u m b e r of chelate r i n g s f o r m e d . I n g e n e r a l o n l y five- o r six-membered rings are encountered. The five-membered ring is favored a n d more stable w h e n t h e r i n g is c o m p l e t e l y s a t u r a t e d , whereas t h e s i x - m e m b e r e d r i n g i s f a v o r e d i f one o r t w o d o u b l e b o n d s a r e p r e s e n t . T h e e x p e r i m e n t a l v a l u e s of t h e s t a b i l i t y c o n s t a n t s of t h e 1 t o 2 chelates f o r m e d b e t w e e n c u p r i c i o n a n d g l y c i n e a n d ^ - a l a n i n e i l l u s t r a t e t h e effect of r i n g size o n chelate s t a b i l i t y . G l y c i n e , w h i c h f o r m s five-membered chelate r i n g s , h a s a p K v a l u e of 15.6 (9) ; ^ - a l a n i n e , w h i c h f o r m s s i x m e m b e r e d chelate r i n g s , h a s a p K v a l u e of 12.8 (8). Ο

Η NU


II CH

I

CH

CH

2

ν

2

CH ,CH

9

2

"C'

1ST Η

II 0

2

\ ,CH

Cu

2

Ν Η

Cupric bis(glycinate)

Cupric bis(/?-alaninate)

B e c a u s e p K ' s a r e l o g v a l u e s , t h e g l y c i n e chelate is a l m o s t 1000 t i m e s as s t a b l e as t h e /^-alanine chelate. A n increase i n n u m b e r of r i n g s w i t h i n a p a r t i c u l a r chelate s t r u c t u r e increases t h e chelate s t a b i l i t y . C a l v i n a n d B a i l e s (3) s t u d i e d t h e c o p p e r chelates of t h e s a l i c y l a l d i m i n e s of m e t h y l a m i n e a n d e t h y l e n e d i a m i n e . T h e t w o s t r u c t u r e s a r e v e r y s i m i l a r , e x c e p t t h a t t h e e t h y l e n e d i a m i n e d e r i v a t i v e h a s one a d d i t i o n a l chelate r i n g . -Cu-

—-CuK^J

CH

3

CH

CH

3

CH

2

K^J

2

Cupric Ν , Ν ' - d i s a l i c y l i d i n e e t h y l e n e d i a m i n e

Cupric bis(salicylidinemethylamine)

T h e h a l f - w a v e p o t e n t i a l s of t h e t w o c o p p e r chelates, d e t e r m i n e d u s i n g a d r o p p i n g m e r c u r y electrode, were + 0 . 0 2 a n d —0.75. A s a g r e a t e r n e g a t i v e v a l u e i n d i c a t e s a m o r e s t a b l e c h e l a t e , t h e a d d i t i o n a l chelate r i n g p r e s e n t i n t h e e t h y l e n e d i a m i n e d e r i v a t i v e seems t o increase t h e s t a b i l i t y . A n o t h e r set of chelates w h i c h i l l u s t r a t e s t h i s p r i n c i p l e is t h e c a l c i u m chelates of A - m e t h y l i m i n o d i a e e t i c a c i d a n d E D T A . These t w o chelates, w h i c h differ o n l y i n t h a t t h e E D T A chelate h a s one a d d i t i o n a l chelate r i n g , s u p p o r t t h e t h e o r y t h a t t h e g r e a t e r t h e n u m b e r of r i n g s , t h e g r e a t e r t h e s t a b i l i t y . T h e p K v a l u e s a r e 7.5 a n d 10.6 f o r t h e m e t h y l i m i n o d i a c e t i c a c i d a n d E D T A {11, 12), respectively. T

Ο II

-c—qv

1

oe--

"/Ν

CH

ΙΝΙ l\CH I

2

2

/

c-j—cii \ 8

II Ο I

\ .CH

2

II

0 Calcium bis(N-methyliminodiacetate)

Calcium (ethylenedinitrilo)tetraacetate


41

KNELL-METAL CHELATES Commercial Importance A

p r o m i s i n g use f o r m e t a l chelates

is t h e t r e a t m e n t

I r o n deficiency i n plants i n h i b i t s c h l o r o p h y l l synthesis.

of m e t a l - d e f i c i e n t

plants.

T h e leaves b e c o m e l i g h t g r e e n

o r y e l l o w ; i f n o t c o r r e c t e d , t h e r e s u l t is s t u n t e d g r o w t h , r e d u c e d y i e l d s , a n d u l t i m a t e l y death

of t h e p l a n t .

Stewart a n d Leonard

(13)

showed

t h a t severe cases of i r o n

c h l o r o s i s c o u l d b e c o r r e c t e d q u i c k l y a n d d r a m a t i c a l l y b y a p p l y i n g s m a l l q u a n t i t i e s of t h e i r o n c h e l a t e of E D T A . chelating

agents

were

Iron E D T A

developed

w a s effective

for more

hydroxyethylethylenediaminetriacetic acid

alkaline

(HEEDTA)

o n l y o n a c i d soils a n d o t h e r soils.


acetic a c i d ( D T P A ) have reached c o m m e r c i a l i m p o r t a n c e

H0CH CH 2

CH COOH

2

H00C-CH

of

also. 2

2

2

CH COOH

2

chelates

HOOCCH,. CH COOH ^NCH CH NCH CH N^ HOOCCH/ rj CH C00H

2

^NCH CH f/ 2

T h e iron

a n d diethylenetriaminepenta-

2

2

2

2

Hz

2

COOH Hydroxyethylethylenediaminetriacetic acid

Diethylenetriaminepentaacetic acid

I t i s e s t i m a t e d t h a t 1,000,000 t o 1,500,000 p o u n d s s o l d i n 1956. B o t h c y c l o h e x a n e d i a m i n e t e t r a a c e t i c

/CH COOH 2

x

of these m e t a l chelates (CDTA)

and Chel

were

138, a n

OH OH I 1 f^il—CHNHCH CH NHCH—η

CH C00H 2

/CH COOH

2

2

-

3

+

3NaC1

2. I n the m e t h o d d e v e l o p e d b y I . G . F a r b e n i n d u s t r i e A . G . (2) e t h y l e n e d i a m i n e , formaldehyde, and hydrogen cyanide (formed i n solution b y the reaction of sodium c y a n i d e w i t h a c i d ) r e a c t . T h e process r e q u i r e s t h e i s o l a t i o n o f t h e i n t e r m e d i a t e ( e t h y l e n e d i n i t r i l o ) t e t r a a c e t o n i t r i l e , b u t t h e a d d e d step ensures t h a t t h e t e t r a s o d i u m E D T A f o r m e d b y h y d r o l y s i s o f t h e n i t r i l e is n o t c o n t a m i n a t e d w i t h i m p u r i t i e s o r i n e r t salts. NCCH

CH CN


2

H NCH CH NH 2

2

2

2

+ 4HCN +

4CH 0

•

2

2

N

NCH CH N 2

NCCH^ NCCH ^ ^Η,ΟΝ ^NCHgCHgN^ + 4H 0 + 4NaOH — > NCCH CH CN 2

2

2

2

+ 4H 0

2

2

N

CH CN 2

NaOOCCH

CHgCOONa NCH CH N + 4NH NaOOCCH^ CH COONa 2

V

2

2

N

3

2

3. T h e process d e v e l o p e d b y B e r s w o r t h (1) c o n v e r t s e t h y l e n e d i a m i n e t o t h e t e t r a s o d i u m salt of E D T A b y t h e s i m u l t a n e o u s a d d i t i o n o f s o d i u m c y a n i d e a n d f o r m a l d e h y d e t o a s o d i u m h y d r o x i d e s o l u t i o n o f t h e d i a m i n e . T h e success o f t h i s process d e p e n d s o n t h e c o m p l e t e r e m o v a l o f t h e a m m o n i a as i t i s l i b e r a t e d i n t h e r e a c t i o n . F o r t h i s reason, E D T A m a d e b y t h i s process a l w a y s c o n t a i n s some nitrilotriacetic acid. NaOOCCH* H NCH CH NH 2

2

2

+ 4NaCN

2

+

4CH 0 2

CH COONa ΝΟΗ,ΟΗ,Ν 2

NaOOCCH

2

+

4NH

3

CH COONa

N

2

2

4. A c a t a l y t i c o x i d a t i o n o f t e t r a ( h y d r o x y e t h y l ) e t h y l e n e d i a m i n e t o E D T A h a s been d e v e l o p e d (5). T h e a m i n o a l c o h o l i s h e a t e d w i t h s o d i u m o r p o t a s s i u m h y d r o x i d e a n d a c a d m i u m o x i d e c a t a l y s t a t 220° t o 2 3 0 ° C . f o r s e v e r a l h o u r s . H y d r o g e n i s l i b e r a t e d a n d the t e t r a s o d i u m salt of E D T A i s o b t a i n e d i n a b o u t 8 5 % y i e l d . T h i s m e t h o d , h o w e v e r , has n o t a t t a i n e d t h e c o m m e r c i a l i m p o r t a n c e of t h e o t h e r m e t h o d s . HOCH CH 2

2

^

NCH CH N 2

HOCH CH 2

2

s

CH CH OH 2

2

+ 4NaOH

2

^ CcIO

CH CH OH 2

NaOOCCH

CH COONa \ / NCH CH N + 8H NaOOCCH^ CH COONa 2

2

2

2

N

2

2

2

M e t a l chelates are n o t n e w . T h e n a t u r a l l y o c c u r r i n g m e t a l p o r p h y r i n s h a v e been k n o w n f o r m a n y y e a r s . T h e best k n o w n m e m b e r s o f t h i s class o f c o m p o u n d s a r e heme, a n i r o n - c o n t a i n i n g chelate p r e s e n t i n a n i m a l b l o o d , a n d c h l o r o p h y l l , a m a g n e s i u m c o n t a i n i n g chelate p r e s e n t i n a l l p l a n t s . A l l o f t h e p o r p h y r i n s t r u c t u r e s are s i m i l a r , i n t h a t t h e y consist o f f o u r p y r r o l e n u c l e i j o i n e d a t t h e i r a l p h a c a r b o n a t o m s b y methene groups. C h l o r o p h y l l a is t h e m o s t p r e v a l e n t f o r m .

Chlorophyll α


KNELL—METAL CHELATES

43


T h e m e t a l p o r p h y r i n s are e x t r e m e l y stable chelates. I n m o s t cases i t is i m p o s s i b l e t o r e m o v e t h e m e t a l a t o m w i t h o u t d e s t r o y i n g t h e rest o f t h e m o l e c u l e . Although c h l o r o p h y l l , because o f i t s a n t i b a c t e r i a l p r o p e r t i e s , c r e a t e d i n t e r e s t as a d e o d o r a n t , i t s a n n u a l p r o d u c t i o n is rather small. F o r t h e last f e w years t h e p r o d u c t i o n of c h l o r o p h y l l i n t h i s c o u n t r y has r e m a i n e d a t a b o u t 12,000 t o 15,000 p o u n d s p e r y e a r , whereas i n t h e p e a k y e a r o f 1952 i t r e a c h e d a b o u t 100,000 p o u n d s . A class o f s y n t h e t i c chelates w h i c h are s t r u c t u r a l l y r e l a t e d t o t h e p o r p h y r i n s i s b e i n g p r o d u c e d i n a p p r e c i a b l e q u a n t i t i e s . T h e s e c o m p o u n d s are k n o w n a s t h e m e t a l p h t h a l o c y a n i n e s a n d a r e u s e d as dyes a n d p i g m e n t s . T h e s t r u c t u r e o f c o p p e r p h t h a l o c y a n i n e i s :

I t w a s d i s c o v e r e d i n 1927 a n d i t was s o o n r e a l i z e d t h a t t h e m e t a l p h t h a l o c y a n i n e s offered p r o m i s e as p i g m e n t s . C o n s i d e r a b l e d e v e l o p m e n t a l w o r k w a s c a r r i e d o u t . B e c a u s e t h e y a r e e x t r e m e l y stable t o l i g h t , a c i d , a n d a l k a l i , t h e y h a v e been w i d e l y u s e d as p i g m e n t s f o r p r i n t i n g o n p a p e r a n d c l o t h a n d f o r t h e c o l o r a t i o n o f p a p e r , rubber, plastics, linoleum, paints, a n d lacquers. T h e commercial phthalocyanine p i g m e n t s r a n g e f r o m b l u e t o g r e e n . T h e 1956 U n i t e d S t a t e s p r o d u c t i o n o f p h t h a l o c y a n i n e p i g m e n t s was a b o u t 6,000,000 p o u n d s . T o m a k e t h e p h t h a l o c y a n i n e s u s e f u l as dyestuffs, i t w a s necessary t o s u b s t i t u t e v a r i o u s g r o u p s i n t h e m o l e c u l e so t h a t t h e r e s u l t i n g p r o d u c t s w o u l d h a v e a p p l i c a t i o n p r o p e r t i e s o f d i r e c t , s u l f u r , o r v a t dyes. F o r d i r e c t d y e s , s o l u b i l i z i n g g r o u p s s u c h a s s u l f o n i c a c i d , c a r b o x y l , a n d q u a t e r n a r y g r o u p s h a v e been u s e d . T h e r e are t w o w a y s of p r e p a r i n g these p h t h a l o c y a n i n e d e r i v a t i v e s : T h e p h t h a l o c y a n i n e p i g m e n t c a n b e made first a n d then the substituent added, o r the p h t h a l o c y a n i n e precursor can be s u b s t i t u t e d a n d t h e n c o n v e r t e d t o t h e p h t h a l o c y a n i n e . T h e 1956 p r o d u c t i o n o f p h t h a l o c y a n i n e d y e s was o n l y a b o u t 763,000 p o u n d s . Commercially, the phthalo c y a n i n e s are p r e p a r e d b y h e a t i n g a p h t h a l i c a c i d d e r i v a t i v e m i x e d w i t h a m e t a l s a l t , urea, catalyst, a n d a high boiling inert solvent t o a temperature of about 200°C. Y i e l d s o f 85 t o 9 8 % o f t h e o r y c a n b e o b t a i n e d . T h e p h t h a l o c y a n i n e s r e p r e s e n t o n l y one class o f m e t a l chelates w h i c h are u s e f u l as d y e s a n d p i g m e n t s . A c t u a l l y , c h e l a t i o n c a n o c c u r w i t h a n y class o f d y e s w h i c h h a s t h e necessary d o n o r g r o u p s i n t h e p r o p e r p o s i t i o n s . E x a m p l e s a r e c o m p o u n d s h a v i n g h y d r o x y l , carboxyl, keto, oximino, a n d amino groups i n either ortho o r peri position w i t h respect t o e a c h o t h e r , o r one o f t h e a b o v e g r o u p s i n t h e o r t h o p o s i t i o n w i t h respect to a n a z o ( — N = N — ) o r a n a z o m e t h i n e (— N = C C ) l i n k a g e . T h e chelate c a n b e formed o n the fabric, as i n m o r d a n t , chrome, a n d aftertreated direct dyes; o r t h e chelate c a n b e f o r m e d p r i o r t o a p p l i c a t i o n a s i n p r e m e t a l l i z e d a c i d a n d c o p p e r e d direct dyes. M a n y o f t h e first dyestuffs u s e d b y m a n w e r e n a t u r a l l y o c c u r r i n g c h e l a t i n g agents w h i c h were c o n v e r t e d t o m e t a l chelates o n t h e f a b r i c d u r i n g t h e d y e i n g o p e r a t i o n . M a d d e r , a dyestuff k n o w n t o t h e a n c i e n t E g y p t i a n s , w a s u s e d w i t h v a r i o u s m e t a l s s u c h as c h r o m i u m , a l u m i n u m , i r o n , c o p p e r , a n d t i n i n t h e m o r d a n t d y e i n g o f cotton. A l i z a r i n , the p r i n c i p a l coloring m a t t e r i n m a d d e r , was discovered i n 1824.



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used. In 1956, mordant and chrome dyes represented a market of about $6,500,000 in the United States. In the last 15 to 20 years, a new group of dyes have joined the class of metal chelates formed on the fabric. These are the aftertreated direct dyes for cotton, which are dyed onto the fabric and then aftertreated with copper salts. The chelate is formed on the fabric giving a very light- and washfast color. Many of the aftertreated direct dyes have been premetallized with copper and are useful as lightfast, direct cotton dyes, thus simplifying the dyeing process. Probably the fastest growing class of chelate dyes are the premetallized dyes for wool and nylon. These dyes are generally azo compounds having hydroxyl, amino, or carboxyl groups ortho to the azo grouping. The chelate is formed in manufacture, and the dyes are sold as the metal chelates. The first dyes to appear in this class were the 1 to 1 dye-chromium chelates, which contained sulfonic acid groups for increased solubility. These are used for dyeing wool and are analogous to the chrome dyes, except that the chelate is formed before application. However, they are less washfast than the chrome dyes. More recently a class of premetallized dyes containing a dye to metal ratio of 2 to 1 has been developed. These dyes are usually cobalt or chromium chelates, containing no sulfonic acid groups but having sufficient solubility or dispersibility for practical application. They are wash- and lightfast and have the added feature of level and penetrating dyeing from a neutral dye bath, whereas the chrome dyes and the 1 to 1 premetallized chelates must be applied from a strongly acid bath. A new class of premetallized dyes developed by the Geigy Chemical Corp. are 2 to 1 cobalt or chromium chelates. These are soluble in acetone and alcohol and have created interest in the mass dyeing of acetate rayon, replacing pigments. It is estimated that premetallized dyes had a sales volume in the United States of about $2,000,000 in 1956. This was expected to increase considerably during the next few years. Literature Cited (1) Bersworth, F. C., U. S. Patent 2,387,735 (Oct. 30, 1945). (2) British Intelligence Objectives Sub-committee, Rept. 1768. In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

KNELL—METAL CHELATES (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13)

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Calvin, M . , Bailes, R. H., J. Am. Chem. Soc. 68, 949 (1946). Carini, F., Martell, Α., Ibid.,74, 5745 (1952). Chitwood, H . C., U. S. Patent 2,384,817 (Sept. 18, 1945). Curme, G.O.,Jr., Chitwood, H . C., Clark, J. W., Ibid.,2,384,818. Geigy Chemical Corp., Ardsley, Ν. Y., "Sequestrene," 1952. Irving, H., "A Discussion of Coordination Chemistry," Butterwick Research Labora tory, Imperial Chemical Industries, Sept. 21, 1950. Monk, C. B., Trans. Faraday Soc. 47, 285 (1951). Munz, F., U. S. Patents 2,130,505 (Sept. 20, 1938) ; 2,240,957 (May 6, 1941). Schwarzenbach, G., Ackermann, H., Helv. Chim. Acta 30, 1798 (1947). Schwarzenbach, G., Ackermann, H., Ruckstuhl, P., Ibid.,32, 1175 (1949). Stewart, I., Leonard, C., Citrus Mag. 14, No. 10, 22 (1952).


RECEIVED for review May 10, 1957. Accepted June 1, 1957.


Metal Chelates

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