METAL-ORGANIC COMPOUNDS

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Chromium Complexes

F. B. HAUSERMAN

Downloaded by TUFTS UNIV on December 2, 2014 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch032

Experimental Station, Grasselli Chemicals Department, Ε. I. du Pont de Nemours & Co., Inc., Wilmington, Del.

Water-soluble, Werner-type chromium complexes of carboxylic acids, which can be used to modify the surface characteristics of many substrates, were de­ veloped from the reaction products of chromyl chlo­ ride and various organic materials. Typical com­ plexes are Quilon chrome complex (chromium com­ plexes of stearic or myristic acid), used as a water repellent and release agent; Volan (methacrylato chromic chloride), used as a coupling agent in vari­ ous reinforced plastic laminates; p-aminobenzoato chromic chloride, used as an ultraviolet screener; and p-nitrobenzoato chromic chloride, used as an anti­ -static agent. The chemistry of chromium complexes of carboxylic acids, methods of manufacture and application, and various uses are discussed.

C h r o m i u m c o m p l e x c o m m o d i t i e s a r e g e n e r a l l y a c i d i c s o l u t i o n s of t h e c h r o m i u m c o m ­ p l e x i n 2 - p r o p a n o l , w a t e r , a n d s o m e t i m e s acetone. T h e c o m p l e x c o n t e n t w i l l v a r y b e t w e e n a b o u t 2 0 a n d 3 5 % , d e p e n d i n g o n t h e m o l e c u l a r w e i g h t of t h e c a r b o x y l i c a c i d . T h e a m o u n t of w a t e r v a r i e s f r o m a b o u t 5 t o 2 5 % , d e p e n d i n g u p o n t h e c o m p l e x i n q u e s t i o n ; t h e acetone c o n t e n t , i f a n y is p r e s e n t , is less t h a n 3 % ; a n d u s u a l l y t h e r e ­ m a i n d e r of t h e c o m m o d i t y is 2 - p r o p a n o l . T h e c o m p l e x e s t h e m s e l v e s m a y be d e s c r i b e d as r e a c t i o n p r o d u c t s of c a r b o x y l i c a c i d s a n d basic c h r o m i c c h l o r i d e : 2Cr(OH)Cl

2

+ R C O O H -> C r ( O H ) C l 0 C R + H 0 2

4

2

(1)

2

T h e b a s i c c h r o m i c c h l o r i d e c a n b e p r e p a r e d i n a n u m b e r of w a y s , a t y p i c a l process (18) b e i n g t h e r e d u c t i o n of c h r o m y l c h l o r i d e w i t h a n a l c o h o l s u c h as 2 - p r o p a n o l : 2Cr0 Cl 2

2

+ 3 ( C H ) C H O H -> 2 C r ( O H ) C l 3

2

2

+ 3(CH ) CO + 2H 0 3

2

2

(2)

A postulated structure for the monomeric, u n h y d r a t e d complex is shown b y f o r m u l a I . T h e complex i n the c o m m o d i t y has alcohol a n d water coordinated w i t h t h e c h r o m i u m , a n d a possible s t r u c t u r e f o r t h e u n p o l y m e r i z e d c o m p l e x i n t h e c o m ­ m o d i t y i s s h o w n b y f o r m u l a I I , a s s u m i n g one w a t e r a n d one a l c o h o l m o l e c u l e a r e coordinated w i t h each c h r o m i u m .

CltCr^ ^CrCl s

2

0

Η

338

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

HAUSERMAN—CHROMIUM COMPLEXES

339 R

C1

£1

2

(H 0)-Cr^ 2

^Οτ-(Ηβ)

β

(ROH)

II

2

(ROH)

I n f o r m u l a s I a n d I I , t h e c h l o r i n e a t o m s a r e s h o w n as b e i n g c o o r d i n a t e d ( c o v a l e n t l y b o u n d ) w i t h t h e c h r o m i u m . P r o b a b l y some exist as c h l o r i d e ions, e v e n w h e n t h e commodity contains only a small amount of water. A s s u m i n g a l l the chlorine atoms are ionic a n d the coordinated chlorine has been replaced w i t h water a n d alcohol, f o r ­ mula I I would be R

+4

Downloaded by TUFTS UNIV on December 2, 2014 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch032

Ο l/(H 0) Cr ^ O ^ ^(ROH) 2

(ROH)f

III

+ 4d"

2

2

U p o n d i l u t i n g the c o m p l e x c o m m o d i t y w i t h w a t e r , a n y a l c o h o l g r o u p s c o o r d i n a t e d w i t h the c h r o m i u m are replaced w i t h water, a n d most of the covalently b o u n d chlorine a t o m s b e c o m e i o n i c c h l o r i d e . T h e e x t e n t of t h i s i o n i z a t i o n c a n b e s h o w n b y a c o n ductometric t i t r a t i o n w i t h silver nitrate. I n stearato chromic chloride, i m m e d i a t e l y a f t e r d i l u t i o n a b o u t 7 4 % of t h e t o t a l c h l o r i d e is i o n i c , a n d w i t h i n s e v e r a l h o u r s 80 t o 8 5 % is i o n i c . I n V o l a n ( D u P o n t , m e t h a c r y l a t o c h r o m i c c h l o r i d e ) , a b o u t 9 0 % o f t h e c h l o r i d e is i o n i c u p o n d i l u t i o n , a n d a f t e r a b o u t 2 h o u r s 9 5 % is i o n i c . T h e r e is also some p o l y m e r i z a t i o n o f t h e c o m p l e x w h e n t h e c o m m o d i t y is d i l u t e d w i t h w a t e r , b u t t h i s is m i n o r c o m p a r e d t o t h e p o l y m e r i z a t i o n w h e n t h e c o m m o d i t y is n e u t r a l i z e d o r heated. W h e n t h e p H of a d i l u t e c h r o m i u m c o m p l e x s o l u t i o n is r a i s e d f r o m a b o u t 3 t o 4 t o 6, a l l c o v a l e n t l y b o u n d c h l o r i n e a t o m s i m m e d i a t e l y b e c o m e i o n i c a n d a n a p p r e ­ c i a b l e a m o u n t of p o l y m e r i z a t i o n o c c u r s . T h i s p o l y m e r i z a t i o n c o n t i n u e s as t h e s o l u ­ t i o n ages as s h o w n b y a g r a d u a l decrease i n p H ; t h e p H of a d i l u t e d , u n n e u t r a l i z e d c o m p l e x s o l u t i o n changes v e r y l i t t l e . P r o b a b l y t h i s decrease i n p H is d u e t o t h e f o r m a t i o n of C r — 0 — C r b r i d g e s b y t h e e l i m i n a t i o n o f h y d r o g e n ions f r o m t h e w a t e r i

H molecules coordinated t o the c h r o m i u m atoms, resulting i n a p o l y m e r i z e d complex, r a t h e r t h a n t o t h e h y d r o l y s i s o f c h l o r i n e a t o m s c o v a l e n t l y b o u n d t o t h e c h r o m i u m (10). T h e base u s e d t o raise t h e p H p r e s u m a b l y serves t o p r o m o t e t h e b r i d g i n g of t h e c h r o m i u m atoms through oxygen b y shifting the following equilibrium t o the right:

Ψ (H 0) Cr 2

+ 8C1"

I

Cr(H 0)

4

2

OH"

H0 2

+

H

+

+

8C1~ +

4

R I

Η

0

0^

+

I

H -0'^'^'\ ^'\ ^Cr y>(H 0) (H 0) Cr Cr3