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
