Organoaluminum Compounds

Organoaluminum Compounds R. F. SCHULTZ Hercules Powder Co., Wilmington, Del.

Downloaded by GEORGETOWN UNIV on February 19, 2015 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch014

Aluminum alkyl reactions which have possible industrial applications are discussed. Ziegler a n d his coworkers have outlined a new field of organic reactions, using organoaluminum compounds, which will have a tremendous impact on both basic and applied organic chemistry.

T h e first o r g a n o a l u m i n u m c o m p o u n d , t r i m e t h y l a l u m i n u m , w a s m a d e i n 1865 b y t h e r e a c t i o n of d i m e t h y l m e r c u r y a n d a l u m i n u m (8). S u b s e q u e n t l y , v e r y l i t t l e w o r k w a s d o n e o n o r g a n o a l u m i n u m c o m p o u n d s u n t i l 1948 w h e n Z i e g l e r a n d h i s c o w o r k e r s o f t h e M a x P l a n c k I n s t i t u t f u r K o h l e n f o r s c h u n g s t a r t e d i n v e s t i g a t i n g t h e m as c a t a l y s t s and chemical intermediates. T h e classical preparative methods using m e r c u r y d i a l k y l s a n d a l u m i n u m , G r i g n a r d reagents a n d a l u m i n u m c h l o r i d e , o r e t h y l c h l o r i d e w i t h a l u m i n u m a n d s o d i u m a r e t o o c o s t l y f o r t h e p r o d u c t i o n o f a l u m i n u m a l k y l s o n a c o m m e r c i a l scale f o r use as chemical intermediates. Ziegler developed several methods for t h e low-cost p r o d u c t i o n of a l u m i n u m t r i a l k y l s w h i c h i n c l u d e : r e a c t i o n of a n a l u m i n u m - m a g n e s i u m a l l o y w i t h a n a l k y l h a l i d e (20, 21), A l · M g + 6 R C 1 -> 2 A 1 R + 3 M g C l 2

3

3

a d d i t i o n of a n olefin t o a l u m i n u m h y d r i d e

(16),

A 1 H + 3 C H = C R -> A 1 ( C H C H R ) 3

(1)

2

2

2

2

2

(2)

3

a n d r e a c t i o n b e t w e e n a l u m i n u m , h y d r o g e n , a n d a n olefin ( 7 , 18). A l + 1 . 5 H + 3 C H „ -> A K C J W O 3 2

n

(3)

2

T h e l a s t r e a c t i o n is c a r r i e d o u t r e a d i l y w i t h 1 , 1 - d i s u b s t i t u t e d olefins s u c h as i s o b u t y l e n e . G o o d y i e l d s of t r i i s o b u t y l a l u m i n u m c a n b e m a d e f r o m finely d i v i d e d a l u m i n u m , h y d r o g e n , a n d i s o b u t y l e n e a t 50 t o 100 a t m o s p h e r e s a n d a b o u t 1 2 0 ° C . W i t h ethylene a n d monosubstituted ethylenes, a n indirect m e t h o d c a n be used. A l u m i n u m , h y d r o g e n , a n d some p r e v i o u s l y p r e p a r e d a l u m i n u m t r i a l k y l react t o f o r m t h e a l u m i n u m d i a l k y l h y d r i d e . T h e n olefin is s u p p l i e d w h i c h a d d s to the a l u m i n u m h y d r o g e n b o n d t o f o r m t h e t r i a l k y l . I n p r a c t i c e , t h i s t a k e s p l a c e i n o n e step b y t h e r e a c t i o n of a l u m i n u m , a n olefin, h y d r o g e n , a n d a n a l u m i n u m t r i a l k y l . F o r e x a m p l e , with ethylene: A l + I.5H2 + 2 A 1 ( C H ) + 3 C H -> 3 A 1 ( C H ) 2

5

3

2

4

2

5

3

(4)

T h e t r i e t h y l a l u m i n u m is a c t i n g as a c a t a l y s t f o r i t s o w n f o r m a t i o n . T h u s , w e n o w h a v e a l o w - c o s t process f o r p r e p a r i n g a n y a l u m i n u m t r i a l k y l f r o m a v a i l a b l e a l p h a olefins. 163

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

164

ADVANCES IN CHEMISTRY SERIES T h e l o w e r m o l e c u l a r w e i g h t a l u m i n u m t r i a l k y l s are w a t e r - w h i t e l i q u i d s ,

g r a v i t y a b o u t 0.8, a n d a r e s o l u b l e i n h y d r o c a r b o n

solvents.

specific

The methyl and ethyl

d e r i v a t i v e s c a n b e d i s t i l l e d a t a t m o s p h e r i c p r e s s u r e s a t 130° a n d 1 9 4 ° C , r e s p e c t i v e l y . H i g h e r m e m b e r s o f t h e series c a n be d i s t i l l e d a t l o w pressures w i t h o u t

decomposition

— e . g . , t r i i s o b u t y l a l u m i n u m , w h i c h has a b o i l i n g p o i n t of 4 0 ° C . a t 0.1 m m . of m e r c u r y pressure. water.

T h e l o w e r m e m b e r s are s p o n t a n e o u s l y

flammable

T h e c h e m i s t r y of a l u m i n u m t r i a l k y l s

is based

i n air and o n contact w i t h l a r g e l y o n t h e r e a c t i o n s of

t r i e t h y l a l u m i n u m a n d the h i g h e r h o m o l o g s , as t h e y a r e m a d e r e a d i l y f r o m c h e a p r a w materials. M e t a l alkyls are extremely reactive chemicals.

R e l a t i v e l y l i t t l e has b e e n

pub

l i s h e d o n t h e r e a c t i o n s of a l u m i n u m a l k y l s , a n d i t has b e e n o n l y i n t h e l a s t few y e a r s


t h a t r e a c t i o n s o f t h e m h a v e b e e n d i s c o v e r e d w h i c h are c o m m e r c i a l l y i m p o r t a n t .

Thermal Decomposition A t y p i c a l r e a c t i o n of a l l a l u m i n u m a l k y l s i s t h e i r ease of t h e r m a l d e c o m p o s i t i o n i n t o m e t a l l i c a l u m i n u m , a n olefin, a n d h y d r o g e n a t e l e v a t e d t e m p e r a t u r e s .

This ap

p e a r s t o i n v o l v e t w o d i s t i n c t steps as s h o w n i n E q u a t i o n s 5 a n d 6 f o r t r i i s o b u t y l a l u m i n u m (14) : CH \

(

/

3

/

\

CH CH X

/

x

CH / 3

3

/

100°C.

/

\

> A1H I C H C H

J

2

CII \

J + CH =C(CH )

2

V

3

\

2

H

/

8

2

(5)

2

CH v 3

/

/

\

A1H f C H C H

\w

V

>200°C.

> A l + 1.5H + 2 C H = C ( C H )

j

2

2

2

3

(6)

2

2

C o m p o u n d s i n w h i c h the a l k y l s are s t r a i g h t - c h a i n e d r a d i c a l s are m u c h m o r e s t a b l e t h a n those i n w h i c h b r a n c h i n g o c c u r s o n t h e s e c o n d c a r b o n a t o m .

Trimethylaluminum

a n d t r i e t h y l a l u m i n u m can be distilled w i t h o u t decomposition a t atmospheric a n d d o n o t b r e a k d o w n u n t i l r e l a t i v e l y h i g h t e m p e r a t u r e s are r e a c h e d .

pressure

Triisobutyl

a l u m i n u m a n d s i m i l a r a l k y l s lose 1 m o l e of olefin a t 1 0 0 ° C . t o f o r m t h e m o n o h y d r i d e . The monohydride

is stable u p t o about

200°C. and then breaks down

completely

(Equation 6). These

reactions show

some p r o m i s e

of h a v i n g c o m m e r c i a l a p p l i c a t i o n where i t

is d e s i r e d t o d e p o s i t films o f a l u m i n u m o n m e t a l a n d n o n m e t a l l i c s u r f a c e s . be d o n e i n t w o w a y s .

This can

G l a s s a n d m e t a l l i c surfaces m a y be c o a t e d b y p a s s i n g v a p o r s of

t r i i s o b u t y l a l u m i n u m o v e r s u c h surfaces w h i l e h e a t i n g t h e m t o a b o u t 2 5 0 ° C .

This must

be d o n e a t r e d u c e d pressures because t h e t r i i s o b u t y l a l u m i n u m c a n n o t b e d i s t i l l e d s u c c e s s f u l l y a b o v e 10 m m .

T h e same r e s u l t is p r o d u c e d b y first m a k i n g d i i s o b u t y l a l u m i n u m

h y d r i d e , into w h i c h the object t o be coated about 250°C. are f o r m e d very

is d i p p e d , a n d subsequently heating t o

I n e i t h e r case, a l u m i n u m i s d e p o s i t e d , a n d i s o b u t y l e n e a n d

a n d m u s t be s w e p t

away.

p u r e a l u m i n u m b y first t r e a t i n g

T h i s decomposition finely

hydrogen

can be used t o prepare

divided, activated a l u m i n u m w h i c h is

relatively i m p u r e w i t h isobutylene a n d hydrogen t o f o r m the a l k y l .

T h e n the a l k y l is

Reaction d e c o m p o s e dwith t o f Active o r m v e r yHydrogen p u r e a l u m i n u m (11). A n o t h e r t y p i c a l reaction of a l u m i n u m a l k y l s a n d a l l m e t a l a l k y l s is t h e i r a c t i o n w i t h a c t i v e h y d r o g e n s u c h as t h a t c o n t a i n e d i n w a t e r , a c i d s , a n d a l c o h o l s . A 1 R + 3 H X -> A 1 X + 3 R H 3

3


(7)

165

SCHULTZ—ORGANOALUMINUM COMPOUNDS

I n t h i s case a s a t u r a t e d h y d r o c a r b o n is f o r m e d , a n d t h e a l u m i n u m a p p e a r s as a l u m i n u m alcoholate, a l u m i n u m hydroxide, o r a n a l u m i n u m salt. T h i s r e a c t i o n c o u l d b e u s e d t o c o n v e r t olefins t o s a t u r a t e d h y d r o c a r b o n s , b u t i t is n o t a c o m m e r c i a l l y a t t r a c t i v e s u b s t i t u t e f o r h y d r o g é n a t i o n . A s i t i s r e s p o n s i b l e f o r m o s t of t h e losses o f a l u m i n u m a l k y l s i n o r d i n a r y c h e m i c a l m a n i p u l a t i o n s , i t necessitates c a r e f u l p u r i f i c a t i o n of olefins a n d o t h e r reagents w h i c h a r e u s e d i n c o n nection w i t h a l u m i n u m a l k y l reactions.

Oxidation A

characteristic

reaction

of a l u m i n u m a l k y l s i s t h e f o r m a t i o n

of a l u m i n u m


a l c o h o l a t e s o n t r e a t m e n t w i t h o x y g e n (14)· A1R + I.5O2-» A l ( O R ) ; 3

T h i s r e a c t i o n shows p r o m i s e as a process f o r p r o d u c i n g p r i m a r y a l c o h o l s f r o m c o m m e r c i a l l y a v a i l a b l e t e r m i n a l olefins. I t i s necessary o n l y t o m a k e t h e a p p r o p r i a t e a l u m i n u m a l k y l , oxidize i t t o t h e alkoxide, a n d then h y d r o l y z e this t o a l u m i n u m h y d r o x i d e a n d the corresponding alcohol, w h i c h is always p r i m a r y .

Olefin Displacement A g e n e r a l r e a c t i o n o f a l u m i n u m a l k y l s i s t h e r e a c t i o n i n w h i c h one olefin c a n d i s p l a c e a n o t h e r t o p r o d u c e a n e w a l k y l a n d a n olefin. T h i s r e a c t i o n enables o n e t o p r e p a r e e a s i l y a n y a l u m i n u m a l k y l f r o m t h e a p p r o p r i a t e olefin a n d t r i i s o b u t y l a l u m i n u m (14), t h e m o s t e a s i l y p r e p a r e d a l u m i n u m a l k y l .

where R a n d R ' can be either hydrogen o r another a l k y l r a d i c a l . T h i s r e a c t i o n m a y h a v e c o m m e r c i a l a p p l i c a t i o n i n p r e p a r i n g alcohols f r o m c e r t a i n p e t r o l e u m r e f i n e r y olefin s t r e a m s . I f t r i i s o b u t y l a l u m i n u m reacts w i t h the a l p h a olefins i n t h e r e f i n e r y s t r e a m a t a b o u t 100° t o 1 2 0 ° C , a n e w a l u m i n u m a l k y l a n d i s o b u t y l e n e are p r o d u c e d . T h e u n r e a c t e d olefins o r h y d r o c a r b o n s c a n b e d i s t i l l e d , a n d t h e r e m a i n i n g a l u m i n u m a l k y l is oxidized a n d hydrolyzed t o produce a n alcohol a n d a l u m i n u m h y d r o x i d e . I n a n a l t e r n a t i v e m e t h o d , t h e olefin reacts w i t h h y d r o g e n a n d suitably activated a l u m i n u m t o produce the a l k y l , w h i c h can then be converted t o an a l c o h o l . T h u s , 2 - p h e n y l e t h y l a l c o h o l c o u l d b e p r e p a r e d f r o m styrène, a p r i m a r y a l c o h o l f r o m t r i i s o b u t y l e n e , o r a p r i m a r y t e r p e n e a l c o h o l f r o m l i m o n e n e (14)·

Reducing

Properties

A l u m i n u m alkyls, particularly triisobutylaluminum and diisobutylaluminum h y d r i d e , are v e r y g o o d r e d u c i n g agents f o r c a r b o n y l g r o u p s i n a l d e h y d e s , k e t o n e s , a n d esters. A l c o h o l s are f o r m e d , a n d the a l u m i n u m a l k y l a p p e a r s t o act l i k e l i t h i u m a l u m i n u m h y d r i d e except t h a t t h e t o t a l reducing c a p a c i t y is n o t always utilized. A l t h o u g h t h i s reagent m a y b e less efficient t h a n l i t h i u m a l u m i n u m h y d r i d e o n a m o l a r basis, t h e l o w cost o f t r i i s o b u t y l a l u m i n u m m o r e t h a n c o m p e n s a t e s f o r t h i s inefficiency (W-


ADVANCES IN CHEMISTRY SERIES

166 Use

as a Grignard

Reagent

O r d i n a r i l y , t h e use of a n a l u m i n u m a l k y l c o m p o u n d as a G r i g n a r d reagent w i t h c a r b o n y l g r o u p s r e s u l t s i n r e d u c t i o n . I n c e r t a i n cases G r i g n a r d - l i k e a d d i t i o n t a k e s p l a c e , b u t o n l y one o f t h e a l u m i n u m a l k y l b o n d s i s i n v o l v e d . T h e f o r m a t i o n of t h e first R A 1 — Ο — b o n d seems to i n a c t i v a t e t h e o t h e r t w o b o n d s (H). 2

Reactions with Halogens and Sulfur Halogens react w i t h t r i a l k y l s a l t a n d a p r i m a r y h a l i d e (10) :

Dioxide

aluminum

compounds

to produce

a n aluminum

A1R + 3 X -> AIX3 + 3 R X


3

(10)

2

S u l f u r d i o x i d e a d d s a l u m i n u m a l k y l s t o f o r m salts o f s u l f i n i c acids (10): AIR3 + 3 S 0 -> A 1 ( S 0 R ) 2

2

(11)

3

Reaction with Metal Salts S a l t s o f m e t a l s w h i c h c a n f o r m stable m e t a l a l k y l s react w i t h a l u m i n u m a l k y l s t o p r o d u c e t h e e x p e c t e d m e t a l a l k y l a n d a n a l u m i n u m s a l t (10) : 2 A 1 R + 3 C d C l -> 2AICI3 + 3 C d R 3

2

AIR3 + 2 H g C l -> AICI3 + H g R 2

AIR3 + B F -> AIF3 + B R 3

aAlR

+ HgRCl

2

4

3

(13) (14)

3

+ z S i F -> S i F R + S i F R

3

(12)

2

2

2

+ SiFR

3

+ SiR

+ A1F

4

(15)

3

T h e last reaction can be controlled t o produce largely S i F R a n d S i F R w h i c h m a y h a v e some a p p l i c a t i o n t o s i l i c o n c h e m i s t r y . Hydrolysis would yield S i R ( O H ) and S i R ( O H ) , w h i c h c o u l d be c o n d e n s e d t o silicones. T h i s process has b e e n d e v e l o p e d b y Kali-Chemie A . - G . in Germany (5). 2

2

3

2

2

3

Formation of Complex Salts A n o t h e r characteristic reaction of a l u m i n u m a l k y l s is the formation of complex salts w i t h a v a r i e t y o f o r g a n i c a n d i n o r g a n i c c o m p o u n d s (2). T h e f o l l o w i n g are e x amples of such complexes: (C H ) 0 · A1(C H ) 2

5

2

CH —CH 2

2

5

(CH ) N ·C H

3

3

\ > · A1(C H ) 2

CH —CH 2

5

2

6

· A1(C H )

n

2

5

3

3

C H N · A1(C H ) 5

5

2

5

3

2

( C H ) N C H · A1(C H ) 3

2

2

6

5

2

5

3

Quinoline · A 1 ( C H ) 2

5

3

V e r y l i t t l e is k n o w n a b o u t t h e p r o p e r t i e s o f s u c h c o m p l e x e s as c a t a l y s t s o r as reagents. O f g r e a t e r i n t e r e s t a r e those c o m p l e x e s f o r m e d w i t h a l k a l i m e t a l salts (H). A 1 ( C H ) + N a F -> N a F - A 1 ( C H ) 2

5

3

2A1(C H ) + N a F 2

5

3

2

5

2

(16)

3

NaF-2Al(C H ) 5

3

(17)

T h e 1 t o 1 c o m p l e x m e l t s a t 7 4 ° C . , whereas t h e 1 t o 2 c o m p l e x i s l i q u i d a t r o o m temperature a n d conducts electricity well. P r a c t i c a l l y a l l of the a l u m i n u m a l k y l s f o r m s u c h c o m p l e x salts w i t h s o d i u m f l u o r i d e a n d p o t a s s i u m f l u o r i d e . T h e s e c o m p l e x salts o f a l u m i n u m a l k y l s a p p e a r t o h a v e a n i n t e r e s t i n g f u t u r e a s



107

e l e c t r o l y t e s f o r use i n t h e e l e c t r o p l a t i n g of m e t a l o b j e c t s w i t h a l u m i n u m (9). U p t o n o w , n o p r a c t i c a l process f o r e l e c t r o p l a t i n g a l u m i n u m i s k n o w n . A process b a s e d o n m o l t e n i n o r g a n i c salts h a s w o r k e d f a i r l y w e l l o n a l a b o r a t o r y scale, b u t s o m e d i f ficult e n g i n e e r i n g p r o b l e m s n e e d s o l v i n g b e f o r e l a r g e - s c a l e o p e r a t i o n i s possible. T h e sodium fluoride-aluminum a l k y l c o m p l e x salts a r e e s s e n t i a l l y m o l t e n salt e l e c t r o l y t e s w h i c h are l i q u i d below 100°C. A s i t i s possible t o p l a t e a l u m i n u m o n c o p p e r w i r e (9), d e v e l o p m e n t s a r e i n progress t o e x t e n d t h i s process t o t h e c o a t i n g of t h i n sheet steel s u c h a s i s u s e d i n m a k i n g c o n t a i n e r s .


A n o t h e r p o t e n t i a l use f o r these salts f r o m t r i e t h y l a l u m i n u m i s i n t h e s y n t h e s i s of t e t r a e t h y l l e a d . T h e c o m p l e x s a l t i s u s e d as a n e l e c t r o l y t e w i t h a l e a d anode a n d a n a l u m i n u m cathode. Passage of current t h r o u g h the cell forms t e t r a e t h y l l e a d , w h i c h d r i p s off t h e a n o d e , a n d p u r e a l u m i n u m , d e p o s i t i n g a t t h e c a t h o d e i n a finely d i v i d e d f o r m (14). NaF.Al(C H ) 2

5

3

+ % P b -> % P b ( C H ) 4 + A l + N a F 2

(18)

5

T r i e t h y l a l u m i n u m m u s t b e a d d e d t o r e p l e n i s h t h e b a t h as t h e r e a c t i o n progresses. Considering the methods available for m a k i n g t r i e t h y l a l u m i n u m , tetraethyllead is m a d e e s s e n t i a l l y f r o m e t h y l e n e , h y d r o g e n , a n d l e a d m e t a l . T h i s process i s b e i n g s t u d i e d t o d e t e r m i n e i t s v a l u e i n c o m p a r i s o n w i t h t h e p r e s e n t c o m m e r c i a l process.

Reaction w i t h M e t a l s a n d Hydrogen A recent p a t e n t describes t h e p r e p a r a t i o n of o t h e r m e t a l a l k y l s f r o m a n a l u m i n u m trialkyl, a metal, a n d hydrogen. T h u s w i t h lead a n d hydrogen, t r i e t h y l a l u m i n u m p r o d u c e s t e t r a e t h y l l e a d a n d a l u m i n u m h y d r i d e (1). 4A1{C II )3 + 6 H + 3 P b -> 4 A 1 H - f 3 P b ( C H ) 5

2

2

3

2

5

(19)

4

A d d i n g ethylene to the a l u m i n u m hydride will reform t r i e t h y l a l u m i n u m w h i c h c a n be r e - u s e d .

G r o w t h Reaction A l u m i n u m t r i a l k y l c o m p o u n d s , e x c e p t those m a d e f r o m i s o b u t y l e n e o r s i m i l a r olefins, c a n a d d e t h y l e n e t o f o r m h i g h e r a l k y l s o r g r o w . T h i s is a n important r e a c t i o n o f a l u m i n u m a l k } l s . C o n t r o l o f t h e r e a c t i o n c o n d i t i o n s enables p r e p a r a t i o n o f h i g h e r a l u m i n u m a l k y l s w h i c h c a n b e u s e d t o p r o d u c e s a t u r a t e d h y d r o c a r b o n s , olefins, or alcohols. I f e t h y l e n e i s passed i n t o t r i e t h y l a l u m i n u m a t a t e m p e r a t u r e o f a b o u t 2 0 0 ° C . a t a t m o s p h e r i c p r e s s u r e , 1-butene is f o r m e d t o g e t h e r w i t h v e r y s m a l l a m o u n t s o f 1-hexene a n d 1 - o c t e n e (14, 16): 200°C

zCH =CH 2

CH =CH—C H

2

2

2

+ (W =CH---CJ-I + C H = C H — C H

5

2

9

2

6

1 3

(20)

Al(CsH6)8

A c t u a l l y t h e p r i m a r y p r o d u c t s a r e t h e c o r r e s p o n d i n g a l k y l s a n d t h e o v e r - a l l r e a c t i o n is : A1(C H ), + 3 C H = C H 2

5

2

2

-* A1(CH CH CH CH ) 2

2

2

3

(21 )

3

then, 200°C

A1(CH CH CH CH ) 2

2

2

3

3

+ 3CH =CH 2

2

» CH =CH—C H 2

2

5

+ A1(C H ) 2

5

3

(22)

T h e n a t u r e of t h e p r o d u c t is determined b y t h e pressure o f ethylene, t h e t i m e of contact, a n d the temperature. U n d e r t h e conditions cited above, only relatively l o w m o l e c u l a r w e i g h t olefins a r e f o r m e d . O c c a s i o n a l l y , s m a l l a m o u n t s o f olefins a r e f o r m e d where t h e double b o n d h a s m o v e d t o w a r d t h e center of t h e molecule. This can be m i n i m i z e d b y using short contact times a n d small amounts of phenylacetylene



168

(ethynylbenzene) to inhibit the migration. T h e o p t i m u m conditions f o r producing 1-butene b y t h i s process i n v o l v e p a s s i n g e t h y l e n e a t 4 0 a t m o s p h e r e s i n t o t r i e t h y l a l u m i n u m a t 100° t o 1 1 0 ° C . c o n t a i n i n g a s m a l l a m o u n t of c o l l o i d a l n i c k e l a n d 0 . 5 % of p h e n y l a c e t y l e n e (13). I f p r o p y l e n e is used i n s t e a d of e t h y l e n e , t h e p r o p y l e n e d i m e r is f o r m e d e x c l u s i v e l y and quantitatively: 2CH =CHCH 2

3

2 Q Q

° ' ) CH =C—C H C

2

A1(C H )3 2

3

CH


(23)

7

J

5

3

A t first t h e s m a l l a m o u n t of e t h y l e n e is d i s p l a c e d b y t h e i n c o m i n g p r o p y l e n e a n d s w e p t o u t o f t h e s y s t e m l e a v i n g t r i p r o p y l a l u m i n u m w h i c h is t h e r e a l c a t a l y s t . H i g h e r p o l y m e r s of p r o p y l e n e are n o t f o r m e d . A p p a r e n t l y , a l u m i n u m a l k y l s i n w h i c h t h e second c a r b o n f r o m t h e m e t a l has a b r a n c h c a n n o t a d d o t h e r olefins, e v e n e t h y l e n e . I n s t e a d , i f t h e t e m p e r a t u r e is h i g h e n o u g h , t h e y react b y s p l i t t i n g o u t t h e b r a n c h e d olefin. I f a n o t h e r olefin is p r e s e n t w h i c h c a n f o r m a n u n b r a n c h e d a l k y l , a n e w a l k y l is f o r m e d . W i t h p r o p y l e n e , 2 - m e t h y l - l - p e n t e n e is s p l i t o u t a n d t r i p r o p y l a l u m i n u m is f o r m e d w h i c h a g a i n reacts w i t h m o r e p r o p y l e n e . T h i s process c a n be a p p l i e d t o 1-butene, 1-pentene, a n d others w i t h a l m o s t e q u a l r e s u l t s . C o d i m e r i z a t i o n o f different olefins is possible b u t u s u a l l y r e s u l t s i n a m i x t u r e o f a l l possible p r o d u c t s . Z i e g l e r ' s w o r k o n t h e d i m e r i z a t i o n r e a c t i o n r e s u l t e d i n a process f o r s y n t h e s i z i n g p - x y l e n e f r o m e t h y l e n e . T h e r e a c t i o n s i n v o l v e d are (6) : 40 atm. 110°C.

2CH =CH 2

>CH =CHCH CH

2

2

2

3

(24)

A l ( C H ) + N i + 0.5% C H — C ^ C H 2

6

3

6

5

2oo°C 2CH =CHCH CH 2

2

CH =CCH CH CH CH

3

2

AUC HB) 2

CH =CCH CH CH CH 2

2

2

2

500°C 3

3

2

2

2

(25)

3

ι C2H5

> 5 5 % p-xylene + 2 6 % o-xylene + 1 9 % ethylbenzene

(26)

Cr 03

J

2

C H 2

6

T h e p r o d u c t o f t h e first step is s u b s t a n t i a l l y p u r e 1-butene a n d excess e t h y l e n e . F r o m t h e second s t e p , o n l y 2 - e t h y l - l - h e x e n e a n d u n c h a n g e d 1-butene a r e o b t a i n e d . T h e a r o m a t i z a t i o n r e a c t i o n uses a c o n v e n t i o n a l c h r o m i t e c a t a l y s t . T h e final p r o d u c t is s e p a r a t e d e a s i l y i n t o i t s c o m p o n e n t s b y f r a c t i o n a l d i s t i l l a t i o n a n d c r y s t a l l i z a t i o n . C o s t c a l c u l a t i o n s s h o w e d t h a t p - x y l e n e m a d e b y t h i s process was c h e a p e r t h a n t h a t available a t the time, but i t was not cheap enough t o compete w i t h predicted future prices for p-xylene made b y other methods f r o m p e t r o l e u m . T h e growth reaction can be extended t o produce high molecular weight alkyls a n d f r o m these t h e c o r r e s p o n d i n g olefins a n d a l c o h o l s . F o r t h i s r e a c t i o n , h i g h e r p r e s sures o f e t h y l e n e a n d l o n g e r c o n t a c t t i m e s are r e q u i r e d a t t e m p e r a t u r e s b e l o w those a t w h i c h olefins a r e d i s p l a c e d . T y p i c a l c o n d i t i o n s are e t h y l e n e pressures o f 100 o r m o r e a t m o s p h e r e s a t 100° t o 1 5 0 ° C . f o r 1 o r m o r e h o u r s . U n d e r s u c h c o n d i t i o n s , t h e r e a c t i o n (14) is s i m i l a r t o E q u a t i o n 2 7 : A1(C H ) 2

5

3

+ zCH =CH 2

100 atm. 2

ioo°C.

(CH —CH ) —C H >Al (CH —CH ) — C H (CH —CH ) — C H 2

2

2

2

2

2

m

r

2

2

5

5

2

(27)

5

T h e p r o d u c t is a l w a y s a m i x t u r e of a l u m i n u m a l k y l s , b u t t h e a v e r a g e l e n g t h o f the a l k y l chain a p p a r e n t l y c a n be peaked somewhat b y regulating t h e conditions. A t y p i c a l r e a c t i o n , i n w h i c h 6 moles o f e t h y l e n e r e a c t e d f o r e a c h m o l e of t rie t h y 1a l u m i n u m u s e d , g a v e a p r o d u c t i n w h i c h t h e a l k y l c h a i n s were d i s t r i b u t e d as i n T a b l e I . T h e l a s t c o l u m n gives t h e w e i g h t - p e r cent d i s t r i b u t i o n of a p r o d u c t w h i c h


169

SC H U LTZ—ORG AN OALUMIN UM COMPOUNDS Table I.

C H 2

Distribution of Reaction Products Wt. %

as R O H

15 26 27 17 9 4 1 1

5.0 18.0 27.5 23.0 15.0 8.0 2.5 1.0

7.0 19.0 27.5 22.0 14.0 7.5 2.0 1.0

5

C4H9 C6H13

CSHIT CioHoi C12H25

CuHw C16H33


wt. %

Mole %

w o u l d be o b t a i n e d b y o x i d a t i o n o f t h e a l k y l s f o l l o w e d b y h y d r o l y s i s o f t h e a l c o h o l a t e s . I n a d d i t i o n t o p r o d u c i n g a l c o h o l s , these a l k y l s c o u l d b e u s e d t o m a k e n o r m a l olefins b y d i s p l a c e m e n t , o r n o r m a l paraffins b y h y d r o l y s i s . B e c a u s e t h e successive m e m b e r s of t h e series differ b y t w o c a r b o n a t o m s , t h e m i x t u r e o f p r o d u c t s c a n be s e p a r a t e d i n t o fairly pure compounds b y fractional distillation. T h e growth reaction followed b y hydrolysis, t h e r m a l decomposition, or oxidation and hydrolysis provides a n attractive means for synthesizing straight-chained saturated h y d r o c a r b o n s , olefins, a n d a l c o h o l s . N o s i g n i f i c a n t c o m m e r c i a l uses a r e k n o w n f o r these h y d r o c a r b o n s o r olefins. T h e a l c o h o l s h a v e m a n y i m p o r t a n t a p p l i c a t i o n s . T h e process i s p r o b a b l y t o o c o s t l y f o r m a k i n g a l c o h o l s w i t h s i x c a r b o n a t o m s o r less. B e c a u s e m a t e r i a l costs d r o p as c a r b o n c o n t e n t increases, i t a p p e a r s v e r y a t t r a c t i v e f o r p r e p a r i n g alcohols i n t h e 1 0 - t o 1 4 - c a r b o n r a n g e : L e s s of t h e e x p e n s i v e a l u m i n u m m e t a l i s c o n s u m e d as t h e c h a i n l e n g t h increases. C o n t i n u e d investigation of the g r o w t h reaction showed that i t could be used t o p r e p a r e olefins w i t h m o l e c u l a r w e i g h t s as h i g h as 5000 (17). T h i s w a s d o n e b y u s i n g a l a r g e excess of e t h y l e n e a n d pressures u p t o s e v e r a l t h o u s a n d p o u n d s . T h e s e h i g h e r m o l e c u l a r w e i g h t p r o d u c t s r a n g e d f r o m soft l o w - m e l t i n g t o v e r y h a r d h i g h - m e l t i n g waxes. I t w a s n o t possible t o p r e p a r e p o l y e t h y l e n e w i t h p l a s t i c - r a n g e m o l e c u l a r w e i g h t s a t m o d e r a t e pressures b y t h e s i m p l e g r o w t h r e a c t i o n f r o m t r i e t h y l a l u m i n u m a n d e t h y l e n e . H o w e v e r , Z i e g l e r o b s e r v e d t h e p r o f o u n d effect o f s m a l l q u a n t i t i e s o f c e r t a i n m e t a l salts o n t h e g r o w t h r e a c t i o n , w h i c h l e d t o h i s process f o r p r e p a r i n g p l a s t i c - g r a d e p o l y e t h y l e n e a t l o w pressures. Z i e g l e r d i s c o v e r e d t h a t a c a t a l y s t , c o m p o s e d of a n a l u m i n u m t r i a l k y l a n d s m a l l a m o u n t s of a t r a n s i t i o n m e t a l salt s u c h a s t i t a n i u m t e t r a c h l o r i d e , w a s c a p a b l e o f p o l y m e r i z i n g ethylene a t l o w pressure t o a v e r y h i g h molecular weight p r o d u c t a t 50° t o 1 0 0 ° C . (8) : *CH ^CH 2

2

1

%

(

_ C H - C H - ) , 2

2

(28)

w h e r e χ c a n b e v a r i e d f r o m 1000 t o 400,000. A s i n the growth reaction, the ethylene h a d t o b e v e r y free f r o m a c t i v e i m p u r i t i e s l i k e o x y g e n , w a t e r , s u l f u r , a n d a c e t y l e n e , b u t d i d n o t r e q u i r e t h e absence of i n e r t m a t e r i a l s l i k e s a t u r a t e d h y d r o c a r b o n s a n d n i t r o g e n . I n m o s t cases, t h e r e a c t i o n w a s c a r r i e d o u t i n a n i n e r t h y d r o c a r b o n s o l v e n t s u c h as D i e s e l o i l . A w i d e v a r i e t y of o r g a n o m e t a l l i c c o m p o u n d s s u c h as a l u m i n u m d i a l k y l halides, zinc a l k y l s , a n d s o d i u m a l u m i n u m a l k y l s c a n b e used i n place of t h e t r i a l k y l a l u m i n u m . A p p a r e n t l y , a n y o f t h e t r a n s i t i o n m e t a l salts c o u l d b e u s e d i n p l a c e o f t i t a n i u m t e t r a c h l o r i d e . Z i e g l e r ' s w o r k c o v e r e d t h e use o f salts o f z i r c o n i u m , h a f n i u m , v a n a d i u m , t a n t a l u m , a n d c h r o m i u m (8). H e f o u n d t h a t t h e molecular weight of t h e product could be v a r i e d a t w i l l a n d seemed t o be c o n t r o l l e d b y t h e r a t i o o f a l u m i n u m a l k y l t o t r a n s i t i o n m e t a l s a l t i n t h e c a t a l y s t (12). T h i s i s i l l u s t r a t e d i n T a b l e I L A h i g h m o l e c u l a r w e i g h t p r o d u c t i n t h e r a n g e of 300,000 r e s u l t e d i f t h e a l u m i n u m a l k y l t o t i t a n i u m s a l t m o l e r a t i o w a s 12 t o 1. T h e m o l e c u l a r w e i g h t of t h e p r o d u c t d i d n o t change m u c h as t h e m o l e r a t i o of a l u m i n u m a l k y l t o t i t a n i u m salt d r o p p e d u n t i l a v a l u e f r o m 0.5 t o 1 w a s r e a c h e d . W i t h t h i s c a t a l y s t c o m p o s i t i o n , t h e m o l e c u l a r w e i g h t d r o p p e d t o 20,000 (12). T h i s t y p e o f c a t a l y s t s y s t e m c a n b e used t o p o l y m e r i z e p r a c t i c a l l y a n y a l p h a olefin f r o m p r o p y l e n e t o s t y r e n e , a n d p r o b a b l y b e y o n d , t o y i e l d e i t h e r a m o r p h o u s



170

Table I!. Effect of Catalyst Composition on Molecular Weight Molar Ratio, AIRs to TiCU 12 6 3


0.63 0.53 0.50 0.20

4-Hr. Yield, Grams 440 430 460 440 480 460 300 10

Av. Mol. Wt. 272.000 292,000 298,000 284,000 160.000 40,000 21,000 31,000

o r c r y s t a l l i n e p o l y m e r s a n d s o m e t i m e s a m i x t u r e o f b o t h (19). A p p a r e n t l y , different m o n o m e f s c a n b e c o p o l y m e r i z e d . I n p r a c t i c a l l y a l l cases, t h e r e a c t i o n r a t e i s s l o w e r t h a n f o r ethylene at a given temperature a n d pressure. W i t h propylene, under certain conditions, t h e p o l y m e r obtained was a m i x t u r e of amorphous a n d crystalline material. B y a suitable extraction procedure, a n amorphous rubber fraction w i t h a m o l e c u l a r w e i g h t o f less t h a n 45,000 w a s s e p a r a t e d . T h e residue f r o m s u c h a n e x t r a c t i o n w a s a c r y s t a l l i n e s o l i d w h i c h m e l t e d a t 100° t o 1 5 0 ° C . a n d h a d a m o l e c u l a r w e i g h t a b o v e 100,000. T h e c r y s t a l l i n e f r a c t i o n c o u l d b e e x t r u d e d i n t o filaments a n d stretch-oriented t o f o r m products w i t h v e r y h i g h tensile strength. C r y s t a l l i n e p o l y s t y r e n e also h a s b e e n m a d e w i t h a m o l e c u l a r w e i g h t a b o v e 2,800,000, a d e n s i t y o f 1.08, a n d a s o f t e n i n g p o i n t a b o v e 2 0 0 ° C . (19). A l a r g e r u b b e r c o m p a n y a n n o u n c e d t h e use o f Z i e g l e r - t y p e c a t a l y s t s t o p o l y m e r i z e i s o p r e n e t o a r u b b e r w h i c h i s a p p a r e n t l y i d e n t i c a l w i t h n a t u r a l r u b b e r (4), as s h o w n b y infrared absorption a n d x - r a y diffraction data. Physical properties a n d t h e r e s u l t s o f f i e l d tests f u r t h e r s u b s t a n t i a t e t h i s .

Summary I t is difficult t o tell w h i c h of Ziegler's m a n y reactions w i l l be the most i m p o r t a n t . C e r t a i n l y , t h e l o w pressure synthesis of polyethylene is most i m p o r t a n t t o i n d u s t r y . P r o b a b l y t h e most notable reactions a r e : t h e synthesis of a l u m i n u m alkyls f r o m olefins, h y d r o g e n , a n d a l u m i n u m ; t h e g r o w t h o f l o n g u n b r a n c h e d a l i p h a t i c c h a i n s f r o m a l u m i n u m a l k y l s a n d e t h y l e n e a n d t h e i r use t o m a k e s a t u r a t e d h y d r o c a r b o n s , olefins, a n d a l c o h o l s ; a n d t h e s y n t h e s i s o f h i g h p o l y m e r s o f e t h y l e n e a n d o t h e r olefins a t l o w pressures u s i n g a c a t a l y s t c o m p o s e d of a l u m i n u m a l k y l s a n d t r a n s i t i o n m e t a l salts. F u t u r e w o r k e r s s h o u l d e x p a n d t h e a p p l i c a t i o n s o f these r e a c t i o n s a n d also d i s c o v e r m a n y more.

Literature Cited (1) Blitzer, S. M . , Milde, R. L., Pearson, T. H., Redman, H . E . (to Ethyl Corp.), Belgian Patent 548,439 (June 7, 1956). (2) Bonitz, E., Chem. Ber. 88, 742 (1955). (3) Buckton, G. B., Odling, W., Ann. Chem. Liebigs Suppl. No. 4, 109 (1865). (4) Home, S. E., Jr., Kiehl, J. P., Shipman, J. J., Folt, Z. L., Gibbs, C. F., Ind. Eng. Chem. 48, 784 (1956). (5) Jenker, J . (to Kali-Chemie A.-G.), German Patent Application K. 20,023 IV/12o (1955). (6) Ziegler, K., Angew. Chem. 64, 323 (1952). (7) Ibid., 68, 721 (1956). (8) Ziegler, K . , Belgian Patents 533,362 (May 16, 1955), 534,792 (Jan. 31, 1955), 535,235 (Feb. 15, 1955). (9) Ibid., 540,411 (Aug. 31, 1955). (10) Ibid., 540,135 (Jan. 27, 1956). (11) Ibid., 540,280 (Feb. 2, 1956). (12) Ibid., 540,459 (Feb. 9, 1956). (13) Ziegler, K., Brennstoff-Chem. 35, 321 (1954). In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.


171 e

(14) Ziegler, K., Experientia, Suppl. No. 2, 14 Congr. intern. chim. pure et appl.,Zurich 1955, 274-87. (15) Ziegler, K., Gellert, H., German Patent 917,006 (Aug. 23, 1954). (16) Ibid., 2,695,327 (Nov. 23, 1954). (17) Ibid., 2,699,437 (Jan. 11, 1955). (18) Ziegler, K., Gellert, J., Zosel, K., Lehmkuhl, W., Pfohl, W., Angew. Chem. 67, 424 (1955). (19) Ziegler, K., and Montecatini Società Generale per l'Industria Mineraria e Chimica Anonima, Belgian Patent 538,782 (Dec. 6, 1955). (20) Ziegler, K., Nagle, K., U . S. Patent 2,744,127 (May 1, 1956). (21) Ziegler, K., Zosel, K., Ibid., 2,691,668 (Oct. 12, 1954).


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


Organoaluminum Compounds

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