Telomerization Reactions Involving Amine-Chelated Lithium Catalysts

9 Telomerization Reactions Involving

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Amine-Chelated Lithium Catalysts W. A. BUTTE and G. G. EBERHARDT Sun Research and Development Co., Marcus Hook, Pa. 19061

Complexes of organolithium compounds with certain diamines are remarkably active in the metalation of unsaturated hydrocarbons and addition to ethylene. These complexes form a new class of initiators for the telomerization of ethylene with aromatic hydrocarbons and olefins. The distribution of the products is in accordance with a mechanism involving competitive transmetalation and addition to ethylene. By proper selection of the telogen and regulation of the ethylene pressure, it is possible to influence the nature of the telomeric products and produce phenylalkanes, polyalkylbenzenes, and long-chain olefins with a variable average degree of telomerization. The assistance of the amine in accelerating the reaction is attributed to the formation of a coordination complex with lithium which facilitates ionization of the carbon-lithium bond.

T n 1955 P i n e s a n d S c h a a p ( J ) d i s c o v e r e d that t o l u e n e w a s a l k y l a t e d b y ·*· ethylene i n the presence of

s o d i u m or p o t a s s i u m m e t a l or,

specifically, t h e i r o r g a n o m e t a l l i c d e r i v a t i v e s .

more

This reaction requires a

h i g h t e m p e r a t u r e ( a b o u t 2 0 0 ° C ) a n d c o n s i d e r a b l e olefin pressure; the o r g a n o m e t a l l i c catalyst is essentially i n s o l u b l e i n t h e r e a c t i o n m e d i u m . T h e catalyst c y c l e — f o r e x a m p l e , i n the s i d e - c h a i n e t h y l a t i o n of t o l u e n e — i n v o l v e s a b e n z y l c a r b a n i o n w h i c h a d d s to ethylene to f o r m a p r i m a r y a l k y l c a r b a n i o n . T h e latter i m m e d i a t e l y abstracts a p r o t o n f r o m the excess toluene r e a c t a n t to f o r m n - p r o p y l b e n z e n e a n d to r e f o r m the e n e r g e t i c a l l y f a v o r e d b e n z y l i c a n i o n i n a c a t a l y t i c cycle. O n f u r t h e r c o n v e r s i o n of t h e n - p r o p y l b e n z e n e ,

additional benzylic

h y d r o g e n s are e t h y l a t e d . T h e h i g h rate of t r a n s m e t a l a t i o n i n v o l v i n g the p r i m a r y a l i p h a t i c o r g a n o s o d i u m or p o t a s s i u m i n t e r m e d i a t e s a n d the a l k y l 186 Langer; Polyamine-Chelated Alkali Metal Compounds Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

9.

BUTTE

AND EBERHARDT

187

Telomerization Reactions H H

H

W

(la)

•C-C-C-C-C


H

H H

prevents

formation

of

(lb)

(le)

c—c—H

H

aromatic hydrocarbon

0

H

telomeric

products

with

these catalysts e v e n at h i g h e r e t h y l e n e pressures. The

carbanionic

ethylene

adduct

c a n also u n d e r g o

a cyclization

r e a c t i o n to i n d a n e s w i t h e l i m i n a t i o n of a h y d r i d e i o n ( R e a c t i o n

la).

T h i s r e a c t i o n is m o r e p r o n o u n c e d w i t h o r g a n o p o t a s s i u m or s o m e c o m p l e x o r g a n o p o t a s s i u m catalysts ( 2 ) .

High-molecular-weight growth

products

are n o t o b t a i n e d f r o m either s o d i u m - or p o t a s s i u m - d e r i v e d catalysts. A n i n i t i a t o r system has b e e n f o u n d i n d e p e n d e n t l y i n the laboratories of E s s o a n d S u n O i l (3, 4).

T h i s system p r o m o t e s t r a n s m e t a l a t i o n a n d

c h a i n p r o p a g a t i o n reactions at c o m p a r a b l e rates so that a t e l o m e r i z a t i o n r e a c t i o n of e t h y l e n e w i t h a r o m a t i c h y d r o c a r b o n s is r e a l i z e d u n d e r r e l a tively m i l d operating conditions. Nature

of the

The

Initiator

i n i t i a t o r consists

of

an organolithium-amine

organolithium component could be

a commercially

complex.

The

available material

s u c h as n - b u t y l l i t h i u m i n h e x a n e s o l u t i o n . T h e a m i n e c o m p o n e n t s h o u l d b e free of r e a c t i v e h y d r o g e n , i n c l u d i n g a r o m a t i c , a l l y l i c , a n d

benzylic

protons, a n d i t is therefore l i m i t e d to t e r t i a r y a l i p h a t i c amines. M a x i m u m catalyst a c t i v i t y is o b t a i n e d w i t h c h e l a t i n g - t y p e d i a m i n e s l i k e t e t r a m e t h y l ethylenediamine

( T M E D A ) and bridgehead-type

ethylenediamine

(TEDA).

bridgehead

Sparteine,

n i t r o g e n atoms, f o r m s

a

amines

diamine

s u c h as t r i -

containing

an exceptionally

tertiary

stable a n d h i g h l y

r e a c t i v e catalyst. T h e i n i t i a t o r m a y b e p r e f o r m e d or g e n e r a t e d in situ s i m p l y b y b i n i n g the organolithium c o m p o u n d

w i t h the a m i n e .

com-

D e s p i t e its h i g h

r e a c t i v i t y , the r e s u l t i n g c o m p l e x c a n b e easily h a n d l e d as a h y d r o c a r b o n s o l u t i o n . I m p u r i t i e s s u c h as w a t e r , a i r , a n d c a r b o n d i o x i d e m u s t b e r i g i d l y e x c l u d e d b e c a u s e of t h e i r r a p i d r e a c t i o n w i t h o r g a n o l i t h i u m

compounds.

Langer; Polyamine-Chelated Alkali Metal Compounds Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

188

POLY AMINE-CHELATED

ALKALI

METAL

COMPOUNDS

H y d r o g e n acts as a p o i s o n b e c a u s e l i t h i u m h y d r i d e r e s u l t i n g f r o m h y d r o genolysis of the l i t h i u m - c a r b o n b o n d is i n a c t i v e as a catalyst c o m p o n e n t . A l l of the e v i d e n c e ( 3 , 4) s t r o n g l y suggests that the f u n c t i o n of the a m i n e is that of associating w i t h the l i t h i u m i n the r e a c t i o n m i x t u r e . A s a r e s u l t the c a r b o n - l i t h i u m b o n d is m o d i f i e d a n d a m o r e reactive i n c i p i e n t c a r b a n i o n results.

A d y n a m i c e q u i l i b r i u m exists b e t w e e n

c o m p l e x a n d the d i s s o c i a t e d species.

the

lithium

T h e i n s t a b i l i t y constant, K „ is a


m e a s u r e of the p o s i t i o n of the e q u i l i b r i u m . Ki

RLi«n Amine

R L i + η Amine

(2)

W i t h T E D A , K is r e l a t i v e l y large. T h e r e f o r e the d e g r e e of associa {

t i o n a n d thus t h e r e a c t i o n rate is m a t e r i a l l y i m p r o v e d b y i n t r o d u c i n g a n excess of the a m i n e . W i t h T M E D A , K is s m a l l so there is l i t t l e a d v a n t a g e t

to u s i n g greater t h a n e q u i m o l a r a m o u n t s of a m i n e . Transmetalation In

contrast w i t h the l o w r e a c t i v i t y o b s e r v e d

solutions i n h y d r o c a r b o n s

(5)

o r ether ( 6 ) ,

with n-butyllithium

the n - b u t y l l i t h i u m - a m i n e

adducts r a p i d l y metalate unsaturated hydrocarbons including even simple olefins. I n this respect t h e y surpass e v e n o r g a n o s o d i u m c o m p o u n d s w i l l probably prove

to b e of c o n s i d e r a b l e

synthetic value.

and

Addition

of a hexane s o l u t i o n c o n t a i n i n g e q u i m o l a r a m o u n t s of n - b u t y l l i t h i u m a n d a n a m i n e to excess t o l u e n e at o r d i n a r y temperatures results i n r a p i d f o r m a t i o n of a b e n z y l l i t h i u m - a m i n e c o m p l e x that i n some cases separates as a y e l l o w c r y s t a l l i n e s o l i d . C H Li.Amine + C H C H 4

9

6

6

3

-> C H C H L i . A m i n e + C H i 6

6

2

4

(3)

0

T h e effecitveness of v a r i o u s amines as p r o m o t e r s for transmetalations c a n b e r e a d i l y d i s c e r n e d b y c o m p a r i n g the amounts of b e n z y l l i t h i u m formed under identical conditions ( T a b l e I ) . TEDA

on

excellent

the

donor

r e a c t i v i t y of

T h e m a r k e d i n f l u e n c e of

n-butyllithium can

characteristics of

the b r i d g e h e a d

that d i s r u p t s t h e n - b u t y l l i t h i u m aggregates ( 8 ) .

be

to

the

nitrogen atom

ascribed

(7)

F u r t h e r m o r e the c o o r d i

n a t i o n of l i t h i u m b y the a m i n e p o l a r i z e s the c a r b o n - l i t h i u m b o n d t h e r e b y easing l i t h i u m - h y d r o g e n interchange. T a b l e I also shows that T M E D A has a m u c h greater effect o n the r e a c t i v i t y of b u t y l l i t h i u m t h a n does either t r i e t h y l a m i n e or N , N ' - d i m e t h y l piperazine.

T o e x p l a i n this difference i t is suggested t h a t t h e r e a c t i v e

species c o n t a i n t w o c o o r d i n a t e d a m i n e groups.

T h e unusual reactivity

w i t h T M E D A is t h e n r e l a t e d to the f a v o r a b l e e n t r o p y c h a n g e u s u a l l y


9.

BUTTE

AND

Table I.

Extent of Metalation of

Amine


β 6

2

2

2

2

2

2

2

2

2

2

2

2

3

2

2

3

Extent of metalaHon, % b

3 1 1 1 1 1 1 2

3

2

Toluene"

Amine/BuLi, molar ratio

Et N M e N (CH CH ) NMe Me NCH NMe Me NCH CH NMe Me NCH CH CH(Me)NMe Sparteine N(CH CH ) N N(CH CH ) N 2

189

Telomerization Reactions

EBERHARDT

2

2

2 5 6 77 60 90 43 66

One hour at 60°C, 1.0M butyllithium. Percent of theory based on butyllithium.

associated w i t h chelate f o r m a t i o n . S u p p o r t f o r this i n t e r p r e t a t i o n comes f r o m the p r e d i c t a b l e effect of r i n g size u p o n the r e l a t i v e r e a c t i v i t y of the a d d u c t s a n d f r o m the h i g h r e a c t i v i t y n o t e d for the r i g i d b i d e n t a t e c o m p l e x f o r m e d w i t h sparteine. Telomerization

of Ethylene

with Aromatic

Hydrocarbons

E t h y l e n a t i o n of n - b u t y l l i t h i u m , p h e n y l l i t h i u m , a n d b e n z y l i c l i t h i u m c o m p o u n d s does not o c c u r at l o w t e m p e r a t u r e a n d o r d i n a r y pressure

(9).

U n d e r m o r e rigorous c o n d i t i o n s , t e l o m e r i z a t i o n of ethylene i n a r o m a t i c h y d r o c a r b o n s p r o c e e d s v i g o r o u s l y i n t h e presence of a n o r g a n o l i t h i u m c o m p o u n d a n d a n a m i n e . A l t h o u g h n - b u t y l l i t h i u m is i n t r o d u c e d i n i t i a l l y , r a p i d t r a n s m e t a l a t i o n occurs to the m o r e a c i d i c a r o m a t i c

hydrocarbon

( t e l o g e n ) w h i c h s u b s e q u e n t l y adds to ethylene ( t a x o g e n ) a n d initiates the c a r b a n i o n i c p o l y m e r i z a t i o n of ethylene. T h i s p o l y m e r i z a t i o n p r o c e e d s to modest m o l e c u l a r w e i g h t , b u t i t is t e r m i n a t e d b y t r a n s m e t a l a t i o n b a c k to the a r o m a t i c h y d r o c a r b o n w h i c h initiates another c h a i n to

complete

the c a t a l y t i c cycle. n-BuLi + A r H ArLi + C H 2

Ar(CH CH )Li + 2

2

4

(η -

•n-BuH + A r L i

(4)

•A r C H C H L i

(5)

2

1) C H 2

4

2

—• Ar(CH CH ) Li

(6)

•A r ( C H C H ) H + ArLi

(7)

2

2

n

fc

3

Ar(CH CH ) Li + ArH 2

2

n

2

2

n

S i n c e thé p r o p a g a t i o n r e a c t i o n ( R e a c t i o n 6 ) a n d the transfer r e a c t i o n (Reaction

7)

are c o m p e t i t i v e , t h e r e s u l t i n g p r o d u c t

is a m i x t u r e of

molecular weights governed b y a simple statistical distribution shown i n



190

POLYAMINE-CHELATED

ALKALI

M E T A L

COMPOUNDS

NUMBER OF ETHYLENE UNITS Figure 1. Distribution of telomeric products obtained from ethylene and benzene at 110°C F i g u r e 1. T h e average degree of p o l y m e r i z a t i o n o f t h e p r o d u c t , n , i s a f u n c t i o n o f the r e l a t i v e rates o f ethylene c o n s u m p t i o n a n d transfer. B y i n v o k i n g t h e steady-state a s s u m p t i o n , i t c a n b e s h o w n that t h e average degree o f p o l y m e r i z a t i o n is g o v e r n e d b y the c o m p e t i t i v e rates o f p r o p a g a t i o n a n d transfer. 1

fc (C2H ) 2

n

4

= kÂÂrÏÏj

+

1

=

β +

,

Λ

1

(

8

Q

.

)

F o r c o n v e n i e n c e , t h e r a t i o of transfer a n d p r o p a g a t i o n rates is ex p r e s s e d as β since this r a t i o is r e l a t e d t o t h e m o l e f r a c t i o n , X , o f p r o d u c t n

w i t h degree of p o l y m e r i z a t i o n , η ( E q u a t i o n 9 ) . T h i s r e l a t i o n s h i p m a y b e m o d i f i e d t o a l l o w c a l c u l a t i n g β f r o m t h e a m o u n t of p r o d u c t a t t w o successive v a l u e s o f n , as s h o w n i n E q u a t i o n 10.

(9)


9.

BUTTE

AND EBERHARDT

191


β = ^

-

1

(10)

E q u a t i o n 6 i m p l i e s t h a t the rate of e t h y l e n e c o n s u m p t i o n d u r i n g t e l o m e r i z a t i o n is a f u n c t i o n of its c o n c e n t r a t i o n b u t is essentially i n d e p e n d e n t of the t e l o g e n c o n c e n t r a t i o n present i n l a r g e excess.

Further

m o r e , a c c o r d i n g to E q u a t i o n 8, t h e β v a l u e m a y b e v a r i e d b y c h a n g i n g the pressure or the n a t u r e of the telogen. T h i s is i n d e e d the case, as seen Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 20, 2017 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0130.ch009

f r o m t h e average m o l e c u l a r w e i g h t of telomers o b t a i n e d f r o m reactions c a r r i e d out at v a r i o u s e t h y l e n e pressures a n d w i t h a n u m b e r of a r o m a t i c telogens. T a b l e I I shows t h a t t h e average d e g r e e of p o l y m e r i z a t i o n rises as the pressure is i n c r e a s e d . C o n s e q u e n t l y the c h a i n l e n g t h — t h a t i s , t h e average m o l e c u l a r w e i g h t of the p r o d u c t — c a n b e r e g u l a t e d b y the p r o p e r Table II. Telogen C6H5CH3

Influence of Pressure on Molecular Weight" Pressure, psig

η

Average molecular weight

100 300 500 800 100 300 500 800

1.4 2.0 2.7 4.0 1.6 2.6 3.9 5.5

131 148 168 204 123 151 187 232

4.0

ETHYLENE PRESSURE, psig Figure 2.

Influence of pressure on product distribution with three aromatic telogens at 100°C


192

POLYAMINE-CHELATED

Table III.

Telomer


Toluene Xylene Ethylbenzene Benzene Isobutylene

C H CH (CH CH )nH CH C H CH (CH CH )nH C H CH(CH ) (CH CH )nH C H (CH CH )nH CH C(CH )CH (CH CH )nH 6

5

2

3

6

6

2

4

2

2

5

6

2

3

5

2

2

Conditions: 100°C, OMM

s e l e c t i o n of

METAL

COMPOUNDS

Effect of Telogen on Telomer Structure"

Telogen

a

ALKALI

2

2

2

2

3

2

2

2

η

Average molecular weight

2.7 3.0 4.4 3.9 8.1

168 190 230 187 380

n-butyllithium, T M E D A .

operating conditions.

T h e r e l a t i o n s h i p of β

to

ethylene

pressure for three telogens is s h o w n i n F i g u r e 2. T h e influence of t h e t e l o g e n u p o n m o l e c u l a r w e i g h t of the t e l o m e r is s h o w n i n T a b l e I I I . S i n c e , u n d e r e q u i v a l e n t c o n d i t i o n s , t h e m o l e c u l a r weight

depends

only on

the

transmetalation rate, the

hydrocarbons

c a n b e r a n k e d i n o r d e r of t h e i r d e c r e a s i n g k i n e t i c a c i d i t y : t o l u e n e xylene >

benzene

>

ethylbenzene.

>

T h e h i g h r e a c t i v i t y of b e n z e n e is

s u r p r i s i n g b u t consistent w i t h the f a c i l e m e t a l a t i o n o f b e n z e n e w i t h the b u t y l l i t h i u m a m i n e c o m p l e x n o t e d elsewhere. Reaction

Rate

T h e r a t e of t e l o m e r i z a t i o n of e t h y l e n e i n t o l u e n e i s , as d i r e c t l y p r o p o r t i o n a l to the R L i - T M E D A

expected,

c o n c e n t r a t i o n at 0 . 0 4 M

to

0 . 1 0 M ( T a b l e I V ) . T h u s s o l u b i l i t y of the catalyst is n o t a l i m i t i n g f a c t o r at these c o n c e n t r a t i o n levels. W i t h other a m i n e s , the influence of s t r u c t u r e a n d c o n c e n t r a t i o n is analogous to t h a t discussed i n c o n n e c t i o n w i t h transmetalation. A

nearly

first-order

d e p e n d e n c e is o b s e r v e d

between

the

initial

r e a c t i o n r a t e a n d the e t h y l e n e pressure. A s m a l l d e v i a t i o n occurs w h i c h Table I V .

Effect of Amine Structure and Concentration Structural type

RLi molarity

Amine mole/mole RLi

Rate

N(CH CH ) N

Bridgehead

(Me N) CH (Me NCH )

C h e l a t e (4) C h e l a t e (5)

0.10 0.10 0.05 0.04 0.04 0.08 0.10 0.04

1 2 4 1 1 1 2 1

12 19 32 12 126 128 130 25

Amine

2

2

2

2

2

2

3

2 2

(Me NCH ) CH 2

2

a

2

2

C h e l a t e (6)

° Number in parentheses indicates ring size of chelate. Moles C = /mole R L i / h r over first hour at 105°C and 500 psig. 6

2


h

9.

BUTTE

AND

193


EBERHARDT

is e x p l i c a b l e i n terms of n o n i d e a l b e h a v i o r of ethylene.

The

observed

d e p e n d e n c e i n d i c a t e s that t h e i n i t i a l a d d i t i o n of e t h y l e n e to t h e c a r b a n i o n d e r i v e d f r o m the telogen is the r a t e - c o n t r o l l i n g step. T h e t e l o m e r i z a t i o n rates v a r y s i g n i f i c a n t l y w i t h t h e n a t u r e of telogen.

T h e o r d e r of i n c r e a s i n g r a t e — t o l u e n e
b e n z e n e > b u t e n e > ethylene i n o r d e r of d e c r e a s i n g a c i d i t y .

T h u s the t e l o m e r i z a t i o n r e a c t i o n p r o v i d e s a means

of c o m p a r i n g the a c i d i t y o f v e r y w e a k l y a c i d i c u n s a t u r a t e d h y d r o c a r b o n s . H o w e v e r , the m e a s u r e m e n t is k i n e t i c i n n a t u r e a n d does n o t n e c e s s a r i l y a c c u r a t e l y reflect the t h e r m o d y n a m i c a c i d i t y .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

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RECEIVED March 13, 1973.


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