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Syngas Homologation of Aliphatic Carboxylic Acids JOHN F. KNIFTON Texaco Chemical Company, P.O. Box 15730, Austin, TX 78761
In this paper we disclose the syngas homologation of carboxylic acids via ruthenium homogeneous catalysis. This novel homologation reaction involves treatment of lower MW carboxylic acids with synthesis gas (CO/H ) in the presence of soluble ruthenium species, e.g., RuO , Ru (CO) , H Ru (CO) , coupled with iodide-containing promoters such as HI or an alkyl iodide (1). 2
2
3
12
4
4
12
Where acetic is the starting acid (eq. 1), homologation selectively yields the corresponding C + aliphatic carboxylic acids. Since acetic acid is itself a "syngas" chemical derived from methanol via carbonylation (2,3), this means the higher MW carboxylic acids generated by this technique could also be built exclusively from CO/H and would thereby be indepent of any petroleum-derived coreactant. The scope and mechanism of carboxylic acid homologation is examined here in relation to the structure of the carboxylic acid substrate, the concentrations and composition of the ruthenium catalyst precursor and iodide promoter, synthesis gas ratios, as well as C labelling studies and the spectral identification of ruthenium iodocarbonyl intermediates. 3
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Results A summary of t y p i c a l p r e p a r a t i v e data for the a c i d homologation regime i s presented i n Tables I and I I . E f f e c t of C a t a l y s t Composition. Where a c e t i c i s the t y p i c a l a c i d s u b s t r a t e , e f f e c t i v e ruthenium c a t a l y s t precursors include ruthenium(IV) oxide, hydrate, ruthenium(III) a c e t y l acetonate, t r i r u t h e n i u m dodecacarbonyl, as w e l l as ruthenium hydrocarbonyls, i n combination with i o d i d e - c o n t a i n i n g p r o moters l i k e HI and a l k y l i o d i d e s . Highest y i e l d s of these higher MW acids are achieved with the Ru0 -Mel combination, 2
0097-6156/81 /0152-0225$05.00/0 © 1981 American Chemical Society Ford; Catalytic Activation of Carbon Monoxide ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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Table Acetic
Catalyst
composition Promoter structure R u t h e n ι urn source Ru0 Mel 4
Ru (CO) 3
1 2
Ru(acac) RuCI
1 2
3
3
RuCI (PPh ) 2
3
3
(mole % ) Butyric
convers ion Propionic
c
Va 1eri
c
Butyric n/iso
37
6. 9
t*2
3^
5. 5
Mel
70
25
7. 2
propionic ~ n-valeric > iso-butyric ~ trimethylacetic > iso-valeric acid
(6)
has b e e n o b s e r v e d a l s o i n r u t h e n i u m - c a t a l y z e d a c i d hydrogénation (13). The two o r d e r i n g s o f r e a c t i v i t y v e r s u s a c i d s t r u c t u r e a r e quite similar. Experimental Section R u t h e n i u m o x i d e s , s a l t s a n d c o m p l e x e s were p u r c h a s e d from o u t s i d e s u p p l i e r s o r , as w i t h H R u ( C 0 ) 1 2 ( 1 5 ) , p r e p a r e d according t o l i t e r a t u r e procedures. C a r b o x y l i c a c i d s and i o d i d e p r o m o t e r s were a l s o p u r c h a s e d a n d s y n t h e s i s g a s m i x t u r e s were s u p p l i e d b y B i g T h r e e I n d u s t r i e s . R e a c t i o n s o l u t i o n s were prepared d i r e c t l y i n the glass l i n e r s o f the pressure reactors u n d e r a n i t r o g e n p u r g e , h o m o l o g a t i o n r e a c t i o n s were c o n d u c t e d as o u t l i n e d b e l o w . The e x t e n t o f r e a c t i o n a n d d i s t r i b u t i o n o f t h e p r o d u c t s were d e t e r m i n e d b y g a s - l i q u i d c h r o m a t o g r a p h y ( g l c ) u s i n g , f o r t h e most p a r t , 6 f t χ 1/8 i n columns o f Porapak-QS w i t h 2 % l o a d i n g o f i s o - p h t h a l i c a c i d , programmed f r o m 120 t o 240°C ( 2 0 c m / m i n H e ) . W a t e r was e s t i m a t e d b y K a r l F i s c h e r titration. P r o d u c t a c i d s were i s o l a t e d b y d i s t i l l a t i o n i n v a c u o o r b y g l c t r a p p i n g a n d i d e n t i f i e d b y one o r more o f t h e f o l l o w i n g t e c h n i q u e s , g l c , F T I R , NMR a n d e l e m e n t a l analyses. H i g h e r MW a c i d s were a n a l y z e d u s i n g a 6 f t χ 1/8 i n column o f P o r a p a k - P S w i t h 8% l o a d i n g o f SP-1000 p l u s 2 % i s o - p h t h a l i c a c i d . 4
4
3
Syngas H o m o l o g a t i o n o f A c e t i c A c i d . To a N - f l u s h e d liquid mix o f a c e t i c a c i d ( 5 0 . 0 gm) a n d m e t h y l i o d i d e (5.67 gm, 40 mmole), s e t i n a g l a s s l i n e r i s added 0.763 gm o f r u t h e n i u m ( I V ) o x i d e , h y d r a t e ( 4 . 0 mmole). The m i x t u r e i s s t i r r e d t o p a r t i a l l y d i s s o l v e t h e ruthenium and t h e g l a s s l i n e r p l u s c o n t e n t s charged t o a 450 m l r o c k i n g a u t o c l a v e . The r e a c t o r i s s e a l e d , f l u s h e d 2
Ford; Catalytic Activation of Carbon Monoxide ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
15.
KNIFTON
Syngas Homologation of Carboxylic Acids
239
w i t h CO/H , p r e s s u r e d t o 272 atm w i t h C0/H ( 1 : 1 ) and h e a t e d , w i t h r o c k i n g , t o 220°C. A f t e r 18 h r , t h e gas u p t a k e i s 163 atm. Upon c o o l i n g , d e p r e s s u r i n g and s a m p l i n g t h e o f f - g a s , t h e c l e a r deep-red l i q u i d p r o d u c t i s r e c o v e r e d from t h e g l a s s - l i n e d reactor. A n a l y s i s o f t h e l i q u i d f r a c t i o n b y g l c shows t h e p r e s ence o f : 26.9 wt % p r o p i o n i c a c i d 2.3 wt % i s o - b u t y r i c a c i d 3.6 wt % η-butyric a c i d 0.4 wt % i s o - v a l e r i c a c i d 0.6 wt % η-valeric a c i d 1.5 wt % e t h y l a c e t a t e 7.7 wt % w a t e r 54.1 wt % u n r e a c t e d a c e t i c a c i d T y p i c a l o f f - g a s s a m p l e s show t h e p r e s e n c e o f : 37% c a r b o n monoxide 4.2% e t h a n e 40% hydrogen 1.3% p r o p a n e 15% carbon dioxide 1.0% methane The p r o p i o n i c and b u t y r i c a c i d p r o d u c t f r a c t i o n s , as w e l l as u n r e a c t e d a c e t i c a c i d , may be i s o l a t e d b y f r a c t i o n a l d i s t i l l a t i o n i n vacuo. 2
2
Syngas H o m o l o g a t i o n o f P r o p i o n i c A c i d . To a N - f l u s h e d l i q u i d m i x o f p r o p i o n i c a c i d (18.15 gm, 245 mmole) and m e t h y l i o d i d e (2.84 gm, 20.0 mmole) s e t i n a g l a s s l i n e r i s added 0.382 gm o f r u t h e n i u m ( I V ) o x i d e , h y d r a t e (2.0 mmole). The m i x t u r e i s s t i r r e d t o p a r t i a l l y d i s s o l v e t h e r u t h e n i u m and t h e g l a s s l i n e r p l u s c o n t e n t s c h a r g e d t o a 450 m l r o c k i n g a u t o c l a v e . The r e a c t o r i s s e a l e d , f l u s h e d w i t h C 0 / H , p r e s s u r e d t o 272 atm w i t h C0/H ( 1 : 1 ) and h e a t e d w i t h r o c k i n g t o 220°C. A f t e r 18 h r , t h e gas u p t a k e i s 59 atm. Upon c o o l i n g , d e p r e s s u r i n g and sam p l i n g t h e o f f - g a s , t h e c l e a r amber l i q u i d p r o d u c t (19.4 gm) i s r e c o v e r e d from t h e g l a s s - l i n e d r e a c t o r . T h e r e i s no s o l i d residue. A n a l y s i s o f t h e crude l i q u i d p r o d u c t f r a c t i o n by g l c shows t h e p r e s e n c e o f : 10.4 wt % η-butyric a c i d 3.3 wt % i s o - b u t y r i c a c i d 1.9 wt % η-valeric a c i d 0.3 wt % i s o - v a l e r i c a c i d / 2 - m e t h y l b u t y r i c a c i d 1.7 wt % a c e t i c a c i d 33.3 wt % w a t e r 25.6 wt % u n r e a c t e d p r o p i o n i c a c i d T y p i c a l o f f - g a s s a m p l e s show t h e p r e s e n c e o f : 29% c a r b o n monoxide 6.6% p r o p a n e 58% hydrogen 1.6% n - b u t a n e 2.6% c a r b o n d i o x i d e 0.6% methane The b u t y r i c a c i d p r o d u c t f r a c t i o n s , a s w e l l a s u n r e a c t e d p r o p i o n i c a c i d , may be i s o l a t e d f r o m t h e c r u d e l i q u i d product by f r a c t i o n a l d i s t i l l a t i o n i n vacuo. 2
2
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Ford; Catalytic Activation of Carbon Monoxide ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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OF CARBON
MONOXIDE
Syngas H o m o l o g a t i o n o f i s o - B u t y r i c A c i d . To a N - f l u s h e d l i q u i d mix o f i s o - b u t y r i c a c i d (21.6 gm, 245 mmole) and m e t h y l i o d i d e (2.84 gm, 20.0 mmole) s e t o n a g l a s s l i n e r i s added 0.382 gm o f r u t h e n i u m ( I V ) o x i d e h y d r a t e (2.0 mmole). The m i x t u r e i s s t i r r e d t o p a r t i a l l y d i s s o l v e the ruthenium and the g l a s s l i n e r p l u s c o n t e n t s c h a r g e d t o a 450 m l r o c k i n g a u t o c l a v e . The r e a c t o r i s s e a l e d , f l u s h e d w i t h C 0 / H , p r e s s u r e d t o 272 atm w i t h C 0 / H ( 1 : 1 ) and h e a t e d w i t h r o c k i n g t o 220°C. A f t e r 18 h r , t h e gas u p t a k e i s 48 atm. Upon c o o l i n g , d e p r e s s u r i n g a n d s a m p l i n g t h e o f f - g a s , t h e c l e a r - y e l l o w , two-phase l i q u i d p r o d u c t (19.8 gm, 18 m l ) i s r e c o v e r e d f r o m t h e g l a s s - l i n e d r e a c t o r . There i s no s o l i d r e s i d u e . A n a l y s i s o f t h e l i g h t e r l i q u i d f r a c t i o n (15 m l ) b y g l c shows t h e p r e s e n c e o f : 14.1% t r i m e t h y l a c e t i c a c i d 0.8% i s o - v a l e r i c a c i d / 2 - m e t h y l b u t y r i c a c i d 0.8% a c e t i c a c i d 2.2% m e t h y l i o d i d e 3.1% w a t e r 62.3% unreacted i s o b u t y r i c a c i d T y p i c a l o f f - g a s samples show t h e p r e s e n c e o f : 49% c a r b o n monoxide 5.3% i s o - b u t a n e 41% hydrogen 0.2% e t h a n e 1.7% c a r b o n d i o x i d e 0.6% methane The t r i m e t h y l a c e t i c a c i d i s i s o l a t e d f r o m t h e u s e d r u t h e n i u m c a t a l y s t and u n r e a c t e d i s o - b u t y r i c a c i d b y f r a c t i o n a l d i s t i l l a t i o n i n v a c u o , a n d i d e n t i f i e d b y NMR and FTIR a n a l y s e s . 2
2
2
Acknowledgements The a u t h o r w i s h e s t o t h a n k Texaco I n c . f o r p e r m i s s i o n t o p u b l i s h t h i s p a p e r , M e s s r s M. Swenson, T. D. E l l i s o n , R. G o n z a l e s and D. W. W h i t e f o r e x p e r i m e n t a l a s s i s t a n c e , and M e s s r s C. L. L e B a s , R. L. B u r k e and J . M. S c h u s t e r f o r C NMR and FTIR d a t a . 1 3
Ford; Catalytic Activation of Carbon Monoxide ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
15. KNIFTON
Syngas Homologation of Carboxylic Acids
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