A New Approach to the Synthesis of Alkyl Silicates and

Chapter 18

A New Approach to the Synthesis of Alkyl Silicates and Organosiloxanes 1

Downloaded by PRINCETON UNIV on July 23, 2013 | http://pubs.acs.org Publication Date: January 7, 1988 | doi: 10.1021/bk-1988-0360.ch018

George B. Goodwin and Malcolm E. Kenney Department of Chemistry, Case Western Reserve University, Cleveland, OH 44106 A new route to alkyl silicates and organosiloxanes is described. This route has three steps. These are (1) the protonation of a silicate (obtained by collection, mining, or laboratory or commercial synthesis), (2) the esterification of the silicic acid formed by the protonation, and (3) the organodealkoxylation of the alkyl silicate resulting from the esterification. An important feature of this route is that it does not depend on elemental silicon. The route is illustrated with the synthesis of (EtO) Si from γ-Ca SiO , Ca SiO O, and portland cement, (EtO) SiOSi(OEt) from Ca ZnSi O , (n-PrO) SiO(n-PrO) SiOSi(On-Pr) from 4

3

2

2

3

7

3

the

9

(EtO) Si O 10

4

3

Ca Si O , 3

2

4

6

7

[5.5.1]

from

2

and [5.3.3]

Cu Si O .6H O 6

6

18

2

3

3

isomers of

and from

Na Ca Si O , 4

4

6

18

and the [5.5.1] and [5.3.3] isomers of Me Si O from the [5.5.1] and [5.3.3] isomers of (EtO) Si O . 10

6

10

6

7

7

As is w e l l known, a number o f d i f f e r e n t k i n d s o f s i l i c a t e i o n s a r e f o u n d in s i l i c a t e s . Thus, among gem s i l i c a t e s b e n i t o i t e , BaTiSi3C>9, c o n t a i n s t h e c y c l o t r i s i l i c a t e i o n and aquamarine ( b e r y l ) , Be3Al2SigOi8» c o n t a i n s t h e c y c l o h e x a s i l i c a t e i o n ( 1 , 2 ) . S i m i l a r l y , among common s i l i c a t e m i n e r a l s hemimorphite, Zn4Si207(OH)2.Η2θ, c o n t a i n s t h e d i s i l i c a t e i o n and e n s t a t i t e , MgSi03, c o n t a i n s t h e i n f i n i t e c h a i n s i l i c a t e i o n ( 1 ) . I n t h e c a s e o f t h e common s y n t h e t i c s i l i c a t e s , p o r t l a n d cement c o n t a i n s phases w h i c h c a n be a p p r o x i m a t e d as Ca2Si04 and Ca3SiC>40 and which c o n t a i n t h e o r t h o s i l i c a t e i o n ( 3 , 4 ) , F i g u r e 1. Some o f t h e many s i l i c a t e s t h a t a r e r e a d i l y a v a i l a b l e have s i l i c a t e i o n s w i t h frameworks t h a t a r e s i m i l a r t o o r t h e same as t h o s e p r e s e n t in common a l k y l s i l i c a t e s and common o r g a n o s i l o x a n e s (5,7). I n l i g h t o f t h i s , a s y n t h e t i c approach t o a l k y l s i l i c a t e s and o r g a n o s i l o x a n e s b a s e d on s u b s t i t u t i o n r e a c t i o n s becomes conceivable. 1

Current address: Glass R&D Center, PPG Industries, Inc., Pittsburgh, PA 15238 0097-6156/88/0360-0238$06.00/0 © 1988 American Chemical Society

In Inorganic and Organometallic Polymers; Zeldin, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.


18.

GOODWIN AND

KENNEY

F i g u r e 1. S t r u c t u r e s (c) c y c l o t r i s i l i c a t e ,

Alkyl Silicates and Organosiloxanes

o f (a) o r t h o s i l i c a t e , (b) and (d) c y c l o h e x a s i l i c a t e

disilicate, ions.


239


240

INORGANIC AND ORGANOMETALLIC POLYMERS

The complete p r o c e s s f o r s y n t h e s i z i n g such s p e c i e s u s i n g t h i s a p p r o a c h would e n t a i l the a c q u i s i t i o n o f an a p p r o p r i a t e n a t u r a l s i l i c a t e o r the p r e p a r a t i o n o f an a p p r o p r i a t e s y n t h e t i c s i l i c a t e and t h e n the c o n v e r s i o n o f t h i s s i l i c a t e i n t o the a l k y l s i l i c a t e or o r g a n o s i l o x a n e by s u i t a b l e s u b s t i t u t i o n r e a c t i o n s . I n terms o f bond c l e a v a g e , t h i s p r o c e s s c o u l d e n t a i l no d e s t r u c t i o n and r e f o r m a t i o n o f framework s i l i c o n - o x y g e n bonds, and, in terms o f o x i d a t i o n number, i t would e n t a i l no r e d u c t i o n and r e o x i d a t i o n o f the s i l i c o n . T h i s p r o c e s s c o n t r a s t s w i t h the e l e m e n t a l - s i l i c o n p r o c e s s e s sometimes u s e d f o r a l k y l s i l i c a t e s (8) and the e l e m e n t a l - s i l i c o n p r o c e s s e s g e n e r a l l y u s e d f o r o l i g o m e r i c and p o l y m e r i c o r g a n o s i l o x a n e s (6 ,7) . S i n c e the s i l i c o n in t h e s e p r o c e s s e s is o b t a i n e d from q u a r t z , t h e s e p r o c e s s e s e n t a i l , in terms o f bond c l e a v a g e , the d e s t r u c t i o n o f f o u r s i l i c o n - o x y g e n bonds p e r s i l i c o n and the subsequent r e f o r m a t i o n o f the r e q u i r e d number o f such bonds. In terms o f o x i d a t i o n number, t h e y e n t a i l the r e d u c t i o n o f the s i l i c o n from f o u r t o z e r o and t h e n i t s r e o x i d a t i o n b a c k t o f o u r , F i g u r e s 2 and 3. Because t h e s e p r o c e s s e s r e q u i r e r e d u c t i o n and r e o x i d a t i o n o f the s i l i c o n , t h e y r e q u i r e l a r g e amounts o f energy p e r u n i t o f product. T h i s makes them i n h e r e n t l y u n a t t r a c t i v e and makes a s e a r c h f o r r e p l a c e m e n t s f o r them w o r t h w h i l e . This n a t u r a l l y leads to a c o n s i d e r a t i o n o f the s i l i c a t e - b a s e d s u b s t i t u t i o n a p p r o a c h t o t h e s e compounds. A number o f p i e c e s o f work i n d i c a t i n g t h a t t h i s a p p r o a c h c a n be d e v e l o p e d have been r e p o r t e d . I n one, a commercial 3.25:1 Si02:Na20 sodium s i l i c a t e was s u c c e s s i v e l y p r o t o n a t e d and b u t o x y l a t e d to a mixture of polymeric b u t y l s i l i c a t e s (9). In a second, c h r y s o t i l e a s b e s t o s , Mg3Si205(0H)4, was s u c c e s s i v e l y p r o t o n a t e d and a l l y l o x y l a t e d t o a p o l y m e r i c a l l y l s i l i c a t e , a p p a r e n t l y w i t h s i l o x a n e framework p r e s e r v a t i o n ( 1 0 ) . A l s o , in a v e r y minor b y p r o d u c t r e a c t i o n p s e u d o w o l l a s t o n i t e , Ca3Si309, was p r o t o n a t e d and p r o p o x y l a t e d t o a p r o p y l s i l i c a t e w i t h framework p r e s e r v a t i o n (11). I n o t h e r e f f o r t s , ( E t 0 ) 3 S i 0 S i ( 0 E t ) 3 was a l k y l d e a l k o x y l a t e d t o o r g a n o d i s i l o x a n e s ( 1 2 ) , and o l i g o m e r i c and p o l y m e r i c o r g a n o a l k o x y s i l o x a n e s were a l k y l d e a l k o x y l a t e d t o o r g a n o s i l o x a n e s w i t h o r a p p a r e n t l y w i t h framework p r e s e r v a t i o n (13,14). A l s o , monomeric and o l i g o m e r i c m e t a l s i l i c a t e s were p r o t o n a t e d and s i l y l a t e d t o o r g a n o s i l y l s i l o x a n e s w i t h f u l l o r s u b s t a n t i a l framework p r e s e r v a t i o n ( 1 5 ) . In the p r e s e n t paper, a r o u t e t o a l k y l s i l i c a t e s and o r g a n o s i l o x a n e s w h i c h has elements in common w i t h t h e s e p i e c e s o f work and w h i c h is b a s e d on the s u b s t i t u t i o n a p p r o a c h is i l l u s t r a t e d and d i s c u s s e d . THE

ROUTE

In the r o u t e u s e d in t h i s work, a monomeric o r o l i g o m e r i c s i l i c a t e is p r o t o n a t e d , the r e s u l t i n g s i l i c i c a c i d is e s t e r i f i e d , and the a l k y l s i l i c a t e is o r g a n o d e a l k o x y l a t e d . I n e a c h s t e p , the s i l o x a n e framework is f u l l y o r s u b s t a n t i a l l y p r e s e r v e d . F o r the case s t a r t i n g w i t h a m e t a l d i s i l i c a t e the r e a c t i o n s c a n be r e p r e s e n t e d as :



18.

GOODWIN AND KENNEY


241

F i g u r e 2. V a r i a t i o n o f o x i d a t i o n number o f s i l i c o n w i t h s t e p and v a r i a t i o n o f number o f oxygens bonded t o s i l i c o n w i t h s t e p in d i r e c t or e l e m e n t a l - s i l i c o n process f o r (EtO)4Si.

F i g u r e 3. V a r i a t i o n o f o x i d a t i o n number o f s i l i c o n w i t h s t e p and v a r i a t i o n o f number o f oxygens bonded t o s i l i c o n w i t h s t e p in u s u a l p r o c e s s f o r (Me2SiO)4.



242 0 SiOSi0 3

6 3

-

+ H

+

+ ROH

>

( H O ) S i O S i ( O H ) - x R O H + ROH 3

3

3

3

> (R0) Si0Si(0R)

3

(R0) Si0Si(0R)

(HO) SiOSi(OH) -xROH 3

+ R'MgX

> R Si0SiR 3

3

(1)

3

(2) (3)

3


I t is p o s s i b l e t h a t some e s t e r i f i c a t i o n o f the s i l i c a t e i o n o c c u r s in t h i s r o u t e b e f o r e the i o n is f u l l y p r o t o n a t e d and thus t h a t the f i r s t two s t e p s o f the r o u t e o v e r l a p . A n o v e l f e a t u r e o f the r o u t e is t h a t i t l e a d s t o monomeric and o l i g o m e r i c a l k y l s i l i c a t e s from m e t a l s i l i c a t e s in good y i e l d and w i t h f u l l o r s u b s t a n t i a l s i l o x a n e framework p r e s e r v a t i o n . Further, i t leads to oligomeric organosiloxanes of intermediate m o l e c u l a r w e i g h t from a l k y l s i l i c a t e s in good y i e l d and w i t h s i l o x a n e framework p r e s e r v a t i o n . EXAMPLES ( E t Q ) & S i from 7-Ca?Si04. A d i l u t e H C l - e t h a n o l s o l u t i o n was added s l o w l y t o a a c o o l e d s u s p e n s i o n o f 7-Ca2Si04 (Cerac I n c . , Milwaukee, WI) in e t h a n o l . The r e s u l t i n g s u s p e n s i o n was f i l t e r e d and t h e s o l i d was washed. The f i l t r a t e and the washings were combined and s l o w l y added t o an e t h a n o l - t o l u e n e s o l u t i o n t h a t was b e i n g d i s t i l l e d a t a moderate r a t e . A f t e r the r e s u l t a n t had been d i s t i l l e d u n t i l a s u b s t a n t i a l amount o f d i s t i l l a t e had been c o l l e c t e d , the s u s p e n s i o n o b t a i n e d was f i l t e r e d and the s o l i d was washed. The f i l t r a t e and washings were combined, c o n c e n t r a t e d , b u l b - t o - b u l b d i s t i l l e d , and f r a c t i o n a l l y d i s t i l l e d . W i t h the a i d o f gas chromatography, gas chromatography-mass s p e c t r o m e t r y , and i n f r a r e d s p e c t r o s c o p y , the p r o d u c t was compared t o a u t h e n t i c (Et0)4Si. The r e s u l t s showed t h a t i t was q u i t e p u r e (99.8%) ( E t 0 ) 4 S i ( c o n t a i n e d y i e l d 33%). The ( E t 0 ) 4 S i c o u l d have been c o n v e r t e d t o Me4Si w i t h a m e t h y l G r i g n a r d reagent i f d e s i r e d (16). ( E t O U S i from MONOCLINIC Ca^SiO^O. M o n o c l i n i c C a S i 0 4 0 ( C o n s t r u c t i o n T e c h n o l o g y L a b o r a t o r i e s , I n c . , S k o k i e , I L ) was t r e a t e d in a manner s i m i l a r t o t h a t u s e d w i t h 7-Ca2Si04. The p r o d u c t was r e l a t i v e l y pure (95%) ( E t 0 ) 4 S i ( c o n t a i n e d y i e l d 4 2 % ) . 3

( E t 0 ) 4 S i from PORTLAND CEMENT. P o r t l a n d cement (Maryneal z e r o C A Type I I I , Lone S t a r I n d u s t r i e s , I n c . , Houston, TX) was a l s o t r e a t e d in a s i m i l a r f a s h i o n . The p r o d u c t a g a i n was r e l a t i v e l y p u r e (94%) ( E t 0 ) 4 S i ( c o n t a i n e d y i e l d 4 1 % ) . 3

( E t O ) ^ S i O S i ( O E t ) ^ from C a 9 Z n S i 9 0 (HARDYSTONITE). An H C l - e t h a n o l s o l u t i o n was added s l o w l y t o a s u s p e n s i o n o f Ca2ZnSi207 ( p r e p a r e d by s i n t e r i n g ZnO and C a S i 0 ( w o l l a s t o n i t e ) ) in e t h a n o l . The s u s p e n s i o n formed was s t i r r e d a t ambient temperature and f i l t e r e d . The f i l t r a t e was c o o l e d and added s l o w l y t o an e t h a n o l - t o l u e n e s o l u t i o n t h a t was b e i n g d i s t i l l e d a t a moderate r a t e . A f t e r the r e s u l t a n t had been d i s t i l l e d u n t i l a s u b s t a n t i a l amount o f d i s t i l l a t e had been c o l l e c t e d , the m i x t u r e p r o d u c e d was decanted. The d e c a n t a t e was c o n c e n t r a t e d and f r a c t i o n a l l y d i s t i l l e d . The p r o d u c t was compared t o a u t h e n t i c ( E t O ) S i O S i ( O E t ) w i t h the a i d 7

3

3

3


18. GOODWIN AND KENNEY


243

o f gas chromatography, gas chromatography-mass s p e c t r o m e t r y , and i n f r a r e d spectroscopy. The r e s u l t s showed t h a t i t was r e l a t i v e l y p u r e (97%) ( E t O ) S i O S i ( O E t ) ( c o n t a i n e d y i e l d 2 9 % ) . The ( E t O ) S i O S i ( O E t ) c o u l d have been c o n v e r t e d t o E t S i O S i E t w i t h an e t h y l G r i g n a r d reagent i f d e s i r e d (12). 3

3

3

3

3

3

( n - P r 0 ) ^ S i 0 ( n - P r 0 ) 9 S i 0 S i ( 0 n - P r H from C a S i 0 9 (PSEUDOWOLLASTONITE) . To a s u s p e n s i o n o f Ca Si C>9 ( p r e p a r e d b y h e a t i n g C a S i 0 ( w o l l a s t o n i t e ) ) in n - p r o p a n o l was added an HCl-np r o p a n o l s o l u t i o n (and t h e a d d i t i o n f u n n e l w a s h i n g s ) . The r e s u l t i n g m i x t u r e was d i s t i l l e d u n t i l a s u b s t a n t i a l amount o f d i s t i l l a t e h a d been c o l l e c t e d and t h e s u s p e n s i o n p r o d u c e d was filtered. The s o l i d was washed, t h e f i l t r a t e and washings were combined, and t h e r e s u l t a n t was c o n c e n t r a t e d and mixed w i t h an HC1-n-propanol s o l u t i o n . A f t e r t h e s o l u t i o n formed h a d been d i s t i l l e d u n t i l a s u b s t a n t i a l amount o f d i s t i l l a t e h a d been c o l l e c t e d , t h e remainder was t w i c e d i l u t e d w i t h pentane, f i l t e r e d , and c o n c e n t r a t e d . The f i n a l c o n c e n t r a t e was b u l b - t o - b u l b d i s t i l l e d and f r a c t i o n a l l y d i s t i l l e d . W i t h t h e a i d o f gas chroma t o g r a p h y , gas chromatography-mass s p e c t r o m e t r y , and i n f r a r e d s p e c t r o s c o p y , t h e p r o d u c t was shown t o be r e l a t i v e l y pure (94%) (n-PrO) SiO(n-PrO)2SiOSi(On-Pr) (contained y i e l d 18%): IR ( n e a t ) 2964 ( s ) , 2938 ( s ) , 2880 ( s ) , 1465 (m) 1088 ( v s ) cm' ; GCMS m/z [ r e l i n t e n s i t y ] 529 [ ( M - 0 P r ) , 7 ] , 235 [ ( ( H 0 ) S i 0 ) + , 1 0 0 ] . 3

3

3

3


3

3

3

1

+

7

3

2

THE [ 5 . 5 . Π and [5.3.3] ISOMERS o f ( E t 0 ) m S i ^ 0 7 from CufiSifi0ia-6H90 (DIOPTASE). An H C l - e t h a n o l s o l u t i o n was added s l o w l y t o a s u s p e n s i o n o f C u g S i g O i g * 6 H 0 (Ward's N a t u r a l S c i e n c e E s t a b l i s h m e n t , I n c . , R o c h e s t e r , NY) in an e t h a n o l - t o l u e n e solution. The r e s u l t i n g m i x t u r e was d i s t i l l e d u n t i l a s u b s t a n t i a l amount o f d i s t i l l a t e h a d been c o l l e c t e d a n d the s u s p e n s i o n formed was c o o l e d and f i l t e r e d . The s o l i d was washed and t h e f i l t r a t e and washings were combined. A f t e r t h e s o l u t i o n p r o d u c e d h a d been c o n c e n t r a t e d , i t was mixed w i t h an H C l - e t h a n o l s o l u t i o n , e t h a n o l , and t o l u e n e . The m i x t u r e formed was d i s t i l l e d u n t i l a s u b s t a n t i a l amount o f d i s t i l l a t e h a d been c o l l e c t e d , and t h e r e m a i n d e r was d i s t i l l e d t w i c e . By gas chromatography, gas chromatography-mass s p e c t r o m e t r y , i n f r a r e d s p e c t r o s c o p y , and ^Si n u c l e a r magnetic r e s o n a n c e s p e c t r o s c o p y , t h e p r o d u c t was shown t o c o n t a i n a s u b s t a n t i a l amount (43%) o f t h e [5.5.1] isomer o f ( E t O ) i o S i 6 0 ( c o n t a i n e d y i e l d 20%): GCMS [ r e l i n t e n s i t y ] 685 [ ( M - 0 E t ) , 6 ] , 415 [ ( ( H 0 ) S i 0 ) , 100]; S i NMR (39.7 MHz, CDC1 ) δ -95.56 (middle type S i ) , -101.55 ( b r a n c h type S i ) . I t was a l s o shown t o c o n t a i n a s i g n i f i c a n t amount (29%) o f t h e [5.3.3] isomer o f ( E t O ) i o i 6 ° 7 ( c o n t a i n e d y i e l d 14%): GCMS m/z [ r e l i n t e n s i t y ] 685 [(M-0Et)+, 1 2 ] , 415 [ ( ( H O ) S i 0 ) , 100]; S i NMR (39.7 MHz, CDC1 ) δ -94.69 ( m i d d l e type S i ) , -96.65 ( m i d d l e type S i ) , -101.27 ( b r a n c h type Si). 2

7

+

+

7

6

2 9

8

3

s

+

7

6

2 9

8

3

THE [5.5.1] and [5.3.3] ISOMERS o f (EtO)ιnSifiOy from N a 4 Ç a 4 S i 6 0 i . Na4Ca4SigOi8 ( p r e p a r e d b y s i n t e r i n g Na2C0 , C a C 0 , a n d S i 0 ) was t r e a t e d in a manner s i m i l a r t o t h a t u s e d w i t h C u g S i g O i g * 6 H 0 . A s u b s t a n t i a l p a r t (46%) o f t h e p r o d u c t was t h e [5.5.1] isomer o f ( E t O ) i o S i 6 0 ( c o n t a i n e d y i e l d 31%): GCIR (Ar m a t r i x ) 2984 (m), 2936 (m), 2905 (m), 1161 ( s ) , 1105 ( v s ) cm" . A s i g n i f i c a n t p a r t 8

3

3

2

2

7

1



244

(28%) o f t h e p r o d u c t was t h e [5.3.3] isomer o f (EtO^QSifcOy ( c o n t a i n e d y i e l d 20%): GCIR (Ar m a t r i x ) 2983 (m), 2935 (m), 2904 (m), 1162 ( s ) , 1106 ( v s ) cm" . 1

THE [5.5.1] and [5.3.3] ISOMERS o f MeioaioOy from t h e [5.5.1] and [5.3.3] ISOMERS o f ( E t O ) m S J 6 0 7 . A s o l u t i o n o f CH MgCl in t e t r a h y d r o f u r a n was s l o w l y added t o a c o o l e d s o l u t i o n o f t h e [5.5.1] and [5.3.3] isomers o f ( E t O ) i o i 6 ° 7 ( p r e p a r e d as above) in tetrahydrofuran. The r e s u l t i n g m i x t u r e was s t i r r e d f o r a c o n s i d e r a b l e p e r i o d o f time w h i l e b e i n g k e p t c o o l and t h e n was concentrated. The c o n c e n t r a t e was s t i r r e d w i t h a m i x t u r e o f d i l u t e HC1 and pentane, and t h e r e s u l t i n g o r g a n i c phase was s e p a r a t e d and washed w i t h an aqueous N a C l s o l u t i o n . I t was t h e n d i s t i l l e d u n t i l a s u b s t a n t i a l amount o f d i s t i l l a t e h a d been collected. The o i l formed was f l a s h chromatographed and t h e e l u a t e was t w i c e f r a c t i o n a l l y d i s t i l l e d . The p r o d u c t was shown b y gas chromatography, gas chromatography-mass s p e c t r o m e t r y , gas chromatography-infrared spectroscopy, high pressure l i q u i d chromatography, and S i n u c l e a r magnetic r e s o n a n c e s p e c t r o s c o p y to c o n t a i n a s u b s t a n t i a l amount (60%) o f t h e [5.5.1] isomer o f M e i o l 6 ° 7 ( c o n t a i n e d y i e l d on the b a s i s o f c o n t a i n e d [5.5.1] isomer o f ( E t O ) i o S i 0 38%): IR (neat) 2966 (m), 1260 ( s ) , 1079 ( v s ) cm" ; GCMS m/z [ r e l i n t e n s i t y ] 415 [(M-Me)+, 68]; S i NMR (39.7 MHz, CDC1 ) δ -19.07 (D type S i ) ; -63.55 (T t y p e S i ) . I n a d d i t i o n , i t was shown t o c o n t a i n a s i g n i f i c a n t amount (29%) o f t h e [5.3.3] isomer o f Μ β χ ο ΐ 6 ° 7 ( c o n t a i n e d y i e l d on t h e b a s i s o f c o n t a i n e d [5.3.3] isomer o f ( E t O ) i o S i 6 0 7 2 9 % ) : IR ( n e a t ) 2966 (m), 1263 ( s ) , 1083 (vs) cm" ; GCMS m/z [ r e l i n t e n s i t y ] 415 [(MMe) , 83]; S i NMR (39.7 MHz, C D C I 3 ) δ -17.98 (D t y p e S i ) , -20.93 (D t y p e S i ) , -62.73 (T type S i ) . The [5.5.1] and [5.3.3] isomers of MeioSi607 known compounds (17,18). 3


s

2 9

s

6

7

1

2 9

3

δ

1

+

2 9

a

r

e

DISCUSSION REACTANTS and CHEMISTRY, STEP 1. The s i l i c a t e s u s e d in t h e examples g i v e n in t h e f i r s t o r p r o t o n a t i o n s t e p o f t h e r o u t e have s i l i c a t e i o n s w i t h v a r i o u s s t r u c t u r e s . Thus, 7-Ca2Si04, mono c l i n i c Ca3Si040, and t h e p r i n c i p a l s i l i c a t e phases in p o r t l a n d cement, a p p r o x i m a t e l y Ca3SiÛ40 and Ca2Si04 c o n t a i n t h e o r t h o s i l i c a t e i o n ( 3 , 4 ) , Ca2ZnSi20y c o n t a i n s t h e d i s i l i c a t e i o n (19), Ca3Si3U9 c o n t a i n s t h e c y c l o t r i s i l i c a t e i o n ( 1 ) , and CugSigO^g.6H2O and Na4Ca4SigO;Lg c o n t a i n t h e c y c l o h e x a s i l i c a t e i o n ( 1 , 2 0 ) . The s t r u c t u r a l and c h e m i c a l d i v e r s i t y o f t h e s e s i l i c a t e s show t h a t a wide v a r i e t y o f s i l i c a t e s c a n be employed in t h i s s t e p . V a r i o u s methods c a n be u s e d t o o b t a i n t h e s i l i c a t e s n e c e s s a r y f o r the step i n c l u d i n g small s c a l e c o l l e c t i o n (e.g., d i o p t a s e ) , m i n i n g , s y n t h e s i s from s i l i c a ( e . g . , N a 4 C a 4 S i g 0 i g ) , and s y n t h e s i s from o t h e r s i l i c a t e s ( e . g . , Ca3Si3U9 and C a 2 Z n S i 2 0 y ) . The r e s u l t s o b t a i n e d so f a r i n d i c a t e t h a t t h e s i l i c a t e s b e s t s u i t e d f o r u s e are o f t e n calcium s i l i c a t e s . No a c i d s o t h e r t h a n HC1 have been t r i e d in t h e s t e p . However, i t is l i k e l y t h a t i t c a n be c a r r i e d o u t w i t h o t h e r s t r o n g acids. From t h e r e s u l t s o f s e v e r a l e x p e r i m e n t s i t h a s b e e n l e a r n e d t h a t i s o p r o p a n o l and n - b u t a n o l can be u s e d t o make a l k y l s i l i c a t e s



18.

GOODWIN AND KENNEY


245

by t h e r o u t e and thus t h a t t h e y c a n be u s e d in t h e f i r s t s t e p . T h i s s u g g e s t s t h a t a v a r i e t y o f a l c o h o l s c a n be u s e d in i t (however, as is o b v i o u s , t h e c h o i c e o f t h e a l c o h o l is governed b y the n a t u r e o f t h e a l k o x y groups needed in t h e second s t e p ). The f a c t t h a t t h e a l k y l s i l i c a t e s p r o d u c e d b y t h e r o u t e r e t a i n t h e s i l o x a n e framework o f t h e p a r e n t s i l i c a t e s f u l l y o r s u b s t a n t i a l l y , F i g u r e 4, shows t h a t t h e framework is a t l e a s t l a r g e l y r e t a i n e d in t h e f i r s t s t e p . A number o f e x p e r i m e n t s i n d i c a t e one f a c t o r a i d i n g s t r u c t u r e r e t e n t i o n in t h i s s t e p is t h e use o f an amount o f HC1 t h a t is j u s t s l i g h t l y above t h a t w h i c h is s t o i c h i o m e t r i c a l l y r e q u i r e d (105-110%). Other experiments i n d i c a t e t h a t in some i n s t a n c e s t h e u s e o f a low t e m p e r a t u r e (~-10 ° C ) l i k e w i s e h e l p s w i t h s t r u c t u r e r e t e n t i o n . A l s o p e r t i n e n t t o s t r u c t u r e r e t e n t i o n in t h i s s t e p a r e r e s u l t s from e x p e r i m e n t s showing t h a t t h e r o u t e y i e l d s a l k y l s i l i c a t e s h a v i n g poor s t r u c t u r e r e t e n t i o n when t h e i n t e r m e d i a t e s i l i c i c a c i d c o n c e n t r a t i o n is h i g h and good r e t e n t i o n when i t is low. These r e s u l t s s u g g e s t t h a t a low s i l i c i c a c i d c o n c e n t r a t i o n (-0.04M) a i d s s t r u c t u r e r e t e n t i o n in t h e f i r s t s t e p . I f so, t h i s is e a s i l y u n d e r s t a n d a b l e in terms o f t h e ease w i t h w h i c h s i l i c i c a c i d s r e a c t w i t h themselves. S i n c e i t is w e l l known t h a t a l c o h o l s form s t r o n g h y d r o g e n bonds, i t is v e r y p r o b a b l e t h a t t h e a l c o h o l in t h i s s t e p h y d r o g e n bonds t o t h e s i l i c i c a c i d ( o r a c i d s ) p r o d u c e d in i t , and as a r e s u l t c r e a t e s a p r o t e c t i v e s h e a t h around each s i l i c i c a c i d molecule. T h i s s h e a t h is c l e a r l y v e r y i m p o r t a n t in framework r e t e n t i o n in v i e w o f t h e r e a c t i v i t y o f s i l i c i c a c i d s . STEP 2. The e x p e r i m e n t s w i t h e t h a n o l , n - p r o p a n o l , i s o p r o p a n o l , and n - b u t a n o l a l r e a d y d e s c r i b e d o r mentioned i n d i c a t e t h a t a v a r i e t y o f a l c o h o l s c a n be u s e d in t h e second s t e p . I t appears t h a t u n h i n d e r e d p r i m a r y and s e c o n d a r y a l c o h o l s g e n e r a l l y w i l l be suitable. The a c i d in t h i s s t e p c l e a r l y f u n c t i o n s as a c a t a l y s t ( a c i d s a r e known t o c a t a l y z e t h e e s t e r i f i c a t i o n o f s i l a n o l s ) ( 2 1 ) . The t o l u e n e , when employed, s e r v e s t o d r i v e t h e e s t e r i f i c a t i o n t o c o m p l e t i o n b y f o r m i n g a w a t e r - t o l u e n e - e t h a n o l a z e o t r o p e (12% water) ( 2 2 ) . I t a l s o renders the r e a c t i o n s o l u t i o n a poor s o l v e n t f o r t h e b y p r o d u c t s a l t s and thus f a c i l i t a t e s t h e s e p a r a t i o n o f t h e s e s a l t s ( t h e pentane, when used, s e r v e s t h i s same f u n c t i o n ) . The f a c t t h a t t h e a l k y l s i l i c a t e s p r o d u c e d b y t h e r o u t e f u l l y o r s u b s t a n t i a l l y r e t a i n t h e o r i g i n a l s i l o x a n e framework a l s o shows t h a t t h e framework is a t l e a s t l a r g e l y r e t a i n e d in t h e second step. The r e s u l t s p e r t a i n i n g t o s i l i c i c a c i d c o n c e n t r a t i o n a l r e a d y m e n t i o n e d l e a d t o t h e c o n c l u s i o n t h a t a low s i l i c i c a c i d concentration aids this structure retention. A l s o a i d i n g i t , no doubt, is t h e a b i l i t y o f t h e a l c o h o l t o s h e a t h and p r o t e c t t h e s i l i c i c acid. (The r i n g o p e n i n g o c c u r i n g in t h e c o n v e r s i o n o f t h e S13O96" i o n t o ( n - P r 0 ) 3 S i 0 ( n - P r 0 ) 2 S i 0 S i ( 0 n - P r ) 3 c o u l d o c c u r in e i t h e r t h e f i r s t o r second step o f the s y n t h e s i s . I t is a t t r i b u t a b l e t o a p r o t o n - a s s i s t e d c l e a v a g e o f t h e s i l o x a n e framework enhanced b y t h e s t r a i n i n h e r e n t in t h e r i n g . The rearrangement w h i c h o c c u r s in the c o n v e r s i o n o f t h e S i ^ O ^ g ^ - l ° ^ [5.3.3] isomer o f (EtO)ioSi6°7 a l s o c o u l d o c c u r in e i t h e r t h e f i r s t o r second s t e p n t

o

β


246


OEt

OEt Etcr EtO

OEt

I

I

-Si.

EtO / EtO

OEt

/

'

(a)

\OEt OEt

(b) OPr

OPr


S i

OPr

I

I I

PrO PrO

-Si

I

s OPr OPr

OPr (c) OEt

EtO

\

I

,Si

EtO

OEt

o

\

Si ~ OEt

EtO-Si'

EtO^

x

/

OEt

N

o^

/

OEt

I

ο

Ο

I

I

EtO-Si, / EtO

Si

ο

I Ο \ (OEt) / Si — O — S i . 2

, Si-OEt \ OEt

EtO'

*OEt EtO

OEt

I

OEt 5.3.3 5.5.1 (d) F i g u r e 4. S t r u c t u r e s o f a l k y l s i l i c a t e s p r o d u c e d from (a) 7-Ca2Si04, Ca3Si040, and p o r t l a n d cement, (b) Ca2ZnSi20y, (c) Ca3Si309, and (d) CugSigOig.6H2O and N a 4 C a 4 S i 6 0 i 8 .


18.

GOODWIN AND KENNEY

of the s y n t h e s i s . framework c l e a v a g e


247

I t c a n be a s c r i b e d t o a p r o t o n - a s s i s t e d f o l l o w e d by r i n g - c o n t r a c t i n g r i n g c l o s u r e s . )


STEP 3. The l a s t o r o r g a n o d e a l k o x y l a t i o n s t e p c a n no doubt be c a r r i e d o u t w i t h a v a r i e t y o f G r i g n a r d r e a g e n t s , and thus i t is c l e a r l y f l e x i b l e too. From t h e r e s u l t s o f v a r i o u s e x p e r i m e n t s , i t is a p p a r e n t t h a t framework r e t e n t i o n in t h i s s t e p is a i d e d b y a low temperature (~0 ° C ) and a moderate G r i g n a r d r e a g e n t t o a l k o x y group r a t i o (-2:1). UTILITY. T h i s r o u t e appears t o o f f e r a p a t h t o a l k y l s i l i c a t e s t h a t is s i m p l e and has t h e p o t e n t i a l o f h a v i n g low energy requirements. I t does n o t o f f e r a c o r r e s p o n d i n g low-energy p a t h t o o r g a n o s i l o x a n e s because a G r i g n a r d r e a g e n t is u s e d in t h e o r g a n o d e a l k o x y l a t i o n s t e p and thus e l e m e n t a l magnesium is u l t i m a t e l y r e q u i r e d f o r t h i s s t e p . However, i t s h o u l d be p o i n t e d o u t t h a t e l e m e n t a l magnesium is needed o n l y f o r t h e f o r m a t i o n o f the S i - C bonds in t h i s r o u t e , whereas e l e m e n t a l s i l i c o n is r e q u i r e d f o r t h e f o r m a t i o n o f a l l bonds in t h e common r o u t e . I n t h i s way t h e new r o u t e is advantageous. Further, i t s existence reemphasizes the f a c t t h a t p o s s i b l e paths t o o r g a n o s i l o x a n e s t h a t a r e n o t b a s e d o n e l e m e n t a l s i l i c o n cannot be summarily d i s m i s s e d . The r o u t e a l s o p r o v i d e s a s a t i s f a c t o r y p a t h t o some a l k y l s i l i c a t e s f o r w h i c h no o t h e r s a t i s f a c t o r y r o u t e s a r e a v a i l a b l e . Some o f t h e s e a l k y l s i l i c a t e s may be o f i n t e r e s t in t h e s y n t h e s i s of ceramics by the s o l - g e l technique. ACKNOWLEDGMENT. We thank R a l p h E. Temple, D a l e R. P u l v e r , a n d Gordon F e a r o n f o r h e l p f u l d i s c u s s i o n s . We a l s o thank Diamond Shamrock and Dow C o r n i n g f o r f i n a n c i a l s u p p o r t . LITERATURE CITED 1. 2. 3.

4. 5.

6.

7.

8. 9.

Liebau, F. Structural Chemistry of Silicates; SpringerVerlag: Berlin, 1985. Fleischer, M. Glossary of Mineral Species 1980; Mineralogical Record: Tucson, AZ, 1980. Helmuth, R. Α.; Miller, F. M.; O'Connor, T. R.; Greening, N. R. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Grayson, M., Ed.; John Wiley: New York, 1979; Vol. 5, p 163. Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Oxford: Oxford, 1984; p 1017. Arkles, B. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Grayson, Μ., Ed.; John Wiley: New York, 1982; Vol. 20, p 912. Stark, F. O.; Fallender, J. R.; Wright, A. P. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 2, p 305. Hardman, Β. B.; Torkelson, A. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Grayson, Μ., Ed.; John Wiley: New York, 1982; Vol. 20, p 922. Ayen, R. J.; Burk, J. H. Mater. Res. Soc. Symp. Proc. 1986, 73 (Better Ceram. Chem. 2), 801. Iler, R. K.; Pinkney, P. S. Ind. Eng. Chem. 1947, 39, 1379.



248 10. 11. 12.

13. 14. 15. 16.


17. 18. 19. 20. C: 21. 22.

Bleiman, C.; Mercier, J. P. Inorg. Chem. 1975, 14, 2853. Calhoun, H. P.; Masson, C. R. J. Chem. Soc., Dalton Trans. 1980, 1282. Smith, B. Ph.D. Thesis, Chalmers Technical High School, Gothenburg, Sweden, 1951 as quoted in Eaborn, C. Organosilicon Compounds; Academic Press: New York, 1960; p 14. Wacker-Chemie G.m.b.H. Br. Patent 732 533, 1955. Compton, R. Α.; Petraitis, D. J. U. S. Patent 4 309 557, 1982. Lentz, C. W. Inorg. Chem. 1964, 3, 574. George, P. D.; Sommer, L. H.; Whitmore, F. C. J. Am. Chem. Soc. 1955, 77, 6647. Jancke, H.; Engelhardt, G.; Magi, M.; Lippman, Ε. Ζ. Chem. 1973, 13, 392. Menczel, G. Acta Chim. Acad. Sci. Hung. 1977, 92, 9. Deer, W. Α.; Howie, R. Α.; Zussman, J. Rock-Forming Minerals; John Wiley: New York, 1962; Vol. 1, p 240. Ohsato, H.; Takéuchi, Y.; Maki, I. Acta Crystallogr., Sect. Cryst. Struct. Commun. 1986, 42, 934. Eaborn, C. Organosilicon Compounds; Academic Press: New York, 1960; p 295. Horsley, L. H. Azeotropic Data II; Advances in Chemistry 35; American Chemical Society: Washington, DC, 1962; p 61.

RECEIVED September 1, 1987


A New Approach to the Synthesis of Alkyl Silicates and

Recommend Documents