Organometals and Organometalloids - American Chemical Society

10 Organosilanes as A q u a t i c A l k y l a t o r s of M e t a l Ions

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 15, 2016 | http://pubs.acs.org Publication Date: January 12, 1979 | doi: 10.1021/bk-1978-0082.ch010

RICHARD E. DESIMONE Department of Chemistry, Wayne State University, Detroit,MI48202

Much of the chemistry of concern to this symposium has in recent years received very broad recognition and consequently has been studied in depth from a variety of perspectives. Ques tions which are now being asked in these areas have become quite detailed and sophisticated, although admittedly much still re mains to be learned. In contrast to this situation, that sur rounding the element silicon, its environmental significance and relevant chemistry, is still in its infancy. Indeed the answer to the simple question "What, if any, is the environmental sig nificance of organosilicon compounds?" is far from clear at this point in time. It is the purpose of what follows to point out some basic and potentially relevant chemistry of silicon and to try to focus to some small degree on i t s environmental import. Silicon:

Occurance and Distribution

It is commonly known that silicon is one of the most abun dant of elements (TABLE I) and also one of the most widely dis tributed (1). The vast majority is tied up in silicate rocks TABLE I.

SILICON - HOW MUCH, AND WHERE? Earth's surface - land, sea and air Oxygen 53.3% Silicon - 15.9% Hydrogen - 15.1% Aluminum - 4.8% Average silicon content 2.77 χ 10 ppm in earth's crust 40 ppm in man 3 ppm in seawater 5

0-8412-0461-6/78/47-082-149$05.00/0 © 1978 American Chemical Society Brinckman and Bellama; Organometals and Organometalloids ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


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ORGANOMETALS AND

ORGANOMETALLOIDS

and m i n e r a l s where i t i s r e l a t i v e l y immobile and of l i t t l e concern to us. I n l i v i n g organisms, s i l i c o n p l a y s (and has played) an important r o l e i n n e a r l y a l l stages of e v o l u t i o n a r y development. From s i l i c a t e b a c t e r i a t o protozoa, algae, and the h i g h e r p l a n t and animal organisms, n e a r l y a l l c o n t a i n and use s i l i c o n i n one form or another. I t i s not the purpose of t h i s a r t i c l e to survey the expanding area of b i o - o r g a n o s i l i c o n chemistry (2) nor t o consider the innumerable occurrences of s i l i c o n i n l i v i n g organisms ( 3 ) . I t i s worth mentioning however, t h a t among the myriad of known s i l i c o n compounds i n a wide v a r i e t y of b i o t a , there i s a conspicuous absence of t r u e o r g a n o s i l i c o n molecules. In the higher animal organisms f o r example, s i l i c o n t y p i c a l l y occurs as o r t h o - and o l i g o s i l i c i c a c i d s and s i l i c a t e s , ortho and o l i g o s i l i c i c e s t e r s of carbohydrates, p r o t e i n s , s t e r o i d s , l i p i d s and p h o s p h o l i p i d s , and as i n s o l u b l e s i l i c o n polymers. While much has been l e a r n e d i n r e c e n t years about s i l i c o n i n l i v i n g o r ganisms a great d e a l c e r t a i n l y remains to be d i s c o v e r e d . We know very l i t t l e about the occurrence of n a t u r a l o r g a n o s i l i c o n compounds and we can by no means make the assumption t h a t they do not e x i s t . Much work i s needed i n t h i s area. At t h i s p o i n t i n time and f o r the purposes of t h i s a r t i c l e i t seems t h a t what should be of concern i s not the occurrence of t o x i c o r g a n o s i l i c o n compounds, but the p o s s i b i l i t y t h a t r e a c t i o n s of s i l i c o n compounds w i t h other,more g e n e r a l l y troublesome metals or m e t a l l o i d s , w i l l produce s p e c i e s which are i n f a c t s i g n i f i c a n t l y damaging from an environmental v i e w p o i n t . I n p a r t i c u l a r we w i l l focus on organo group t r a n s f e r r e a c t i o n s i n aqueous media. S i l i c o n as an Organo Group Donor Organo group t r a n s f e r from s i l i c o n has been known f o r some time, the f i r s t r e p o r t e d i n s t a n c e being i n 1896 w i t h the format i o n of an organomercurial, p-dimethylaminophenylmercurie c h l o r i d e ( 4 ) . The r e a c t i v i t y of the c h l o r o s i l a n e i s not s u r p r i s i n g

+

s i n c e these are among the more r e a c t i v e of s i l i c o n s p e c i e s . However, s i m i l a r organo group t r a n s f e r r e a c t i o n s occur i n aqueous media w i t h a l k y l a r y l s i l a n e s , w i t h t r a n s f e r of the a r y l group, and these proceed r e l a t i v e l y q u i c k l y to s u b s t a n t i a l completion (5).

Brinckman and Bellama; Organometals and Organometalloids ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

10.

DESIMONE

151

Organosihnes

f—\ H

3

EtOH

Si

H

+ SC1

CH

— \0)— < 3>3

C

H C—(Ο)— 8 H

C 1

+


h

(CH ) SiOH

3

/—\ (O/ HCΛ -

2

3

>

Q

+ HCl

3

(2)

HOAc S 1 ( C H

+

3)3

Hg(0Ac)

>

2

7

H

3

^0)"

Ç((^$1C1 + 2

S i G 1

5

3

(^^

+

2

3

+

+ GaCl

+

2

3

HCl
(CH ) SiCl

3

3

(CH ) Si - 0 - Si(CH ) 3

k

I

^Q^Sb0(0H)

(CH )i Si

S h C 1

3

+

3

+ GaCl

3

3

(CH ) SiCl 3

3

'

H 0

(4)

2

+ CH GaCl

2

> CH GaCl

2

3

3

+

(5)

((CH ) Si0) 3

2

(6)

n

(6) i s noteworthy i n t h a t the s i l i c o n compound, h e x a m e t h y l d i s i l oxane, i s u s u a l l y considered t o be the s i m p l e s t s i l i c o n e . Thayer has reported t h a t t h i s molecule r e a c t s - w i t h mercuric s a l t s i n a very complex r e a c t i o n y i e l d i n g ^20 products ( 9 ) . The other major c l a s s o f a l k y l a t i n g agents among s i l i c o n compounds i s the o r g a n o f l u o r o s i l i c a t e s . These have been extens i v e l y s t u d i e d by Wuller and co-workers (6, 10). Reaction w i t h H g C l , i n the presence o f NHi+Cl t o i n c r e a s e s o l u b i l i t y , occurs r e a d i l y t o g i v e monomethyl and dimethylmercurie s p e c i e s . 2

20°C HgCl + ( N H ) ( C H S i F ) 2

1+

2

3

5

> Η 0/ΝΗ^01

CH HgCl + (NH ) ( S i F C l ) 3

l+

2

5

2

(

7

)

100°C CH HgCl + ( N H ) ( C H S i F ) - ^ - ^ (CH ) Hg + (NH^) ( S i F C l ) 3

1 +

2

3

5

3

2

2


5

ORGANOMETALS AND

152

ORGANOMETALLOIDS

S i m i l a r l y , elements such as Sb and B i can be a l k y l a t e d or a r y l a ted w i t h s u b s t a n t i a l y i e l d s (11).

SbF + 3 ( N H ) ( C H S i F ) 3

4

2

3

> H0

5

Sb(CH ) 3

+ 3(ΝΗ ) (SiF )

3

4

2

6

(8)

2


Bi(OH)

/(")V-SiF

+ 3

3

\

( 10" M" s e c " f o r both DSS TSP, but more r a p i d l y w i t h TSP. For Hg(0Ac) and DSS k=6.6xl0" M" s e c " ( 9 ) . 3

3

2

2

3

2

1

6

1

1

2

1

t

1

1

2

3

2

1

1



10.

DESIMONE

Organosilanes

153

S p e c u l a t i o n on the mechanism has centered on two p o i n t s ; an i n t r a m o l e c u l a r acid-base i n t e r a c t i o n between the s i l i c o n and a t e r m i n a l oxygen of the anion, and the a c i d i t y of the a t t a c k i n g (and q u i t e v a r i a b l e ) mercuric s p e c i e s . The former (12) would be c o n s i s t e n t w i t h the f a c t that TSP always r e a c t s f a s t e r than DSS, which has an e x t r a carbon and would probably not adapt as w e l l to the required- conformation. The second p o i n t , the nature of the a t t a c k i n g mercuric s p e c i e s , i s g e n e r a l l y of great s i g n i f i c a n c e (for any metal). Anion dependent and pH dependent s t u d i e s r e v e a l dramatic e f f e c t s on r a t e f o r these environmental parameters (14). The d e t a i l e d understanding o f any transmethylation r e a c t i o n w i l l r e q u i r e adequate s p e c i a t i o n o f a l l r e a c t a n t s and products under any g i v e n s e t of c o n d i t i o n s . This has g e n e r a l l y been one of the major weaknesses of most s t u d i e s to date. In some work c u r r e n t l y i n progress, Bellama has reported the f a c i l e t r a n s f e r of organo groups t o mercuric s a l t s using a number of 1-organosilatranes i n p r o t i c or a p r o t i c media (15). >p 1 R-Si(OCH CH ) N 2

2

+

3

HgX

+

2

> RHgX

>t 1 X-Si(OCH CH ) N 2

2

(11)

3

I n t e r e s t i n g l y , the parent o r g a n o t r i a l k o x y s i l a n e s a r e i n e r t under s i m i l a r r e a c t i o n c o n d i t i o n s . Presumably the e x t r a e l e c t r o n dens i t y a t the s i l i c o n a c t i v a t e s the Si-C bond t o a t t a c k by H g ( I I ) . Environmental

Considerations

We come now t o the environmental s i g n i f i c a n c e of the chemis t r y j u s t discussed. I n the absence o f s i g n i f i c a n t knowledge of n a t u r a l l y o c c u r r i n g o r g a n o s i l i c o n compounds, i t seems worthw h i l e t o consider the impact of man-made o r g a n o s i l i c o n compounds. By f a r the l a r g e s t group of such substances a r e the s i l i c o n e s , which have found l i t e r a l l y hundreds of uses (Table I I ) , almost a l l i n s p i r e d because o f the chemical i n e r t n e s s of the polymeric m a t e r i a l (16, 17). The estimated s i l i c o n e market i n the United States i n 1973 was 91 m i l l i o n pounds. Most a p p l i c a t i o n s i n v o l v e complete r e l e a s e of the s i l i c o n e i n t o the environment. Most uses, except f o r the proposed use i n e l e c t r i c a l transformers as a replacement f o r PCB s, i n v o l v e very s m a l l q u a n t i t i e s (18). A l e g i t i m a t e question a t t h i s p o i n t seems to be What u l t i m a t e l y happens t o a l l of t h i s m a t e r i a l ? " There appears to be no published work on m i c r o b i a l demethylation of s i l i c o n ( e s ) and i t i s not c l e a r how v a r i o u s environmental f a c t o r s a f f e c t the degradation o f the polymeric m a t e r i a l . Dow-Corning has reported that moist s o i l seems t o be the most d e s t r u c t i v e environment t o f

M


154

ORGANOMETALS AND

ORGANOMETALLOIDS


TABLE I I . APPLICATIONS OF SILICONES (16)

1) 2) 3) 4) 5) 6)

Waxes and p o l i s h e s Foaming and antifoaming agents Release agents ( i n molding processes) P r o t e c t i v e coatings Lubricants Cosmetics

n)

Cooling f l u i d s i n e l e c t r i c a l

transformers*

* a "bulk volume" a p p l i c a t i o n (pending)

the s i l i c o n e molecule (18). i t i s p o s t u l a t e d that the degradation process begins w i t h a d e - p o l y m e r i z a t i o n of the long s i l o x a n e chain to form v o l a t i l e c y c l i c s i l o x a n e s of 4-5 S i - 0 u n i t s , a process w i t h a h a l f l i f e of VLO days. Under the i n f l u e n c e of moisture, oxygen and u.v. l i g h t , the v o l a t i l e c y c l i c s i l o x a n e s are then presumed to degrade i n the atmosphere to SiU2, H2O, and CO2. D e t a i l s on these s t u d i e s are l a c k i n g . One i s c u r i o u s to know f o r example whether the s o i l i n the experiments was s t e r i l e , whether the process could be i n t e r r u p t e d or a l t e r e d by the pre sence of other substances such as methyl acceptors, and whether *C l a b e l i n g s t u d i e s have been used to t r a c e the methyl group carbon to product CO2. H o p e f u l l y these d e t a i l s w i l l be f o r t h coming . I n other experiments, Dow-Corning r e p o r t s that a 15% emul s i o n of s i l i c o n f l u i d subjected to the a c t i o n of a c t i v a t e d sewage sludge f o r a p e r i o d of 70 days showed no evidence of bio-degrada t i o n (18). However Bellama r e p o r t s that r e l a t i v e l y low v i s c o s i t y s i l i c o n e f l u i d s w i l l methylate H g ( I I ) ( 1 9 ) . I n summary, we have b a r e l y scratched the s u r f a c e of some very i n t e r e s t i n g and p o s s i b l y s i g n i f i c a n t chemistry. Much work remains to be done i n areas mentioned and s u r e l y i n others not yet discovered. ll

Literature Cited

1. 2.

Ochiai, Ε., "Bioinorganic Chemistry, An Introduction", 5-12, A l l y n and Bacon, Inc., Boston, 1977. Voronkov, M.G., Chem. Brit.(1973) 9, 411.


pp.

10.

DESIMONE

3. 4. 5.


6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Organosilanes

155

Voronkov, M.G., Zelchan, G.I., Lukevitz, E.J., " S i l i c o n and L i f e " , Zinatne Publishing House, Riga, 1971. Combes, C., Compt. Rend., (1896), 122, 622. Eaborn, C., "Organosilicon Compounds", Butterworths, London, 1960. Müller, R., Organometal. Chem. Revs., (1966), 1, 359. Jakubowitch, A. J., and Mozarew, G.W., J. Gen. Chem. USSR, (1953), 23, 1414. Schmidbaur, H., Angew. Chem., (1964), 76, 753. Thayer, J.S., personal communication. Müller, R. and Dathe, C., Chem. Ber. (1965), 98, 235. Müller, R. and Dathe, C., Chem. Ber. (1966), 99, 1609. DeSimone, R.E., J.C.S. Chem. Comm. (1972), 780. Bellama, J.M. and Nies, J.D., personal communication. Jewett, K.L., Brinckman, F.E. and Bellama, J.M., following paper. Bellama, J.M. and Nies, J.D., J.C.S. Chem. Comm., submitted. Howard, P.H., Durkin, P.R., and Hanchett, A., "Assessment of Liquid Siloxanes", Report # PB 247778, National Technical Information Service, U.S. Dept. of Commerce, 1974. Calandra, J.C., Keplinger, M.L., Hobbs, E.J., and Tyler, L.J. Polymer Preprints, (1976), 17, 1. Pollution Engineering, Aug., 1977, p. 41. Bellama, J.M., personal communication.

Discussion G. E. PARRIS (Food and Drug A d m i n i s t r a t i o n ) : Have there been d i r e c t t o x i c i t y s t u d i e s on s i l i c o n e s from the standpoint of e n v i ronmental impact?. DeSIMONE: There have been many s t u d i e s on d i r e c t t o x i c i t y , i n c l u d i n g intravenous s t u d i e s . Except f o r minor eye i r r i t a t i o n i n c e r t a i n cases, these appear harmless t o j u s t about e v e r y t h i n g . PARRIS: The r e a c t i o n s you showed suggest that s i l i c o n e s may be new m e t h y l a t i n g agents i n the environment. DeSIMONE: I t remains t o be found out whether i n f a c t enough o r g a n o s i l i c o n compounds do e x i s t i n the environment, where they e x i s t , and whether what you j u s t suggested i s t r u e . PARRIS: One of the c r i t i c a l p l a c e s w i l l be i f s i l i c o n e s f i n d more use as d i e l e c t r i c f l u i d s . I doubt that s i l i c o n e s w i l l be the major replacement f o r PCB's. I t h i n k t h a t most people who a r e d e a l i n g w i t h the t o x i c i t y o f s i l i c o n e s and the importance o f e n v i ronmental chemistry of s i l i c o n e s have not considered them as pot e n t i a l m e t h y l a t i n g agents. C. FREY (Dow Corning C o r p o r a t i o n ) :

I would l i k e t o make a



156

ORGANOMETALS AND

ORGANOMETALLOIDS

couple of comments on the i m p l i c a t i o n s of the paper. The data there showing 91,000,000 l b s . of s i l i c o n e s g a i n i n g entry i n t o the environment could very w e l l be an item f o r some concern, but the great b u l k of t h a t m a t e r i a l , as many people know, i s p o l y d i m e t h y l s i l o x a n e . I t ' s i n t e r e s t i n g to note that the subsequent work of Dr. Thayer [vide i n f r a ] seems to show that mercuric n i t r a t e , which was j u s t about the most potent m e c u r i a l c l e a v i n g agent, i s without e f f e c t on c y c l o d i m e t h y l s i l o x a n e s a f t e r s e v e r a l months of contact. So the n o t i o n t h a t the o r g a n o s i l i c o n compounds, which are not natu r a l l y - o c c u r r i n g but f i n d t h e i r way i n t o the environment, w i l l be cleaved by mercury i s probably d i f f i c u l t to s u s t a i n . De SIMONE : The question i s not whether mercury w i l l these compounds, but r a t h e r during the decomposition ( i n s o i l as you suggest i s the most e f f i c i e n t way to do i t ) , pens i f some methyl acceptor i s present w h i l e you've got cleavage products f l o a t i n g around.

cleave moist what hapthese

FREY: I t h i n k i t ' s important to d i f f e r e n t i a t e between what might be c a l l e d environmental chemistry and the chemistry of s p i l l s ; that i s , what happens i f you have l a r g e concentrations of s i l o x a n e i n contact w i t h l a r g e concentrations of some metal. On an environmental s c a l e , I t h i n k one has to be concerned w i t h the r e a c t i o n of m e t h y l s i l i c o n compounds w i t h n a t u r a l l y - o c c u r r i n g e l e ments or compounds. As f a r as the s o i l i s concerned, w e ' l l present the d e t a i l s t h i s summer at the 5th I n t e r n a t i o n a l O r g a n o s i l i con Symposium i n Karlsruhe [August, 1978]. There i s no unusual chemistry there t h a t i n v o l v e s the c a r b o n - s i l i c o n bonds themselves. J . J . ZUCKERMAN ( U n i v e r s i t y of Oklahoma): The h a l f - l i f e of 10 days, d i d that r e f e r t o the d e p o l y m e r i z a t i o n - c y c l i z a t i o n to the 5- or 4-membered r i n g s ? DeSIMONE: That was the impression I got. ZUCKERMAN: There was another r e a c t i o n you mentioned which i n d i c a t e d the decomposition w i t h respect t o u l t r a - v i o l e t l i g h t g i v i n g C0 2

DeSIMONE: I got t h i s impression from an a r t i c l e i n " P o l l u t ion Engineering" [Reference 18] , an i n t e r v i e w w i t h John Ryan. FREY: I t h i n k the question has something to do w i t h the r a t e s of s o i l - c a t a l y z e d r e a c t i o n , whatever that happens t o be. The d e t a i l s of that r e a c t i o n , l i k e a l l o t h e r s , depend on the circumstances, and w e ' l l be going i n t o that d e t a i l i n a paper t h a t i s i n preparation. J . M. BELLAMA ( U n i v e r s i t y of Maryland): About the nature of water-soluble o r g a n o s i l i c o n chemistry, the TSP and DSS to which you r e f e r r e d are extended chains; s e v e r a l people have proposed a h e a d - t o - t a i l i n t e r a c t i o n where the presence of an e l e c t r o n - r i c h species (an a v a i l a b l e Lewis base moiety somewhere remote i n a molecule from the s i l i c o n ) can bend around and j o i n . We have looked at these k i n d s of i n t e r a c t i o n s [Inorg. Chem. (1965), 14,



10.

DESIMONE

Organosifones

157

1618], and we have two f e e l i n g s about them. One i s that these i n t e r a c t i o n s can be important when η (the number of i n t e r v e n i n g methylene groups) i s 1 or 2. Models of these compounds show t h a t the i n t e r a c t i n g atoms are e s s e n t i a l l y i n contact. With longer chains (n = 3-5), there seem to be some i n t e r a c t i o n . When you get t o η = 6, i t looks l i k e no i n t e r a c t i o n remains. Secondly, the nature of the group on the s i l i c o n seems t o be very important. Craig's o r i g i n a l paper J j . Chem. Soc. (1954), 332] p o s t u l a t e s the n e c e s s i t y of inducing a p o s i t i v e charge on s i l i c o n . I t would seem t h a t organic groups such as methyls or phenyls are not going to be p a r t i c u l a r l y good i n t h i s r e s p e c t . I f you have s u b s t i t u e n t s on the s i l i c o n l i k e a c h l o r i n e , or perhaps l i k e a hydrogen, which i s very e l e c t r o n e g a t i v e w i t h respect t o the s i l i c o n , the chances f o r these kinds of i n t e r a c t i o n s are going to be f a r g r e a t e r . So, using water-soluble t r i m e t h y l s i l y l compounds suggests t h a t these kinds of i n t e r a c t i o n s are going to be l e s s important i n e s t a b l i s h i n g a s i t e f o r a t t a c k by an e l e c t r o p h i l i c mercury than would be the case i f other s u b s t i t u e n t s were present on the s i l i c o n . DeSIMONE: The d i f f e r e n c e between the r a t e s of DSS and TSP may be a r e f l e c t i o n of t h a t e x t r a carbon; i t i s a f a c t o r of a couple orders of magnitude. BELLAMA: M u l l e r and Frey [Z. anorg. a l l g . Chem. (1969) 368, 113] p o s t u l a t e d the n e c e s s i t y f o r ammonium f l u o r i d e a d d i t i o n to the m e t h y l t r i c h l o r o s i l a n e p l u s mercuric c h l o r i d e . They c l a i m t h a t i t ' s necessary to have a m e t h y l p e n t a f l u o r o s i l i c a t e species as the intermediate and as the a c t i v e methylating agent. We have done t h i s r e a c t i o n without adding the ammonium f l u o r i d e . We don't know what intermediate i s present, or what i s a c t u a l l y doing the methyl a t i n g , but i t ' s not necessary t o add the ammonium f l u o r i d e i n order t o get t h i s k i n d of r e a c t i o n to occur. J . S. THAYER ( U n i v e r s i t y of C i n c i n n a t i ) : We have found t h a t the DeSimone r e a c t i o n [equation 10] i s not confined t o mercury. One gets s i m i l a r r e a c t i o n s w i t h t h a l l i u m t r i a c e t a t e , w i t h l e a d t e t r a a c e t a t e and, we b e l i e v e , w i t h potassium h e x a c h l o r o p l a t i n a t e . We s t u d i e d the k i n e t i c s of t h i s r e a c t i o n and our f i g u r e s agree moderately w e l l the ones that were quoted here. Secondly, the other r e a c t i o n was the d i r e c t r e a c t i o n between h e x a m e t h y l d i s i l o x ane and mecuric n i t r a t e . The two dozen products a l l u d e d t o are a s e r i e s of l i n e a r and c y c l i c s i l o x a n e s , formed here by a d i s p r o p o r t i o n t i o n r e a c t i o n , p l u s a v a r i e t y of species we have not yet i d e n t i f i e d . Our b e l i e f i s that t h i s r e a c t i o n proceeds by i n i t i a l removal of a methyl group by mercury, from the s i l o x a n e moiety f o l l o w e d by rearrangement. We f i n d t h a t a s i m i l a r r e a c t i o n occurs w i t h the germanium analog, hexamethyldigermoxane. RECEIVED August 22,

1978.


Organometals and Organometalloids - American Chemical Society

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