Direct Process for Preparation of Arylhalosilanes

Direct

Process

for

Preparation

of Arylhalosilanes

A. J. BARRY, J. W. GILKEY, and D. E. HOOK Dow Corning Corp., Midland, Mich.

Downloaded by CORNELL UNIV on October 12, 2016 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch023

A practical method for the synthesis of arylhalosilanes is afforded by the high-pressure reaction of aromatic hydrocarbons with hydrogen containing halosilanes, as represented by: C H + HSiCl -->PhSiCl + H 6

6

3

3

2

This reaction proceeds under autogenous pressure at about 400°C. without a catalyst, or as low as 230°C. in the presence of a catalyst of the FriedelCrafts type. The threshold temperature is further lowered, markedly, by organosubstitution of the halosilane and, to lesser degree, by substitution on the aromatic ring. As an example, in the reaction of methyldichlorosilane with benzene to produce methylphenyldichlorosilane, the threshold temperature is 130°C. These processes yield interesting by-products resulting from polyarylation of the silane as well as polysilylation of the aromatic nucleus. The synthetic method is described here in some detail and a possible siliconium ion reaction mechanism is considered in an effort to explain the nature of the products and by-products.

T h e industrially important field of organopolysiloxane chemistry was founded upon the Grignard process in the early 1940's. That process was versatile and afforded a ready route to the required organochlorosilane intermediates, but the raw materials were costly and the large amounts of solvent required made for a process of low volume efficiency. It was apparent that further growth of the infant industry would be materially facilitated by the development of direct methods for synthesis of intermediates. The search for direct synthetic methods was rewarded by two major breakthroughs. The first, a result of work done simultaneously at General Electric Co. and The Dow Chemical Co., rested upon the reaction of methyl and phenyl halides with silicon metal at 300°C. to produce the corresponding organochlorosilanes (2, 8-12), the methyl compounds more efficiently than the phenyl. The other direct process which has become commercially important for its wide versatility and good efficiency was the result of work initiated at The Dow Chemical Co., in November 1944, and continued at the Dow Corning Corp. This work embraced high pressure reactions of hydrogen containing halosilanes and organohalosilanes 246

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

247

BARRY, GILKEY, AND HOOK—PREPARATION OF ARYLHALOSILANES

of t h e t y p e s H S i X , R H S i X , R H S i X , w i t h u n s a t u r a t e d h y d r o c a r b o n s a n d b e n z e n o i d compounds. A l k y l c h l o r o s i l a n e s so s y n t h e s i z e d w e r e r e p o r t e d i n o n e c o m m u n i c a t i o n (3) a n d i n a series o f p a t e n t s (S), t h e first o" w h i c h w ere a p p l i e d f o r J u n e 6, 1946. T h e p r e p a r a t i o n of arylchlorosilanes b y this m e t h o d was t h e subject of several patents (1, 4) > t h e first o f w h i c h w e r e a p p l i e d f o r J u n e 6, 1946. T h i s p a p e r describes t h e fundamental observations that characterize this interesting m e t h o d of synthesis. 3

2

2

T


Thermal Reactions in Vapor Phase T h e r e a c t i o n o f benzene a n d t r i c h l o r o s i l a n e w a s first t r i e d as a v a p o r - p h a s e r e a c t i o n a t h i g h temperatures. W h e n m i x t u r e s of t h e t w o v a p o r s were passed t h r o u g h a 3 - i n c h χ 10-foot i r o n t u b e a t a t m o s p h e r i c p r e s s u r e u n d e r v a r i e d c o n d i t i o n s o f t e m perature a n d contact time, w i t h a n d w i t h o u t a v a r i e t y of catalysts, o n l y v e r y small a m o u n t s o f p h e n y l t r i c h l o r o s i l a n e w e r e o b t a i n e d . F o r e x a m p l e , a m i x t u r e o f 6.6 g r a m - m o l e s o f t r i c h l o r o s i l a n e a n d 13.5 g r a m - m o l e s o f benzene w a s p u t t h r o u g h t h e t u b e p a c k e d w i t h p o r o u s p l a t e a n d t h e c o n d e n s e d effluent r e t u r n e d t o a s t r i p s t i l l f r o m w h i c h t h e r e c o v e r e d r e a c t a n t s were r e c y c l e d t h r o u g h t h e t u b e . A f t e r 4 3 h o u r s a t c a . 6 0 0 ° C , w h e n 9 8 % o f t h e t r i c h l o r o s i l a n e h a d b e e n c o n s u m e d , o n l y 0.52 g r a m - m o l e of p h e n y l t r i c h l o r o s i l a n e w a s o b t a i n e d , w i t h a l a r g e a m o u n t o f b y - p r o d u c t s i l i c o n t e t r a c h l o r i d e a n d c o n s i d e r a b l e b r o w n , t a r r y s t i l l r e s i d u e . O v e r h a l f t h e benzene w a s r e c o v e r e d u n c h a n g e d . T h u s , t h e first a p p r o a c h t o t h e p r o b l e m w a s r a t h e r d i s c o u r a g i n g .

Thermal Reactions at High Pressures Preparation of Phenyltrihalosilanes. Be nzene-Trichlorosilane System. Auto c l a v e r e a c t i o n s a t m o d e r a t e l y h i g h t e m p e r a t u r e s a n d pressures a f f o r d e d a m o r e success f u l a p p r o a c h t o t h e synthesis of arylchlorosilanes b y t h e t y p e r e a c t i o n :

C H + HSiCla -> PhSiCla + H 6

6

2

W h e n m i x t u r e s o f 18 g r a m - m o l e s e a c h o f benzene a n d t r i c h l o r o s i l a n e w e r e h e a t e d u n d e r a u t o g e n o u s pressures i n a r o t a t i n g 1 4 . 4 - l i t e r stoel b o m b , a p p r e c i a b l e y i e l d s o f p h e n y l t r i c h l o r o s i l a n e a n d p h e n y l d i c h l o r o s i l a n e w e r e ol s t a i n e d a t t e m p e r a t u r e s i n t h e o r d e r o f 400°C. T h e pressures r a n g e d s y s t e m a t i c a l l y f r o m a b o u t 1300 p . s . i . a t 3 5 0 ° C . t o a b o u t 1900 p . s . i . a t 5 0 0 ° C . T h e detailed d a t a f o r several t y p i c a l runs are summarized i n T a b l e I a n d r e p r e s e n t e d i n F i g u r e 1, w h e r e y i e l d s o f t h e d e s i r e d p h e n y l t r i c h l o r o s i l a n e

Table I. Charge.

Run PB—117 181 116 180 142 115 179 156 114 178 177 99 F C B — 78

Av. Temp., °C. 350 353 375 378 378 400 403 408 425 430 454 465 505

Reaction of Trichlo*osilane with Benzene

14.4-liter autoclave 1402 grams (18 moles) CeHe 16-hr. reaction time 2460 grams (18.16 moles) H S i C h Still CeHiSiCU, CeHe, CeHsSiHCh, Charge, SiCU, HSiCh, Grams Grams Grams Grams Grams Grams 69 340 985 245 3688 1380 3763 1917 249 1324 0 48 3754 648 400 758 97 735 3772 1698 309 1152 48 293 3649 1634 278 1333 0 80 3793 514 498 815 150 968 3804 1060 648 1139 127 533 3687 1139 553 1309 37 188 3690 454 681 974 115 788 3643 713 617 922 206 999 3635 423 826 909 120 1075 3690 194 1218 1233 0 831 3558 144 786 900 0 1038

Residue, Grams 90 26 380 55 51 382 33 34 176 120 144 171 570

a r e p l o t t e d as a f u n c t i o n o f t e m p e r a t u r e . T h e t h r e s h o l d t e m p e r a t u r e f o r t h e r e a c t i o n is a b o u t 3 4 0 ° C . a n d t h e y i e l d increases g e n e r a l l y w i t h t e m p e r a t u r e u p t o a l i m i t . H o w e v e r , t h e r e i s so m u c h s c a t t e r i n t h e r e c o r d e d d a t a , a n d a d d i t i o n a l d a t a n o t t a b u lated b u t included i n the plot, that a valid linear relationship m a y n o t be presumed. T h e m o s t s i g n i f i c a n t , y e t a d m i t t e d l y generous, c u r v e t h a t m i g h t b e d r a w n t o s h o w y i e l d

American Chemical Sonify Library

METAL-ORGANIC COMPOUNDS Advances in Chemistry; American ΛChemical Society: Washington, DC, 1959. m mm *ΜΕΛ. *UL * « *a«

ADVANCES IN CHEMISTRY SERIES

248

PHENYLTRICHLOROSILANE YIELD VS. REACTION TEMPERATURE


1400

,

,

1

1

vs. t e m p e r a t u r e w o u l d e n v e l o p t h e d a t a as s h o w n b y t h e h e a v y l i n e o f F i g u r e 1. F r o m t h i s , i t a p p e a r s t h a t t h e p h e n y l t r i c h l o r o s i l a n e y i e l d a p p r o a c h e s a l i m i t o f 1075 g r a m s a t about 450°C. ( r u n 177). T h i s a m o u n t s t o 5.08 g r a m - m o l e s o r 3 3 . 8 % t h e o r e t i c a l ( b a s e d on consumed reagent). S o m e a d j u s t m e n t s h o u l d be m a d e f o r t h e b y - p r o d u c t p h e n y l d i c h l o r o s i l a n e , because t h i s c o m p o u n d , a c a d e m i c a l l y , r e p r e s e n t s s i l y l a t i o n o f t h e b e n z e n e a n d c a n be c o n v e r t e d t o a u s e f u l p r o d u c t , b y r a t h e r s i m p l e m e a n s . I f t h i s b y - p r o d u c t be so i n c l u d e d i n t h e y i e l d p l o t , t h e d o t t e d c u r v e o f F i g u r e 1 is o b t a i n e d . F r o m t h i s t h e o p t i m u m t e m p e r a ture for the reaction appears t o be 430°C. R e f e r r i n g t o the table, the pertinent r u n ( N o . 178) s h o w s a y i e l d o f 4.72 g r a m - m o l e s o f p h e n y l t r i c h l o r o s i l a n e , w h i c h i s 3 6 . 4 % of t h e o r e t i c a l , b a s e d o n c o n s u m e d t r i c h l o r o s i l a n e . A l l o w i n g f o r t h e 1.16 g r a m - m o l e s of b y - p r o d u c t p h e n y l d i c h l o r o s i l a n e , t h e t o t a l s i l y l a t i o n y i e l d b e c o m e s 4 5 . 3 % t h e o retical. T h e l o w y i e l d s a r e reflected i n t h e l a r g e a m o u n t s o f b y - p r o d u c t s i l i c o n t e t r a c h l o r i d e c h a r a c t e r i s t i c o f t h i s series. I t i s f o r m e d b y t h e r m a l r e a r r a n g e m e n t o f t r i c h l o r o s i l a n e (13): 4 H S i C l -> 3 S i C l + 2 H 3

4

2

+ Si

A c c o r d i n g l y , t h e 3.63 g r a m - m o l e s o f s i l i c o n t e t r a c h l o r i d e of r u n 178 i s e q u i v a l e n t t o 4.84 g r a m - m o l e s o f t h e i n i t i a l t r i c h l o r o s i l a n e . T h u s , m o r e o f t h i s reagent was c o n s u m e d i n t h e side r e a c t i o n t h a n was c o n v e r t e d i n t o t h e d e s i r e d p r o d u c t , i n n e a r l y a l l r u n s . W i t h r e g a r d t o m a t e r i a l s b a l a n c e i n r u n 178, the p h e n y l t r i c h l o r o s i l a n e a n d p h e n y l d i c h l o r o s i l a n e a c c o u n t for 5.88 g r a m - m o l e s o r 9 5 . 6 % o f t h e 6.15 g r a m - m o l e s o f benzene consumed. T h e s e t w o p r o d u c t s a n d the s i l i c o n t e t r a c h l o r i d e a c c o u n t f o r 10.72 g r a m m o l e s o r 8 3 . 2 % o f t h e 12.89 g r a m - m o l e s o f t r i c h l o r o s i l a n e c o n s u m e d . These values m i g h t b e benefited b y some c o r r e c t i o n f o r t h e difference b e t w e e n b o m b l o a d a n d s t i l l c h a r g e , b u t because t h e d i s c r e p a n c y c a n n o t be a l l a t t r i b u t e d t o m e c h a n i c a l losses, s u c h correction cannot b e p r o p e r l y assayed. S m a l l a m o u n t s o f d i p h e n y l d i c h l o r o s i l a n e were i s o l a t e d f r o m t h e h i g h e r b o i l i n g residues f r o m these e x p e r i m e n t s . W h i l e sufficient f o r g o o d c h a r a c t e r i z a t i o n , t h e a m o u n t s o b t a i n e d were too s m a l l t o affect the m a t e r i a l s b a l a n c e s i g n i f i c a n t l y .



249

Benzene-Tribromosilane System. T h e analogous reaction of tribromosilane w i t h benzene w a s d e m o n s t r a t e d b y a u t o c l a v i n g a m i x t u r e o f 3 g r a m - m o l e s o f e a c h f o r 16 hours a t 490° t o 510°C. D i s t i l l a t i o n o f t h e p r o d u c t a f f o r d e d 2 0 2 g r a m s of p h e n y l t r i b r o m o s i l a n e (0.6 g r a m - m o l e ) , t h e p r i n c i p a l 3ut o f w h i c h b o i l e d a t 9 4 - 9 ° C . a n d 2.3 t o 2.9 m m . A l i t t l e b i p h e n y l w a s p r o d u c e d ; m d , because o f i t s close b o i l i n g p o i n t , contaminated the distilled product. T h e analytical data shown i n Table I X are com p a r e d w i t h t h e t h e o r e t i c a l c a l c u l a t e d o n t h e hi;,sis o f 6 % s u c h c o n t a m i n a t i o n .


Chlorobenzene-Trichlorosilane System. I n t h e hope that chlorobenzene w o u l d react w i t h t r i c h l o r o s i l a n e u n d e r less r i g o r o u s c o n d i t i o n s t h a n benzene a n d c o n s e q u e n t l y a f f o r d a m o r e efficient s y n t h e s i s o f p h e n y l t r i c h l o r o s i l a n e , a series o f e x p e r i m e n t s w a s r u n i n w h i c h 12 g r a m - m o l e s o f c h l o r o b e n z e n e a n d 24 g r a m - m o l e s o f t r i c h l o r o s i l a n e w e r e b o m b e d f o r 16 h o u r s a t v a r i e d t e m p e r a t u r e s a n d a u t o g e n o u s pressures. T h e d a t a a r e

2000

PHENYLTRICHLOROSILANE YIELD VS. REACTION TEMPERATURE

1800 1600

V — P h i >lCI

3

1400 2E 1200 ο

- 1000

-I UJ

>- 800 600 400

^""^BY-PRO )UCED

——+~

200 300

'

BENZENE

350 400 450 REACTION Τ EMPERA TURE, *C.

Figure 2 . Thermal reaction of trichlorosilane with chlorobenzene s u m m a r i z e d i n T a b l e I I a n d r e p r e s e n t e d i n 1he y i e l d - t e m p e r a t u r e p l o t o f F i g u r e 2 ; 390°C. appears t o be the o p t i m u m reaction temperature. A t 300°C. essentially n o p h e n y l t r i c h l o r o s i l a n e w a s f o r m e d i n 16 h o u r s ; t h e o n l y s i g n i f i c a n t r e a c t i o n o c c u r r i n g t h e r e w a s t h e r e d u c t i o n o f c h l o r o b e n z e n e b y t r i c h l o r o s i l a n e t o g i v e benzene. Above 4 0 0 ° C . t h e y i e l d of p h e n y l t r i c h l o r o s i l a n e d r o p p e d off s h a r p l y a n d t h e f o r m a t i o n o f benzene i n c r e a s e d m a r k e d l y , as s h o w n i n t h e l o w e r c u r v e . R u n 135 a t 3 8 7 ° C . p r o v e d t h e m o s t efficient o f t h e series. I t s 7.89 g r a m - m o l e y i e l d o f p h e n y l t r i c h l o r o s i l a n e r e p resents 3 8 . 1 % o f t h e 20.7 g r a m - m o l e s o f t r i c h l o r o s i l a n e c o n s u m e d a n d 6 5 . 8 % o f t h e 12 g r a m - m o l e s o f c h l o r o b e n z e n e c h a r g e d ; 2.7 g r a m - m o l e s ( 2 2 . 5 % ) o f t h e l a t t e r w a s r e d u c e d t o benzene. I t m i g h t be concluded from the viewpoint of slightly lower threshold a n d lower o p t i m u m t e m p e r a t u r e s , t h a t t h e c h l o r o b e n z e n e is m o r e s u s c e p t i b l e t o r e a c t i o n t h a n 1


250

ADVANCES IN CHEMISTRY SERIES Table II.

Reaction of Trichlorosilane with Chlorobenzene


Charge.

Run

Av. Temp., °C.

FCB—236 P B —133 102 103 135 104 134 105 136

300 325 355 375 387 400 416 425 445

244

408

165

423

1352 grams (12 moles) CeHsCl 3257 grams (24 moles) HSiCls Still Charge, HSiCls, SiCU, Grams Grams Grams 16-hour runs 4416 2060 301 4403 1054 1174 4443 437 1985 4518 236 1872 4352 454 1778 4554 291 1936 4594 365 1861 4473 349 1982 4475 587 1817 6-hour run 4452 285 2001 2-hour run 4244 422 1740

14.4-liter autoclave CeHe, Grams

C6H C1, Grams

CeHeSiCh, Grams

Residue, Grams

264 174 30 163 212 228 336 339 504

1098 513 112 0 0 0 0 0 0

0 1027 1624 1696 1668 1745 1394 1565 1053

93 140 68 128 84 86 180 85 206

176

39

1721

190

197

89

1693

68

6

benzene. T h e process s t i l l is n o t m o r e efficient w i t h respect t o t h e e c o n o m i c a l l y c r i t i c a l r e a g e n t — t r i c h l o r o s i l a n e — i n a s m u c h as m o r e s i l i c o n t e t r a c h l o r i d e t h a n t h e d e s i r e d product is formed. T h i s i s i n h e r e n t i n t h e r e a c t i o n because, f o r e v e r y m o l e c u l e o f t r i c h l o r o s i l a n e r e p r e s e n t e d i n s i l y l a t i o n , one m o r e is c o n s u m e d b y t h e h y d r o g e n c h l o ride formed. T h e ideal reaction i s : PhCl + 2 HSiCl ->PhSiCl + SiCl + H 3

3

4

2

I t i s a c c o m p a n i e d b y r e a r r a n g e m e n t o f t r i c h l o r o s i l a n e as a side r e a c t i o n w h i c h also generates s i l i c o n t e t r a c h l o r i d e . T w o series o f r u n s o f 6 - a n d 2 - h o u r d u r a t i o n o v e r t h e t e m p e r a t u r e r a n g e of 325° to 450° C . i n d i c a t e d incomplete reaction below 370°C. T h e 6-hour runs approached c o m p l e t e c o n s u m p t i o n o f reagents a n d p e a k y i e l d s a t a b o u t 4 1 0 ° C , t h e 2 - h o u r r u n s a t about 420°C. T h e p e a k r u n i n e a c h case is i n c l u d e d i n t h e t a b l e . T h e y i e l d s a n d efficiencies a r e close t o those c i t e d a b o v e f o r t h e 1 6 - h o u r r u n s . V a r y i n g t h e m o l e r a t i o of t r i c h l o r o s i l a n e - c h l o r o b e n z e n e f r o m 2 : 1 t o 1:2 s h o w e d n o effect u p o n y i e l d o r effi c i e n c y based u p o n t h e t r i c h l o r o s i l a n e . I n these r u n s , b y - p r o d u c t p h e n y l d i c h l o r o s i l a n e w a s p r o d u c e d i n v a r i a b l e a m o u n t s , b u t m a r k e d l y less t h a n i n t h e benzene r e a c t i o n s . A c o m p o s i t e o f t h e d i s t i l l a t i o n r e s i dues o f a d o z e n r u n s a t 4 0 0 ° C . w a s s u b j e c t e d t o a f u r t h e r f r a c t i o n a l d i s t i l l a t i o n , f r o m w h i c h s m a l l amounts of bis(trichlorosilyl)benzene ( 1 1 . 4 % of t a i l s ) , d i p h e n y l d i c h l o r o s i l a n e ( 3 9 . 4 % ) , a n d b i p h e n y l t r i c h l o r o s i l a n e ( 1 5 . 3 % ) were i s o l a t e d a n d i d e n t i f i e d (Table I X ) . A trace of chlorophenyltrichlorosilane was indicated. Preparation of Tolyltrichlorosilane. T o l y l t r i c h l o r o s i l a n e w a s p r e p a r e d i n t h e same m a n n e r as p h e n y l t r i c h l o r o s i l a n e . N i n e g r a m - m o l e s e a c h o f t o l u e n e a n d t r i c h l o r o s i l a n e w e r e h e a t e d i n a 1 4 . 4 - l i t e r steel b o m b f o r 16 h o u r s a t 420° t o 4 4 0 ° C . Eighty-two per cent o f t h e l o a d w e i g h t w a s r e c o v e r e d a n d f r a c t i o n a t e d . T h i s a f f o r d e d 0.75 g r a m m o l e o f t o l y l t r i c h l o r o s i l a n e ( 8 . 3 % t h e o r e t i c a l ) . A l s o i s o l a t e d w a s 0.64 g r a m - m o l e o f phenyltrichlorosilane. I n o t h e r p r e p a r a t i o n s o f t h i s c o m p o u n d , h a l o t o l u e n e s were e m p l o y e d t o t a k e a d vantage of t h e somewhat lower temperatures t h a t characterized t h e chlorobenzene r e a c t i o n s . T h u s , i n T a b l e I I I a r e s h o w n t h r e e r u n s o f 12 t o 13 h o u r s ' d u r a t i o n a t 3 7 0 ° t o 3 8 0 ° C . i n a 2 . 4 - l i t e r steel b o m b c h a r g e d w i t h 6 g r a m - m o l e s o f t r i c h l o r o s i l a n e and 3 gram-moles of t h e indicated halotoluene. I n r u n 283, using chlorotoluene, t h e 3 8 . 5 % y i e l d (based o n t r i c h l o r o s i l a n e c o n s u m e d ) i s c o m m e n s u r a t e w i t h t h e a n a l o g o u s p h e n y l t r i c h l o r o s i l a n e p r e p a r a t i o n s . R e d u c t i o n o f a r y l h a l i d e w a s less t h a n i n t h e c h l o r o b e n z e n e r e a c t i o n (0.53 g r a m - m o l e o f t o l u e n e f o u n d ) . T h e reactions w i t h t h e bromotoluenes were produced i n each r u n ; t h e mole ratio r o s i l a n e i n e a c h case i s v e r y n e a r l y 2.0. r a n d o m d i s t r i b u t i o n of halogen i n a system

were interesting, i n t h a t t w o compounds of tolyltrichlorosilane to tolylbromodichloT h i s fits t h e p r o b a b i l i t y c a l c u l a t i o n f o r a c o n t a i n i n g six atoms of chlorine t o one of


251

BARRY, GILKEY, AND HOOK-PREPARATION OF ARYLHALOSILANES Table III. Charge.

Reaction of Trichloroiilane with Aryl Halides 3 moles aryl halide 6 moles H S i C h Reaction Av. Still Time, Temp., Charge, Hr. °C. Grams 12 375 1173

2.4-liter autoclave HSiCh, SiCU, Grams Grams 457 148

Run -283

Aryl Halide p-Chlorotoluene

328

o-Bromotoluene

13

374

1272

131

375

335

7>-Bromotoluene

12

369

1248

131

373

Residue, Other Wt., Grams Compounds Grams Chlorotoluene 51 41 Toluene 49 Tolyl SiCU 425 BrSiCls 292 17 BrzSiCh + toluene 275 Tolyl SiCU 81 Tolyl SiBrCh 51 BrSiCh 235 18 Br SiCh + toluene 275 Tolyl SiCU 107 Tolyl SiBrCh 64 Chloroethylbenzene 132 42 Ethylbenzene 70 Ethylphenyl SiCls 409 Cumylchloride 100 29 Cumene 55 Cumyl SiCle 432 Biphenyl 319 26 w-Biphenyl-SiCls 176 p-Biphenyl-SiCh 84 Biphenyl 329 23 ra-Biphenyl-SiCh 131 p-Biphenyl-SiCh 57


2

288

Chloroethylbenzene

12

375

1210

124

405

289

Cumylchloride

12

375

1253

191

374

358

2-Chlorobiphenyl

16

373

1316

185

479

360

4-Chlorobiphenyl

14

374

1168

102

435

b r o m i n e . T h e p - b r o m o t o l u e n e s h o w e d a h i g h e r y i e l d t h a n t h e o r t h o i s o m e r (14.3 a n d 1 0 . 4 % , r e s p e c t i v e l y ) , b u t b o t h a r e f a r less efficient t h a n t h e c h l o r o t o l u e n e r e a c t i o n . T h e l o w y i e l d s a r e reflected i n l a r g e a m o u n t s c f b y - p r o d u c t t e t r a c h l o r o s i l a n e , b r o m o trichlorosilane (boiling point 8 0 ° C ) , dibromocichlorosilane (boiling point 1 0 4 . 5 ° C ) , a n d t o l u e n e . I n e a c h r u n , o v e r 2 m o l e s o f t h e l a t t e r were f o r m e d b y t h e easy r e d u c tion of the bromotoluene b y trichlorosilane. Preparation of Other Aryltrichlorosilanes. T h e a d a p t a t i o n o f t h i s process t o t h e synthesis of substituted arylchlorosilanes i n general is illustrated b y the last four e x a m ples o f T a b l e I I I . T h e s e r u n s were o f 12 t o 13 h o u r s ' d u r a t i o n a t 368° t o 3 8 0 ° C . o n a b o m b charge of 3 gram-moles of a r y l halide a n d 6 gram-moles of trichlorosilane. T h e e t h y l p h e n y l t r i c h l o r o s i l a n e p r e p a r a t i o n ( r u n 2 8 8 ) i n v o l v e d t h e use o f a m i x ture of isomers of chloroethylbenzene. P r o d u c e c u t s , d i s t i l l i n g o v e r t h e range o f 129° t o 1 3 2 ° C . a t 3 0 m m . , a m o u n t e d t o 1.71 g r a m - m o l e s ( 3 4 . 3 % o n t r i c h l o r o s i l a n e ) . T h e m a j o r amount, about 1 mole, was isolated over a n a r r o w range, 130-30.5°C. at 30 m m . U l t i m a t e a n a l y s i s a g r e e d w e l l w i t h t h e o r y a s s h o w n i n T a b l e I X ; because o f i t s r e l a tively l o w boiling point, t h e compound is believed t o be the m e t a derivative. T h e h i g h e r b o i l i n g p r o d u c t p r e s u m a b l y c o n t a i n i n g :he p a r a i s o m e r w a s n o t w e l l r e s o l v e d , but i t , too, showed the expected ultimate analysis. T h e cumyltrichlorosilane was made from a m i x t u r e of chlorocumene isomers. A b o u t 6 0 % o f t h e 1.7 g r a m - m o l e p r o d u c t d i s t i l l e d o v e r t h e n a r r o w r a n g e s h o w n i n T a b l e I X . T h i s cut, a p p a r e n t l y the m e t a derivative, a n d other cuts u p t o 144°C. a t 31 m m . , p r e s u m a b l y c o n t a i n i n g t h e p a r a i s o m B r , s h o w e d a n a l y s e s i n excellent a g r e e m e n t w i t h t h e o r e t i c a l . A s w a s t h e case w i t h c h l o r o t o l u e n e , b o t h c h l o r o c u m e n e a n d c h l o r o e t h y l b e n z e n e s h o w e d less r e d u c t i o n t h a n c h l o r o b e n z e n e i n r e a c t i o n s a t c o m parable temperatures. B i p h e n y l y l t r i c h l o r o s i l a n e s were p r e p a r e d HORN t h e O- a n d p - c h l o r o b i p h e n y l s a s shown i n t h e last t w o runs of T a b l e I I I . T h e t w o isomers gave i d e n t i c a l products, a n d i n n e a r l y t h e same r a t i o s . T h e 2 - c h l o r o b i p h e n y l r u n gave a l i t t l e b e t t e r y i e l d t h a n t h e 4 - c h l o r o b i p h e n y l , b u t b o t h gave less t h a n 2 0 % t h e o r e t i c a l b a s e d o n t r i c h l o r o s i l a n e . E a c h s h o w e d a b o u t 2.1 g r a m - m o l e s o:c b i p h e n y l f r o m r e d u c t i o n o f t h e a r y l halide. T h e t w o biphenylyltrichlorosilane isomers were isolated as s h a r p cuts i n frac tional distillation. B o t h showed analytical d a t a i n good agreement w i t h theoretical, and a p p r o p r i a t e i n f r a r e d absorptions f o r t h e isomer indicated. T h e designation of the p a r a isomer is further supported b y its hig'ier boiling point a n d crystalline nature. Preparation of Phenylmethyldichlorosilane. Benzene-Methyldichlorosilane Sys-



252


tern. T h a t t h i s g e n e r a l s y n t h e t i c m e t h o d i s a p p l i c a b l e t o t h e r e a c t i o n o f m e t h y l d i chlorosilane w i t h a r y l compounds is illustrated b y the following study. T h r e e g r a m - m o l e s each of benzene a n d m e t h y l d i c h l o r o s i l a n e were h e a t e d t o g e t h e r i n a 2 . 4 - l i t e r b o m b a t 470° t o 5 3 0 ° C . f o r 8 h o u r s . D i s t i l l a t i o n o f t h e m a t e r i a l afforded a c u t of 110 g r a m s b o i l i n g i n t h e range o f 102° t o 1 0 3 ° C . a t 3 0 m m . w h i l e 2.2 g r a m m o l e s of benzene a n d 0.32 g r a m - m o l e of m e t h y l d i c h l o r o s i l a n e were r e c o v e r e d . Con s i d e r e d as m e t h y l p h e n y l d i c h l o r o s i l a n e , t h i s c u t represents a y i e l d of a b o u t 2 1 % t h e o r e t i c a l (based o n m e t h y l d i c h l o r o s i l a n e c o n s u m e d ) . T h e h i g h d e n s i t y (1.19) a n d c h l o r i n e c o n t e n t ( 3 9 . 3 % ) of t h e p r o d u c t c o m p a r e d w i t h t h e t h e o r e t i c a l (1.18 a n d 3 7 . 2 % , respectively) f o r this compound, indicated that the methylphenyldichlorosilane was c o n t a m i n a t e d w i t h a s m a l l a m o u n t of p h e n y l t r i c h l o r o s i l a n e whose b o i l i n g p o i n t i s t o o close t o a f f o r d a c l e a n s e p a r a t i o n . A s i m i l a r e x p e r i m e n t a t 329° t o 3 4 7 ° C . y i e l d e d n o p r o d u c t . A series o f f o u r r u n s w a s m a d e a t a v a r i e t y o f closely c o n t r o l l e d t e m p e r a t u r e s t o d e t e r m i n e t h e o p t i m u m . T h e s e r u n s e m p l o y e d 18 g r a m - m o l e s each o f benzene a n d m e t h y l d i c h l o r o s i l a n e i n a 14.4-liter steel b o m b . T h e y were h e l d a t a p a r t i c u l a r t e m p e r a t u r e f o r 16 h o u r s . T h e d a t a a r e s u m m a r i z e d i n T a b l e I V , f r o m w h i c h i t i s a p p a r e n t t h a t a m a x i m u m y i e l d of

Table IV.

Reactions with Methyldichlorosilane

Celle + C H S i H C l 1402 grams (18 moles) CeHe 2046 grams (17.78 moles) CHsSiHCh 3

Charge.

Run PB—121 120 119 118

Av. Still Temp., Charge, Charge HSiCls, °C. Grams Grams 3271 149 355 208 380 3244 162 405 3636 124 428 2976

14.4-liter autoclave 16-hr. reaction time CeH (CH )Residue, SiCl , CHsSiHCh, SiCU, C H S i C l , C H , CeHeSiHCh, Grams Grams Grams Grams Grams Grams Grams 362 551 133 517 126 357 526 364 550 237 691 0 506 325 634 602 509 79 630 369 286 541 562 200 74 416 780 177 5

3

C H C 1 + CH3S1HCI2 2031 grams (18.1 moles) CeH Cl 4055 grams (35.3 moles) C H S i H C h 6

Charge.

2

3

6

3

2

6

a

6

6

3

14.4-liter autoclave 16-hr. reaction time CeH Cl Grams 1527 6

PB—128 355 5989 37 ° Contaminated with CeHeSiCh.

901

2330

524

a

107

289

1010 g r a m s o f m e t h y l p h e n y l d i c h l o r o s i l a n e ( 3 3 . 2 % t h e o r e t i c a l ) i s o b t a i n e d i n t h e r a n g e of 400° t o 4 1 0 ° C . T h e product yields i n this system are generally equivalent o r s l i g h t l y i n f e r i o r t o those o f t h e b e n z e n e - t r i c h l o r o s i l a n e s y s t e m ( c o m p a r e w i t h F i g u r e 1) a n d f o l l o w t h e same t r e n d w i t h t e m p e r a t u r e . T h e p r o d u c t c u t w a s c o n t a m i n a t e d w i t h phenyltrichlorosilane, a n d considerable phenyldichlorosilane was isolated. T h e latter was probably formed from dichlorosilane arising from the t h e r m a l rearrange m e n t o f t h e m e t h y l d i c h l o r o s i l a n e . T h i s r e a r r a n g e m e n t i s reflected also i n s i g n i f i c a n t q u a n t i t i e s of t r i c h l o r o s i l a n e , s i l i c o n t e t r a c h l o r i d e , a n d m e t h y l t r i c h l o r o s i l a n e i s o l a t e d i n t h e d i s t i l l a t i o n s . E x c e s s i v e a m o u n t s o f h i g h b o i l i n g residues r e m a i n e d a f t e r i s o l a t i o n of t h e p r o d u c t c u t s . T h e y a v e r a g e a b o u t s e v e n f o l d t h e a m o u n t o f residue i n c i d e n t a l to t h e preparation of phenyltrichlorosilane i n t h e benzene-trichlorosilane system. Chlorobenzene-Methyldichlorosilane System. I n a n orientation experiment, a m i x t u r e o f 4 g r a m - m o l e s of m e t h y l d i c h l o r o s i l a n e w i t h 2 o f c h l o r o b e n z e n e w a s h e a t e d i n a 2 . 4 - l i t e r b o m b f o r 16 h o u r s a t 445° t o 4 6 0 ° C . D i s t i l l a t i o n of t h e b o m b p r o d u c t a f f o r d e d a c u t of 116 g r a m s b o i l i n g a t 1 1 4 - 1 5 ° C . a t 5 0 m m . , w h i c h s h o w e d a specific g r a v i t y ( 2 0 ° C . / 2 0 ° C . ) of 1.200 a n d a c h l o r i n e a n a l y s i s o f 3 9 . 5 % , b o t h t o o h i g h f o r pure methylphenyldichlorosilane. B y calculation, t h e chlorine value indicated t h e presence of 15.7 m o l e % p h e n y l t r i c h l o r o s i l a n e t o be p r e s e n t . T h i s is c o n f i r m e d b y m o l e v o l u m e c a l c u l a t i o n s f r o m w h i c h a specific g r a v i t y of 1.204, i n a g r e e m e n t w i t h t h a t f o u n d , i s c o m p u t e d f o r a m i x t u r e o f 84.3 m o l e % m e t h y l p h e n y l d i c h l o r o s i l a n e w i t h 15.7 m o l e % p h e n y l t r i c h l o r o s i l a n e . T h e p r o d u c t y i e l d w a s o n l y a b o u t 1 6 % t h e o r e t i c a l b a s e d o n c o n s u m e d m e t h y l d i c h l o r o s i l a n e . T h e l o w y i e l d w a s reflected


BARRY, GILKEY, AND HOOK-PREPARATION OF ARYLHALOSI LANES

253

i n b y - p r o d u c t s , 2.04 g r a m - m o l e s of m e t h y l t r i c h l o r o s i l a n e a n d 0.12 g r a m - m o l e o f dimethyldichlorosilane from thermal redistribution reaction of methyldichlorosilane. O f the 2 moles o f c h l o r o b e n z e n e c h a r g e d , 1.3 moles w a s r e d u c e d t o benzene. I n one l a r g e r i m , 35.3 g r a m - m o l e s o f me1 h y l d i c h l o r o s i l a n e a n d 18.1 g r a m - m o l e s of c h l o r o b e n z e n e were h e a t e d t o g e t h e r i n a 14.4-liter steel b o m b f o r 16 h o u r s a t 350° to 360°C. T h e d a t a are p r e s e n t e d a t t h e b o t t o m o f T a b l e I V . T h e p r o d u c t ( 8 . 0 m o l e s ) c o r r e s p o n d s t o a y i e l d of 2 9 . 7 % based u p o n c o n s u m e d s i l a n e . O n l y a t r a c e of t r i c h l o r o s i l a n e was p r o d u c e d , b u t 3 7 % of t h e c h l o r o b e n z e n e c h a r g e d ( o r 4 3 % of t h e 15.5 g r a m - m o l e s c o n s u m e d ) was r e d u c e d t o benzene. I t appears that m e t h y l d i c h l o r o s i l a n e i s a m o r e p o w e r f u l r e d u c i n g age i t t h a n t r i c h l o r o s i l a n e ( c o m p a r e T a b l e Π).


Catalyzed Reactions Preparation of Phenyltrichlorosilane. T h e p r e p a r a t i o n of a r y l c h l o r o s i l a n e s f r o m hydrogen-containing chlorosilanes a n d t h e a p p r o p r i a t e benzenoid compounds w a s successful, b u t a c c o m p a n i e d b y a n u m b e r o i d i s a d v a n t a g e s . T e m p e r a t u r e s i n t h e o r d e r of 4 0 0 ° C . were r e q u i r e d . O p e r a t i n g pressures w e r e c o n s e q u e n t l y h i g h ( r a n g i n g u p t o 2000 p . s . i . ) . T h e y i e l d s o f desirec. p r o d u c t w e r e o n l y f a i r , b y - p r o d u c t s were excessive, p a r t i c u l a r l y those c o m i n g f r o m t h e r m a l d e s t r u c t i o n of t h e s t a r t i n g c h l o r o h y d r o s i l a n e . T h e efficiencies w e r e c o r r e s p o n d i n g l y l o w . B e n z e n e - T r i c h l o r o s i l a n e - M X System. Τ 3 i m p r o v e u p o n t h e process, c a t a l y z e d s y s t e m s were i n v e s t i g a t e d . T h e i n i t i a l w o r k e m b r a c e d c a t a l y s t s o f t h e F r i e d e l - C r a f t s t y p e . A c c o r d i n g l y , a series o f e x p e r i m e n t s was r u n w i t h a v a r i e t y o f c a t a l y s t s , e a c h o v e r a r a n g e of t e m p e r a t u r e s . A l l o t h e r v a r i a b l e s were h e l d c o n s t a n t . T h e r e a c t a n t s c h a r g e d t o t h e 1 4 . 4 - l i t e r steel b o m b c o m p r i s e d 1402 g r a m s o f benzene a n d 2440 grams of trichlorosilane (18 gram-moles each). C a t a l y s t a m o u n t was h e l d i n t h e o r d e r of 1 t o 2 % o f t o t a l c h a r g e (safely a b o v e a d e t e r m i n e d m i n i m u m r e q u i r e m e n t ) . R e a c t i o n t i m e w a s 16 h o u r s . T h e d a t a p e i t i n e n t t o t h i s s t u d y a r e c o m p i l e d i n T a b l e V . T h e t e m p e r a t u r e s o f i n d i v i d u a l r u i s were h e l d g e n e r a l l y w i t h i n ± 8 ° C . of t h e r e c o r d e d figure. T h e pressures were autogenous, t h e m a x i m u m b e i n g r e c o r d e d i n each case. T h e r e p o r t e d results a r e based u p o n c a r e f u l f r a c t i o n a l d i s t i l l a t i o n s u s i n g a c o l u m n o f 2 0 t h e o r e t i c a l p l a t e r a t i i g . D i s c u s s i o n o f t h e results w i l l b e f a c i l i t a t e d b y reference t o F i g u r e 3, w h i c h delineates t h e s i g n i f i c a n t o b s e r v a t i o n s . 3

A l u m i n u m C h l o r i d e Catalyst. T h e use o f a l u m i n u m c h l o r i d e p r o m o t e d t h e r e a c t i o n of benzene w i t h t r i c h l o r o s i l a n e a t l o w e r t e m p e r a t u r e s t h a n w e r e o p e r a b l e w i t h out i t . Whereas the u n c a t a l y z e d reaction showed only a trace of p r o d u c t a t 3 4 5 ° C , t h e use o f a l u m i n u m c h l o r i d e afforded a n a p p a r e n t m a x i m u m o f n e a r l y 4.5 g r a m moles a t t h i s t e m p e r a t u r e . A s i g n i f i c a n t b u t d i m i n i s h i n g y i e l d w a s r e a l i z e d a s t h e t e m p e r a t u r e was d r o p p e d t o 3 0 5 ° C . Despite operability a t lower temperature and c o n s e q u e n t l y l o w e r p r e s s u r e , t h e u l t i m a t e y i e l d s of t h i s c a t a l y z e d s y s t e m w e r e n o t i m p r o v e d o v e r t h e u n c a t a l y z e d , n o r was t h e b y - p r o d u c t s i l i c o n t e t r a c h l o r i d e s u p p r e s s e d . L a r g e d i s t i l l a t i o n residues a p p e a r e d a n d c o n s i d e r a b l e d e c o m p o s i t i o n o c c u r r e d d u r i n g t h e d i s t i l l a t i o n , a t t r i b u t a b l e t o cleavage c a t a l y z e d b y a l u m i n u m c h l o r i d e a n d i t s c o m p l e x e s i n t h e p o t residues. A p r e l i m i n a r y flash d i s t i l l a t i o n f r o m t h e a l u m i n u m c h l o r i d e a f f o r d e d some r e l i e f ; so d i d s e p a r a t i o n o f t h e a l u m i n u m c h l o r i d e as a e u t e c t i c w i t h s o d i u m c h l o r i d e . H o w e v e r , n e i t h e r offered a c o m p l e t e l y c l e a n s o l u t i o n t o t h e problem. B o r o n F l u o r i d e Catalyst. T h e p r e c e d i n g o b s e r v a t i o n s suggested a s e a r c h f o r a m o r e v o l a t i l e c a t a l y s t o r o n e whose c o m p l e x e s w o u l d b e less d e s t r u c t i v e d u r i n g d i s t i l l a t i o n . T h e d a t a o n b o r o n fluoride c a t a l y s i s p r o v e d v e r y p r o m i s i n g . O n e m i n o r , but practically important, difficulty appearec. W h i l e excellent y i e l d s o f p h e n y l t r i c h l o r o s i l a n e were o b t a i n e d , p r o d u c t i s o l a t i o n w a s c o m p l i c a t e d b y t h e presence o f phenyldichlorofluorosilane and phenylchlorodifluorosilane. F o r consideration of p r o d u c t y i e l d s , t h e m o l e e q u i v a l e n t w e i g h t s of thase c o m p o u n d s c a l c u l a t e d as p h e n y l t r i -



1

79 44 40 37 50 39 40 43 90 44 40 50 45 42 41

46 81 64 94 50 39 52 41 113 47

226 229 251 261 275 276 278 290 299 311 318 332 354 370 399

264 295 305 317 323 329 352 360 375 375

Av. Temp., °C. 305 324 346 364 375 400

Also 75 grams CeH»SiClF2.

3

3

3

3

3

3

3

3

8

3

3

BC1 BC1 BC1 BCla BC1 BC1 BC1 BC1 BCls BC1 BC1 BC1 BC1 BC1 BC1

304 296 297 315 316 312 298 317 284 313 288 299 289 300 305

3

3

3

3

3

3

3

3

3

BF BFs BF BF BF BF BF BF BF BF

Catalyst, Grams A1CU 38 A1CU 38 AlCls 38 A l C h 38 AlCh 38 A l C h 39

290 291 279 292 280 293 281 294 282 283

Run PB—202 203 274 275 276 306

420 500 600 780 880 900 840 900 980 1100 1230 1010 1240 1400 1500

860 1020 1020 1100 1150 1180 1400 1400 1450 1380

1500

Max. Press., P.S.I. 1020 1250

3571 3405 3384 3440 3358 3400 3428 3405 3422 3378 3464 3415 3443 3435 3292

3358 3200 3444 3337 3348 3420 3392 3331 3297 3456 2001 1911 1552 890 396 450 320 321 420 475 455 421 408 347 307

298 359 289 329 449 399 518 268 259 331

HSiCh, Grams 773 636 418 164 271 281

97 64 111 254 412 389 344 421 515 486 495 505 525 581 618

374 458 514 622 545 533 530 602 668 585

SiCU, Grams 543 462 597 343 559 539

6

1402 grams (18 moles) C i H 2440 grams (18 moles) HSiCli

1079 1146 1108 826 569 585 588 746 639 661 694 606 620 680 555

565 614 644 673 83 631 767 690 731 705

CeHe, Grams 946 851 928 946 807 691

0 0 412 1042 1452 1510 1583 1498 1357 1360 1218 1415 1435 1131 1069

1343 1054 1358 1024 1043 1185 959 1304 854 1265

CeHiSiCh, Grams 619 847 943 661 932 927 6

2

143 128 145 100* 81 77 146 67 214

CeH SiCl F, Grams

14.4-liter autoclave 16-hr. reaction item

C a t a l y z e d Reaction of Trichlorosilane with Benzene

Still Charge, Grams 3609 3586 3364 2405 2853 3345

Charge.

Table V.


208 168 166 310 426 368 303 353 416 380 564 380 315 377 586

379 480 341 377 297 447 446 196 272 326

Residue, Grams 255 383 41 86 248 705 6

0 0 412 1042 1452 1510 1583 1498 1357 1360 1218 1415 1435 1131 1069

1498 1182 1515 1222 1131 1268 1117 1377 1086 1265

6

8

Product as C H SiCl , Grams 619 847 943 661 932 927

0 0 3.71 4.10 3.53 3.88 4.60 3.56 2.64 2.80 2.46 2.80 2.74 2.39 1.73

4.00 2.58 2.95 1.96 2.08 2.37 2.09 2.28 1.60 2.16

SiCU Wt. Ratio 1.14 1.83 1.58 1.93 1.67 1.72

CeHsSiCla

CO

3

ζ π

Π

Ζ

Ό

>



255

REACTION TEMPERATURE, *C.

Figure 3 .

Catalyzed reaction of trichlorosilane with benzene

c h l o r o s i l a n e were i n c l u d e d i n t h e r e c o r d e d p r o d u c t . Because the data o n catalysis w i t h b o r o n f l u o r i d e were i n d i s t i n g u i s h a b l e f r o m those o n b o r o n c h l o r i d e a n d because the latter m u s t have been formed even i n t h e present system b y r a n d o m halide r e a r r a n g e m e n t , t h i s s y s t e m i s discussed i n c o n j u n c t i o n w i t h t h e b o r o n c h l o r i d e e x periments t o follow. B o r o n C h l o r i d e C a t a l y s t . T h e d a t a of T a b l e V a n d t h e i r p l o t s i n F i g u r e 3 s h o w b o r o n c h l o r i d e ( o r b o r o n fluoride) t o b e o u t s t a n d i n g i n c a t a l y s i s o f t h e r e a c t i o n o f benzene w i t h t r i c h l o r o s i l a n e . T h e t h r e s h o l d t e m p e r a t u r e f o r t h e r e a c t i o n i s l o w e r e d to 240°C. T h e y i e l d c u r v e f o r t h e b o r o n h a l i d e - c a t a l y z e d r u n s shows a m a x i m u m i n t h e r a n g e o f 265° t o 2 8 0 ° C . T h e y i e l d s o f p h e n y l t r i c h l o r o s i l a n e a r e s i g n i f i c a n t l y b e t t e r t h a n those o b t a i n e d w i t h o u t c a t a l y s t o r w i t h a l u m i n u m c h l o r i d e . F u r t h e r m o r e , p r o d u c t i o n o f s i l i c o n t e t r a c h l o r i d e i s s u p p r e s s e d , as i s e v i d e n t b y s t u d y i n g t h e p l o t o f phenyltrichlorosilane-silicon tetrachloride weight ratios. A t o p t i m u m temperatures, these l i e c o m f o r t a b l y close t o 4.0 f o r b o r o n c h l o r i d e c a t a l y s i s as o p p o s e d t o 1.8 w i t h a l u m i n u m c h l o r i d e o r less t h a n 1.5 w i t h o u t c a t a l y s t . I n c o n t r a s t t o t h e i s o l a b l e y i e l d s of p h e n y l d i c h l o r o s i l a n e n o t e d i n t h e u n c a t a l y z e d e x p e r i m e n t s , t h e b o r o n h a l i d e - c a t a lyzed runs showed only a little of this by-product. I t was detected i n t h e b o m b product v i a infrared spectroscopy. B y reference t o T a b l e V , i t i s seen t h a t t h e b o r o n h a l i d e - c a t a l y z e d r u n s a r e c h a r a c t e r i z e d b y h i g h e r d i s t i l l a t i o n residues, a b o u t t h r e e f o l d t h e a m o u n t s o b s e r v e d i n u n c a t a l y z e d o p e r a t i o n . H o w e v e r , these residues c o n t a i n u s e f u l b y - p r o d u c t s a n d t h e i r s i l y l a t i o n v a l u e s s h o u l d b e i n c l u d e d i n a n y assay o f t h e r e a c t i o n efficacy. F o r e x a m p l e , w h e n t h e d i s t i l l a t i o n residue o f s i x r u n s ( 2 8 8 , 2 9 6 - 7 , 3 0 4 - 5 , 3 1 2 ) were combined t o afford enough still l o a d f o r a f u r t h e r careful fractional distillation, t h e f o l l o w i n g were i s o l a t e d : p h e n y l t r i c h l o r o s i l a n e ( 8 . 9 % o f s t i l l l o a d ) ; d i p h e n y l d i c h l o r o silane ( 1 4 . 0 % ) ; h e x a c h l o r o d i s i l y l b e n z e n e ( 1 4 . 9 % ) ; phenylpentachlorodisilylbenzene ( 9 . 3 % ) ; remainder, a black t a r incapable of further resolution. Identification of these c o m p o u n d s , t w o o f t h e m i s o l a t e d a s b o t h l i q u i d a n d c r y s t a l l i n e i s o m e r s , a n d t h e i r characterizations will be found i n Table I X . T h e boron-catalyzed system is m a r k e d l y superior t o the uncatalyzed. F o r c o m p a r i s o n , e v a l u a t i o n o f t h e best b o r o n - c a t a l y z e d r u n ( 3 1 2 ) i s s u m m a r i z e d i n t h e f o l lowing table.



256

Boron-Catalyzed Reaction Actual


Phenyltrichlorosilane yield, % Trichlorosilane basis Benzene basis Silylation yield, % Trichlorosilane basis Benzene basis Silicon balance, gram-atoms Phenyl balance, gram-moles

Potential

49.8 69.6

58.0 87.0

56.6 79.2 14.38 15.56

65.8 98.7 17.21 17.60

T h e a c t u a l results i n t h e first c o l u m n r e p r e s e n t p r o d u c t s i s o l a t e d f r o m t h e s t i l l l o a d . T h e p o t e n t i a l results a r e based u p o n a c o r r e c t i o n o f t h e d i s t i l l a t i o n d a t a t o a c c o u n t f o r m e c h a n i c a l losses, p a r t i c u l a r l y i n d i s c h a r g i n g t h e b o m b . Thephenyltri c h l o r o s i l a n e y i e l d s a r e based u p o n reagents c o n s u m e d ; t h e s i l y l a t i o n y i e l d s r e l a t e the n u m b e r o f S i — C b o n d s e s t a b l i s h e d ( i n p r o d u c t a n d i d e n t i f i e d b y - p r o d u c t s ) t o the mole-reagent c o n s u m p t i o n ; the silicon balance is a total g r a m - a t o m count i n a l l identifiable compounds, remembering t h a t each gram-mole of silicon tetrachloride represents 1.33 g r a m - a t o m s of s i l i c o n ; t h e p h e n y l b a l a n c e c o u n t s a l l p h e n y l g r o u p s identifiable. B e c a u s e i n these systems l o w e r t e m p e r a t u r e s were r e q u i r e d t h a n i n t h e u n c a t a l y z e d s y s t e m s , t h e o p e r a t i n g pressures were l o w e r . T h e y v a r i e d c o n s i s t e n t l y w i t h t e m p e r a t u r e f r o m a b o u t 4 0 0 p . s . i . a t 2 2 5 ° C . t o 1500 p . s . i . a t 4 0 0 ° C . Preparation of Aryltrichlorosilanes. T o l u e n e - T r i c h l o r o s i l a n e - B o r o n Chloride System. C o m p a r e d w i t h benzene, t h e g e n e r a l l y g r e a t e r r e a c t i v i t y of t o l u e n e u n d e r o n i u m i o n a t t a c k m a d e i t a p o i n t of i n t e r e s t i n t h e s y n t h e s i s o f a r y l t r i c h l o r o s i l a n e s . A c c o r d i n g l y , t h e r e a c t i o n of t o l u e n e w i t h t r i c h l o r o s i l a n e w as s t u d i e d i n e x a c t l y t h e same m a n n e r as f o r benzene. T h e pertinent data are condensed i n T a b l e V I a n d the s i g n i f i c a n t t r e n d s p l o t t e d i n t h e t w o c u r v e s of F i g u r e 4. 7

Table VI.

Catalyzed Reaction of Trichlorosilane with Toluene

Charge.

Run PB—361 343 344 345 301 346 347

1656 grams (18 moles) C6ÏI5CH3 2440 grams (18 moles) HSiCla B C h : 1.0-1.3% of charge

Av. Still Temp., Charge, HSiCh, °C. Grams Grams 222 3880 2251 242 3799 966 3869 261 438 286 3999 587 300 3870 433 312 3986 374 279 351 3915

SiCU, MeSiCh, Grams Grams 0 0 232 0 420 0 505 39 459 28 89 565 638 157

14.4-liter autoclave 16-hr. reaction time

C H , C H CH , Grams Grams 1384 0 0 843 0 689 28 648 35 776 34 714 52 701 6

6

6

6

3

C6H SiCl , Grams 0 0 0 33 80 104 135 6

3

CH C H SiCl , Grams 0 1475 1772 1534 1376 1330 1147 3

6

4

3

Residue, Grams 180 232 443 578 590 686 776

T h e t h r e s h o l d t e m p e r a t u r e f o r t h e r e a c t i o n l i e s b e t w e e n 222° a n d 2 4 2 ° C , some 2 0 ° C . l o w e r t h a n f o r t h e benzene r e a c t i o n s . T h e y i e l d o f t o l y l t r i c h l o r o s i l a n e a p p r o a c h e s a m a x i m u m n e a r 2 6 0 ° C , also l o w e r t h a n f o r benzene r e a c t i o n s . A t h i g h e r t e m p e r a t u r e s , t h e y i e l d s b e c o m e p r o g r e s s i v e l y l o w e r because o f t h e t h e r m a l r e a r r a n g e m e n t of t r i c h l o r o s i l a n e , reflected i n p r o g r e s s i v e l y g r e a t e r a m o u n t s of s i l i c o n t e t r a c h l o r i d e . A t t e m p e r a t u r e s a b o v e 2 8 5 ° C , p h e n y l t r i c h l o r o s i l a n e , benzene, a n d m e t h y l t r i c h l o r o s i l a n e m a k e t h e i r a p p e a r a n c e , p o s s i b l y as scission p r o d u c t s o f a n i n t e r m e d i a t e o r t h o - a d d u c t discussed i n t h e t h e o r e t i c a l section b e l o w . T h e m a x i m u m y i e l d o f t o l y l t r i c h l o r o s i l a n e i n t h i s series a m o u n t e d t o 7.86 g r a m moles o r 5 3 . 2 % theoretical, based u p o n unrecovered trichlorosilane. H o w e v e r , t h e h i g h e s t p r o d u c t - s i l i c o n t e t r a c h l o r i d e r a t i o is o b s e r v e d i n r u n 3 4 3 , nearest t h e t h r e s h o l d t e m p e r a t u r e . H e r e t h e r e a c t i o n w a s f a r s h o r t of c o m p l e t i o n i n t h e 1 6 - h o u r r e a c t i o n t i m e a t 2 4 2 ° C , b u t i t p r o v e d t h e m o s t efficient of t h e series since t h e 6.54 g r a m - m o l e y i e l d represents 6 0 . 4 % theoretical based u p o n consumed trichlorosilane. Mesitylene-Trichlorosilane-Boron C h l o r i d e System. I t was interesting t o s t u d y t h i s r e a c t i o n , i n a s m u c h as scission o f a n o r t h o - a d d u c t ( ^ - e l i m i n a t i o n ) affords a reasonable e x p l a n a t i o n f o r f o r m a t i o n o f some p h e n y l c o m p o u n d s i n t h e t o l u e n e r u n s



BARRY. GILKEY, AND HOOK-PREPARATION OF ARYLHALOSILANES

257

a b o v e . W i t h m e s i t y l e n e t h e a t t a c k i n g g r o u p c a n o n l y go o r t h o t o a m e t h y l g r o u p o n the benzene r i n g . A m i x t u r e o f 2.08 g r a m - m o l e s o f m e s i t y l e n e a n d 4.0 g r a m - m o l e s of t r i c h l o r o s i l a n e was b o m b e d w i t h 0.08 g r a m - m o l e o f b o r o n t r i c h l o r i d e i n a 2 . 4 - l i t e r u n i t , f o r 15 h o u r s a t 308° t o 3 1 6 ° C . W h i l e the t e m p e r a t u r e was a c c i d e n t a l l y h i g h e r t h a n i n t e n d e d , the r e a c t i o n was s l u g g i s h a n d o n l y 0.34 g r a m - m o l e of m e s i t y l t r i c h l o r o silane was o b t a i n 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 t w a s i s o l a t e d as a c u t a t 1 4 2 - 2 . 5 ° C . at 3 0 m m . a n d was i d e n t i f i e d b y p r o p e r a n a l y t i c a l d a t a as s h o w n i n T a b l e I X . I t is significant t h a t 0.34 g r a m - m o l e o f x y l e n e was r e c o v e r e d i n l o w - b o i l i n g f o r e c u t s . A n 8 6 - g r a m c u t b o i l i n g o v e r the range of 127° t o 1 3 4 ° C . a t 3 0 m m . was i d e n t i f i e d a s x y l y l t r i c h l o r o s i l a n e . M o s t s i g n i f i c a n t l y , 0.42 g r a m - m o l e o f m e t h y l t r i c h l o r o s i l a n e w a s found. I t is t o be e x p e c t e d i n the e v e n t o f o r t h o e l i m i n a t i o n , w h i c h m u s t b e t h e reason for the o b s e r v e d x y l e n e a n d its d e r i v a t i v e ; the a m o u n t i s large c o m p a r e d w i t h toluene r u n s , as e x p e c t e d , because m e s i t y l e n e offers o n l y o r t h o sites f o r r e a c t i o n . Biphenyl-Trichlorosilane-Boron Chloride System. Biphenylyltrichlorosilane was m a d e b y h e a t i n g a m i x t u r e of 18 g r a m - m o l e s e a c h o f b i p h e n y l a n d t r i c h l o r o s i l a n e c o n t a i n i n g 0.5 g r a m - m o l e of b o r o n t r i c h l o r i d e i n a 14.4-liter b o m b f o r 16 h o u r s a t 265° t o 2 7 0 ° C . T h e b o m b was i n c o m p l e t e l y d i s c h a r g e d , b u t 4648 g r a m s o f p r o d u c t g a v e o n d i s t i l l a t i o n 2.21 g r a m - m o l e s of m - b i p h e n y l y l t r i c h l o r o s i l a n e a n d 3.97 g r a m - m o l e s of t h e c r y s t a l l i n e p a r a i s o m e r (6.18 g r a m - m o l e t o t a l ) . A l l o w i n g for 2.16 g r a m - m o l e s of r e c o v e r e d t r i c h l o r o s i l a n e , the y i e l d is c a l c u l a t e d t o b e c o n s e r v a t i v e l y 3 9 . 0 % t h e o r e t i cal. Phenyltriehlorosilane-Trichlorosilane-Boron Chloride System. P h e n y l t r i c h l o r o -



Still Charge, Grams 3566 3455 3427 3574 3495 3511 3519

Av. Temp., °C. 144 151 160 182 203 241 274 302

Av. Temp., °C. 150 169 177 186 206 241 250

Run PB—395 413 394 393 386 385 384 357

Run PB—412 398 418 383 397 366 367

HSiCU, Grams 0 0 0 60 0 50 51 93

HSiCls, Grams 0 0 0 27 0 141 85

3

3

2

2

3

3

2 l

3

3

3

2

3

2

2

6

6

3

14.4-liter autoclave 2070 grams (18 moles) C H S i H C l 16-hr. reaction time 1656 grams (18 moles) CeHoCHs BC1 : 0.7-1.0% of charge C H CH , (CH ) SiCl , CH SiCl , CH SiHCl Grams Grams Grams Grams 1469 1828 79 0 1251 947 169 88 1051 510 374 198 1093 901 915 189 403 329 932 207 346 234 986 309 341 187

3

6

CH C H SiCl Grams 0 46 42 79 62 38 40 4

CeHsSiCls, Grams 0 0 0 38 39 25 106 210

Catalyzed Reaction of Methyldichlorosilane with Toluene

Charge.

Table VIII.

Still Charge, Grams 3343 2822 3332 3265 3268 3242 3221 2854

14.4-liter autoclave 1402 grams (18 moles) CeHe 16-hr. reaction time 2070 grams (18 moles) C H S i H C h B C h : 1.0-1.3% of charge CeHe, (CH ) SiCl , CHjSiCla, CHaSiHCh, Grams Grams Grams Grams 1815 1295 0 0 1179 888 1299 1044 59 95 947 59 198 664 819 34 263 615 677 57 458 250 698 94 435 187 640 151 307 227

Catalyzed Reaction of Methyldichlorosilane with Benzene

Charge.

Table VII.


3

3

6

6

3

3

2

2

Residue, Grams 199 146 175 288 381 789 1136 1187

C H C H 4 ( C H ) S i C l , LResidue, Grams Grams 161 0 333 380 316 731 182 873 430 1003 579 774 587 662

6

C H (CH )SiCl , Grams 0 299 427 771 1035 761 289 139

ζ η

Π

> Ζ

Ό

BARRY, GILKEY, AND HOOK-PREPARATION OF ARYLHALOSILANES

259

silane (3810 g r a m s ) , t r i c h l o r o s i l a n e (2440 g r a m s ) , a n d b o r o n c h l o r i d e (64 g r a m s ) w e r e b o m b e d a t 2 9 0 ° t o 3 1 0 ° C . f o r 16 h o u r s . T h e 5917 g r a m s of m a t e r i a l d i s c h a r g e d f r o m the r e a c t o r c o n t a i n e d u n r e a c t e d t r i c h l o r o s i l a n e (940 g r a m s ) , p h e n y l t r i c h l o r o s i l a n e (1354 g r a m s ) , b y - p r o d u c t benzene ( 5 7 g r a m s ) , a n d t e t r a c h l o r o s i l a n e (1132 g r a m s ) . I n a d d i t i o n , t h e following c o m p o u n d s boiling above phenyltrichlorosilane were isolated :

(C H ) SiCl m-Cl.,SiC H SiCl p-Cl SiC H SiCl CeHôSiC^Ce^SiCls Cl SiC H SiCl C H SiCl 6

5

2

2

6

3


3

6

6

4

4

3

4

?

2

6

4

3

Grams 80 476 141 356 73

F i v e h u n d r e d a n d t w e n t y g r a m s o f h i g h e r b o i l i n g m a t e r i a l r e m a i n e d a s s*Ul r e s i d u e . T h e first f o u r o f t h e c o m p o u n d s were f o u n d i n t h e s t i l l residues o f b o r o n chloride-catalyzed benzene-trichlorosilane reaction products. T h e last was p r o b a b l y t h e r e also, b u t i n a m o u n t t o o s m a l l f o r i s o l a t i o n . T h e f o u r n e w c o m p o u n d s a r e characterized i n Table I X . Preparation of Arylmethyldichlorosilanes. T h a t the method just described f o r the silylation of benzenoid compounds b y trichlorosilane m a y be extended more generally t o other chlorohydrosilanes, was established b y the following w o r k . Pro cedures were i d e n t i c a l w i t h those of t h e f o r e g o i n g e x p e r i m e n t s e m p l o y i n g b o r o n c h l o r i d e as a c a t a l y s t . Benzene-Methyldichlorosilane-Boron Chloride System. A series of r u n s w a s m a d e i n t h e 1 4 . 4 - l i t e r b o m b u s i n g 18 g r a m - m o l e s each o f b e n z e n e a n d m e t h y l d i c h l o r o silane w i t h 1.0 t o 1.5% b o r o n c h l o r i d e o n t o t a l l o a d w e i g h t . T h e r u n s were o f 16 h o u r s ' d u r a t i o n a n d c o v e r e d a w i d e range of r e a c t i o n t e m p e r a t u r e s . Pressures ranged f r o m 150 p . s . i . a t 1 5 0 ° C . t o 1300 p . s . i . a t 3 0 0 ° C . T a b l e V I I s u m m a r i z e s t h e d a t a essential for d i s c u s s i o n . R e a c t i o n o f m e t h y l d i c h l o r o s i l a n e w i t h b e n z e n e c o m m e n c e s a t a m u c h l o w e r t e m p e r a t u r e (145° t o 1 5 1 ° C . ) t h a n t h e c o r r e s p o n d i n g t r i c h l o r o s i l a n e r e a c t i o n w i t h e i t h e r benzene o r t o l u e n e , b u t the t h r e s h o l d is m u c h less s h a r p l y defined (see F i g u r e 5 ) . W i t h increase i n t e m p e r a t u r e , t h e y i e l d of m e t h y l p h e n y l d i c h l o r o s i l a n e increases t o a m a x i m u m a t a b o u t 203 ° C , t h e n f a l l s off a t h i g h e r t e m p e r a t u r e s as r e d i s t r i b u t i o n r e a c t i o n s b e t w e e n the d e s i r e d p r o d u c t a n d t h e i n i t i a l m e t h y l d i c h l o r o silane y i e l d p r o g r e s s i v e l y m o r e t r i c h l o r o s i l a n e , p h e n y l t r i c h l o r o s i l a n e , m e t h y l t r i c h l o r o silane, a n d d i m e t h y l d i c h l o r o s i l a n e . E x t r a o r d i n a r i l y h i g h residues were o b s e r v e d a t t e m p e r a t u r e s a b o v e 2 4 0 ° C . T h e best a t t e m p t a t p l o t t i n g a p r o d u c t - b y - p r o d u c t r a t i o w o u l d relate t h e s u m o f t h e t w o p h e n y l s i l a n e s ( b o t h u s e f u l s i l y a t i o n p r o d u c t s ) t o the s u m o f t h e t w o m e t h y l s i l a n e s . A s p l o t t e d a g a i n s t t e m p e r a t u r e i n F i g u r e 5, t h e c u r v e seems t o p e a k a t a b o u t 2 0 3 ° C , w h e r e t h e m a x i m u m y i e l d also o c c u r s . T h e 5.60 g r a m - m o l e p r o d u c t represents a y i e l d of 4 4 . 3 % t h e o r e t i c a l w h e n a l l o w a n c e i s m a d e f o r r e c o v e r y o f 615 g r a m s (5.35 g r a m - m o l e s ) of m e t h y l d i c h l o r o s i l a n e . Toluene-Methyldichlorosilane^Boron C h l o r i d e System. T h e reaction of toluene w i t h methyldichlorosilane was almost i d e n t i c a l i n character t o the foregoing benzene r e a c t i o n . T h e essential d a t a are c o n d e n s e d i n T a b l e V I I I , a n d p l o t t e d i n F i g u r e 5 a l o n g w i t h c o r r e s p o n d i n g d a t a o n t h e b e n z e n e r e a c t i o n . T h e t w o sets o f d a t a a r e h a r d l y d i s t i n g u i s h a b l e . T h e t h r e s h o l d t e m p e r a t u r e lies i n t h e r a n g e of 1 5 0 ° C , b u t is n o t s h a r p l y defined. T h e y i e l d rises w i t h t e m p e r a t u r e t o a m a x i m u m of 4.9 g r a m moles i n the v i c i n i t y of 2 0 6 ° C . H o w e v e r , the best p r o d u c t - b y - p r o d u c t ratio appears i n t h e v i c i n i t y o f 1 8 6 ° C . a n d , i n d e e d , t h e r e a c t i o n efficiency was best a t t h i s t e m p e r a ture (run 383). H e r e , t h e t o l y l m e t h y l d i c h l o r o s i l a n e y i e l d w a s 4.26 g r a m - m o l e s ; a l l o w i n g f o r 901 g r a m s (7.84 g r a m - m o l e s ) o f r e c o v e r e d m e t h y l d i c h l o r o s i l a n e , t h e y i e l d i s calculated t o be 4 1 . 9 % theoretical. I f the useful tolyltrichlorosilane be included i n t h e p r o d u c t , t h e s i l y l a t i o n y i e l d b e c o m e s 4 5 . 4 % t h e o r e t i c a l . T h e s e figures a r e c o n s e r v a t i v e i n t h e face o f some 4 % h a n d l i n g losses.



260 4

BENZENE REACTION · TOLUENE

REACTION©


1200

140

200 250 REACTION TEMPERATURE G.

300

e

Figure 5 . New

Catalyzed reaction of methyldichlorosilane with benzene and toluene

Compounds M a n y of t h e p r o d u c t s s y n t h e s i z e d b y t h i s d i r e c t process a r e w e l l k n o w n i n t h e of o r g a n o s i l i c o n c h e m i s t r y . M a n y o t h e r s r e p o r t e d here a r e less c o m m o n o r

field

Table IX.

N e w Compounds Analyses

Boiling Point, °C./30 M m . Compound Pressure w-CHaCeHiSiCh/ 118 116-119 TO-CHiCeH SiCli» 116-119 w-CHaCeHiSiCls* 131-134 m-CHuCeHiSiBrCla' 131-134 m-CHaCeKUSiBrW m-CH C6H4(CH )SiCl 117-118 m-C2H C6H4SiCl 130-130.5 135-136 w-(CH )2CHC6H SiCle 2,4,6-fCH )3C6H2SiCli 142-142.5 CeftSiBn 94-99* C H SiClF 130-135 C H SiCl F 163-166

Direct Process for Preparation of Arylhalosilanes

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