SECTION 14
Boron
Η. J . BECHER
Boro n
I. A c c o r d i n g to M o i s s a n , v e r y i m p u r e a m o r p h o u s b o r o n , c o n t a i n i n g about 80-90% B, i s o b t a i n e d by t h e r e a c t i o n of B203 w i t h m a g n e s i u m . A c c o r d i n g t o K r o l l t h e o p t i m u m y i e l d s a r e o b t a i n e d a s follows: A f i r e c l a y c r u c i b l e , a p p r o x i m a t e l y 20 c m . high and 16 c m . in d i a m e t e r , i s p a i n t e d with a p a s t e of ignited MgO and s i n t e r e d M g C l2 and d r i e d in a l o w - t e m p e r a t u r e o v e n . A m i x t u r e of 110 g. of B203, 115 g. of Mg s h a v i n g s (the u s e of Mg p o w d e r f r e q u e n t l y l e a d s t o e x p l o s i v e r e a c t i o n s ) and 94 g. of p o w d e r e d S i s p l a c e d in t h e c r u c i b l e . T h e r e a c t i o n i s s t a r t e d with an ignition p e l l e t , a f t e r w h i c h it p r o c e e d s v i g o r o u s l y . After t h e m i x t u r e h a s c o o l e d , it i s e x t r a c t e d in w a t e r and t h e n in d i l u t e HC1 f o r a w e e k . T h e r e s i d u e i s t r e a t e d s e v e r a l t i m e s by h e a t i n g w i t h H F and HC1, w a s h e d w i t h w a t e r and d r i e d in v a c u u m at 100°C. T h e y i e l d s a r e v a r i a b l e , w i t h a m a x i m u m of 46%.
II. A c c o r d i n g to K i e s s l i n g , p u r e b o r o n c a n b e m a d e by r e d u c i n g B B r3 w i t h H2 at 800°C. T h e r e a c t i o n t a k e s p l a c e in t h e a p p a r a t u s shown in F i g . 2 3 8 . T h e B B r3 i s p r e p a r e d by t h e m e t h o d of M e y e r and Z a p p n e r f r o m B r2 and c o m m e r c i a l b o r o n (usually 7 0 - 8 0 % p u r e ) (cf. t h e m e t h o d d e s c r i b e d on p . 782). T h u s , 15 g. of Β i s p r e s s e d into p e l l e t s , and t h e q u a r t z t u b e b i s filled w i t h t h e m . T h e t u b e i s h e a t e d to 700°C and d r y B r2 i s a d d e d in d r o p s f r o m d r o p p i n g funnel a. T h e r e s u l t i n g B B r3 w i l l t h e n c o l l e c t in t r a p c, w h i c h i s c o o l e d with an i c e - s a l t m i x t u r e . After about 30 m i n u t e s , 5-10 m l . of
B B r3 w i l l h a v e a c c u m u l a t e d . T h e a d d i t i o n of B r2 i s s t o p p e d and e x c e s s B r2 f r o m b and ο i s f l u s h e d out with H2. T h e r e s u l t i n g B B r3 should b e c o l o r l e s s . T h e H2 flow i s t h e n a d j u s t e d to 2 - 4 b u b b l e s p e r s e c o n d , t h e t e m p e r a t u r e of t h e q u a r t z t u b e h e a t e r i s r a i s e d to 750-800°C, and t h e B B r3 in ο a l l o w e d to e v a p o r a t e in t h e H2 s t r e a m at a m b i e n t t e m p e r a t u r e . A s a r e s u l t e l e m e n t a l Β p r e c i p i t a t e s in d. U n r e a c t e d B B r3 r e c o n d e n s e s in e% w h i c h i s c o o l e d with i c e - s a l t m i x t u r e . When no f u r t h e r B B r3 i s left in c , t r a p s e and ο a r e i n t e r c h a n g e d and t h e d e c o m p o s i t i o n c o n t i n u e d in d. When t h e B B r3 i s all r e a c t e d , m o r e m a t e r i a l i s p r e p a r e d by allowing f r e s h B r 2 t o d r o p into q u a r t z t u b e b. One c h a r g e of 15 g. of Β w i l l
7 7 0
1 4 . B O R O N 7 7 1
b e sufficient f o r p r e p a r a t i o n of 75 m l . of B B r3. B o r o n t h a t h a s p r e c i p i t a t e d in d a p p e a r s to c a t a l y z e f u r t h e r d e c o m p o s i t i o n . T h e r e f o r e , t h i s t u b e s h o u l d not b e e m p t i e d too e a r l y . T h e r e s u l t i n g Β i s w a s h e d and d r i e d w i t h hot H20 . A c c o r d i n g to K i e s s l i n g t h e c o m p o s i t i o n i s : 98.9% B , 0.04% Al, 0 . 1 % Si a n d t r a c e s of Ο, Η and M g .
F i g , 2 3 8 . P r e p a r a t i o n of high p u r i t y b o r o n , a—dropping funnel f o r B r2, p r o t e c t e d a g a i n s t a t m o s p h e r i c m o i s t u r e ; b— q u a r t z t u b e for Β p e l l e t s (10 m m . in d i a m e t e r a n d 700 m m . long); c—first c o n d e n s a t i o n t r a p f o r B B r3, c a p a c i t y about 25 m l .; d —q u a r t z t u b e f o r r e d u c t i o n of B B r3; e — s e c o n d c o n d e n s a t i o n t r a p f o r B B r3, c a p a c i t y 25 m l . ; ο—tubular e l e c t r i c a l h e a t e r s , about 600 m m . long; p —j o i n t s c e m e n t e d with p i c e i n ; g — m e r c u r y s e a l s ; t h e i r d e s i g n i s shown e n l a r g e d n e x t to t h e p r i n c i p a l f i g u r e ; it i l l u s t r a t e s t h e s e a l f o r t h e top of t h e
c o n d e n s a t i o n f l a s k .
PROPERTIES:
A t o m i c w e i g h t 1 0 . 8 2 . G r a y - b r o w n t o y e l l o w - b r o w n p o w d e r . M . p . 2 3 0 0 ° C ; d 2 . 3 . I g n i t e s in a i r a t 70CPC. R e a c t s v i o l e n t l y with c o n c e n t r a t e d H N 03.
REFERENCES:
I. H. M o i s s a n . C o m p t . R e n d . Hebd. S e a n c e s A c a d . Sci. 114, 392 (1892); W. K r o l L Z. a n o r g . a l l g . C h e m . 102, 1 (1918).
II. R. K i e s s l i n g . A c t a C h e m . Scand. 2, 707 (1948).
F o r o t h e r p r o c e d u r e s , cf. A. W. L a u b e n g a y e r . D, T. H u r d , A. E. N e w k i r k a n d J . L. H o a r d . J . A m e r . C h e m . Soc. 65, 1924 (1943).
772 Η . J . B E C H E R
Aluminu m Borid e A1B2, A1B12
A1B2 Al + 2 Β = A1B2
26.97 21.64 48.61
F i n e l y p o w d e r e d p u r e b o r o n and a l u m i n u m a r e m i x e d in s t o i c h i o m e t r i c p r o p o r t i o n s and p l a c e d in a g r a p h i t e t u b e c l o s e d w i t h a g r a p h i t e s t o p p e r . T h e s t o p p e r h a s a few fine g r o o v e s t h r o u g h w h i c h t h e i n s i d e of t h e t u b e c a n b e d e g a s s e d . T h e filled g r a p h i t e t u b e i s p l a c e d i n s i d e a q u a r t z t u b e w h i c h h a s b e e n w e l l p r e r i n s e d with h e l i u m , and t h e q u a r t z t u b e i s e v a c u a t e d . T h e t u b e i s h e a t e d o v e r night a t 800°C. T h e g r a p h i t e t u b e w i l l t h e n c o n t a i n a g r a y p o w d e r . T h e x - r a y a n a l y s i s i n d i c a t e s t h e p r e s e n c e of A l Ba, a l o n g w i t h s o m e g r a p h i t e and B4C i m p u r i t i e s . T h e s e i m p u r i t i e s a r e v i s i b l e and m a y b e m e c h a n i c a l l y r e m o v e d .
PROPERTIES:
D a r k - g r a y , finely c r y s t a l l i n e m a t e r i a l . F a i r l y r e s i s t a n t to d i l u t e a c i d s .
REFERENCES:
E . F . F e l t o n . J . A m e r . C h e m . Soc. 7 8 , 5977 (1956).
F . Lihl and P . J e n i t s c h e k . Z . M e t a l l k u n d e 4 4 , 414 (1953).
A1B12
A m i x t u r e of 50 g. of B203, 75 g. of S a n d 100 g. of Al (all t h e r e a g e n t s m u s t b e dry) i s r e a c t e d in a f i r e c l a y c r u c i b l e . A f t e r cooling, t h e m e l t i s r e m o v e d f r o m t h e c r u c i b l e a n d p u l v e r i z e d , a n d w a t e r i s a d d e d . A f t e r e l u t r i a t i o n of t h e s l a g , t h e r e d u c e d p a r t i c l e s a r e s o r t e d out f r o m t h e r e s i d u e , s e p a r a t e d a s f a r a s p o s s i b l e f r o m t h e s l a g , a n d t r e a t e d w i t h c o n c e n t r a t e d HC1 u n t i l a b r i l l i a n t b l a c k c r y s t a l l i n e r e s i d u e r e m a i n s . T h e l a t t e r i s t r e a t e d w i t h 40% H F in a P t c r u c i b l e , w a s h e d w i t h w a t e r and left in HC1 u n t i l g a s evolution c e a s e s . It i s t h e n f i l t e r e d , w a s h e d and d r i e d .
SYNONYM:
T e t r a g o n a l b o r o n .
PROPERTIES:
V e r y h a r d , s t a b l e b l a c k c r y s t a l s .
REFERENCES:
H. B i l t z . B e r . d t s c h . c h e m . G e s . 4 1 , 2643 (1908).
H. L i h l a n d P . J e n i t s c h e k . Z . M e t a l l k u n d e 4 4 , 414 (1953).
F o r i n f o r m a t i o n on m a n y o t h e r m e t a l b o r i d e s , cf. t h e s e c t i o n on A l l o y s and I n t e r m e t a l l i c C o m p o u n d s .
1 4 . B O R O N 773 Diborcm e
Β2ΗΒ
6LiH + 8 B F3 ' 0 ( C2H5)2 = B2H6 + 6 LiBF4 + 8 (C2H5)20
47.70 1135.52 27.69 562.56 592.96
3 LiBH4 + 4 B F3 · 0 ( C2H5)2 = 2 B2He + 3 LiBF4 + 4 (C2H5)20
65.37 567.76 55.38 281.28 296.48
D i b o r a n e w a s f i r s t o b t a i n e d f r o m t h e m i x t u r e of b o r o n h y d r i d e s r e s u l t i n g f r o m t h e h y d r o l y s i s of m a g n e s i u m b o r i d e ; l a t e r it w a s p r o d u c e d by s p a r k d i s c h a r g e in m i x t u r e s of B C 13 o r B B r3 w i t h H2 [ l , 2, 3 ] . It now c a n b e p r o d u c e d m o r e e a s i l y a n d in l a r g e r q u a n t i t i e s by t h e r e a c t i o n of LiH, NaH o r a l k a l i b o r o h y d r i d e s with B F3 d i e t h y l e t h e r a t e [ 4 ] . To o b t a i n good y i e l d s , t h e a l k a l i h y d r i d e s m u s t b e v e r y finely p o w d e r e d . Since a l k a l i h y d r i d e s a r e h y g r o s c o p i c and difficult to g r i n d , t h e u s e of a l k a l i b o r o h y d r i d e s , w h i c h a r e fine p o w d e r s to s t a r t w i t h , h a s c e r t a i n a d v a n t a g e s f o r l a b o r a t o r y - s c a l e s y n t h e s i s . On t h e o t h e r h a n d , LiH i s a p a r t i c u l a r l y e c o n o m i c a l s t a r t i n g m a t e r i a l f o r t h e p r o d u c t i o n of l a r g e r q u a n t i t i e s of B2He.
T h e p r o c e d u r e to follow c a n b e a p p l i e d r e g a r d l e s s of w h e t h e r a n a l k a l i h y d r i d e o r a l k a l i b o r o h y d r i d e i s u s e d . T h e r e a c t i o n v e s s e l a ( F i g . 239), w h i c h c a n h a v e a c a p a c i t y of 0.5 to 2 l i t e r s , d e p e n d i n g on n e e d , i s u s e d . T h e c o l d f i n g e r b a c t s a s a r e f l u x c o n d e n s e r . F r o m b9 t h e p r o d u c t B2H6 i s p a s s e d t h r o u g h f o u r s u c c e s s i v e c o l d t r a p s /x t o /4. G r o u n d j o i n t s a n d s t o p c o c k s s h o u l d b e g r e a s e d w i t h s i l i c o n e l u b r i c a n t , but in q u a n t i t a t i v e w o r k it i s b e s t to u s e m e r c u r y s e a l s . T h e f o u r t r a p s a r e c o n n e c t e d t o a s t o r a g e f l a s k w h i c h in t u r n
F i g . 2 3 9 . P r e p a r a t i o n of Β2Ηβ.
a— r e a c t i o n v e s s e l ; b— c o l d f i n g e r ;/χ t o /4- - t r a p s ; ft x t o hg—stopcocks; vx t o ν 4— m e r c u r y - f i l l e d p r e s s u r e r e
l e a s e v a l v e s .
7 7 4 H . J . B E C H E R
i s c o n n e c t e d to a h i g h - v a c u u m p u m p . All t h e e q u i p m e n t m u s t b e t h o r o u g h l y d r i e d p r i o r t o t h e r u n . T h e finely divided h y d r i d e o r b o r o h y d r i d e i s p l a c e d in t h e r e a c t i o n v e s s e l and s u s p e n d e d in s o m e a n h y d r o u s e t h e r , and t h e r e q u i r e d quantity of B F 3 e t h e r a t e i s p l a c e d in t h e d r o p p i n g funnel. U s e double t h e s t o i c h i o m e t r i c quantity of B F3 e t h e r a t e . T h e e n t i r e a p p a r a t u s i s t h o r o u g h l y f l u s h e d with d r y , p u r i f i e d N2; t h e c o l d f i n g e r b and t r a p / χ a r e c o o l e d to —78°C a n d t r a p s f2 a n d /3 to t h e t e m p e r a t u r e of liquid N2. W h e n a l l t h e e q u i p m e n t i s p r o p e r l y f l u s h e d w i t h Ν 2, s t o p c o c k s hl9h^ h*?, hQ and h9 a r e c l o s e d and t h e B F3 e t h e r a t e i s a d d e d slowly in d r o p s to t h e h y d r i d e , u s i n g c o n s t a n t , v i g o r o u s s t i r r i n g . At t h e s a m e t i m e t h e r e a c t i o n v e s s e l i s h e a t e d t o 60°C. W h e n g a s g e n e r a t i o n e n d s t h e B2He i s f l u s h e d into t h e t r a p s (using Ν 3), w h e r e it f r e e z e s out at —196°C.
After t h e r e a c t i o n , s o m e e t h e r a n d a t r a c e of B2H8 w i l l b e found in fx. T h e p r o d u c t w i l l b e l a r g e l y i n /2, w i t h a s m a l l e r a m o u n t i n /3. Now s t o p c o c k s h2 a n d h3 a r e c l o s e d and t h e c o o l i n g b a t h u n d e r t r a p fx i s r e p l a c e d by a D e w a r f l a s k filled w i t h liquid N2. T h i s t r a p i s u s e d to c o l l e c t t h e r e s i d u e s f o r m i n g w h e n B2H6 i s p u r i f i e d by f r a c t i o n a l c o n d e n s a t i o n . To purify, t r a p s /2 t o /4 a r e e v a c u a t e d and t h e B2He c o n d e n s e d in /2. T h e n t r a p f3 i s c o o l e d to — 100°C and t r a p / 4 t o —196°C, and by s l o w h e a t i n g t h e c o n t e n t s of f2 a r e t r a n s f e r r e d into f3 and /4. After a s i n g l e f r a c t i o n a t i o n , /4 w i l l c o n t a i n p u r e d i b o r a n e . T h e f r a c t i o n a t i o n c a n b e r e p e a t e d w i t h f3 c o o l e d t o - 1 4 0 ° C .
To p r e v e n t ignition on d i s a s s e m b l y of t h e a p p a r a t u s , t h e f l a s k i s flushed a g a i n with N2, w h i c h c a n e s c a p e v i a V2 if s t o p c o c k s h2 and h3 a r e left o p e n . S o m e m e t h a n o l i s a d d e d d r o p w i s e t o t h e r e a c t i o n f l a s k and t h e c o n t e n t s of t r a p /x a r e a l l o w e d to t h a w . T h e N2 w i l l t h e n c o n t a i n enough m e t h a n o l v a p o r t o r e n d e r h a r m l e s s a l l B2H6 r e s i d u e s i n / χ .
PROPERTIES:
Spontaneously igniting g a s w i t h s t r o n g , c h a r a c t e r i s t i c o d o r . M . p . —165.7°C, b . p . —92.5 C. R e a c t s quickly w i t h w a t e r to f o r m H3B 03 and H2.
REFERENCES:
1. A. Stock, E . W i b e r g and H. M a r t i n . Z . a n o r g . a l l g . C h e m . 188, 32 (1930) and e a r l i e r r e p o r t s of Stock et a l .
2 . Η. I. S c h l e s i n g e r and A. B . B u r g . J . A m e r . C h e m . Soc. 5 3 . 4321 (1931).
3 . A. Stock and W. S u t t e r l i n . B e r . d t s c h . c h e m . G e s . 6 7 , 407 (1934).
4 . Η. I. S c h l e s i n g e r , H. C. B r o w n , J . R. G i l b r e a t h a n d J . J . K a t z . J. A m e r . C h e m . Soc. 75, 195 (1953).
1 4 . B O R O N 7 7 5
Lithium Borohydrid e LiBH4
I. 4 LiH + BF3 · 0 ( C2H5)2 = LiBH4 + 3LiF + 0 ( C2H5)2
31.8 141.4 21.8 77.8 74.1
A s t e e l a u t o c l a v e , p r o v i d e d w i t h a t h r e a d e d , r e m o v a b l e h e a d , i s filled w i t h finely p o w d e r e d LiH, and sufficient a b s o l u t e e t h e r i s a d d e d t o c o v e r t h e L i H w i t h a t h i c k l a y e r . T h e n about 2 / 3 of t h e s t o i c h i o m e t r i c a m o u n t of B F3 e t h e r i s a d d e d . T h e a u t o c l a v e i s c l o s e d at o n c e , s i n c e t h e r e a c t i o n s t a r t s i m m e d i a t e l y . T h e r e a c t a n t s a r e h e a t e d a t 120-130°C f o r s e v e r a l h o u r s . A f t e r t h e a u t o c l a v e h a s c o o l e d , it i s o p e n e d , a n d i t s c o n t e n t s a r e d i l u t e d w i t h l i b e r a l a m o u n t s of e t h e r a n d t r a n s f e r r e d t o a f l a s k . T h e e t h e r s o l u t i o n i s t h e n d e c a n t e d a n d t h e r e s i d u a l s o l v e n t d i s t i l l e d off. T h e L i B H4 p r o d u c t i s r e c r y s t a l l i z e d f r o m a b s o l u t e e t h e r , t a k i n g c a r e t o e x c l u d e m o i s t u r e . T h e L i B H4 c r y s t a l l i z e s w i t h o n e m o l e of e t h e r of c r y s t a l l i z a t i o n ; t h i s c a n b e r e m o v e d in v a c u u m a t 33°C.
Π. 2 LiH + B2HG = 2 LiBH4
15.9 27.7 43.6
T h e a p p a r a t u s s h o w n in F i g . 240 i s u s e d . T h e r e q u i r e d a m o u n t of B2He i s c o n d e n s e d in t r a p/ χ a t —196°C u n d e r a n Na b l a n k e t . T h e n t h e t r a p i s c o n n e c t e d t o t h e a p p a r a t u s and t h e d r y r e a c t i o n v e s s e l i s filled w i t h 10 g. of finely d i v i d e d LiH and 400 m l . of a b s o l u t e e t h e r . Stopcock h4 i s o p e n e d t o a l l o w N2 t o e n t e r . T h e l a t t e r c a n i n i t i a l l y e s c a p e v i a u2 and l a t e r , a f t e r t h e s t o p c o c k s a t t r a p /x and Hb h a v e b e e n o p e n e d , v i a u1 # T h e a p p a r a t u s i s t h o r o u g h l y f l u s h e d w i t h Na; t h e n h± and h3 a r e c l o s e d . T h e D e w a r f l a s k /x i s r e m o v e d f r o m t r a p fl9 a n d t r a p /s i s t h e n i m m e r s e d in a D e w a r f l a s k a t
—196°C. A s a r e s u l t , Β3H6 w i l l s l o w l y e v a p o r a t e f r o m fx t o /2. Any
F i g . 2 4 0 . P r e p a r a t i o n of L i B H4 f r o m L i H a n d B2He.
Λ Λ — t r a p s ; hx to ? i4— s t o p c o c k s ; l\ .2% — p r e s s u r e r e l e a s e v a l v e s .
776 H . J . B E C H E R
e n t r a i n e d N2 c a n e s c a p e v i a ul e T h e r e a c t i o n v e s s e l i s w e l l s t i r r e d w h i l e B2H6 p a s s e s t h r o u g h i t . Any u n r e a c t e d B2H6 w i l l c o n d e n s e in /2. W h e n /X i s e m p t y , t h e l a s t t r a c e s of B2H6 a r e f l u s h e d out f r o n y* ii n t o /s (u s e Ns ) *c l o s e ha9 openh3 and, by p l a c i n g t h e D e w a r flask a t /x a n d r e m o v i n g it f r o m /2, a l l o w B2H6 t o e v a p o r a t e in t h e o p p o s i t e d i r e c t i o n . If t h e LiH i s sufficiently r e a c t i v e , t w o s u c h p a s s e s of B2H6 t h r o u g h t h e r e a c t i o n v e s s e l , i . e . , o n c e in e a c h d i r e c t i o n , w i l l suffice. N i t r o g e n i s a l l o w e d t o e n t e r v i a ^ ; t h i s will f l u s h t h e r e m a i n d e r of t h e Β 2 HQ into /T , w h e r e it will f r e e z e out. T h e t r a p i s t h e n c l o s e d a n d t h e a p p a r a t u s m a y b e d i s a s s e m b l e d . The r e a c t i o n v e s s e l i s r i n s e d w i t h e t h e r , t h e c o m b i n e d e t h e r p h a s e i s d e c a n t e d off, and t h e L i B H4 i s i s o l a t e d by e v a p o r a t i n g t h e s o l v e n t .
PROPERTIES:
L o o s e w h i t e p o w d e r . H y d r o l y z e s in t h e p r e s e n c e of a t m o s p h e r i c m o i s t u r e . In t h e p r e s e n c e of H20 , g i v e s off H2 in a v i o l e n t r e a c t i o n . A p p r o x i m a t e l y 2.5 g. of L i B H4 will d i s s o l v e in 100 m l . of e t h e r a t 1 9 ° C U s e d a s a r e d u c i n g a g e n t in t h e s a m e m a n n e r a s L i A l H4.
REFERENCES:
Η. I. S c h l e s i n g e r . and H. C. B r o w n . J . A m e r . C h e m . Soc. 62, 3429 (1940).
G. W i t t i g a n d P . H o r n b e r g e r . Z. N a t u r f o r s c h . 6b, 225 (1951).
Η. I. S c h l e s i n g e r , H. C. B r o w n , H. R. H o e k s t r a a n d L. R. R a p p . J . A m e r . C h e m . Soc. 7 5 , 199 (1953).
Sodiu m Borohydrid e NaBH4
4 NaH + B ( O C H3)3 = N a B H4 + 3 N a O C H3
96.02 103.92 37.85 162.09
T h e r e a c t i o n i s c a r r i e d out in a r o u n d - b o t t o m , t h r e e - n e c k c y l i n d r i c a l f l a s k . A m e r c u r y - s e a l M o n e l s t i r r e r i s p l a c e d in t h e c e n t r a l n e c k . T h e s t i r r e r i s equipped with five b l a d e s , a r r a n g e d o n e o v e r t h e o t h e r . T h e b l a d e d i m e n s i o n s s h o u l d b e s u c h t h a t t h e s t i r r e r c a n fit t h r o u g h t h e n e c k , b u t s t i l l fit t h e w a l l of t h e f l a s k a s c l o s e l y a s p o s s i b l e . A t h e r m o m e t e r i s p l a c e d in t h e s e c o n d n e c k a n d a c o n d e n s e r on t h e t h i r d . T h e t o p of t h e c o n d e n s e r i s e q u i p p e d with a w y e - t u b e a d a p t e r , one s i d e of w h i c h c o n n e c t s to a d r o p p i n g funnel and t h e o t h e r to a s o d a - l i m e d r y i n g t u b e . T h e f l a s k i s p l a c e d in a n e l e c t r i c f u r n a c e , t h e t o p of w h i c h i s c o v e r e d w i t h g l a s s wool and an a s b e s t o s lid. T h e t h e r m o m e t e r i s r e m o v e d , and t h e f l a s k f l u s h e d with N2 t h r o u g h t h i s n e c k . T h e n 50 g. of NaH i s r a p i d l y a d d e d and 50 g. of B ( O C H 3 )3 i s p l a c e d in t h e d r o p p i n g funnel. T h e s t i r r e r and t h e f u r n a c e a r e t h e n t u r n e d on. A s s o o n a s t h e t h e r m o m e t e r i n d i c a t e s
1 4 . B O R O N 777 a t e m p e r a t u r e of 200°C in t h e f l a s k , t h e e t h e r i s a d d e d d r o p w i s e at a u n i f o r m r a t e . T h e a d d i t i o n s h o u l d r e q u i r e 2 0 - 4 0 m i n u t e s , d u r i n g w h i c h t h e t e m p e r a t u r e i s k e p t a t 2 3 0 - 2 7 0 ° C . T h e s t i r r i n g i s c o n t i n u e d at t h i s t e m p e r a t u r e f o r a n o t h e r h o u r . T h e f l a s k i s t h e n a l l o w e d to c o o l a n d t h o r o u g h l y d r i e d i s o p r o p y l a m i n e o r liquid N H3 i s u s e d to e x t r a c t t h e N a B H4 f r o m t h e now s o l i d m i x t u r e , w h i c h , h o w e v e r , s h o u l d h a v e b e c o m e w e l l p u l v e r i z e d a s a r e s u l t of t h e c o n s t a n t s t i r r i n g . T h e e x t r a c t i o n w i t h i s o p r o p y l a m i n e i s c a r r i e d out by r e f l u x i n g f o r a few m i n u t e s ; t h e e x t r a c t i o n w i t h N H3 i s done by s t i r r i n g t h e r e a c t i o n p r o d u c t f o r a few m i n u t e s . In e i t h e r c a s e t h e e x t r a c t i s f i l t e r e d t h r o u g h a f r i t t e d g l a s s f i l t e r a n d t h e s o l v e n t i s e v a p o r a t e d . T h e N a B H4 r e m a i n s a s a fine w h i t e p o w d e r , with a p u r i t y of 9 0 - 9 6 % . T h e y i e l d i s 8 6 - 9 4 % . T h e N a B H4 i s p u r i f i e d by r e c r y s t a l l i z a t i o n f r o m e i t h e r i s o p r o p y l a m i n e o r w a t e r (it f o r m s a d i h y d r a t e ) .
F o r unknown r e a s o n s t h e n a t u r e of t h e NaH u s e d e x e r t s a g r e a t influence on t h e y i e l d and p u r i t y of t h e final p r o d u c t . T h e r e f o r e , it i s b e s t to c h e c k t h e s u i t a b i l i t y of t h e s t a r t i n g m a t e r i a l by m a k i n g a s m a l l - s c a l e p r e p a r a t i o n f i r s t . If t h e p r o d u c t i s u n s a t i s f a c t o r y , t h e NaH i s p r e h e a t e d t o 250°C a n d a s m a l l quantity of i m p u r e N a B H4 f r o m a p r e c e d i n g r u n i s a d d e d t o s t a r t t h e r e a c t i o n . T h e y i e l d c a n a l s o b e i m p r o v e d by a m o r e u n i f o r m r a t e of a d d i t i o n of t h e B ( O C H3)3.
PROPERTIES:
F i n e , w h i t e c r y s t a l s (cubic s y s t e m ) . D e c o m p o s e s s l i g h t l y in n e u t r a l a q u e o u s s o l u t i o n s , f r o m w h i c h it c a n b e p a r t i a l l y r e c r y s t a l l i z e d a s a d i h y d r a t e . R a p i d l y h y d r o l y z e s in a c i d s o l u t i o n . Stable u p t o 4 0 0 ° C
REFERENCES:
Η. I. S c h l e s i n g e r , H . C. B r o w n a n d A. E . F i n h o l t . J . A m e r . C h e m . S o c 77, 205 (1953).
Sodiu m Trimethoxyborohydrid e NaHB(OCH3)3
NaH + B(OCH3)3 = NaHB(OCH3)3
24.01 103.92 127.93
A o n e - l i t e r , r o u n d - b o t t o m f l a s k equipped with a r e f l u x c o n d e n s e r i s w e l l d r i e d a n d flushed w i t h N2. F i n e l y p o w d e r e d NaH (43 g.) i s added, followed by 230 g. of B ( O C H3)3, s l o w l y a d d e d f r o m a d r o p p i n g funnel on t o p of t h e c o n d e n s e r . T h e r e a c t i o n , w h i c h b e g i n s a t o n c e , l i b e r a t e s a c o n s i d e r a b l e a m o u n t of h e a t . A f t e r t h e a d d i t i o n of t h e e s t e r , t h e c o n t e n t s a r e r e f l u x e d a t 7 0 ° C f o r s e v e r a l h o u r s . T h i s c a u s e s a fivefold i n c r e a s e in t h e v o l u m e of t h e p r o d u c t , w h i c h
778 Η . J . B E C H E R
s i m u l t a n e o u s l y b e c o m e s p u r e w h i t e . When t h e v o l u m e no l o n g e r i n c r e a s e s , t h e r e f l u x c o n d e n s e r i s r e p l a c e d by a d o w n w a r d c o n d e n s e r a n d t h e e x c e s s B ( O C H 3 )3 i s d i s t i l l e d off. T h e y i e l d i s n e a r l y q u a n t i t a t i v e . It i s b e s t , h o w e v e r , to p r e t e s t t h e a v a i l a b l e NaH in a s m a l l e x p e r i m e n t a l r u n and, if n e c e s s a r y , modify t h e r e a c t i o n
PROPERTIES:
L o o s e w h i t e p o w d e r . Stable in d r y a i r ; h y d r o l y z e s slowly in m o i s t a i r . D e c o m p o s e s when h e a t e d to 230°C. R a p i d l y r e a c t s w i t h B2H6 to f o r m N a B H4 a n d B ( O C H3)3. D e c o m p o s e d by a l c o h o l , f o r m i n g Hs.
REFERENCE:
H. C. B r o w n , Η. I. S c h l e s i n g e r , I. S h e f t a n d D. M. R i t t e r . J . A m e r . C h e m . Soc. 7 7 , 192 (1953).
Borin e Trimethylaminat e B H3N ( C H3)3
LiBH4 + [N(CH3)3H]C1 = BH3 N(CH3)3 + LiCl + H2
21.79 95.58 72.95 42.40 2.02
A 1 0 0 - m l . t h r e e - n e c k f l a s k , e q u i p p e d w i t h a s t i r r e r , a r e f l u x c o n d e n s e r and a d r o p p i n g funnel, i s u s e d a n d l . 6 8 g. of [ N ( C H3) 3 H ] C 1 i s a d d e d t o it. A s o l u t i o n c o n s i s t i n g of 0.42 g. of L i B H4 in d i e t h y l e t h e r i s s l o w l y i n t r o d u c e d f r o m t h e d r o p p i n g funnel. If v i g o r o u s l y s t i r r e d , t h e r e a c t i o n p r o c e e d s at r o o m t e m p e r a t u r e . W h e n t h e g e n e r a t i o n of H2 d i m i n i s h e s , t h e c o n t e n t s a r e r e f l u x e d f o r a n o t h e r h o u r . All s o l v e n t i s t h e n d i s t i l l e d and t h e s o l i d r e s i d u e i s t r a n s f e r r e d t o a v a c u u m s u b l i m a t i o n a p p a r a t u s , w h e r e t h e B H3 · N ( C H3)3 i s s u b l i m e d in v a c u u m at 40°C and c o l l e c t e d in a c o o l e d r e c e i v e r . T h e y i e l d i s 85%.
PROPERTIES:
W h i t e h e x a g o n a l c r y s t a l s . S t a b l e . M . p . 94°C.
REFERENCES:
G. W. Schaeffer and E. R. A n d e r s o n . J . A m e r . C h e m . Soc. 7 1 , 2143 (1949).
A. B . B u r g a n d Η. I. S c h l e s i n g e r . J . A m e r . C h e m . Soc. 59^ 780 (1937).
1 4 . B O R O N 7 7 9
Borazol e
( H B N H )3
B o r a z o l e w a s d i s c o v e r e d w h e n a m i x t u r e c o n s i s t i n g of Β2H6 a n d N H3 ( o r t h e a d d i t i o n p r o d u c t Β2Η6· Ν Η3) w a s h e a t e d in a s e a l e d t u b e [ 1 , 2 1 . It c a n a l s o b e p r o d u c e d by p y r o l y s i s of a m i x t u r e of L i B H4 and NH4CI [ 3 ] . T h e b e s t y i e l d i s o b t a i n e d by r e d u c i n g (C1BNH) 3 ( s e e below) w i t h L i B H4 in η - b u t y l e t h e r . T h i s r e a c t i o n a l s o y i e l d s B2H6. F o r d e t a i l s s e e t h e l i t e r a t u r e [ 4 1 .
SYNONYM:
s - T r i a z a b o r a n e .
REFERENCES:
1. A. Stock a n d E . P o h l a n d . B e r . d t s c h . c h e m . G e s . 59, 2215 (1926).
2 . E. W i b e r g a n d A. B o l z . B e r . d t s c h . c h e m . G e s . 7 3 , 209 (1940).
3 . G. W. Schaeffer, R. Schaeffer and Η. I. S c h l e s i n g e r . J . A m e r . C h e m . Soc. 7 3 , 1612 (1951).
4 . R. Schaeffer, M. S t e i n d l e r , L. H o h n s t e d t , H. S. S m i t h , J r . , L.
B. Eddy a n d Η. I. S c h l e s i n g e r . J . A m e r . C h e m . S o c 76, 3303 (1954).
s-Trichloroborazol e (C1BNH)3
3NH4C1 + 3BC13 = (C1BNH)3 + 9HC1
160.49 351.57 183.88 328.19
A t h r e e - n e c k , t w o - l i t e r f l a s k e q u i p p e d w i t h a m e r c u r y - s e a l s t i r r e r and a r e f l u x c o n d e n s e r i s u s e d . A c o l d f i n g e r i s i n s e r t e d on t o p of t h e c o n d e n s e r and i s c o o l e d w i t h a m i x t u r e of Dry Ice and a c e t o n e . A s i m i l a r f i n g e r , c o o l e d t o —78°C, i s i n s e r t e d in t h e t h i r d n e c k . D u r i n g t h e r e a c t i o n , B C 13 i s i n t r o d u c e d t h r o u g h t h i s n e c k ; t h e r e a g e n t c o n d e n s e s on t h e c o l d f i n g e r a n d t h u s i s a d d e d to t h e f l a s k d r o p w i s e . T h e f l a s k i s filled w i t h a m i x t u r e of 50 g.
of d r y N H4C 1 a n d p o w d e r e d g l a s s w i t h 400 m l . of c h l o r o b e n z e n e . T h e f l a s k i s t h e n h e a t e d to 140-150°C, t h e inlet c o l d f i n g e r i s c o n n e c t e d to a t r a p w i t h B C 13, a n d t h e l a t t e r i s a l l o w e d to e v a p o r a t e at s u c h a r a t e t h a t a d r o p of l i q u i d B C 13 e n t e r s t h e r e a c t i o n m i x t u r e e v e r y t h r e e s e c o n d s . After about five h o u r s t h e r a t e of t h e i n i t i a l l y v e r y v i g o r o u s g e n e r a t i o n of HC1 d r o p s off. T h e a d d i t i o n of B C 13 i s
7 8 0 Η . J . B E C H E R
i n t e r r u p t e d and t h e e x c e s s B C 13 s t i l l r e m a i n i n g in t h e f l a s k i s allowed to r e c o n d e n s e on t h e i n l e t c o l d f i n g e r f o r a n o t h e r h o u r . T h e cooling i s t h e n s t o p p e d and t h e e x c e s s B C 13 d i s t i l l e d off. T h e liquid p h a s e i s s i p h o n e d out f r o m t h e f l a s k and c e n t r i f u g e d for f u r t h e r c l a r i f i c a t i o n , if n e c e s s a r y . T h e c h l o r o b e n z e n e i s d i s t i l l e d u n t i l s o l i d (C1BNH) 3 r e m a i n s a s a r e s i d u e . T h e l a t t e r i s p u r i f i e d by v a c u u m s u b l i m a t i o n at 5 0 - 6 0 ° C . T h e y i e l d i s a p p r o x i m a t e l y 40%. If t h e r e c o v e r e d c h l o r o b e n z e n e i s r e c y c l e d b a c k t o t h e f l a s k which s t i l l c o n t a i n s t h e s o l i d r e s i d u e and if f r e s h N H4C 1 i s a d d e d , t h e y i e l d c a n b e i n c r e a s e d a p p r e c i a b l y by f u r t h e r r e a c t i o n .
PROPERTIES:
C o l o r l e s s c r y s t a l s , e x c e e d i n g l y s e n s i t i v e to m o i s t u r e . M . p . 84°C; d (25°C) 1.58. Soluble in b e n z e n e , C C 14 and o t h e r o r g a n i c s o l v e n t s .
REFERENCES:
Ch. A. B r o w n and A. W. L a u b e n g a y e r . J . A m e r . C h e m . Soc. 77, 3699 (1955).
R. Schaeffer, M. S t e i n d l e r , L. H o h n s t e d t , H. S. S m i t h , J r . , L. B.
Eddy a n d Η. I. S c h l e s i n g e r . J . A m e r . C h e m . S o c 76, 3303 (1954).
F o r p r e p a r a t i o n and p r o p e r t i e s of s o m e o t h e r b o r a z o l e d e r i v a t i v e s , s e e E. W i b e r g , N a t u r w i s s . 3 5 , 182, 212 (1948); H. J . B e c h e r and S. F r i c k , Z, a n o r g . a l l g . C h e m . 2 9 5 , 83 (1958).
Boro n Trichlorid e BC13
F a i r l y l a r g e q u a n t i t i e s of B C 13 c a n b e p r o d u c e d by h e a t i n g d i l u t e b o r a x with c h a r c o a l in a s t r e a m of C l2 at t e m p e r a t u r e s of 400 t o 700°C. In t h e l a b o r a t o r y it i s m o r e c o n v e n i e n t to p r o d u c e it f r o m B F3 and A1C13.
I. B F3 4- AICI3 = BCI3 + AIF3.
67.8 133.4 117. 2 84.0
T h e r e a c t i o n i s c a r r i e d out in t h e a p p a r a t u s shown in F i g . 2 4 1 . The l o w e r f l a s k h a s a c a p a c i t y of one l i t e r ; t h e u p p e r b u l b , half t h a t . A n h y d r o u s A1C13(67 g. = 0.5 mole) i s p l a c e d in t h e l o w e r f l a s k . T h e inlet t u b e i s c o n n e c t e d to a B F3 g e n e r a t o r and t h e B F3 flow a d j u s t e d in s u c h a m a n n e r t h a t 132 g. o r two m o l e s of BF3 a r e a d d e d t o t h e v e s s e l o v e r a p e r i o d of 30 m i n u t e s . At t h e s a m e t i m e ,
1 4 . BORON 7 8 1
F i g . 2 4 1 . P r e p a r a t i o n of b o r o n t r i c h l o r i d e .
t h e l o w e r f l a s k i s h e a t e d w i t h an open f l a m e . L a t e r t h e bulb i s a l s o h e a t e d . T h e B C 13 d i s t i l l s off w h i l e t h e A 1 F3 p e e l s off f r o m t h e w a l l s of t h e f l a s k a s a light p o w d e r . T h e B C 13 i s c o o l e d in a U t u b e c o o l e d t o — 80°C. M o i s t u r e i s e x c l u d e d by m e a n s of a d r y i n g t u b e . T h e i m p u r e p r o d u c t i s s h a k e n with s o m e Hg a n d r e c o n d e n s e d . T h e y i e l d i s 47 g.
II. KBF4 + A1C13 = BCI3 + KF + AIF3
125.9 133.4 117.2
An i n t i m a t e m i x t u r e of 133.3 g. of A 1 C 13 and 62 g. of K B F4 i s p l a c e d in t h e a p p a r a t u s d e s c r i b e d a b o v e , w h i c h i s t h e n slowly h e a t e d in a n o i l b a t h t o 1 5 0 - 1 7 0 ° C . U s i n g t h e m e t h o d d e s c r i b e d a b o v e , t h e B C 13 t h a t h a s b e e n d i s t i l l e d off i s t r a p p e d and p u r i f i e d . T h e y i e l d i s p o o r e r t h a n t h a t p r o d u c e d by m e t h o d I.
PROPERTIES:
M . p . —107°C, b . p . 12.5°C; d (0°C) 1.434. C o l o r l e s s liquid, fuming in m o i s t a i r .
REFERENCES:
I and II: E . L. G a m b l e in: L. F . A u d r i e t h , I n o r g . S y n t h e s e s , Vol.
Ill, New Y o r k - L o n d o n , 1950, p . 2 7 . S y n t h e s i s of B C 13 f r o m a m o r p h o u s Β and C l3: L. G a t t e r m a n n . B e r . d t s c h . c h e m . G e s . 22, 195 (1889).
Boro n Tribromid e BBr3
I. AlBr3 + B F3 = BBr3 + A1F3
266.7 67,8 250.6 84.0
One half m o l e (133.4 g.) of A l B r3 i s d i s t i l l e d into t h e f l a s k d e s c r i b e d f o r t h e p r e p a r a t i o n of B C 13; B F3 i s a d d e d w h i l e h e a t i n g
7 8 2 H . J . B E C H E R
t h e f l a s k . After s o m e t i m e t h e f l a s k c o n t e n t s solidify. T h e h e a t i n g and a d m i s s i o n of B F3 a r e c o n t i n u e d . A s a r e s u l t , t h e B B r3 p r o d u c t d i s t i l l s o v e r into t h e —78°C t r a p . T h e d i s t i l l a t e s t i l l c o n t a i n s s o m e B r2 w h i c h c a n t h e n b e r e m o v e d b y s h a k i n g w i t h Hg. T h e
B B r3 m u s t b e d i s t i l l e d for f u r t h e r p u r i f i c a t i o n . T h e y i e l d i s 87.7 g.
(70%).
An a l t e r n a t i v e i s t o h e a t a m i x t u r e of A l B r3 a n d K B F4 in t h e flask itself, but t h i s r e s u l t s in a m u c h l o w e r y i e l d of B B r3.
II. Β + lV2Br2 = BBr3
10,8 239,8 250.6
T h i s p r o c e d u r e h a s b e e n p r e v i o u s l y d e s c r i b e d in c o n n e c t i o n with t h e K i e s s l i n g m e t h o d for p r e p a r i n g p u r e b o r o n . If B B r 3 i s d e s i r e d , t h e a p p a r a t u s shown in F i g . 238 i s c l o s e d off by m e a n s of a d r y i n g t u b e i n s e r t e d b e h i n d c o n d e n s a t i o n t r a p o. B e f o r e t h e r e a c t i o n t h e b o r o n i s t h o r o u g h l y d r i e d by p r o l o n g e d h e a t i n g at 600°C in a q u a r t z t u b e f l u s h e d with a s t r e a m of H2. T h e n d r o p w i s e B r2 a d dition i s s t a r t e d , and t h e t e m p e r a t u r e of t h e r e a c t i o n t u b e i s r a i s e d t o 700-750 C. T h e p r o d u c t B B r3 i s p u r i f i e d a s in m e t h o d I.
PROPERTIES:
M . p . - 4 6 ° C , b . p . 90.8°C; d (0°C) 2 . 6 5 . C o l o r l e s s , e a s i l y h y d r o - l y z e d liquid.
REFERENCES:
I. E. L. G a m b l e in: L. F . A u d r i e t h , I n o r g . S y n t h e s e s , Vol. Ill, New Y o r k - L o n d o n , 1950, p . 2 7 .
II. F r . M e y e r and R. Z a p p n e r . B e r . d t s c h . c h e m . G e s . 54, 551 (1921); H. M e n z e l . U n p u b l i s h e d .
Boro n T r i i o d i d e
B I3
3 LiBH4 + 8 I2 = 3LiI + 3 B I3 + 4 H2 + 4 HI
65,37 2030,56 401.55 1174.65 8,06 511,67
T h e a p p a r a t u s shown in F i g . 242 i s u s e d and 170 g. of I2 i s added to flask a, w h i l e 5.1 g. of L i B H4 i s p l a c e d in a d d i t i o n b u l b b u n d e r a n N2 b l a n k e t . T h e e n t i r e a s s e m b l y i s t h o r o u g h l y f l u s h e d with N2 by e v a c u a t i n g it s e v e r a l t i m e s t h r o u g h ν a n d i n t r o d u c i n g
1 4 . B O R O N 783 d r y , o x y g e n - f r e e N2 t h r o u g h h. T h e n f l a s k α i s s l o w l y h e a t e d on a b a t h u n t i l i t s i n s i d e t e m p e r a t u r e i s b e t w e e n 120 and 125°C. T h e b u l b b i s t u r n e d in t h e joint s o a s to add s m a l l q u a n t i t i e s of L i B H4 to t h e f l a s k . T h e r e a c t i o n w i t h I2 i s v e r y v i g o r o u s . T r a p / χ i s c o o l e d t o 0°C, t r a p /s t o —78°C, a n d t r a p /3 to —196°C. At t h e end of t h e r e a c t i o n , t h e p r o d u c t in a i s s u b l i m e d into t r a p fx , w h i c h i s c o o l e d to —78°C. W o r k i n g u n d e r N2, t r a p /x i s d i s c o n n e c t e d at d and g and c l o s e d w i t h g r o u n d g l a s s s t o p p e r s . P u r e C S2 i s a d d e d
F i g . 2 4 2 . P r e p a r a t i o n of b o r o n t r i i o d i d e . a) r e a c t i o n flask; b) addition b u l b ; o) t h e r m o m e t e r ; d, g, e, v)
g r o u n d j o i n t s ; /x t o /3) l o w - t e m p e r a t u r e t r a p s ; h) s t o p c o c k .
t h r o u g h e in o r d e r to d i s s o l v e t h e s u b l i m a t e . T h e n Hg a n d Zn d u s t a r e a d d e d in o r d e r to r e d u c e any e n t r a p p e d I2. After it h a s b e c o m e c o l o r l e s s , t h e s o l u t i o n i s left t o s t a n d , and a s m a l l g l a s s wool p l u g i s p l a c e d in joint g9 c o n n e c t e d to a s u b l i m a t i o n f l a s k , w h i c h in t u r n i s fused to a s u b l i m a t i o n t u b e w i t h t h r e e bulb e n l a r g e m e n t s . T h e C S2 s o l u t i o n i s c a r e f u l l y p o u r e d into t h e s u b l i m a t i o n f l a s k t h r o u g h t h e g l a s s wool p l u g . T h e e n t i r e s u b l i m a t i o n a s s e m b l y i s t h e n e v a c u a t e d (high v a c u u m ) , t h u s v a p o r i z i n g t h e s o l v e n t . T h e s u b l i m a t i o n f l a s k i s d e t a c h e d f r o m t h e r e m a i n d e r of t h e a p p a r a t u s and t h e i m p u r e B I3 i s s l o w l y s u b l i m e d into t h e f i r s t b u l b , t h e n into t h e s e c o n d , e t c . T h e final p r o d u c t i s p u r e w h i t e and c r y s t a l l i n e . If t h e r e a c t i o n i s c a r r i e d out in h e x a n e in t h e p r e s e n c e of a n e x c e s s of L i B H3, it will go at r o o m t e m p e r a t u r e .
PROPERTIES:
C o l o r l e s s shiny c r y s t a l s w h e n c o m p l e t e l y p u r e . M . p . 49.9°C.
Soluble in C S2. U n s t a b l e in a i r .
REFERENCES:
W. C. S c h u m b , E . L. G a m b l e a n d M. D. B a n u s . J . A m e r . C h e m . S o c 7 1 , 3228 (1949).
7 8 4 H . J . B E C H E R
Ε. G. Hofling, T h e s i s , S t u t t g a r t , 1956.
T. R e n n e r , Angew. C h e m . 69, 478 (1957).
Boro n Trifluoride Dihydrat e
B F3 · 2 H20
BF3 + 2 H20 = BF3 · 2 H20
67.8 36,0 103.8
T h i s c o m p o u n d i s b e s t p r e p a r e d by adding t h e c a l c u l a t e d a m o u n t of B F3 to a l m o s t i c e - c o l d w a t e r . T h e a b s o r p t i o n i s s l o w at f i r s t , but t h e n p r o c e e d s m o r e r a p i d l y . T h e i n t e r m e d i a t e Η3B 03 s e p a r a t e s out, but g o e s b a c k in s o l u t i o n a s B F3 i s a d d e d . A c l e a r , m o b i l e liquid, with t h e c o m p o s i t i o n B F3- 2 HaO , i s o b t a i n e d . H o w e v e r , on f r a c t i o n a l d i s t i l l a t i o n u n d e r r e d u c e d p r e s s u r e , p a r t i a l d e c o m p o s i t i o n o c c u r s , with t h e f o r m a t i o n of B F30 H · H20 and o t h e r p r o d u c t s . If a s m a l l e x c e s s of one of t h e r e a g e n t s i s u s e d in t h e p r e p a r a t i o n , p u r e B F3- 2 H20 c a n b e s e p a r a t e d out by p a r t i a l f r e e z i n g .
PROPERTIES:
M.p. 5 . 9 - 6 . 1 ° C . d (20°C) 1.6315. C r y s t a l l i z e s in r h o m b i c f o r m , i s i s o m o r p h o u s with N H4B F4 and s h o u l d p r o b a b l y b e w r i t t e n a s H30 [ B F3O H ] . T h e liquid d o e s not a t t a c k g l a s s a n d i s s t a b l e at r o o m t e m p e r a t u r e .
REFERENCES:
H. M e e r w e i n . B e r . d t s c h . c h e m . G e s . 66, 411 (1933).
H. M e e r w e i n and W. P a n n w i t z . J . p r a k t . C h e m . , N. S. 1 4 1 , 123 (1934).
L. J . K l i n k e n b e r g and J . A. A. K e t e l a a r . R e c T r a v , C h i m . P a y s - B a s . 54, 4, 959 (1935); J . S. M c G r a t h , G. G. Stack and P . A.
M c C u s k e r . J . A m e r . C h e m . Soc. 66, 1263 (1944).
Dihydroxyfluorobori c Aci d
H [ B F2( O H )2]
I. H3B 03 + 3 H20 + 2 B F3 = 3 H[BF2(OH)2]
61.8 54.0 135,6 251.4
Two m o l e s of B F3 a r e s t i r r e d into a s u s p e n s i o n of one m o l e of H3B 03 in t h r e e m o l e s of H20 . T h i s r e s u l t s in a c l e a r liquid w h i c h
1 4 . B O R O N 7 8 5
d i s t i l l s a t 85°C (25 m m . ) a n d w h i c h i s p u r e d i h y d r o x y f l u o r o b o r i c a c i d .
II. 4 H3B 03 + 2BF3 = 2H[BF2(OH)2] + 4 H B 02 + 2HF
247,2 135,6 167,6 175,2 40
An e x c e s s of B F3 i s a d d e d to a P y r e x v e s s e l c o n t a i n i n g s o m e b o r i c a c i d . T h e B F3 i s a b s o r b e d in a n e x o t h e r m i c r e a c t i o n , w i t h t h e m a t e r i a l in t h e v e s s e l finally liquefying. T h e r e s u l t i n g d i - h y d r o x y f l u o r o b o r i c a c i d c a n t h e n b e d i s t i l l e d off u n d e r a t m o s p h e r i c p r e s s u r e .
T h i s a c i d i s a l s o f o r m e d w h e n B F3 i s p r o d u c e d f r o m C a F2, B203 and c o n c e n t r a t e d HsS 04, o r f r o m B203 and H F , and c a n b e o b t a i n e d a t t h e end of B F3 g e n e r a t i o n by f r a c t i o n a l d i s t i l l a t i o n of t h e r e s i d u e in t h e g e n e r a t o r .
PROPERTIES:
C o l o r l e s s , s y r u p y liquid. B . p . 159-160°C (745 m m . ) W h e n t h e liquid i s c o o l e d to 0°C, t h e c o m p o u n d b e c o m e s v e r y v i s c o u s , but no definite f r e e z i n g point c a n b e o b s e r v e d . Does not a t t a c k g l a s s . H y d r o l y z e d by w a t e r e i t h e r to H B 02 o r to H3B 03.
REFERENCES:
I. J . S. M c G r a t h , G. G. Stack a n d P . A. M c C u s k e r , J . A m e r . C h e m . Soc. 6 6 , 1263 (1944).
II. F. J. Sowa, J . W. K r o g e r and J . A. Nieuwland. J . A m e r . C h e m . Soc. 57, 454 (1935); 59, 965 (1937).
Boro n T r i f l u o r i d e Ammoniat e
B F 3 N H 3
BF3 + NH3 = BFs-NHs
67.8 17 0 84.8
I. A s l o w s t r e a m of N H3 g a s i s l e d into a t h r e e - n e c k , o n e - l i t e r f l a s k . W h e n t h e f l a s k h a s b e e n f l u s h e d , a n e q u i v a l e n t a m o u n t of B F3 i s a l l o w e d to e n t e r t h e f l a s k t h r o u g h a s e c o n d n e c k . An e x - c e s s of B F3 c a n b e d e t e c t e d by f o r m a t i o n of a w h i t e c l o u d at t h e f l a s k o u t l e t . T h e B F3N H d e p o s i t s in t h e flask a s a w h i t e p o w d e r . II. A p o r t i o n of B F3 d i e t h y l e t h e r a t e i s d i l u t e d w i t h t w i c e i t s quantity of e t h e r . T h e s o l u t i o n i s p l a c e d in a flask, a n d a u n i f o r m s t r e a m of N H3 i s i n t r o d u c e d . T h e r e a c t i o n m u s t b e c o n d u c t e d in t h e a b s e n c e of a i r and with v i g o r o u s s t i r r i n g . T h e p r o d u c t s e t t l e s
H . J . B E C H E R
a s a fine p r e c i p i t a t e . After t h e r e a c t i o n i s c o m p l e t e , t h e e t h e r i s d e c a n t e d and t h e r e s i d u a l B F3 · N H3 w a s h e d s e v e r a l t i m e s with f r e s h e t h e r .
P R O P E R T I E S:
W h i t e , c r y s t a l l i n e m a t e r i a l . M . p . l 6 3 ° C . d (25°C) 1.864. Soluble in w a t e r . H y d r o l y z e s slowly in w a t e r a t 0°C. D e c o m p o s e s a b o v e 125°C.
R E F E R E N C E S:
I. A. W. L a u b e n g a y e r and G. F . C o n d i k e . J . A m e r . C h e m . Soc.
70, 2274 (1948).
II. Ch. A. K r a u s and Ε. H. B r o w n . J . A m e r . C h e m . Soc. 5 1 , 2690 (1929).
Boro n Trifluoride Etherat e
B F30 ( C2H5)2
BF3 + 0 ( C2H5)2 = B F30 ( C2H5)2
67.8 7 4 . 1 141. 9
Two m o l e s (135.6 g.) of B F3 a r e g e n e r a t e d a s d e s c r i b e d on p . 2 1 9 . It i s t h e n i n t r o d u c e d into a d r y o n e - l i t e r f l a s k c o n t a i n i n g 148 g. of d i e t h y l e t h e r . A l t e r n a t e l y , t h e B F3 m a y b e f r o z e n a t liquid n i t r o g e n t e m p e r a t u r e a n d a d d e d a s a s o l i d . T h e f l a s k i s c o o l e d in i c e - s a l t m i x t u r e and a c c e s s of a t m o s p h e r i c m o i s t u r e i s p r e v e n t e d by c l o s i n g off t h e f l a s k w i t h a C a C l2t u b e . T h e s t r e a m of B F3 s h o u l d not b e too f a s t b e c a u s e s o m e of it w i l l not b e t a k e n u p by t h e e t h e r in t h a t c a s e . A f t e r t h e end of t h e r e a c t i o n a c o n d e n s e r i s c o n n e c t e d to t h e f l a s k and t h e B F3- 0(C2K^2 d i s t i l l e d off at 125°C into a r e c e i v e r , p r e f e r a b l y at r e d u c e d p r e s s u r e . T h e e t h e r a t e d i s t i l l s r e a d i l y at 38°C (6 m m . ) .
P R O P E R T I E S:
C o l o r l e s s liquid. M . p . - 6 0 . 4 ° C , b . p . 125-126°C; d (25°C) 1.125.
nD 1.348. H y d r o l y z e s q u i t e r e a d i l y . U s e d in o r g a n i c r e a c t i o n s and f o r r e a c t i o n s w i t h a l k a l i h y d r i d e s .
R E F E R E N C E S:
V. G a s s e l i n . Ann. C h i m P h y s . [7] 3 , 5 (1894).
G. F . Hennion, H. D. Hinton and J . A. N i e u w l a n d . J . A m e r . C h e m . Soc. 55, 2858 (1933);
1 4 . B O R O N 7 8 7 Η. M e e r w e i n and W. P a n n w i t z . J . p r a k t . C h e m . , N. S. 1 4 1 , 123
(1934).
E . W i b e r g and W. M a t h i n g . B e r . d t s c h . c h e m . G e s . 70^ 690 (1937).
A. W. L a u b e n g a y e r and G. R. F i n l a y . J. A m e r . C h e m . Soc. 6 5 , 884 (1943).
H. C. B r o w n and R. M. A d a m s . J. A m e r . C h e m . Soc. 64, 2557 (1942).
Boro n (III) Oxid e
B203
VITREOUS B203
2H3BO3 = B203 + 3 H20
123.6 69.6 54.0
R e c r y s t a l l i z e d H3B 03 ( s e v e r a l t i m e s f r o m w a t e r ) i s p l a c e d in a P t c r u c i b l e and d r i e d in v a c u u m o v e r P305, slowly r a i s i n g t h e t e m p e r a t u r e to 200°C. T h i s r e s u l t s in w h i t e , only s l i g h t l y s i n t e r e d
B2O3 w h i c h i s r e a d i l y p o w d e r e d .
PROPERTIES:
A m o r p h o u s , M . p . 294°C; d 1.84. T h e g l a s s l i k e p i e c e s t h a t a r e o b t a i n e d by a l l o w i n g m o l t e n B203 to solidify a r e b r i t t l e , v e r y h a r d and h y g r o s c o p i c .
REFERENCES:
E . T i e d e and A. R a g o h s , B e r . d t s c h . c h e m . G e s . 5 5 , 594 (1922).
E . T i e d e and P . Wulff, B e r . d t s c h . c h e m . G e s . 56, 656 (1923).
CRYSTALLINE B203
F u s e d b o r i c a c i d i s h e a t e d in a l o o s e l y s t o p p e r e d P y r e x f l a s k to 225-250°C; a f t e r t h i s t r e a t m e n t t h e m e l t r e t a i n s 8-15% w a t e r . C r y s t a l l i z a t i o n r e q u i r e s a few d a y s . If a s m a l l a m o u n t of c r y s t a l l i n e B203 s e e d i s a d d e d to t h e m e l t , w h i c h c o n t a i n s s o m e w a t e r , c r y s t a l l i z a t i o n o c c u r s v e r y r a p i d l y a n d t h e w a t e r s e p a r a t e s out.
A l t e r n a t i v e l y , fused b o r i c a c i d i s h e a t e d to 175°C, at w h i c h point c r y s t a l l i n e H B Os (I) s e p a r a t e s . T h e m a t e r i a l i s t h e n t r a n s f e r r e d t o a c l o s e d t u b e a n d t h e t e m p e r a t u r e i s r a i s e d t o about 236°C, i . e . , j u s t b e l o w t h e m . p . of H B 02 (I). A s a r e s u l t t h e l a t t e r e v o l v e s w a t e r and t r a n s f o r m s to c r y s t a l l i n e B203.
788 H . J . B E C H E R PROPERTIES:
M.p. 450°C; d 2 . 4 2 - 2 . 4 6 . H e x a g o n a l c r y s t a l s .
REFERENCES:
L . M c C u l l o c h . J . A m e r . C h e m . Soc. 59, 2650 (1937).
2 B 21.6
Boro n (III) Sulfid e B2S3
+ 3H2S = B2S3 + 3 H2
102.2 117.8 6.0
T h i s c o m p o u n d i s s y n t h e s i z e d by t h e m e t h o d of Sliwinski in t h e a p p a r a t u s shown in F i g . 2 4 3 . B e f o r e t h e r e a c t i o n t h e a p p a r a t u s i s flushed with d r y H2 until f r e e of e x p l o s i v e o x y h y d r o g e n m i x t u r e . A m o r p h o u s b o r o n i s p l a c e d in a V y c o r t u b e and h e a t e d to a dull r e d . A s t r e a m of d r y , C Os- f r e e H2S i s p a s s e d o v e r t h e b o r o n . Molten b o r o n sulfide c o n d e n s e s c l o s e to t h e point w h e r e t h e h e a t h a s b e e n a p p l i e d (point a , F i g . 243). Upon c o o l i n g , t h e m a t e r i a l b e c o m e s t r a n s p a r e n t . F u r t h e r d o w n s t r e a m , at b9 p o r c e l a i n l i k e
sulfide f o r m s , w h i l e c r y s t a l l i n e B2S3 f o r m s a t c . T h e s u b l i m a t i o n z o n e s h o u l d not b e c o o l e d o r t h e c r y s t a l s w i l l not b e w e l l f o r m e d . A s t e a d y s t r e a m of H2S i s m a i n t a i n e d t h r o u g h o u t t h e e n t i r e r e a c t i o n and c o n t r o l l e d to give a flow of a p p r o x i m a t e l y 3 l i t e r s / h o u r .
ti,s
(dry, free of 02)
sHica P2 05 g e l
|Ξ) \ξ\, oxyhydrogen test
F i g . 2 4 3 . S y n t h e s i s of b o r o n (III) sulfide.
A c c o r d i n g t o Hoffmann it i s p o s s i b l e to s u b s t i t u t e i r o n (III) b o r i d e for t h e e l e m e n t a l b o r o n . T h e i r o n b o r i d e (finely divided powder) i s p l a c e d in t h e t u b e , w h e r e it r e a c t s with t h e H2S . T h e r e a c t i o n s t a r t s a t 200°C; t h e o p t i m u m t e m p e r a t u r e l i e s b e t w e e n 300 and 400°C. T h e r e s u l t i n g B2S3 s u b l i m e s into t h e end of t h e t u b e w h e r e it f o r m s b u n d l e s of fine, h a i r l i k e c r y s t a l s . V i t r e o u s and a m o r p h o u s r e s i d u e s c a n b e c o n v e r t e d t o t h e c r y s t a l l i n e f o r m by
1 4 . B O R O N 7 8 9
c a u t i o u s h e a t i n g . T h e p r o c e d u r e i s s u i t a b l e for t h e p r o d u c t i o n of r e l a t i v e l y l a r g e a m o u n t s of BaS3.
PROPERTIES:
E x t r e m e l y r e a d i l y h y d r o l y z e d ; d e c o m p o s e s e v e n in m o i s t a i r . The p r o d u c t s of h y d r o l y s i s a r e H3B 03 and HaS . T h e c r y s t a l l i n e f o r m c o n s i s t s of w h i t e , b r i l l i a n t , n e e d l e l i k e c r y s t a l s . A l s o o c c u r s in a n a m o r p h o u s f o r m . B e c o m e s v i s c o u s on h e a t i n g and b e g i n s to m e l t at 310°C.
REFERENCES:
P . S a b a t i e r . C o m p t . R e n d . Hebd. S e a n c e s A c a d . Sci. 112, 862 (1891).
H. M o i s s a n . C o m p t . R e n d . Hebd. S e a n c e s A c a d . Sci. 1 1 5 , 205 (1892).
S. S l i w i n s k i . T h e s i s , D r e s d e n , 1944.
J . Hoffmann. Z. a n o r g . a l l g . C h e m . 66, 362 (1910).
Boro n Nitrid e
B N
I. B203 + NH2CONH2 = 2BN + C 02 + 2 H20
69,6 60.0 49.7
One p a r t by w e i g h t of fused, finely divided Ba03 i s i n t i m a t e l y m i x e d w i t h 1.5-2 p a r t s by w e i g h t of u r e a a n d i g n i t e d in a c o v e r e d p r o c e l a i n c r u c i b l e u n t i l it b e c o m e s r e d hot. T h e r e s u l t i n g m a t e r i a l i s g r o u n d a n d w a s h e d with w a t e r to w h i c h a few d r o p s of HC1 h a v e b e e n a d d e d . It i s t h e n f i l t e r e d ; t h e r e s u l t i n g b o r o n n i t r i d e i s o v e n - d r i e d . T h e y i e l d i s 34%, a s Ba03 e v a p o r a t e s d u r i n g ignition.
Π. B203 + 2 N H3 = 2BN + 3 H20
69.6 34.0 49.7
One p a r t of finely divided H3B 03 i s t r i t u r a t e d w i t h two p a r t s of p u r e C a3( P 0 4 )a and t h e m i x t u r e i s d e h y d r a t e d in a H e s s i a n c r u c i b l e . T h i s p r o d u c e s a p o r o u s m i x t u r e , w h i c h i s t h e n p l a c e d in a c r u c i b l e c o v e r e d w i t h a l i d t h r o u g h w h i c h a c l a y t u b e , t o u c h i n g t h e b o t t o m of t h e c r u c i b l e , i s p a s s e d . T h e c r u c i b l e i s i g n i t e d in a g a s - h e a t e d f u r n a c e . S i m u l t a n e o u s l y , N H3 i s b u b b l e d s l o w l y t h r o u g h t h e c r u c i b l e v i a t h e c l a y t u b e . W h e n t h e r e a c t i o n i s c o m p l e t e t h e c o o l e d c r u c i b l e c o n t e n t s a r e s t i r r e d w i t h s o m e w a t e r a n d t r a n s f e r r e d to a b e a k e r ; sufficient HC1 to d i s s o l v e t h e p h o s p h a t e i s a d d e d and t h e m i x t u r e i s b r o u g h t to a b o i l . T h e BN r e s i d u e i s w a s h e d with acidified w a t e r (by decanting) u n t i l t h e w a s h w a t e r i s f r e e of b o t h C as + and P O | ~ i o n s . T h e p r o d u c t i s f i l t e r e d , w a s h e d o n c e a g a i n with w a t e r and d r i e d , f i r s t on a c l a y p l a t e and l a t e r in v a c u u m . T h e y i e l d i s 80-90%, b a s e d on B203.
