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Fluorine, Hydrogen Fluoride
SECTION 3
Fluorine, Hydrogen
Fluoride
H. vo n WARTENBER G
Fluorin e F
2
F l u o r i n e i s p r o d u c e d a t p r e s e n t e i t h e r by e l e c t r o l y s i s of m o l t e n K H F , b e i n g l i b e r a t e d a t a g r a p h i t e a n o d e b e t w e e n 200 a n d 300°C ( s l i g h t c o n t a m i n a t i o n by C F ) , o r f r o m m o l t e n K F · 3 H F a t a Ni a n o d e a t a p p r o x i m a t e l y 100°C, a c c o r d i n g t o t h e m e t h o d of L e b e a u (if t h e m e l t c o n t a i n s w a t e r , c o n t a m i n a t i o n b y O ) . T h e l a t t e r method is the m o s t t r a c t a b l e and h a s been tested extensively. The only suitable v e s s e l m a t e r i a l s a r e F e (which develops a r u s t c o a t i n g on t h e s u r f a c e ) , Cu a n d M g . T h e s a l t i s a v a i l a b l e in a pot m a d e e n t i r e l y of b r a z e d C u w i t h a b o u t 2 - m m . w a l l t h i c k n e s s ( F i g . 104). T h e c o v e r r e s t s l i g h t l y on t h r e e p i e c e s of C a F , p l a c e d in t h e u p p e r t r o u g h , a n d h e l d in p l a c e by a l a y e r of c e m e n t . A l t e r n a t i v e l y , t h e c o v e r r e s t s on a g a s k e t c u t f r o m 5 - m m . - t h i c k soft r u b b e r s h e e t , w h i c h in t u r n r e s t s on t h e flat l i p of t h e p o t . T o s l o w down t h e p e n e t r a t i o n of h u m i d a i r i n t o t h e t r o u g h , t h e l a t t e r i s a l s o p a c k e d w i t h C a F p o w d e r . T h e a n o d e , m a d e of 3 - m m . n i c k e l w i r e , i s attacked only at its e x t r e m e end. T h e r e f o r e , g r e a t e r s e r v i c e life i s o b t a i n e d b y c o i l i n g t h e e l e c t r o d e o r a t t a c h i n g to it a 1 - c m . n i c k e l r o d . T h u s , t h e u s e f u l life of a n e l e c t r o d e m a y b e e x t e n d e d t o t h e e l e c t r o l y s i s of a p p r o x i m a t e l y t w o c o m p l e t e s a l t b a t c h e s . A f t e r t h a t , a n e w a n o d e c a n e a s i l y b e i n s e r t e d into t h e connecting copper adapter. The melt usually s p a t t e r s and c r e e p s up the w a l l s . T h i s i s the r e a s o n for placing the insulation so high in t h e t h i c k - w a l l Cu a d a p t e r , w h i c h i s c e m e n t e d i n t o t h e u p p e r tube with l i t h a r g e - g l y c e r o l . T h i s a d a p t e r should p r e f e r a b l y be t a k e n out w i t h s t r o n g p l i e r s a t t h e end of e a c h e l e c t r o l y s i s c y c l e and thoroughly washed. The s t u r d y fluorite stopper is s e c u r e d with t h e s a m e c e m e n t . It i s e v e n s i m p l e r t o u s e a o n e - h o l e r u b b e r stopper, coated with polytrifluorochloroethylene oil. The anode is s u r r o u n d e d by a c o p p e r o r , b e t t e r , a n i c k e l t u b e . T h r e e s t r u t s extend downward f r o m the tube and a r e attached, by keyed c o p p e r c o n n e c t i o n s , t o a Cu p l a t e . T h i s p l a t e a c t s a s p r o t e c t i o n a g a i n s t 3
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t h e H r i s i n g f r o m t h e w a l l of t h e p o t . T h e pot s e r v e s a s t h e c a t h o d e . T h i s i s t h e b e s t a r r a n g e m e n t s i n c e it l e a v e s a l a r g e f r e e c r o s s s e c t i o n f o r t h e e l e c t r o l y t e s a l t . T h e Cu t u b e m a y b e c o m e c o a t e d w i t h an i n s u l a t i n g l a y e r of f l u o r i d e , w h i c h , h o w e v e r , s o m e t i m e s d i s s o l v e s if t h e t e m p e r a t u r e r i s e s t o o h i g h , m a k i n g it n e c e s s a r y to r e p l a c e the tube from t i m e to t i m e . The tube cannot b e r e p l a c e d w i t h s i n t e r e d a l u m i n a , w h i c h d i s s o l v e s in t h e m e l t . T h i s inconvenience is unfortunately encountered with all apparatus f o r p r o d u c t i o n of f l u o r i n e . In o r d e r t o g e n e r a t e t h e F u n d e r a p r e s s u r e of a b o u t 10 c m . of w a t e r , t h e pot i s intentionally m a d e tall. The outlet tubing m u s t be at l e a s t 6 m m . inside d i a m e t e r , since some electrolyte particles a r e always entrained with the g a s . A single e l e c t r o l y s i s b a t c h r e q u i r e s 1.2 k g , of d i f l u o r i d e of t h e h i g h e s t p u r i t y and 300 g . of f r e s h l y d i s t i l l e d , a n h y d r o u s H F . T h e a p p a r a t u s i s put on a hot p l a t e w h i c h i s p l a c e d on a n o r d i n a r y p l a t f o r m s c a l e , m a k i n g it e a s y t o d e t e r m i n e f r o m t h e l o s s in w e i g h t (300 g.) w h e t h e r r e f i l l i n g i s n e c e s s a r y and t o avoid u n n e c e s s a r y o v e r s h o o t i n g of t h e t e m p e r a t u r e . At t h e b e g i n n i n g of t h e p r e p a r a t i o n a h o r i z o n t a l l y d i r e c t e d Bunsen flame is used as auxiliary heat, so t h a t t h e s a l t i s m e l t e d and h e a t e d t o 70°C in half an h o u r ( a t t a c h a t h e r m o m e t e r ) . No F i g . 104. P r e p a r a heat i s applied during the e l e c t r o l y s i s , a t i o n of f l u o r i n e . w h i c h p r o c e e d s a t a b o u t t e n v o l t s and about 4 - 5 a m p . ( w i t h Ni r o d a n o d e s , 6 a m p . y i e l d s 40 m l . of F / m i n . ) . T h e hot p l a t e s e r v e s only t o k e e p t h e c o n t e n t s of t h e pot in t h e liquid s t a t e d u r i n g i n t e r r u p t i o n s in t h e r u n . A f t e r e l e c t r o l y t e d e p l e t i o n , t h e c o v e r i s r e m o v e d and t h e r e s i d u a l s a l t i s a l l o w e d t o solidify w h i l e t h e c o n t a i n e r i s b e i n g r o t a t e d , t h u s c r e a t i n g a c a v i t y ( w o r k u n d e r a hood, w e a r i n g g o g g l e s ; p at 150°C i s 130 m m . ) . F r e s h H F i s a d d e d t o t h e c a v i t y , t h e v e s s e l i s c o v e r e d w i t h a p i e c e of Cu s h e e t , and t h e H F i s left t o b e a b s o r b e d b y t h e s a l t o v e r n i g h t . A f t e r h e a t i n g t o 90°C, t h e c o v e r w i t h t h e a n o d e c a n b e r e p l a c e d . In o r d e r t o r e m o v e t h e s m a l l a m o u n t s of H F , t h e p r o d u c t g a s i s f i r s t l e d t h r o u g h a 10 x 50 m m . , D r y I c e c o o l e d Cu b o t t l e b r a z e d t o a t u b e of p o o r l y h e a t - c o n d u c t i n g n i c k e l s i l v e r alloy ( p ~ 1 m m . ) a n d t h e n t h r o u g h a C u t u b e filled w i t h g r a n u l a r N a F and p r o v i d e d w i t h c o p p e r plug v a l v e s . D e t e c t i o n of F in t h e e x i t s t r e a m ( a s w e l l a s at l e a k s ) i s e a s y . A j e t of i l l u m i n a t i n g g a s o r a r a g s o a k e d in m a c h i n e o i l and a t t a c h e d t o a w i r e w i l l i g n i t e on c o n t a c t w i t h F . If t h e s a l t m a s s h a s b e e n w e l l d r i e d , t h e t r a c e s of w a t e r d i s a p p e a r c o m p l e t e l y a f t e r t h e f i r s t h o u r of e l e c t r o l y s i s . Any 0 which may be formed cannot be 2
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H F
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F
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FLUORINE,
HYDROGEN
FLUORIDE
145
s e p a r a t e d f r o m t h e F ; it m a y b e d e t e r m i n e d , a l t h o u g h not c o n v e n i e n t l y , b y s h a k i n g w i t h Hg [2], W i t h t h e p a c k i n g m a t e r i a l s now on t h e m a r k e t , f o r e x a m p l e , T e f l o n , it i s e a s y t o b u i l d s i m i l a r e q u i p m e n t m a d e of s o m e w h a t t h i c k e r s h e e t c o p p e r o r of c a s t m a g n e s i u m by u s i n g T e f l o n i n s u l a t e d g a s k e t s and t i g h t e n i n g t h e a p p a r a t u s w i t h s c r e w s . W h e n a C u pot w i t h 5 - m m . - t h i c k w a l l s , 35 c m . h i g h a n d 15 c m . in d i a m e t e r , c o n t a i n i n g 5 k g . of K H F , i s u s e d , a c u r r e n t of 5 a m p . m a y b e a p p l i e d . T h e H F g a s c a n t h e n b e fed a l m o s t c o n t i n u o u s l y t o t h e o u t e r c h a m b e r , t h u s r e p l a c i n g t h e r a w m a t e r i a l a s it i s consumed. 3
2
PROPERTIES:
Atomic weight 19.00. M.p. - 2 2 3 ° C , b.p. - 1 8 7 ° C ; d ( l i q . ) l . l l , d (gas) 1.31 ( a i r = 1). F l u o r i n e d o e s n o t a t t a c k q u a r t z and v e r y d r y g l a s s . F o r h e a t i n g in a F a t m o s p h e r e , P t t u b e s a r e u s e d , o r e v e n b e t t e r , s i n t e r e d a l u m i n a t u b e s (up t o 600°C), w h i l e C u t u b e s a r e u s e f u l u p t o 350°C and Ni t o 600 o r 700°C. T e f l o n o r K e l - F i s u s e d a s g a s k e t i n g m a t e r i a l and K e l - F g r e a s e i s u s e d f o r l u b r i c a t i o n of s t o p c o c k s and g r o u n d j o i n t s . F o r c o m m e r c i a l a p p a r a t u s , s e e [3, 4 ] , 2
REFERENCES:
1. H. v . W a r t e n b e r g . Z . a n o r g . a l l g . 244, 337 ( 1 9 4 0 ) . 2. H. v . W a r t e n b e r g . Z . a n o r g . a l l g . H. S c h m i t z and H. J . S c h u m a c h e r . Z . 221 ( 1 9 4 0 ) . 3 . Ind. E n g . C h e m . , Ind. E d . 3 9 , 2 4 4 - 2 8 6 4 . Angew. C h e m . 1 9 , 256 ( 1 9 4 7 ) .
Chem.
1 9 3 , 409 ( 1 9 3 0 ) ;
C h e m . 2 4 2 , 408 ( 1 9 3 8 ) ; anorg. allg. Chem. 245, (1946).
Hydroge n Fluorid e HF
Precautionary measures: Since hydrogen fluoride solutions, p a r t i c u l a r l y w h e n c o n c e n t r a t e d , c a u s e e x t r e m e l y painful and p r o t r a c t e d b u r n s , a p a s t e m a d e of m a g n e s i u m o x i d e w i t h a l i t t l e g l y c e r o l s h o u l d b e k e p t on h a n d w h e n w o r k i n g w i t h l a r g e r q u a n t i t i e s . T h e e y e s m u s t b e p r o t e c t e d and r u b b e r g l o v e s m u s t b e w o r n . I. CRUDE HYDROFLUORIC ACID [1]
L a b o r a t o r y p r e p a r a t i o n of t h i s m a t e r i a l w i l l a l m o s t n e v e r b e u n d e r t a k e n . T o o b t a i n 0.25 k g . of H F , 1 k g . of f i n e l y p u l v e r i z e d f l u o r i t e o r , e v e n b e t t e r , c r y o l i t e (for S i - f r e e HF) i s v i g o r o u s l y
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h e a t e d w i t h 2.25 t o 2.5 k g . of 97.5% A s - f r e e H S 0 in a s m a l l a u t o c l a v e p l a c e d on an a i r b a t h . A l e a d t u b e 1.5 m e t e r s long and 2 c m . in d i a m e t e r , w i t h an a t t a c h e d L i e b i g c o n d e n s e r , i s s o l d e r e d t o t h e c o v e r . Run d u r a t i o n , 4 h o u r s . T h e p r o d u c t i s c o l l e c t e d in a copper flask cooled with i c e - s a l t m i x t u r e . I m p u r i t i e s : H S i F , H C l , H S 0 , H S 0 , H S 0 F , Pb. 2
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II. PURE, 3 5 % HYDROFLUORIC ACID
T h i s s o l u t i o n i s c o m m e r c i a l l y a v a i l a b l e in p o l y e t h y l e n e b o t t l e s a n d i s a l r e a d y q u i t e p u r e . F o r f u r t h e r p u r i f i c a t i o n , it i s d i s t i l l e d f r o m a N a F - c o n t a i n i n g P t r e t o r t into a P t r e c e i v e r , l e a v i n g b e h i n d t h e S O | " and S i F | ~ i o n s . A l i t t l e P b C 0 i s a d d e d t o r e m o v e t h e C I " ; t h i s y i e l d s P b C I F , w h i c h i s i n s o l u b l e in c o n c e n t r a t e d H F . An e x c e s s of P b C 0 d o e s no h a r m , e v e n in t h e p r e s e n c e of H S 0 . O r g a n i c m a t e r i a l i s r e m o v e d only w h e n K M n 0 i s a d d e d ( d r o p w i s e ) . V e s s e l m a t e r i a l s : P t , Ag, C u , Mg (but not P b ) , c e l l u l o i d ( m a y b e e a s i l y s h a p e d in w a r m w a t e r ) , p o l y e t h y l e n e , p a r a f f i n , m e t a l d i s h e s c o a t e d w i t h B a k e l i t e , T e f l o n , e t c . See a l s o s e c t i o n on F . B o i l i n g p o i n t s of v a r i o u s H 0 / H F m i x t u r e s a r e g i v e n in [4]. 3
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III. ANHYDROUS HYDROGEN FLUORIDE
D i s t i l l a t i o n of 1.2 k g . of a n h y d r o u s K H F a t 500°C y i e l d s 250 g . of H F . T e c h n i c a l g r a d e K H F i s d i s s o l v e d in w a r m w a t e r , s o m e P b C 0 i s a d d e d t o e l i m i n a t e C I " , t h e K S i F and P b C I F a r e a l l o w e d t o s e t t l e , and t h e c l e a r s o l u t i o n i s e v a p o r a t e d in C u o r Mg d i s h e s u n t i l c r y s t a l l i z a t i o n o c c u r s . A l t e r n a t i v e l y , a q u a n t i t y of h y d r o f l u o r i c a c i d i s d i v i d e d into two e q u a l p a r t s , o n e of w h i c h i s n e u t r a l i z e d w i t h K C O , m i x e d w i t h t h e o t h e r p a r t and e v a p o r a t e d . F i l t e r hot t h r o u g h a Cu funnel. T h e c r y s t a l s w h i c h s e p a r a t e on c o o l i n g a r e a l l o w e d t o d r a i n and a r e d r i e d i n i t i a l l y on f i l t e r p a p e r , at 100°C, F u r t h e r d r y i n g m u s t b e c a r r i e d out w i t h g r e a t c a r e at 130 t o 140°C. A t h i n l a y e r of c r y s t a l s i s p l a c e d on a Mg o r Cu s h e e t t u r n e d u p 1-2 c m . a l o n g t h e e d g e s , a n d t h e s h e e t i s p l a c e d on a l a r g e h o t p l a t e . A f t e r 2 - 3 d a y s t h e c r y s t a l s a r e g r o u n d in a coffee m i l l and d r i e d f o r a n o t h e r d a y , a f t e r w h i c h t h e y a r e s t o r e d in p a r a f f i n coated g l a s s bottles. The dust from the salt is disagreeable. The c o m p o u n d c a n b e o b t a i n e d m o r e r e a d i l y by d e c o m p o s i t i o n of N a H F , but t h e d e c o m p o s i t i o n s t a r t s a l r e a d y d r y i n g , and N a H F i s t h e r e f o r e not r e c o m m e n d e d a s a r a w m a t e r i a l . D i s t i l l a t i o n i s c a r r i e d out in a Cu f l a s k , 24 c m . h i g h , p r o v i d e d w i t h a c o n i c a l g r o u n d s t o p p e r , 4 c m . in d i a m e t e r , h e l d in p l a c e w i t h s c r e w c l a m p s ( F i g , 105). T h e c o n e i s l u b r i c a t e d w i t h g r a p h i t e p a r a f f i n oil o r K e l - F g r e a s e t o p r e v e n t f r e e z i n g of t h e j o i n t . T h e l - m . - l o n g Cu t u b e m u s t b e 2 - 2 . 5 c m . in d i a m e t e r , s i n c e s a l t i s c a r r i e d o v e r and i n c o n v e n i e n t p l u g g i n g c a n o c c u r in t h e m i d d l e of 2
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t h e r u n . T h e g l a s s c o n d e n s e r i s g a s k e t e d w i t h a p i e c e of r u b b e r h o s e , a n d to s l o w down t h e d e c o m p o s i t i o n , a few t u r n s of w a t e r c o o l e d t i n t u b i n g a r e wound on it. T h e Cu t u b e i s a l l o w e d to s t a n d in H C l / B r u n t i l it i s b r i g h t , o r t h e i n i t i a l Η F f r a c t i o n w i l l b e b r o w n . T h e r e t o r t s h o u l d b e p r o v i d e d w i t h a Cu t h e r m o w e l l , p r o j e c t i n g u p w a r d for 5 c m . f r o m t h e b o t t o m a n d e x t e r n a l l y b r a z e d in p l a c e , t o a c c o m m o d a t e a c o p p e r - c o n s t a n t a n t h e r m o c o u p l e . T h e r e t o r t i s h e a t e d e i t h e r on a m u l t i p l e b u r n e r in a n i r o n j a c k e t o r , p r e f e r a b l y , in a n e l e c t r i c f u r n a c e . B e f o r e filling it s h o u l d b e c l e a n e d w i t h HC1 u n t i l b r i g h t and d r i e d c a r e f u l l y in a s t r e a m of C 0 . T h e Cu r e c e i v e r (250 m l . ) i s c o n n e c t e d by a s p e c i a l c o u p l i n g ( F i g . 106) and m u s t b e c l e a n e d w i t h HC1 u n t i l b r i g h t . It i s t h e n d r i e d and r e d u c e d in a s t r e a m of H at 300°C. D u r i n g d i s t i l l a t i o n , u s e an i c e - s a l t m i x t u r e (—10°C) f o r c o o l i n g . A s e c o n d c o n tainer provides protection against overflow. The r e t o r t is first h e a t e d s l o w l y f o r a p p r o x i m a t e l y 3 / 4 h o u r to a b o u t 400 to 500°C, t h a t i s until H F b e g i n s to d r i p into a Pt d i s h below (leave the s c r e w c o u p l i n g a t Ε o p e n ) . V a p o r p r e s s u r e s of K F a n d H F a r e g i v e n in [6]. A f t e r about 10 m l . h a s b e e n c o l l e c t e d , a t e s t i s m a d e t o d e t e r m i n e w h e t h e r a s t r i p of f i l t e r p a p e r g e l a t i n i z e s i m m e d i a t e l y . If s o , t h e a c i d i s a n h y d r o u s . Now t h e c o u p l i n g a t Ε i s t i g h t e n e d ( u s e p l i e r s and r u b b e r g l o v e s ) and t h e f r e e z i n g b a t h i s put in p l a c e . R a i s i n g of t h e t e m p e r a t u r e t o 500°C m u s t b e a c c o m p l i s h e d w i t h g r e a t c a r e , s i n c e at t h a t t e m p e r a t u r e K F b e g i n s t o s e p a r a t e f r o m t h e m e l t and v i o l e n t e v o l u t i o n of H F a l s o o c c u r s [2], T h e o p e r a t i o n i s d e c i d e d l y m o r e c o n v e n i e n t if a t h i c k - w a l l e d Cu c a p i l l a r y ( s h o w n w i t h d o t t e d l i n e s ) i s b r a z e d t o t h e Cu t u b e . T h e c a p i l l a r y s h o u l d d i p about 2 c m . into a Hg pool in a P t d i s h . If t h i s i s d o n e , t h e c o u p l i n g s on t h e r e c e i v e r s m a y b e t i g h t e n e d b e f o r e t h e r u n and t h e f i r s t few m i l l i l i t e r s a l l o w e d t o d r i p f r o m t h e c a p i l l a r y u n t i l t h e p a p e r t e s t s h o w s t h e a b s e n c e of w a t e r . T h e c a p i l l a r y m a y t h e n b e s e a l e d off s i m p l y b y r a i s i n g t h e l e v e l of t h e m e r c u r y . Should t h e e v o l u t i o n of H F b e t o o v i o l e n t , e x c e s s H F c a n e s c a p e t h r o u g h t h e c a p i l l a r y , a c c o m p a n i e d , of c o u r s e , b y n o x i o u s f u m e s . 2
2
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F i g . 1 0 5 . D i s t i l l a t i o n of a n h y d r o u s h y d r o f l u o r i c acid. A ) d i s t i l l a t i o n r e t o r t ( C u ) ; B) c o n d e n s e r ( i n n e r t u b e of C u ) ; C) r e c e i v e r ( C u ) , —10°C;£) s e c o n d r e c e i v e r , —10°C; E,F) c o n i c a l s c r e w c o u p l i n g s .
148
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T h e e v o l u t i o n s u b s i d e s a f t e r about 3 h o u r s and t h e h e a t i n g i s d i s c o n t i n u e d . L o o s e n Ε and F a n d c l o s e t h e m off w i t h Cu c o n e s . If t h e d i s t i l l e d a c i d i s t o b e s t o r e d , t h e t u b e s c a n b e c l o s e d off at Ε and F w i t h s o l i d Cu c o n e s e q u i p p e d w i t h s c r e w c a p s . A f t e r c o o l i n g , t h e c o n t e n t s of t h e r e t o r t m a y b e d i s s o l v e d in b o i l i n g w a t e r and r e g e n e r a t e d w i t h a q u e o u s H F .
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F i g . 106. D e t a i l s of t h e c o n i c a l copper coupling. The cones a r e interchangeable. F o r r e g e n e r a t i o n , t h e s o l u t i o n i s t r e a t e d in a l a r g e Cu o r Mg d i s h w i t h sufficient p u r e , c o m m e r c i a l (35-40%) H F to t u r n l i t m u s completely r e d . The solution i s then e v a p o r a t e d o v e r an open f l a m e but not to t h e p o i n t w h e r e s p a t t e r i n g o c c u r s . T h e s a l t m a s s i s t h e n c r u s h e d and d r i e d a s d e s c r i b e d p r e v i o u s l y . T h e r e s u l t a n t H F s t i l l c o n t a i n s t r a c e s of e n t r a i n e d K F and c a n b e r e d i s t i l l e d at 30-35°C into t h e s e c o n d r e c e i v e r . F o r v e r y p u r e H F , s i l v e r e q u i p m e n t should b e u s e d [2]. Since o r g a n i c s u b s t a n c e s a r e i m m e d i a t e l y d e c o m p o s e d by H F v a p o r , j o i n t s c a n b e m a d e t i g h t o n l y by m e a n s of t h e Cu c o n e s d e s c r i b e d . A l t e r n a t i v e l y f u s e d s u l f u r m a y b e u s e d , w i t h p i c e i n o r a l i k e s u b s t a n c e c o v e r i n g c r a c k s in t h e sulfur m a s s . A s a t e m p o r a r y e x p e d i e n t , r e s u l t i n g in not q u i t e anhydrous acid, the seal can be made with w e l l - d r i e d l i t h a r g e glycerol cement. L i q u i d H F i s a v a i l a b l e in s t e e l t a n k s o r c y l i n d e r s . ( H e a t g e n t l y w i t h f l a m e t o m a k e it flow.) In o r d e r t o r e n d e r t h e l i q u i d H F c o m p l e t e l y a n h y d r o u s , f l u o r i n e m a y be bubbled through using a silver capillary. The F g a s d e c o m p o s e s t r a c e s of w a t e r . T h u s a c y l i n d e r H F c a n b e p a r t i a l l y d r i e d by s o m e w h a t l o o s e n i n g t h e m a i n v a l v e w i t h a w r e n c h in a c o l d r o o m and t h e n p u t t i n g t h e c y l i n d e r in a c o n t a i n e r of a p p r o p r i a t e height, filled with i c e - s a l t m i x t u r e ; after the cylinder h a s cooled down, t h e v a l v e i s r e m o v e d c o m p l e t e l y and F i s b u b b l e d t h r o u g h o r half an h o u r f r o m a f l u o r i n e c y l i n d e r t h r o u g h a s i l v e r c a p i l l a r y ; t h e v a l v e i s t h e n s c r e w e d b a c k on and t i g h t e n e d w i t h t h e w r e n c h . T h e f l u o r i n e p r e s s u r e p r o d u c e d in t h e u s u a l l a b o r a t o r y g e n e r a t o r s i s not sufficient f o r t h e H F c y l i n d e r s . F o r a l l p r a c t i c a l p u r p o s e s , F d o e s n o t d i s s o l v e in liquid H F . I n s t e a d of u s i n g f l u o r i n e , t h e w a t e r m a y b e r e m o v e d by d r o p w i s e a d d i t i o n of t h i o n y l c h l o r i d e , w h i c h l i b e r a t e s g a s e o u s HC1, S 0 a n d S O F , all i n s o l u b l e in H F [K. W i e c h e r t , Z . a n o r g . C h e m . 2 6 1 , 314 ( 1 9 5 0 ) ] . 2
2
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HYDROGEN
149
FLUORIDE
P u r e H F for v e r y s m a l l s c a l e e x p e r i m e n t s b e e a s i l y o b t a i n e d (together with hydrogen) by placing a copper boat with w e l l d r i e d P b F in a p l a t i n u m o r c o p p e r t u b e in f r o n t of t h e c o m p o u n d to be r e a c t e d with the nascent H F . The boat is heated to r e d heat in a s t r e a m of h y d r o g e n . C o n d u i t s f o r H F g a s a r e m a d e of w e l l - d r i e d c o p p e r t u b e s p r o v i d e d w i t h c o n i c a l c o p p e r j o i n t s . In s u c h t u b e s H F g a s m a y b e h e a t e d to 1000°C (of c o u r s e , p r o t e c t i o n f r o m t h e a t m o s p h e r e m u s t be provided). Sintered alumina tubes may be used up to 500°C. C o p p e r c a p s , t e m p o r a r i l y c e m e n t e d on w i t h l i t h a r g e g l y c e r o l , m a y s e r v e a s c l o s u r e s , b u t it i s b e t t e r t o s o l d e r t h e m onto t h e a l u m i n a t u b e . T o a c c o m p l i s h t h i s , t h e a l u m i n a t u b e i s e l e c t r o l y t i c a l l y c o a t e d w i t h c o p p e r , a n d soft s o l d e r i s u s e d f o r a t t a c h i n g t h e c a p s . C o m p l e t e l y a n h y d r o u s H F d o e s not a t t a c k q u a r t z . L e a d and o r g a n i c s u b s t a n c e s a r e d e s t r o y e d , e x c e p t f o r p o l y m e r i z e d t e t r a f l u o r o e t h y l e n e (Teflon) [ 5 ] . C o p p e r (not b r a s s ) s t o p c o c k s o r , p r e f e r a b l y , p l a t i n u m v a l v e s ( B o d e n s t e i n d e s i g n ) s e r v e t o s h u t off t h e flow. It i s a d v i s a b l e t o m a k e t h e s t o p c o c k b o d y of c o p p e r and t o t u r n out t h e plug f r o m a T e f l o n b l o c k on a l a t h e . Such a p l u g t u r n s e a s i l y and n e e d s n o l u b r i c a t i o n . 2
PROPERTIES:
F o r m u l a weight 20.01. B.p. 1 9 . 5 ° C ; f o r b . p . at v a r i o u s p r e s s u r e s s e e [3]; m . p . - 8 5 ° C ; d (liq.) 0 . 9 8 7 . t 188°C, p 66.2 k g . / c m . , d 0.29. 2
c r
c
r
c r
REFERENCES:
1. O. Ruff. C h e m i e d e s F l u o r s [ F l u o r i n e C h e m i s t r y ] B e r l i n , 1920, d e t a i l e d d e s c r i p t i o n on t h e p r e p a r a t i o n of n u m e r o u s compounds. 2 . K. F r e d e n h a g e n . Z . a n o r g . a l l g . C h e m . 1 7 8 , 289 (1929); U l l m a n n , E n c y k l o p a d i e d. t e c h n . C h e m . [ E n c y c l o p e d i a of T e c h n i c a l C h e m i s t r y ] 3 r d E d . , V o l . 7, p . 585 (1957). 3 . K. F r e d e n h a g e n . Z . a n o r g . a l l g . C h e m . 210, 220 ( 1 9 3 3 ) . 4 . K. F r e d e n h a g e n . Z . p h y s i k . C h e m . A 1 6 2 , 4 6 4 ( 1 9 3 2 ) : U l l m a n n , E n c y k l o p a d i e d. t e c h n . C h e m . [ E n c y c l o p e d i a of T e c h n i c a l C h e m i s t r y ] 3 r d E d . , V o l . 7, p . 585 (1957). 5. W. H a n f o r d and R. J o y c e . J . A m e r . C h e m . S o c . 6 8 , 2082 (1946). 6. G H. C a d y . J . A m e r . C h e m . S o c . 5 6 , 1431 ( 1 9 3 4 ) . e
Fluorine, Hydrogen
Fluoride
H. vo n WARTENBER G
Fluorin e F
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F l u o r i n e i s p r o d u c e d a t p r e s e n t e i t h e r by e l e c t r o l y s i s of m o l t e n K H F , b e i n g l i b e r a t e d a t a g r a p h i t e a n o d e b e t w e e n 200 a n d 300°C ( s l i g h t c o n t a m i n a t i o n by C F ) , o r f r o m m o l t e n K F · 3 H F a t a Ni a n o d e a t a p p r o x i m a t e l y 100°C, a c c o r d i n g t o t h e m e t h o d of L e b e a u (if t h e m e l t c o n t a i n s w a t e r , c o n t a m i n a t i o n b y O ) . T h e l a t t e r method is the m o s t t r a c t a b l e and h a s been tested extensively. The only suitable v e s s e l m a t e r i a l s a r e F e (which develops a r u s t c o a t i n g on t h e s u r f a c e ) , Cu a n d M g . T h e s a l t i s a v a i l a b l e in a pot m a d e e n t i r e l y of b r a z e d C u w i t h a b o u t 2 - m m . w a l l t h i c k n e s s ( F i g . 104). T h e c o v e r r e s t s l i g h t l y on t h r e e p i e c e s of C a F , p l a c e d in t h e u p p e r t r o u g h , a n d h e l d in p l a c e by a l a y e r of c e m e n t . A l t e r n a t i v e l y , t h e c o v e r r e s t s on a g a s k e t c u t f r o m 5 - m m . - t h i c k soft r u b b e r s h e e t , w h i c h in t u r n r e s t s on t h e flat l i p of t h e p o t . T o s l o w down t h e p e n e t r a t i o n of h u m i d a i r i n t o t h e t r o u g h , t h e l a t t e r i s a l s o p a c k e d w i t h C a F p o w d e r . T h e a n o d e , m a d e of 3 - m m . n i c k e l w i r e , i s attacked only at its e x t r e m e end. T h e r e f o r e , g r e a t e r s e r v i c e life i s o b t a i n e d b y c o i l i n g t h e e l e c t r o d e o r a t t a c h i n g to it a 1 - c m . n i c k e l r o d . T h u s , t h e u s e f u l life of a n e l e c t r o d e m a y b e e x t e n d e d t o t h e e l e c t r o l y s i s of a p p r o x i m a t e l y t w o c o m p l e t e s a l t b a t c h e s . A f t e r t h a t , a n e w a n o d e c a n e a s i l y b e i n s e r t e d into t h e connecting copper adapter. The melt usually s p a t t e r s and c r e e p s up the w a l l s . T h i s i s the r e a s o n for placing the insulation so high in t h e t h i c k - w a l l Cu a d a p t e r , w h i c h i s c e m e n t e d i n t o t h e u p p e r tube with l i t h a r g e - g l y c e r o l . T h i s a d a p t e r should p r e f e r a b l y be t a k e n out w i t h s t r o n g p l i e r s a t t h e end of e a c h e l e c t r o l y s i s c y c l e and thoroughly washed. The s t u r d y fluorite stopper is s e c u r e d with t h e s a m e c e m e n t . It i s e v e n s i m p l e r t o u s e a o n e - h o l e r u b b e r stopper, coated with polytrifluorochloroethylene oil. The anode is s u r r o u n d e d by a c o p p e r o r , b e t t e r , a n i c k e l t u b e . T h r e e s t r u t s extend downward f r o m the tube and a r e attached, by keyed c o p p e r c o n n e c t i o n s , t o a Cu p l a t e . T h i s p l a t e a c t s a s p r o t e c t i o n a g a i n s t 3
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t h e H r i s i n g f r o m t h e w a l l of t h e p o t . T h e pot s e r v e s a s t h e c a t h o d e . T h i s i s t h e b e s t a r r a n g e m e n t s i n c e it l e a v e s a l a r g e f r e e c r o s s s e c t i o n f o r t h e e l e c t r o l y t e s a l t . T h e Cu t u b e m a y b e c o m e c o a t e d w i t h an i n s u l a t i n g l a y e r of f l u o r i d e , w h i c h , h o w e v e r , s o m e t i m e s d i s s o l v e s if t h e t e m p e r a t u r e r i s e s t o o h i g h , m a k i n g it n e c e s s a r y to r e p l a c e the tube from t i m e to t i m e . The tube cannot b e r e p l a c e d w i t h s i n t e r e d a l u m i n a , w h i c h d i s s o l v e s in t h e m e l t . T h i s inconvenience is unfortunately encountered with all apparatus f o r p r o d u c t i o n of f l u o r i n e . In o r d e r t o g e n e r a t e t h e F u n d e r a p r e s s u r e of a b o u t 10 c m . of w a t e r , t h e pot i s intentionally m a d e tall. The outlet tubing m u s t be at l e a s t 6 m m . inside d i a m e t e r , since some electrolyte particles a r e always entrained with the g a s . A single e l e c t r o l y s i s b a t c h r e q u i r e s 1.2 k g , of d i f l u o r i d e of t h e h i g h e s t p u r i t y and 300 g . of f r e s h l y d i s t i l l e d , a n h y d r o u s H F . T h e a p p a r a t u s i s put on a hot p l a t e w h i c h i s p l a c e d on a n o r d i n a r y p l a t f o r m s c a l e , m a k i n g it e a s y t o d e t e r m i n e f r o m t h e l o s s in w e i g h t (300 g.) w h e t h e r r e f i l l i n g i s n e c e s s a r y and t o avoid u n n e c e s s a r y o v e r s h o o t i n g of t h e t e m p e r a t u r e . At t h e b e g i n n i n g of t h e p r e p a r a t i o n a h o r i z o n t a l l y d i r e c t e d Bunsen flame is used as auxiliary heat, so t h a t t h e s a l t i s m e l t e d and h e a t e d t o 70°C in half an h o u r ( a t t a c h a t h e r m o m e t e r ) . No F i g . 104. P r e p a r a heat i s applied during the e l e c t r o l y s i s , a t i o n of f l u o r i n e . w h i c h p r o c e e d s a t a b o u t t e n v o l t s and about 4 - 5 a m p . ( w i t h Ni r o d a n o d e s , 6 a m p . y i e l d s 40 m l . of F / m i n . ) . T h e hot p l a t e s e r v e s only t o k e e p t h e c o n t e n t s of t h e pot in t h e liquid s t a t e d u r i n g i n t e r r u p t i o n s in t h e r u n . A f t e r e l e c t r o l y t e d e p l e t i o n , t h e c o v e r i s r e m o v e d and t h e r e s i d u a l s a l t i s a l l o w e d t o solidify w h i l e t h e c o n t a i n e r i s b e i n g r o t a t e d , t h u s c r e a t i n g a c a v i t y ( w o r k u n d e r a hood, w e a r i n g g o g g l e s ; p at 150°C i s 130 m m . ) . F r e s h H F i s a d d e d t o t h e c a v i t y , t h e v e s s e l i s c o v e r e d w i t h a p i e c e of Cu s h e e t , and t h e H F i s left t o b e a b s o r b e d b y t h e s a l t o v e r n i g h t . A f t e r h e a t i n g t o 90°C, t h e c o v e r w i t h t h e a n o d e c a n b e r e p l a c e d . In o r d e r t o r e m o v e t h e s m a l l a m o u n t s of H F , t h e p r o d u c t g a s i s f i r s t l e d t h r o u g h a 10 x 50 m m . , D r y I c e c o o l e d Cu b o t t l e b r a z e d t o a t u b e of p o o r l y h e a t - c o n d u c t i n g n i c k e l s i l v e r alloy ( p ~ 1 m m . ) a n d t h e n t h r o u g h a C u t u b e filled w i t h g r a n u l a r N a F and p r o v i d e d w i t h c o p p e r plug v a l v e s . D e t e c t i o n of F in t h e e x i t s t r e a m ( a s w e l l a s at l e a k s ) i s e a s y . A j e t of i l l u m i n a t i n g g a s o r a r a g s o a k e d in m a c h i n e o i l and a t t a c h e d t o a w i r e w i l l i g n i t e on c o n t a c t w i t h F . If t h e s a l t m a s s h a s b e e n w e l l d r i e d , t h e t r a c e s of w a t e r d i s a p p e a r c o m p l e t e l y a f t e r t h e f i r s t h o u r of e l e c t r o l y s i s . Any 0 which may be formed cannot be 2
2
2
H
H F
2
2
2
F
3.
FLUORINE,
HYDROGEN
FLUORIDE
145
s e p a r a t e d f r o m t h e F ; it m a y b e d e t e r m i n e d , a l t h o u g h not c o n v e n i e n t l y , b y s h a k i n g w i t h Hg [2], W i t h t h e p a c k i n g m a t e r i a l s now on t h e m a r k e t , f o r e x a m p l e , T e f l o n , it i s e a s y t o b u i l d s i m i l a r e q u i p m e n t m a d e of s o m e w h a t t h i c k e r s h e e t c o p p e r o r of c a s t m a g n e s i u m by u s i n g T e f l o n i n s u l a t e d g a s k e t s and t i g h t e n i n g t h e a p p a r a t u s w i t h s c r e w s . W h e n a C u pot w i t h 5 - m m . - t h i c k w a l l s , 35 c m . h i g h a n d 15 c m . in d i a m e t e r , c o n t a i n i n g 5 k g . of K H F , i s u s e d , a c u r r e n t of 5 a m p . m a y b e a p p l i e d . T h e H F g a s c a n t h e n b e fed a l m o s t c o n t i n u o u s l y t o t h e o u t e r c h a m b e r , t h u s r e p l a c i n g t h e r a w m a t e r i a l a s it i s consumed. 3
2
PROPERTIES:
Atomic weight 19.00. M.p. - 2 2 3 ° C , b.p. - 1 8 7 ° C ; d ( l i q . ) l . l l , d (gas) 1.31 ( a i r = 1). F l u o r i n e d o e s n o t a t t a c k q u a r t z and v e r y d r y g l a s s . F o r h e a t i n g in a F a t m o s p h e r e , P t t u b e s a r e u s e d , o r e v e n b e t t e r , s i n t e r e d a l u m i n a t u b e s (up t o 600°C), w h i l e C u t u b e s a r e u s e f u l u p t o 350°C and Ni t o 600 o r 700°C. T e f l o n o r K e l - F i s u s e d a s g a s k e t i n g m a t e r i a l and K e l - F g r e a s e i s u s e d f o r l u b r i c a t i o n of s t o p c o c k s and g r o u n d j o i n t s . F o r c o m m e r c i a l a p p a r a t u s , s e e [3, 4 ] , 2
REFERENCES:
1. H. v . W a r t e n b e r g . Z . a n o r g . a l l g . 244, 337 ( 1 9 4 0 ) . 2. H. v . W a r t e n b e r g . Z . a n o r g . a l l g . H. S c h m i t z and H. J . S c h u m a c h e r . Z . 221 ( 1 9 4 0 ) . 3 . Ind. E n g . C h e m . , Ind. E d . 3 9 , 2 4 4 - 2 8 6 4 . Angew. C h e m . 1 9 , 256 ( 1 9 4 7 ) .
Chem.
1 9 3 , 409 ( 1 9 3 0 ) ;
C h e m . 2 4 2 , 408 ( 1 9 3 8 ) ; anorg. allg. Chem. 245, (1946).
Hydroge n Fluorid e HF
Precautionary measures: Since hydrogen fluoride solutions, p a r t i c u l a r l y w h e n c o n c e n t r a t e d , c a u s e e x t r e m e l y painful and p r o t r a c t e d b u r n s , a p a s t e m a d e of m a g n e s i u m o x i d e w i t h a l i t t l e g l y c e r o l s h o u l d b e k e p t on h a n d w h e n w o r k i n g w i t h l a r g e r q u a n t i t i e s . T h e e y e s m u s t b e p r o t e c t e d and r u b b e r g l o v e s m u s t b e w o r n . I. CRUDE HYDROFLUORIC ACID [1]
L a b o r a t o r y p r e p a r a t i o n of t h i s m a t e r i a l w i l l a l m o s t n e v e r b e u n d e r t a k e n . T o o b t a i n 0.25 k g . of H F , 1 k g . of f i n e l y p u l v e r i z e d f l u o r i t e o r , e v e n b e t t e r , c r y o l i t e (for S i - f r e e HF) i s v i g o r o u s l y
146
Η.
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h e a t e d w i t h 2.25 t o 2.5 k g . of 97.5% A s - f r e e H S 0 in a s m a l l a u t o c l a v e p l a c e d on an a i r b a t h . A l e a d t u b e 1.5 m e t e r s long and 2 c m . in d i a m e t e r , w i t h an a t t a c h e d L i e b i g c o n d e n s e r , i s s o l d e r e d t o t h e c o v e r . Run d u r a t i o n , 4 h o u r s . T h e p r o d u c t i s c o l l e c t e d in a copper flask cooled with i c e - s a l t m i x t u r e . I m p u r i t i e s : H S i F , H C l , H S 0 , H S 0 , H S 0 F , Pb. 2
4
3
2
3
2
4
s
3
II. PURE, 3 5 % HYDROFLUORIC ACID
T h i s s o l u t i o n i s c o m m e r c i a l l y a v a i l a b l e in p o l y e t h y l e n e b o t t l e s a n d i s a l r e a d y q u i t e p u r e . F o r f u r t h e r p u r i f i c a t i o n , it i s d i s t i l l e d f r o m a N a F - c o n t a i n i n g P t r e t o r t into a P t r e c e i v e r , l e a v i n g b e h i n d t h e S O | " and S i F | ~ i o n s . A l i t t l e P b C 0 i s a d d e d t o r e m o v e t h e C I " ; t h i s y i e l d s P b C I F , w h i c h i s i n s o l u b l e in c o n c e n t r a t e d H F . An e x c e s s of P b C 0 d o e s no h a r m , e v e n in t h e p r e s e n c e of H S 0 . O r g a n i c m a t e r i a l i s r e m o v e d only w h e n K M n 0 i s a d d e d ( d r o p w i s e ) . V e s s e l m a t e r i a l s : P t , Ag, C u , Mg (but not P b ) , c e l l u l o i d ( m a y b e e a s i l y s h a p e d in w a r m w a t e r ) , p o l y e t h y l e n e , p a r a f f i n , m e t a l d i s h e s c o a t e d w i t h B a k e l i t e , T e f l o n , e t c . See a l s o s e c t i o n on F . B o i l i n g p o i n t s of v a r i o u s H 0 / H F m i x t u r e s a r e g i v e n in [4]. 3
3
2
4
4
2
2
III. ANHYDROUS HYDROGEN FLUORIDE
D i s t i l l a t i o n of 1.2 k g . of a n h y d r o u s K H F a t 500°C y i e l d s 250 g . of H F . T e c h n i c a l g r a d e K H F i s d i s s o l v e d in w a r m w a t e r , s o m e P b C 0 i s a d d e d t o e l i m i n a t e C I " , t h e K S i F and P b C I F a r e a l l o w e d t o s e t t l e , and t h e c l e a r s o l u t i o n i s e v a p o r a t e d in C u o r Mg d i s h e s u n t i l c r y s t a l l i z a t i o n o c c u r s . A l t e r n a t i v e l y , a q u a n t i t y of h y d r o f l u o r i c a c i d i s d i v i d e d into two e q u a l p a r t s , o n e of w h i c h i s n e u t r a l i z e d w i t h K C O , m i x e d w i t h t h e o t h e r p a r t and e v a p o r a t e d . F i l t e r hot t h r o u g h a Cu funnel. T h e c r y s t a l s w h i c h s e p a r a t e on c o o l i n g a r e a l l o w e d t o d r a i n and a r e d r i e d i n i t i a l l y on f i l t e r p a p e r , at 100°C, F u r t h e r d r y i n g m u s t b e c a r r i e d out w i t h g r e a t c a r e at 130 t o 140°C. A t h i n l a y e r of c r y s t a l s i s p l a c e d on a Mg o r Cu s h e e t t u r n e d u p 1-2 c m . a l o n g t h e e d g e s , a n d t h e s h e e t i s p l a c e d on a l a r g e h o t p l a t e . A f t e r 2 - 3 d a y s t h e c r y s t a l s a r e g r o u n d in a coffee m i l l and d r i e d f o r a n o t h e r d a y , a f t e r w h i c h t h e y a r e s t o r e d in p a r a f f i n coated g l a s s bottles. The dust from the salt is disagreeable. The c o m p o u n d c a n b e o b t a i n e d m o r e r e a d i l y by d e c o m p o s i t i o n of N a H F , but t h e d e c o m p o s i t i o n s t a r t s a l r e a d y d r y i n g , and N a H F i s t h e r e f o r e not r e c o m m e n d e d a s a r a w m a t e r i a l . D i s t i l l a t i o n i s c a r r i e d out in a Cu f l a s k , 24 c m . h i g h , p r o v i d e d w i t h a c o n i c a l g r o u n d s t o p p e r , 4 c m . in d i a m e t e r , h e l d in p l a c e w i t h s c r e w c l a m p s ( F i g , 105). T h e c o n e i s l u b r i c a t e d w i t h g r a p h i t e p a r a f f i n oil o r K e l - F g r e a s e t o p r e v e n t f r e e z i n g of t h e j o i n t . T h e l - m . - l o n g Cu t u b e m u s t b e 2 - 2 . 5 c m . in d i a m e t e r , s i n c e s a l t i s c a r r i e d o v e r and i n c o n v e n i e n t p l u g g i n g c a n o c c u r in t h e m i d d l e of 2
2
3
2
2
s
a
2
2
3.
FLUORINE,
HYDROGEN
FLUORIDE
147
t h e r u n . T h e g l a s s c o n d e n s e r i s g a s k e t e d w i t h a p i e c e of r u b b e r h o s e , a n d to s l o w down t h e d e c o m p o s i t i o n , a few t u r n s of w a t e r c o o l e d t i n t u b i n g a r e wound on it. T h e Cu t u b e i s a l l o w e d to s t a n d in H C l / B r u n t i l it i s b r i g h t , o r t h e i n i t i a l Η F f r a c t i o n w i l l b e b r o w n . T h e r e t o r t s h o u l d b e p r o v i d e d w i t h a Cu t h e r m o w e l l , p r o j e c t i n g u p w a r d for 5 c m . f r o m t h e b o t t o m a n d e x t e r n a l l y b r a z e d in p l a c e , t o a c c o m m o d a t e a c o p p e r - c o n s t a n t a n t h e r m o c o u p l e . T h e r e t o r t i s h e a t e d e i t h e r on a m u l t i p l e b u r n e r in a n i r o n j a c k e t o r , p r e f e r a b l y , in a n e l e c t r i c f u r n a c e . B e f o r e filling it s h o u l d b e c l e a n e d w i t h HC1 u n t i l b r i g h t and d r i e d c a r e f u l l y in a s t r e a m of C 0 . T h e Cu r e c e i v e r (250 m l . ) i s c o n n e c t e d by a s p e c i a l c o u p l i n g ( F i g . 106) and m u s t b e c l e a n e d w i t h HC1 u n t i l b r i g h t . It i s t h e n d r i e d and r e d u c e d in a s t r e a m of H at 300°C. D u r i n g d i s t i l l a t i o n , u s e an i c e - s a l t m i x t u r e (—10°C) f o r c o o l i n g . A s e c o n d c o n tainer provides protection against overflow. The r e t o r t is first h e a t e d s l o w l y f o r a p p r o x i m a t e l y 3 / 4 h o u r to a b o u t 400 to 500°C, t h a t i s until H F b e g i n s to d r i p into a Pt d i s h below (leave the s c r e w c o u p l i n g a t Ε o p e n ) . V a p o r p r e s s u r e s of K F a n d H F a r e g i v e n in [6]. A f t e r about 10 m l . h a s b e e n c o l l e c t e d , a t e s t i s m a d e t o d e t e r m i n e w h e t h e r a s t r i p of f i l t e r p a p e r g e l a t i n i z e s i m m e d i a t e l y . If s o , t h e a c i d i s a n h y d r o u s . Now t h e c o u p l i n g a t Ε i s t i g h t e n e d ( u s e p l i e r s and r u b b e r g l o v e s ) and t h e f r e e z i n g b a t h i s put in p l a c e . R a i s i n g of t h e t e m p e r a t u r e t o 500°C m u s t b e a c c o m p l i s h e d w i t h g r e a t c a r e , s i n c e at t h a t t e m p e r a t u r e K F b e g i n s t o s e p a r a t e f r o m t h e m e l t and v i o l e n t e v o l u t i o n of H F a l s o o c c u r s [2], T h e o p e r a t i o n i s d e c i d e d l y m o r e c o n v e n i e n t if a t h i c k - w a l l e d Cu c a p i l l a r y ( s h o w n w i t h d o t t e d l i n e s ) i s b r a z e d t o t h e Cu t u b e . T h e c a p i l l a r y s h o u l d d i p about 2 c m . into a Hg pool in a P t d i s h . If t h i s i s d o n e , t h e c o u p l i n g s on t h e r e c e i v e r s m a y b e t i g h t e n e d b e f o r e t h e r u n and t h e f i r s t few m i l l i l i t e r s a l l o w e d t o d r i p f r o m t h e c a p i l l a r y u n t i l t h e p a p e r t e s t s h o w s t h e a b s e n c e of w a t e r . T h e c a p i l l a r y m a y t h e n b e s e a l e d off s i m p l y b y r a i s i n g t h e l e v e l of t h e m e r c u r y . Should t h e e v o l u t i o n of H F b e t o o v i o l e n t , e x c e s s H F c a n e s c a p e t h r o u g h t h e c a p i l l a r y , a c c o m p a n i e d , of c o u r s e , b y n o x i o u s f u m e s . 2
2
2
F i g . 1 0 5 . D i s t i l l a t i o n of a n h y d r o u s h y d r o f l u o r i c acid. A ) d i s t i l l a t i o n r e t o r t ( C u ) ; B) c o n d e n s e r ( i n n e r t u b e of C u ) ; C) r e c e i v e r ( C u ) , —10°C;£) s e c o n d r e c e i v e r , —10°C; E,F) c o n i c a l s c r e w c o u p l i n g s .
148
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WARTENBERG
T h e e v o l u t i o n s u b s i d e s a f t e r about 3 h o u r s and t h e h e a t i n g i s d i s c o n t i n u e d . L o o s e n Ε and F a n d c l o s e t h e m off w i t h Cu c o n e s . If t h e d i s t i l l e d a c i d i s t o b e s t o r e d , t h e t u b e s c a n b e c l o s e d off at Ε and F w i t h s o l i d Cu c o n e s e q u i p p e d w i t h s c r e w c a p s . A f t e r c o o l i n g , t h e c o n t e n t s of t h e r e t o r t m a y b e d i s s o l v e d in b o i l i n g w a t e r and r e g e n e r a t e d w i t h a q u e o u s H F .
ο
ζ
3 cm
F i g . 106. D e t a i l s of t h e c o n i c a l copper coupling. The cones a r e interchangeable. F o r r e g e n e r a t i o n , t h e s o l u t i o n i s t r e a t e d in a l a r g e Cu o r Mg d i s h w i t h sufficient p u r e , c o m m e r c i a l (35-40%) H F to t u r n l i t m u s completely r e d . The solution i s then e v a p o r a t e d o v e r an open f l a m e but not to t h e p o i n t w h e r e s p a t t e r i n g o c c u r s . T h e s a l t m a s s i s t h e n c r u s h e d and d r i e d a s d e s c r i b e d p r e v i o u s l y . T h e r e s u l t a n t H F s t i l l c o n t a i n s t r a c e s of e n t r a i n e d K F and c a n b e r e d i s t i l l e d at 30-35°C into t h e s e c o n d r e c e i v e r . F o r v e r y p u r e H F , s i l v e r e q u i p m e n t should b e u s e d [2]. Since o r g a n i c s u b s t a n c e s a r e i m m e d i a t e l y d e c o m p o s e d by H F v a p o r , j o i n t s c a n b e m a d e t i g h t o n l y by m e a n s of t h e Cu c o n e s d e s c r i b e d . A l t e r n a t i v e l y f u s e d s u l f u r m a y b e u s e d , w i t h p i c e i n o r a l i k e s u b s t a n c e c o v e r i n g c r a c k s in t h e sulfur m a s s . A s a t e m p o r a r y e x p e d i e n t , r e s u l t i n g in not q u i t e anhydrous acid, the seal can be made with w e l l - d r i e d l i t h a r g e glycerol cement. L i q u i d H F i s a v a i l a b l e in s t e e l t a n k s o r c y l i n d e r s . ( H e a t g e n t l y w i t h f l a m e t o m a k e it flow.) In o r d e r t o r e n d e r t h e l i q u i d H F c o m p l e t e l y a n h y d r o u s , f l u o r i n e m a y be bubbled through using a silver capillary. The F g a s d e c o m p o s e s t r a c e s of w a t e r . T h u s a c y l i n d e r H F c a n b e p a r t i a l l y d r i e d by s o m e w h a t l o o s e n i n g t h e m a i n v a l v e w i t h a w r e n c h in a c o l d r o o m and t h e n p u t t i n g t h e c y l i n d e r in a c o n t a i n e r of a p p r o p r i a t e height, filled with i c e - s a l t m i x t u r e ; after the cylinder h a s cooled down, t h e v a l v e i s r e m o v e d c o m p l e t e l y and F i s b u b b l e d t h r o u g h o r half an h o u r f r o m a f l u o r i n e c y l i n d e r t h r o u g h a s i l v e r c a p i l l a r y ; t h e v a l v e i s t h e n s c r e w e d b a c k on and t i g h t e n e d w i t h t h e w r e n c h . T h e f l u o r i n e p r e s s u r e p r o d u c e d in t h e u s u a l l a b o r a t o r y g e n e r a t o r s i s not sufficient f o r t h e H F c y l i n d e r s . F o r a l l p r a c t i c a l p u r p o s e s , F d o e s n o t d i s s o l v e in liquid H F . I n s t e a d of u s i n g f l u o r i n e , t h e w a t e r m a y b e r e m o v e d by d r o p w i s e a d d i t i o n of t h i o n y l c h l o r i d e , w h i c h l i b e r a t e s g a s e o u s HC1, S 0 a n d S O F , all i n s o l u b l e in H F [K. W i e c h e r t , Z . a n o r g . C h e m . 2 6 1 , 314 ( 1 9 5 0 ) ] . 2
2
2
3
2
3.
FLUORINE,
HYDROGEN
149
FLUORIDE
P u r e H F for v e r y s m a l l s c a l e e x p e r i m e n t s b e e a s i l y o b t a i n e d (together with hydrogen) by placing a copper boat with w e l l d r i e d P b F in a p l a t i n u m o r c o p p e r t u b e in f r o n t of t h e c o m p o u n d to be r e a c t e d with the nascent H F . The boat is heated to r e d heat in a s t r e a m of h y d r o g e n . C o n d u i t s f o r H F g a s a r e m a d e of w e l l - d r i e d c o p p e r t u b e s p r o v i d e d w i t h c o n i c a l c o p p e r j o i n t s . In s u c h t u b e s H F g a s m a y b e h e a t e d to 1000°C (of c o u r s e , p r o t e c t i o n f r o m t h e a t m o s p h e r e m u s t be provided). Sintered alumina tubes may be used up to 500°C. C o p p e r c a p s , t e m p o r a r i l y c e m e n t e d on w i t h l i t h a r g e g l y c e r o l , m a y s e r v e a s c l o s u r e s , b u t it i s b e t t e r t o s o l d e r t h e m onto t h e a l u m i n a t u b e . T o a c c o m p l i s h t h i s , t h e a l u m i n a t u b e i s e l e c t r o l y t i c a l l y c o a t e d w i t h c o p p e r , a n d soft s o l d e r i s u s e d f o r a t t a c h i n g t h e c a p s . C o m p l e t e l y a n h y d r o u s H F d o e s not a t t a c k q u a r t z . L e a d and o r g a n i c s u b s t a n c e s a r e d e s t r o y e d , e x c e p t f o r p o l y m e r i z e d t e t r a f l u o r o e t h y l e n e (Teflon) [ 5 ] . C o p p e r (not b r a s s ) s t o p c o c k s o r , p r e f e r a b l y , p l a t i n u m v a l v e s ( B o d e n s t e i n d e s i g n ) s e r v e t o s h u t off t h e flow. It i s a d v i s a b l e t o m a k e t h e s t o p c o c k b o d y of c o p p e r and t o t u r n out t h e plug f r o m a T e f l o n b l o c k on a l a t h e . Such a p l u g t u r n s e a s i l y and n e e d s n o l u b r i c a t i o n . 2
PROPERTIES:
F o r m u l a weight 20.01. B.p. 1 9 . 5 ° C ; f o r b . p . at v a r i o u s p r e s s u r e s s e e [3]; m . p . - 8 5 ° C ; d (liq.) 0 . 9 8 7 . t 188°C, p 66.2 k g . / c m . , d 0.29. 2
c r
c
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c r
REFERENCES:
1. O. Ruff. C h e m i e d e s F l u o r s [ F l u o r i n e C h e m i s t r y ] B e r l i n , 1920, d e t a i l e d d e s c r i p t i o n on t h e p r e p a r a t i o n of n u m e r o u s compounds. 2 . K. F r e d e n h a g e n . Z . a n o r g . a l l g . C h e m . 1 7 8 , 289 (1929); U l l m a n n , E n c y k l o p a d i e d. t e c h n . C h e m . [ E n c y c l o p e d i a of T e c h n i c a l C h e m i s t r y ] 3 r d E d . , V o l . 7, p . 585 (1957). 3 . K. F r e d e n h a g e n . Z . a n o r g . a l l g . C h e m . 210, 220 ( 1 9 3 3 ) . 4 . K. F r e d e n h a g e n . Z . p h y s i k . C h e m . A 1 6 2 , 4 6 4 ( 1 9 3 2 ) : U l l m a n n , E n c y k l o p a d i e d. t e c h n . C h e m . [ E n c y c l o p e d i a of T e c h n i c a l C h e m i s t r y ] 3 r d E d . , V o l . 7, p . 585 (1957). 5. W. H a n f o r d and R. J o y c e . J . A m e r . C h e m . S o c . 6 8 , 2082 (1946). 6. G H. C a d y . J . A m e r . C h e m . S o c . 5 6 , 1431 ( 1 9 3 4 ) . e