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Chlorine, Bromine, Iodine

M. SCHMEISSER

Chlorin e

C I2

C o m m e r c i a l l y a v a i l a b l e liquid c h l o r i n e , w h i c h i s o b t a i n e d by e l e c t r o l y s i s of a l k a l i , i s not sufficiently p u r e and m u s t t h e r e f o r e b e p u r i f i e d b y m e t h o d I.

On t h e o t h e r h a n d , a g a s t h a t i s a l r e a d y l a r g e l y f r e e of s u c h i m p u r i t i e s a s Os and c h l o r i n e o x i d e s i s p r o d u c e d by t h e r e a c t i o n of h y d r a t e d m a n g a n e s e dioxide with p u r e h y d r o c h l o r i c a c i d . F o r t h i s p r e p a r a t i o n , s e e m e t h o d II b e l o w .

I. C h l o r i n e f r o m a s t e e l c y l i n d e r i s p a s s e d c o n s e c u t i v e l y t h r o u g h t w o w a s h b o t t l e s o r c o l u m n s c o n t a i n i n g c o n c e n t r a t e d H2S 04, a t u b e o r c o l u m n c o n t a i n i n g C a O (to r e m o v e any HC1 t h a t m i g h t be p r e s e n t ) , a t u b e c o n t a i n i n g P2Os, and finally into a c o n t a i n e r p l a c e d in a D r y I c e - a c e t o n e b a t h , w h e r e it i s c o n d e n s e d and liquefied. T h e liquefied C l2 i s r e p e a t e d l y v a p o r i z e d and c o n d e n s e d w h i l e n o n c o n d e n s a b l e g a s e s ( 02) a r e c o n t i n u o u s l y r e m o v e d w i t h a p u m p . F i n a l l y , t h e liquid C l2 i s f r a c t i o n a t e d in high v a c u u m and p a s s e d into r e c e i v e r s c o o l e d with liquid n i t r o g e n . ( F o r t h e a p p a - r a t u s s e e , for e x a m p l e , P a r t I, p . 66 ff.) Only the m i d d l e f r a c - tion i s u s e d for f u r t h e r w o r k .

II. M n 02x H20 * + 4 HC1 = MnCl2 + (x + 2)H20 + Cl2

~ 100 145.88 70.91

*x ~ 0.8 for a p r o d u c t of about 86% p u r i t y .

C o n c e n t r a t e d , a i r - f r e e h y d r o c h l o r i c a c i d (d 1.16) i s added d r o p w i s e t o p r e c i p i t a t e d h y d r a t e d m a n g a n e s e dioxide ( e . g . , t h e 86% p u r e c o m m e r c i a l l y o b t a i n a b l e m a t e r i a l ) in a flask e q u i p p e d w i t h a d r o p p i n g funnel and a g a s outlet t u b e . T h e g a s f o r m a t i o n m a y b e r e g u l a t e d by m o d e r a t e h e a t i n g .

T h e c h l o r i n e t h u s f o r m e d i s p a s s e d t h r o u g h w a t e r (to r e m o v e e n t r a i n e d HC1) and H2S 04 ( c a r r i e d out a s in m e t h o d I, t h a t i s ,

272

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5 . C H L O R I N E , B R O M I N E , I O D I N E 273 H2S 04, a t u b e c o n t a i n i n g C a O , a t u b e with P205) and liquefied in a r e c e i v e r c o o l e d with a D r y I c e - a c e t o n e b a t h . S u b s e q u e n t p u r i f i ­ c a t i o n i s a s in m e t h o d I.

Other preparative methods:

III. E l e c t r o l y s i s of an N a C l solution s a t u r a t e d with HC1 in t h e e l e c t r o l y t i c c e l l d e s c r i b e d by B o d e n s t e i n and P o h l . T h e oxygen c o n t e n t of t h e C l2 p r o d u c e d in t h i s m a n n e r i s 0.01%.

E x t r e m e l y p u r e C l2 c a n b e p r o d u c e d in s m a l l q u a n t i t i e s by t h e following m e t h o d s :

IV. H e a t i n g A u C l3 ( p r e p a r e d f r o m finely divided Au and d r y Clg) a t 250°C in v a c u u m .

V . S u b l i m a t i o n - c r y s t a l l i z a t i o n p r o c e d u r e c a r r i e d out in high v a c ­ u u m . (In t h i s p r o c e s s , t h e p u r i t y of t h e C l2 p r o d u c t i s c h e c k e d by m e a s u r i n g t h e r a t e of f o r m a t i o n of p h o s g e n e f r o m CO and C l2. T h i s r e a c t i o n i s r e t a r d e d by t h e s l i g h t e s t i m p u r i t i e s . )

K l e m e n c c o n s i d e r s t h e m o s t effective m e a n s of r e m o v i n g t h e l a s t t r a c e s of 02 f r o m C l2 t o be t h e bubbling of v e r y p u r e H2 t h r o u g h liquid C l2 at —78°C for 24 h o u r s .

PROPERTIES:

Y e l l o w - g r e e n , pungent g a s . M . p . —101.0°C, b . p . —34.0°C. Heat of fusion 1531 c a l . / m o l e ; h e a t of v a p o r i z a t i o n 4878 c a l . / m o l e . T r i p l e p o i n t p r e s s u r e 10.4 m m . , c r i t . t. 143.5°C, c r i t . p . 76.1 a t m . d,(liq.) (—34°C) 1.557. Solubility in w a t e r : 1 v o l . of w a t e r d i s s o l v e s 4.6 v o l . of C l2 at 0°C, 2.15 v o l . a t 20°C, 1.22 v o l . at 50°C, 0.39 v o l . a t 90°C.

C h l o r i n e a t t a c k s r u b b e r , c o r k , s t o p c o c k g r e a s e and Hg but c a n b e s t o r e d in g l a s s c o n t a i n e r s o v e r c o n c e n t r a t e d H2S 04 o r a s a liquid in s t e e l c y l i n d e r s . T h e v i g o r o u s r e a c t i o n of c h l o r i n e with m a n y c o m m o n l y u s e d m e t a l s o c c u r s only at e l e v a t e d t e m p e r a t u r e s ; t h e r e a c t i o n w i t h s t e e l , for e x a m p l e , s t a r t s a b o v e 250°C [G.

H e i n e m a n n , F . G. G a r r i s o n and P . A. H a b e r , Ind. E n g . C h e m . , Ind.

E d . 3 8 , 497 (1946)].

REFERENCES:

I. A. K l e m e n c . Die B e h a n d l u n g und R e i n d a r s t e l l u n g von G a s e n [ T r e a t m e n t and P u r i f i c a t i o n of G a s e s ] , 2nd e d . , V i e n n a , 1948, p . 1 5 3 .

II. L . W b h l e r and S. S t r e i c h e r . B e r . d t s c h . c h e m . G e s . 4 6 , 1596 (1913).

W. F . Giauque and Τ . M. P o w e l l , J . A m e r . C h e m . S o c 6 1 , 1970 (1939).

III. M. B o d e n s t e i n . Z . E l e k t r o c h e m . 22, 204 (1916).

IV. A. C o e h n and G. J u n g . Z . p h y s . C h e m . 110, 705 (1924).

H. von W a r t e n b e r g and F . A. H e n g l e i n . B e r . d t s c h . c h e m . G e s . 5 5 , 1003 (1922).

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V. P . Μ. F y e and J. J . B e a v e r . J . A m e r . C h e m . Soc. 6 3 , 1268 (1941).

Chlorin e Hydrat e Cl2 · 6 H20

Cl2 + 6 H20 = Cl2 · 6 H20

70.9 108 178.9

I. C h l o r i n e i s d i s s o l v e d in w a t e r at 0°C, f o r m i n g a thin s l u r r y w h i c h i s t h e n f i l t e r e d t h r o u g h a g l a s s f i l t e r funnel s u r r o u n d e d by a j a c k e t c o o l e d w i t h i c e w a t e r . T h e c r y s t a l s , w h i c h a r e t h u s l a r g e l y f r e e d f r o m w a t e r , a r e s e a l e d into a g l a s s t u b e and h e a t e d t o 30 t o 40°C. D e c o m p o s i t i o n into liquid C l2 ( u n d e r i t s own p r e s ­

s u r e ) and C l3- s a t u r a t e d w a t e r r e s u l t s . T h e s e a l e d t u b e i s allowed to cool f r o m 40 t o 0°C in a l a r g e w a t e r b a t h for two d a y s . T h u s , t h e m i x t u r e c o m p o n e n t s r e c o m b i n e and f o r m l a r g e r c r y s t a l s . II. B e t t e r - f o r m e d c r y s t a l s c a n b e p r e p a r e d in t h e following w a y :

C h l o r i n e h y d r a t e , p r e p a r e d a s a b o v e , i s p l a c e d in one a r m of a t h i c k - w a l l U tube and the tube i s s e a l e d off. T h e h y d r a t e i s d e c o m p o s e d by h e a t i n g and t h e c h l o r i n e f o r m e d i s c o n d e n s e d by i m m e r s i n g t h e o t h e r a r m of t h e U t u b e in a r e f r i g e r a n t . T h e n t h e r e f r i g e r a n t i s r e m o v e d w h i l e t h e o t h e r s i d e of t h e t u b e , w h i c h c o n t a i n s w a t e r s a t u r a t e d with C l2, i s i m m e r s e d in a v e s s e l full of cold w a t e r . After s o m e t i m e l a r g e , v e r y g l i t t e r i n g , p a l e - y e l l o w c r y s t a l s a r e f o r m e d in t h i s a r m .

PROPERTIES:

Yellow c r y s t a l s . D e c o m p o s i t i o n t e m p e r a t u r e at 1 a t m . +9.6°C;

c r i t i c a l d e c o m p o s i t i o n point 28.7°C, 6 a t m . ; d i s s o c i a t i o n p r e s s u r e ( a t 0°C) 252 m m . ; d. ( c a l c . ) 1.29. Cubic c r y s t a l s , w i t h the t h e o r e t i c a l c o m p o s i t i o n of C l3 · 53/4 H20 .

REFERENCES:

I. E. Biewend. J . p r a k t . C h e m . 15, 440 (1838).

H. W. B , R o o z e b o o m . R e c . T r a v . C h i m . P a y s - B a s 3 , 59 (1884);

4, 65 (1885).

II. A. D i t t e . C o m p t . Rend. Hebd. S e a n c e s A c a d . Sci. 95^, 1283 (1882).

P . V H l a r d . Ann. C h i m . (7) 1 1 , 292 (1897).

S c h r o d e r . Die C h e m i e d e r G a s h y d r a t e [ C h e m i s t r y of H y d r a t e s of G a s e s ] , S t u t t g a r t , 1926.

M. von S t a c k e l b e r g . N a t u r w i s s . 36, 327, 359 (1949).

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5 . C H L O R I N E , B R O M I N E , I O D I N E 275 M. von S t a c k e l b e r g and R. H0 M i i l l e r . Z. E l e k t r o c h e m . 5 8 , 25 (1954).

Bromin e Br2

E v e n t h e p u r e s t c o m m e r c i a l b r o m i n e c o n t a i n s a p p r o x i m a t e l y 0.05% CI a s w e l l a s t r a c e s of I, and m u s t t h e r e f o r e b e p u r i f i e d for s p e c i a l u s e s .

I. In o r d e r to r e m o v e m o s t of t h e s t i l l p r e s e n t c h l o r i n e , b r o m i n e m a y be s t o r e d with p u l v e r i z e d K B r for a c o n s i d e r a b l e t i m e and t h e n d i s t i l l e d off in high v a c u u m into a r e c e i v e r c o o l e d with a D r y I c e - e t h e r m i x t u r e .

II. V e r y p u r e b r o m i n e m a y b e p r e p a r e d , a c c o r d i n g t o H o n i g s c h m i d and B a x t e r , in t h e following m a n n e r : A c o n c e n t r a t e d s o l u t i o n of C a B r2 o r K B r i s p l a c e d in a r o u n d - b o t t o m f l a s k c o n n e c t e d w i t h g r o u n d j o i n t s to a b r o m i n e - c o n t a i n i n g d r o p p i n g funnel and t o an exit t u b e , b e n t at r i g h t a n g l e s . T h e t u b e p a s s e s t h r o u g h a c o n - d e n s e r into a r e c e p t a c l e c o n t a i n i n g i c e - c o l d , v e r y p u r e w a t e r . [The v e r y p u r e C a B r2 s t a r t i n g m a t e r i a l i s p r e p a r e d by d r o p w i s e addition of b r o m i n e (which h a s b e e n s u b j e c t e d t o t h e p u r i f i c a t i o n d e s c r i b e d above) t o a m m o n i a c a l c a l c i u m h y d r o x i d e . T h e c a l c i u m h y d r o x i d e i s p r e p a r e d f r o m the v e r y p u r e s t , h a l o g e n - f r e e l i n e . ] B r o m i n e i s added f r o m the funnel to the flask and i s then d i s t i l l e d off f r o m t h e s o l u t i o n . A s t h e B r3 d i s t i l l s off, m o r e b r o m i n e i s added below t h e s u r f a c e of t h e C a B r2 ( o r K B r ) solution f r o m t h e d r o p p i n g funnel. T h e d i s t i l l e d b r o m i n e i s r e d u c e d t o K B r by d r o p w i s e addition t o a hot solution of r e c r y s t a l l i z e d , h a l o g e n - f r e e p o t a s s i u m o x a l a t e . T h e K B r solution i s e v a p o r a t e d . D u r i n g e v a p o r a t i o n , s m a l l q u a n t i t i e s of B r2 a r e l i b e r a t e d f r e q u e n t l y by addition of acidified K M n 04 s o l u t i o n , which t h r o u g h e v a p o r a t i o n a l s o r e m o v e s any I2 t h a t m a y b e p r e s e n t . A c c o r d i n g to B a x t e r , s m a l l q u a n t i t i e s of a b s o l u t e l y p u r e B r2 f r o m a p r e v i o u s r u n m a y b e a d d e d t o a c h i e v e t h e s a m e r e s u l t . In o r d e r t o d e c o m p o s e t r a c e s of o r g a n i c m a t e r i a l s , t h e K B r t h a t c r y s t a l l i z e s out i s fused in a P t c r u c i b l e . It c a n t h e n b e c o n s i d e r e d c o m p l e t e l y f r e e f r o m CI and I.

B r o m i n e i s now l i b e r a t e d by t r e a t m e n t of t h e K B r w i t h v e r y p u r e K2C r207 and v e r y p u r e H2S 04 (the l a t t e r i s o b t a i n e d by d i s - t i l l a t i o n o v e r K2C r207, d i s c a r d i n g t h e f o r e r u n ) . H o w e v e r , t h e r e a c t i o n w i t h K2C r207 i s not c o m p l e t e , s i n c e only about 75% of t h e n e e d e d K2C r207 e n t e r s into t h e r e a c t i o n . T h u s , t h e r e m a i n i n g B r2 m u s t be d i s t i l l e d a g a i n f r o m t h e K B r solution f o r m e d . T h e p r o d u c t B r2 i s w a s h e d w i t h w a t e r to r e m o v e H B r , s e p a r a t e d f r o m t h e e n t r a i n e d H20 , and t h e n d r i e d o v e r v e r y p u r e C a O and C a B r2 o r o v e r P2Ob. F i n a l l y , it i s f r e e d of t h e s e s u b s t a n c e s by d i s - t i l l a t i o n in v a c u u m .

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PROPERTIES:

Bromin e Hydrat e Br2 · 8 H20

Br2 + 8 H20 = Br2 · 8 H20

159.8 144 303.8

A 4% (by weight) s o l u t i o n of B r2 in w a t e r ( s a t u r a t e d solution at 0°C) i s c o o l e d t o 0°C. T h i s c a u s e s a s m a l l q u a n t i t y of b r o m i n e h y d r a t e (about 4% of t h e B r2- HsO m i x t u r e ) t o s e p a r a t e out.

U s u a l l y , h o w e v e r , t h e s o l u t i o n m u s t b e e i t h e r s e e d e d w i t h s o m e b r o m i n e h y d r a t e o r c o o l e d for a s h o r t t i m e t o —5°C, a f t e r w h i c h t h e t e m p e r a t u r e i s r e s t o r e d t o 0°C. T h e p r e c i p i t a t e i s f i l t e r e d on a g l a s s f i l t e r funnel s u r r o u n d e d by a j a c k e t c o n t a i n i n g i c e w a t e r . In o r d e r t o f o r m l a r g e r c r y s t a l s , t h e p r o d u c t h y d r a t e i s s e a l e d into a t u b e t o g e t h e r with a l a r g e e x c e s s of 4% b r o m i n e w a t e r and k e p t for about four w e e k s on i c e . T h e t u b e i s w a r m e d t o 5-6°C o n c e e a c h d a y .

PROPERTIES:

L i g h t - r e d c r y s t a l s , w h i c h m u s t b e s t o r e d in a s e a l e d t u b e at t e m p e r a t u r e s b e l o w 6.2°C. C r i t i c a l d e c o m p o s i t i o n p o i n t . 6.2°C,

93 m m . ; d i s s o c i a t i o n p r e s s u r e (0°C), 45 m m . ; d (solid) (0°C) 1.49.

T h e c o m p o s i t i o n i s s o m e w h a t u n c e r t a i n . C u b i c c r y s t a l s h a v e t h e t h e o r e t i c a l c o m p o s i t i o n B r3 · 7s/3 Η Ο.

REFERENCES:

H . W . B . R o o z e b o o m . R e c . T r a v . C h i m . P a y s - B a s 3 , 73 (1884); 4 , 65 (1885).

H. G i r a n . C o m p . R e n d . Hebd. S e a n c e s A c a d . Sci. 159, 246 (1914).

F o r m u l a weight 159.84. R e d d i s h - b r o w n , pungent liquid. M . p . - 7 . 3 ° C , b . p . 5 8 . 8 \ ) ; d (0°C) 3.19. Solubility in w a t e r (20°C) 3.53 g.

of B r3 p e r 100 g. of H20 .

REFERENCES:

I. W. A. N o y e s , J r . J . A m e r . C h e m . Soc. 4 5 , 1194 (1923).

II. O. H o n i g s c h m i d and E . Z i n t l . L i e b i g s Ann. C h e m . 4 3 3 , 216 (1923).

G. P . B a x t e r , C. J . M o o r e and A. C. B o y l s t o n . J . A m e r . C h e m . S o c 34»26 0 (1912).

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5 . C H L O R I N E , B R O M I N E , I O D I N E 277 W. He H a r r i s , J . C h e m . S o c . (London) 1 9 3 3 , 5 8 2 .

M. v o n S t a c k e l b e r g . N a t u r w i s s . 3 £ , 3 2 7 , 359 (1949).

M. v o n S t a c k e l b e r g a n d H. R. Mfiller. Z . E l e k t r o c h e m . 5 8 , 2 5 (1954).

Iodin e

It

Since e v e n t h e p u r e s t c o m m e r c i a l KI t o be u s e d f o r t h e p r e p a r a ­ t i o n of s p e c i a l l y p u r i f i e d iodine m a y s t i l l c o n t a i n s u c h i m p u r i t i e s a s C I , B r , I C N , a l k a l i s u l f a t e , c a r b o n a t e a n d s u l f i d e , a s w e l l a s t r a c e s of o r g a n i c m a t e r i a l , s p e c i a l p u r i f i c a t i o n i s n e c e s s a r y . I. P r e p a r a t i o n of v e r y p u r e iodine a c c o r d i n g t o H b n i g s c h m i d .

2 K I + C u S 04 · 5 H20 = C u l + K2S 04 + V2 h + 5 H20 332 249.7 190.5 174.3 126.9 90

A s u p e r s a t u r a t e d s o l u t i o n of C . P . p u r i t y KI i s m i x e d with a s o l u t i o n of t h r i c e r e c r y s t a l l i z e d , c o m p l e t e l y h a l o g e n - f r e e C u S 04 · 5 H20 . T h e C u l f o r m e d i s a l l o w e d t o s e t t l e a n d t h e s u p e r ­ n a t a n t s o l u t i o n of I2 in KI i s d e c a n t e d a n d d i s t i l l e d . T h e I2 i s s t e a m - d i s t i l l e d . T h e w a t e r i s d e c a n t e d f r o m t h e c o n d e n s a t e a n d t h e I2 i s a g a i n d i s t i l l e d f r o m t h e K I s o l u t i o n a n d finally f r o m p u r e w a t e r . A f t e r f i l t e r i n g t h r o u g h a g l a s s f r i t , t h e iodine i s d r i e d in a d e s i c c a t o r o v e r c o n c e n t r a t e d H2S 04 a n d finally s u b l i m e d in a q u a r t z t u b e in a s t r e a m of n i t r o g e n .

II. If e x t r e m e p u r i f i c a t i o n i s u n n e c e s s a r y , c o m m e r c i a l iodine o r i o d i n e r e g e n e r a t e d f r o m w a s t e s c a n , a c c o r d i n g t o a m e t h o d d e ­ s c r i b e d b y P l o t n i k o w , b e s u b l i m e d , f i r s t o v e r KI a n d t h e n o v e r B a O . It i s t h e n s t o r e d in g r o u n d g l a s s c o n t a i n e r s p l a c e d in a d e s i c c a t o r o v e r P2OB.

PROPERTIES:

F o r m u l a weight 2 5 3 . 8 4 . G r a y - b l a c k f l a k e s w i t h a m e t a l l i c s h e e n . M . p . 113.7°C, b . p . 184.4°C; d 4 . 9 3 . Solubility (20°C) 0.29 g./lOO m l . of H20 .

REFERENCES:

O . H o n i g s c h m i d a n d W . S t r i e b e l . Ζ · p h y s . C h e m . (A) 1 5 6 a ( B o d e n s t e i n A n n i v e r s a r y V o l u m e ) , 286 (1931).

M . G u i c h a r d . Ann. C h i m . e t P h y s . ( 9 ) 7 , 28 (1916).

W. A. P l o t n i k o w a n d W. E . Rokotjan. Z . p h y s . C h e m . 8 4 , 365 (1913).

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RECOVERY OF IODINE FROM LABORATORY WASTE SOLUTIONS In t h e A r n d t m e t h o d , t h e oxidation of iodide r e s i d u e s w i t h e l e m e n t a r y oxygen, u s i n g n i t r i c o x i d e s a s c a r r i e r s , p r o c e e d s in a c c o r d a n c e with t h e following r e a c t i o n s :

1. HI + H N 02 = V2I2 + NO + H20 2. NO + V2 02 = N 02

3. 2 HI + N 02 = I2 + NO + H20

4. 2 N 02 + V2 02 + H20 = 2 H N O 3

T h i s p r o c e d u r e i s f e a s i b l e b e c a u s e r e a c t i o n 4 p r o c e e d s slowly in r e l a t i o n t o r e a c t i o n s 1-3 s o t h a t , a s long a s iodine i s p r e s e n t , n o s i g n i f i c a n t l o s s of n i t r i c o x i d e s o c c u r s .

A l a r g e f l a s k i s c l o s e d off with a r u b b e r s t o p p e r . A g a s inlet i s i n s e r t e d t h r o u g h t h e s t o p p e r , r e a c h i n g a l m o s t t o t h e b o t t o m ; t h i s tube i s a t t a c h e d t o t h e inlet tube of an e m p t y w a s h b o t t l e by a f a i r l y long p i e c e of flexible t u b i n g ; t h e o t h e r t u b e of t h e w a s h b o t t l e i s a t t a c h e d to a g a s o m e t e r filled w i t h 03 f r o m a c y l i n d e r . T h e a l k a l i n e solution of iodine r e s i d u e s , a f t e r c o n c e n t r a t i o n by e v a p o r a t i o n , i s p l a c e d in t h e f l a s k , w h i c h s h o u l d b e n o m o r e t h a n half full. It i s t h e n acidified w i t h c o n c e n t r a t e d H2S 04 and t h e f r e e s p a c e of t h e flask—with t h e s t o p p e r left l o o s e — i s filled with oxygen. T h e g a s o m e t e r s t o p c o c k i s t h e n c l o s e d and n i t r i t e s o l u t i o n i s a d d e d t o t h e f l a s k u n t i l t h e f r e e s p a c e a c q u i r e s an i n t e n s e r e d d i s h - b r o w n c o l o r . T h e s t o p p e r i s t h e n p u s h e d f i r m l y down and t h e g a s o m e t e r c o c k o p e n e d . T h e oxygen b e g i n s t o flow into t h e c l o s e d f l a s k e i t h e r i m m e d i a t e l y o r a f t e r v e r y s l i g h t r o t a t i o n of t h e s t o p c o c k . T h e f l a s k i s s h a k e n , at f i r s t g e n t l y and t h e n v i g o r ­ o u s l y and c o n t i n u o u s l y . T h e r a t e of oxygen a b s o r p t i o n i s c h e c k e d f r o m t i m e t o t i m e by i n t e r r u p t i n g t h e s h a k i n g t o d e t e r m i n e w h e t h e r 02 i s s t i l l flowing r a p i d l y in and w h e t h e r t h e g a s e o u s p h a s e i s s t i l l r e d - b r o w n . Should t h i s not b e t h e c a s e , due t o t h e a c c u m u l a t i o n of i n e r t g a s e s ( f r o m t h e N2 in t h e 02 u s e d o r f r o m r e d u c t i o n of a s m a l l quantity of t h e n i t r i c oxide t o N20 o r N2) , t h e s t o p p e r i s r a i s e d for a m o m e n t . If t h i s d o e s not r e s t o r e t h e 02 a b s o r p t i o n and t h e f o r m a t i o n of N Os, t h e s t o p c o c k i s c l o s e d , f u r t h e r n i t r i t e s o l u t i o n i s a d d e d , and t h e p r o c e d u r e i s c o n t i n u e d . If s h a k i n g i s s t a r t e d o r s t o p p e d too q u i c k l y , s o m e liquid m a y b e d r i v e n into t h e w a s h b o t t l e due t o a t e m p o r a r y r i s e in p r e s s u r e . H o w e v e r , t h e 02 s t r e a m which a g a i n s t a r t s t o flow d r i v e s it b a c k into t h e f l a s k . C o m p l e t i o n of t h e oxidation m a y be r e c o g n i z e d by t h e c e s s a t i o n of 02 a b s o r p t i o n and by t h e fact t h a t t h e g a s e o u s p h a s e b e c o m e s c o l o r l e s s . After t h e b l a c k , c r y s t a l l i n e iodine h a s s e t t l e d , t h e c o m p l e t e n e s s of t h e iodine p r e c i p i t a t i o n m a y b e c h e c k e d by adding a few d r o p s of n i t r i t e s o l u t i o n . T h e m o t h e r l i q u o r (which c o n t a i n s only about 0.5 g. of iodine p e r l i t e r ) i s d e c a n t e d and t h e iodine

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5 . C H L O R I N E , B R O M I N E , I O D I N E 279 p r e c i p i t a t e i s p l a c e d in a r o u n d - b o t t o m f l a s k , w h e r e i t m a y b e c o m b i n e d w i t h iodine p r e p a r e d in o t h e r r u n s . T h e I2 i s t h e n s t e a m - d i s t i l l e d f r o m t h i s f l a s k . No c o n d e n s e r i s u s e d ; i n s t e a d , t h e v a p o r m i x t u r e i s p a s s e d t h r o u g h a l a r g e t u b e ( 1 0 - 1 5 m m . in d i a m e t e r ) d i r e c t l y into t h e c e n t e r of a l a r g e t w o - l i t e r E r l e n m e y e r f l a s k w h i c h i s c l o s e d w i t h a p a r a f f i n - c o a t e d c o r k s t o p p e r and i m m e r s e d in a b a t h with flowing w a t e r . A s e c o n d h o l e in t h e c o r k s t o p p e r c o n t a i n s a vent t u b e about 0.5 m . long and 1 c m . in d i a m ­ e t e r . T h e I2 s e p a r a t e s on t h e w a l l s a s a c o m p a c t m a s s . T h e s u b ­ s t a n c e m a y e a s i l y b e d e t a c h e d f r o m t h e s e s u r f a c e s by s h a k i n g and c o o l i n g . It i s c r u s h e d w i t h a g l a s s r o d and s u c t i o n - d r i e d w h i l e p r e s s i n g t h e w a t e r out.

T h e f i l t e r e d I2 i s g i v e n a p r e l i m i n a r y and final d r y i n g o v e r C a C l2 o r c o n c e n t r a t e d H2S 04 in an u n g r e a s e d d e s i c c a t o r and t h e n s u b l i m e d . T h e iodine i s p l a c e d in a s p o u t l e s s b e a k e r , w h i c h i s i m m e r s e d in a hot w a t e r b a t h w h i l e a r o u n d - b o t t o m f l a s k , filled w i t h c o l d w a t e r , i s s e t on t o p of t h e b e a k e r . T h e f l a s k b e c o m e s c o v e r e d with m o i s t u r e and s o m e iodine and i s r e p l a c e d with a s e c o n d f l a s k b e f o r e t h e c o n d e n s e d w a t e r c a n d r o p b a c k . T h i s i s r e p e a t e d a s long a s m o i s t u r e i s e v o l v e d . T h e end of t h e w a t e r e v o l u t i o n c a n b e r e c o g n i z e d by t h e fact t h a t d r y I2 s t i c k s f i r m l y t o t h e w a t e r - c o o l e d g l a s s , w h e r e a s m o i s t iodine m a y e a s i l y b e w a s h e d off t h e g l a s s w i t h a s t r e a m f r o m a w a s h b o t t l e . T h e w e t b e a k e r i s now c a r e f u l l y wiped and c a r e f u l l y h e a t e d on an a s b e s t o s w i r e g a u z e . T h e r o u n d - b o t t o m f l a s k i s now c o o l e d on the i n s i d e with flowing w a t e r . A s soon a s a 0 . 5 - 1 c m . c r u s t of iodine f o r m s , it i s s c r a p e d off and put in a s t o r a g e f l a s k . T h e s u b l i m a t i o n i s t h e n c o n t i n u e d u n t i l a l l t h e I2 in t h e b e a k e r h a s s u b l i m e d .

T h e m e t h o d d e s c r i b e d m u s t b e modified in s o m e c a s e s , e . g . : If t h e iodine r e s i d u e s c o n t a i n c o n s i d e r a b l e q u a n t i t i e s of F e , t h e oxidation m u s t b e c a r r i e d out w i t h h e a t i n g in o r d e r t o d e c o m p o s e F e - N O c o m p l e x e s . If Hg o r P b s a l t s a r e p r e s e n t , t h e p r o c e d u r e d e s c r i b e d in C h e m i k e r - Z t g . 4 7 , 16 (1923) i s u s e d .

Other preparative methods: A p r o c e d u r e for t h e r e c o v e r y of I2 (and Ag) f r o m Agl r e s i d u e s i s g i v e n by J . R. S p i e s , Ind. E n g . C h e m . , A n a l . Ed. 7, 118 (1935); J . R. S p i e s in: W. C. F e r n e l i u s , I n o r g . S y n t h e s e s , Vol. II, New Y o r k - L o n d o n , 1946, p . 6.

If iodine i s t o b e r e c o v e r e d f r o m o r g a n i c iodine c o m p o u n d s , t h e o r g a n i c p o r t i o n i s d e c o m p o s e d with a K C 1 03- C 12 m i x t u r e

[Ε. M. M a r s h a l l , J . C h e m . E d . 7, 1131 (1930)].

A n o t h e r p r o c e d u r e , b a s e d on r e a c t i o n w i t h C l2, i s d e s c r i b e d by C. de W i t t , J . C h e m . Ed. 14, 215 (1937).

In c o l l e c t i n g t h e iodine r e s i d u e s t h e g r e a t e s t c a r e should b e t a k e n t o avoid t h e p r e s e n c e of any v o l a t i l e o r g a n i c s o l v e n t s in t h e c o n t a i n e r . If n o n v o l a t i l e o r g a n i c m a t e r i a l s s u c h a s s t a r c h e s a r e a b s e n t , t h e s t e a m d i s t i l l a t i o n d e s c r i b e d above m a y b e o m i t t e d .

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G r e a t c a r e should b e t a k e n t o avoid c o n t a m i n a t i n g t h e iodine r e s i d u e s with a m m o n i u m s a l t s . Violent e x p l o s i o n s m a y b e c a u s e d by t h e f o r m a t i o n of n i t r o g e n i o d i d e .

REFERENCES:

F . A r n d t , B e r . d t s c h . c h e m . G e s . 5 2 , 1131 (1919).

F . A r n d t , C h e m . Z t g . 4 7 , 16 (1923).

Hydroge n Chlorid e

H C 1

I. An e a s i l y c o n t r o l l a b l e s t r e a m of h y d r o g e n c h l o r i d e g a s m a y b e r e a d i l y o b t a i n e d by allowing p u r e , c o n c e n t r a t e d h y d r o c h l o r i c a c i d to flow into c o n c e n t r a t e d H2S 04.

An e s s e n t i a l c o n s t i t u e n t of t h e a p p a r a t u s shown in F i g . 143 i s t h e c a p i l l a r y t u b e . T h i s m u s t b e c o m p l e t e l y filled w i t h h y d r o c h l o r i c a c i d b e f o r e t h e evolution i s s t a r t e d , in o r d e r t o a s s u r e t h e h y d r o ­ s t a t i c p r e s s u r e n e c e s s a r y t o c a u s e t h e l i g h t e r h y d r o c h l o r i c a c i d t o flow t o t h e b o t t o m of t h e v e s s e l w h i c h c o n t a i n s t h e h e a v i e r H2S 04. Only by allowing t h e a c i d t o flow in t h i s w a y i s t h e g e n e r a ­ t i o n of t h e g a s c o m p l e t e l y u n i f o r m and c o n t r o l l a b l e .

A s e p a r a t o r y funnel i s filled w i t h a p ­ p r o x i m a t e l y 200 m l . of c o n c e n t r a t e d H2S 04, and c o n c e n t r a t e d h y d r o c h l o r i c a c i d ( d . 1.18) i s a d d e d f r o m a d r o p p i n g funnel a t s u c h a r a t e a s t o g i v e t h e g a s flow d e s i r e d . When 200 m l . of c o n c e n t r a t e d h y d r o c h l o r i c a c i d ( i . e . , the s a m e v o l u m e a s t h e v o l u m e of H2S 04 u s e d ) h a s b e e n a d d e d , g a s evolution s t o p s and t h e d i l u t e s u l f u r i c a c i d , w h i c h now c o n t a i n s v e r y l i t t l e HC1, i s d i s c h a r g e d and r e p l a c e d by f r e s h Hg S 04. (If m o r e t h a n an e q u a l v o l u m e of h y d r o c h l o r i c a c i d i s a d d e d , HC1 c o n t i n u e s t o be f o r m e d for a while a f t e r t h e s t o p c o c k i s c l o s e d ; h o w ­ e v e r , t h e y i e l d i s r e d u c e d . ) T h e y i e l d f r o m 200 m l . of c o n c e n t r a t e d h y d r o c h l o r i c a c i d i s 67.4 g. of HC1.

If a u n i f o r m s t r e a m of HC1 i s r e q u i r e d f o r a l o n g e r p e r i o d , t h e a p p a r a t u s d e s i g n e d b y Seidel ( F i g . 144) i s r e c o m m e n d e d . C o n ­

c e n t r a t e d h y d r o c h l o r i c a c i d and c o n c e n t r a t e d s u l f u r i c a c i d a r e d r o p p e d c o n t i n u o u s l y f r o m t u b e s a and b into t h e r e a c t i o n t u b e ,

t o chiUed

c o n e . H2S<k

F i g . 1 4 3 . P r e p a r a ­ t i o n of h y d r o g e n

c h l o r i d e .

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5 . C H L O R I N E , B R O M I N E , I O D I N E 2 8 1

w h i c h i s about 5 c m . in d i a m e t e r and c o n t a i n s a 2 0 - t o 2 5 - c m . l a y e r ο of p a c k i n g , s u c h a s s i l i c a o r g l a s s b e a d s . T h e s p e n t liquid m i x t u r e a u t o m a t i c a l l y d r a i n s off b e l o w . W i t h a n a p p a r a t u s of t h e s e d i m e n s i o n s , u p t o t h r e e l i t e r s of HC1 g a s c a n b e p r o d u c e d p e r m i n ­ u t e .

In o r d e r t o r e m o v e m o i s t u r e t h a t m a y b e p r e s e n t , t h e p r o d u c t g a s i s l e d t h r o u g h a w a s h b o t t l e

/ A s

F i g . 144. P r e p a r a t i o n of h y ­ d r o g e n c h l o r i d e . a, b) D r o p ­ p i n g t u b e s f o r c o n c e n t r a t e d HC1 a n d c o n c e n t r a t e d H2S 04; o) r e a c t i o n t u b e p a c k i n g ( s i l i c a o r g l a s s b e a d s , d i a m e t e r 2 - 5 m m . ) .

H2S Q4 c o n t a i n i n g c o n c e n t r a t e d

( P2Os m u s t not b e u s e d b e c a u s e t h e g a s f o r m s v o l a t i l e p h o s p h o r u s c o m p o u n d s w i t h it) a n d into a r e ­ c e i v e r c h i l l e d w i t h liquid n i t r o g e n . T h e r e c e i v e r i s t h e n d e t a c h e d f r o m t h e g e n e r a t o r a n d t h e g a s i s f r a c ­ t i o n a l l y d i s t i l l e d . Only t h e m i d d l e f r a c t i o n i s p u r e e n o u g h for u s e in f u r t h e r w o r k . ( F o r t h e a p p a r a t u s s e e P a r t I, p . 66 ff.)

If an e s p e c i a l l y p u r e p r o d u c t i s not r e q u i r e d , t h e g r o u n d g l a s s p a r t of t h e s e p a r a t o r y funnel in F i g . 143 m a y b e r e p l a c e d by a t w o - h o l e r u b b e r s t o p p e r . T h e f r e e z i n g a n d 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 h y d r o ­ g e n c h l o r i d e m a y b e o m i t t e d in t h i s c a s e .

PROPERTIES:

F o r m u l a w e i g h t 3 6 . 4 7 . C o l o r l e s s , pungent g a s . M . p . —112°C, b . p . - 8 5 . 0 ° C ; c r i t . t. 51.3°C, c r i t . p . 83 a t m . ; d. (liq.) (— 85°C) 1.189.

Solubility in w a t e r : 1 v o l . (15°C) d i s s o l v e s about 450 v o l . of HC1 (47% by w e i g h t ) .

A t t a c k s r u b b e r and s t o p c o c k g r e a s e ; g l a s s s t o p c o c k s should t h e r e f o r e b e l u b r i c a t e d w i t h c o n c e n t r a t e d H2S 04. T h e g a s c a n b e

s t o r e d o v e r Hg o r o v e r H2S 04.

II. A c c o r d i n g t o H o n i g s c h m i d , v e r y p u r e a q u e o u s s o l u t i o n s of HC1 c a n b e o b t a i n e d by d i l u t i n g p u r e l a b o r a t o r y h y d r o c h l o r i c a c i d t o 20% with w a t e r , b o i l i n g it w i t h s m a l l a m o u n t s of K M n 04 t o r e m o v e b r o m i n e and i o d i n e , and t h e n d i s t i l l i n g it t h r o u g h a q u a r t z c o n ­ d e n s e r . If t h e p u r i f i e d h y d r o c h l o r i c a c i d p r e p a r e d in t h i s w a y i s n e e d e d in m o r e c o n c e n t r a t e d f o r m , HC1 g a s i s g e n e r a t e d f r o m t h i s d i l u t e s o l u t i o n with H2S 04 a c c o r d i n g t o t h e m e t h o d g i v e n u n d e r I, and t h i s p r o d u c t g a s i s t h e n b u b b l e d t h r o u g h p u r i f i e d 20% h y d r o ­ c h l o r i c a c i d u n t i l t h e l a t t e r b e c o m e s s a t u r a t e d .

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REFERENCES:

I. Re N. M a x s o n in: H. S. Booth. I n o r g . S y n t h e s e s , Vol. I, New Y o r k - L o n d o n , 1939, p . 147.

O. R„ Sweeney. J . A m e r . C h e m . Soc. 3 9 , 2186 (1917).

A. K l e m e n c Die B e h a n d l u n g und R e i n d a r s t e l l u n g von G a s e n [ T r e a t m e n t and P u r i f i c a t i o n of G a s e s ] , 2nd e d . , V i e n n a , 1948, p . 2 3 4 .

W. S e i d e l . C h e m . F a b r i k 1 1 , 408 (1938).

II. O. H o n i g s c h m i d . Safder B e d r Chan and L . B i r c k e n b a c h . Z . a n o r g . a l l g . C h e m . 1 6 3 , 315 (1927).

Hydroge n Bromid e HBr

T h e m e t h o d c h o s e n for p r o d u c i n g h y d r o g e n b r o m i d e d e p e n d s upon w h e t h e r it i s to b e a n h y d r o u s o r in a q u e o u s s o l u t i o n , a s w e l l a s on t h e a m o u n t r e q u i r e d and t h e r e q u i s i t e d e g r e e of p u r i t y of t h e p r o d u c t .

M e t h o d s I and II, which a r e s u i t a b l e for t h e p r e p a r a t i o n of a n h y d r o u s H B r , m a y a l s o b e modified t o g i v e a q u e o u s s o l u t i o n s , but t h e s p e c i a l p r o c e d u r e s for obtaining a q u e o u s s o l u t i o n s (V) c a n n o t be modified t o g i v e a n h y d r o u s H B r . H o w e v e r , r e g a r d l e s s of t h e m a n n e r in which t h e y h a v e b e e n p r e p a r e d , H B r s o l u t i o n s c a n b e d e h y d r a t e d w i t h P2 05 v i a m e t h o d III.

W h i l e m e t h o d I ( t e t r a l i n p l u s B r2) i s v e r y c o n v e n i e n t , it should b e r e a l i z e d t h a t half of t h e B r2 input i s l o s t by r e a c t i o n with t h e t e t r a l i n . T h e r e f o r e , m e t h o d II ( H2 + B r2) i s p r e f e r r e d for p r e ­ p a r i n g l a r g e r q u a n t i t i e s of H B r .

How f a r t h e d e s c r i b e d p r o c e d u r e s c a n b e s i m p l i f i e d if a highly p u r i f i e d p r o d u c t i s not r e q u i r e d w i l l b e i n d i c a t e d u n d e r t h e r e ­ s p e c t i v e m e t h o d s .

I. P r e p a r a t i o n of a n h y d r o u s H B r f r o m t e t r a l i n ( t e t r a h y d r o n a p h - t h a l e n e ) and B r2:

C1 0H1 2 + 4Br2 = C1 0H8Br4 4- 4 HBr

132.2 639.4 447.9 323.7

B r o m i n e i s g r a d u a l l y added by d r o p s t o a m i x t u r e of t e t r a l i n and p u r e i r o n filings c o n t a i n e d in a r o u n d - b o t t o m flask equipped w i t h a d r o p p i n g funnel and a g a s outlet t u b e . ( P r i o r t o u s e , t h e t e t r a l i n i s d r i e d o v e r a n h y d r o u s N a2S 04 and d i s t i l l e d ; b . p . of t h e t e t r a l i n i s 207°C, v a p o r p r e s s u r e at 15°C, 0.3 m m . ; C. P . g r a d e B r2 s h o u l d b e u s e d . ) Since i n i t i a l cooling i s n e c e s s a r y , t h e f l a s k i s p l a c e d in a w a t e r b a t h , w h i c h , a s soon a s t h e r e a c t i o n b e c o m e s s l u g g i s h , i s h e a t e d t o 30 t o 4 0 ° C T h e g a s f o r m e d in t h e r e a c t i o n i s p a s s e d

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5 . C H L O R I N E , B R O M I N E , I O D I N E 283 t h r o u g h a w a s h b o t t l e filled w i t h t e t r a l i n ( a l s o p r e d r i e d and d i s ­ t i l l e d ) in o r d e r t o e l i m i n a t e s m a l l q u a n t i t i e s of B r2, and t h r o u g h a t r a p c o o l e d t o — 60°C in o r d e r t o r e m o v e t h e l a s t t r a c e s of m o i s ­ t u r e . It i s t h e n f r o z e n in a s e c o n d t r a p c o o l e d w i t h liquid n i t r o g e n . After c o m p l e t i o n of t h e r e a c t i o n , t h e r e c e i v e r t r a p i s s e p a r a t e d f r o m t h e g a s g e n e r a t i n g a p p a r a t u s by m e l t i n g t h e c o n n e c t i o n .

A m o r e effective m e t h o d f o r r e m o v a l of t h e l a s t t r a c e s of w a t e r i n v o l v e s t r a p p i n g a t — 70°C i n s t e a d of —60°C, s o t h a t s o m e liquid H B r c a n a c c u m u l a t e t h r o u g h w h i c h t h e r e m a i n i n g H B r g a s w i l l b u b b l e .

T h e c o n d e n s e d H B r i s p u r i f i e d by s u b l i m i n g p a r t of t h e s o l i d p r o d u c t and c o l l e c t i n g t h e m i d d l e f r a c t i o n in a r e c e i v e r cooled w i t h liquid n i t r o g e n . T h e c o n t a i n e r i s t h e n s e a l e d off. T h e p r e s s u r e s in t h e p r e p a r a t i o n and f r a c t i o n a t i o n s e c t i o n s of t h e a p p a r a t u s should b e m o n i t o r e d by m e a n s of an a t t a c h e d m a n o m e t e r . ( F o r s u i t a b l e a p p a r a t u s , s e e P a r t I, p . 66 ff.)

II. H2 + Br2 = 2 HBr

2 159.9 161.9

T h e a r r a n g e m e n t shown in F i g . 145 i s u s e d ; h y d r o g e n b u b b l e s t h r o u g h w a s h b o t t l e A, s e r v i n g a s a f l o w m e t e r . It t h e n a c c u m u l a t e s

F i g . 145. P r e p a r a t i o n of h y d r o g e n b r o m i d e .

in f l a s k B, t o w h i c h B r2 c a n b e added in d r o p s f r o m d r o p p i n g funnel 0. T h e c o n n e c t i n g t u b e f r o m A m u s t r e a c h t o t h e b o t t o m of B. B e t w e e n A and Β SL p a r t of t h e H2 s t r e a m i s d i v e r t e d t o 0 s o t h a t when t h e c l o s e d - o f f v e s s e l 0 i s d e p l e t e d , p r e s s u r e e q u i l i b r i u m will b e m a i n t a i n e d . T h e H2 s t r e a m c a r r y i n g t h e B r2 v a p o r t h e n e n t e r s P y r e x t u b e D ( 4 0 - 5 0 c m . l o n g , 2 - 4 c m . in d i a m e t e r ) , filled with p l a t i n i z e d a s b e s t o s o r p l a t i n i z e d s i l i c a g e l h e l d in p l a c e by g l a s s wool p l u g s . T h i s t u b e i s h e a t e d in e l e c t r i c f u r n a c e E. T h e t u b e i s c o n n e c t e d t o t u b e E, w h i c h c o n t a i n s r e d p h o s p h o r u s d i s ­ p e r s e d on g l a s s s p h e r e s o r R a s c h i g r i n g s , and t o a w a s h b o t t l e G,

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w h i c h c o n t a i n s a few m i l l i l i t e r s of w a t e r t o r e m o v e e n t r a i n e d p h o s p h o r u s c o m p o u n d s . T h e H B r - H2 m i x t u r e finally p a s s e s t h r o u g h a d r y i n g t u b e Η filled w i t h C a C l3 ( C a B r2 i s b e t t e r , of c o u r s e ) and i s f r o z e n in t r a p J by c o o l i n g w i t h liquid n i t r o g e n .

Procedure: B e f o r e adding t h e B r2 t o B% t h e a i r in t h e a p p a r a t u s i s d i s p l a c e d by a s t r e a m of H2. When t h i s h a s b e e n a c c o m p l i s h e d , t h e f u r n a c e i s h e a t e d t o 350°C and t h e f i r s t p o r t i o n of about 50 m l . of B r2 i s a d m i t t e d t o c o n t a i n e r B. T h e H2 should p a s s t h r o u g h t h e b r o m i n e l a y e r (25°C) in a r a t h e r fast s t r e a m in o r d e r t o a s s u r e a c o n s t a n t e x c e s s of H2. D e t e r i o r a t i o n of t h e c a t a l y s t m a y be r e c o g ­ n i z e d by t h e i n c r e a s e d p r e s e n c e of f r e e B r2 in t h e p a r t of t h e a p p a r a t u s c o n n e c t e d t o t u b e D. C a r e should b e e x e r c i s e d t o avoid c h a n n e l i n g of t h e g a s t h r o u g h t u b e Ό due t o s h r i n k a g e of t h e c a t a l y s t . If no s u c h p r e c a u t i o n s a r e t a k e n , t h e H2- B r2 m i x t u r e i s l i k e l y t o e m e r g e u n c o n v e r t e d f r o m t h e r e a c t o r .

T h e H B r f r o z e n out in J i s p u r i f i e d by f r a c t i o n a l d i s t i l l a t i o n a s i n d i c a t e d in m e t h o d I.

A s a s a f e t y m e a s u r e it i s d e s i r a b l e t h a t c o n t a i n e r Β not b e e x p o s e d t o d i r e c t l i g h t . It i s b e s t t o p a i n t Β b l a c k ( l e a v i n g s o m e p e e p h o l e s in o r d e r to b e a b l e to c h e c k the a m o u n t of B r2 p r e s ­ e n t ) . W h e n n e e d e d , r u b b e r s t o p p e r s (which then m u s t b e f r e ­ quently changed) and r u b b e r tubing o v e r t h e g l a s s - t o - g l a s s c o n ­ n e c t i o n s m a y b e u s e d . G r o u n d g l a s s o r fused j o i n t s a r e b e t t e r , h o w e v e r . B e c a u s e of t h e n e c e s s a r y p r e s s u r e in t h e s y s t e m , t h e s t o p p e r s on t h e w a s h b o t t l e s should b e c o r r e s p o n d i n g l y w e l l s e c u r e d .

Other preparative method:

III. D e h y d r a t i o n of c o n c e n t r a t e d H B r s o l u t i o n s w i t h P2Og. A r o u n d - b o t t o m f l a s k i s p a r t l y filled w i t h v e r y p u r e P s 05; H B r s o l u t i o n i s t h e n a d d e d in d r o p s f r o m a d r o p p i n g funnel, with s i m u l ­ t a n e o u s c o o l i n g . P u r i f i c a t i o n of t h e g a s s t r e a m t h u s p r o d u c e d i s c a r r i e d out a s d e s c r i b e d in m e t h o d I (A. K l e m e n c ) .

PROPERTIES:

F o r m u l a w e i g h t 8 0 . 9 3 . C o l o r l e s s g a s . M . p . —87°C, b . p . —67°C;

d. (—68°C) 2 . 1 7 . A s a t u r a t e d solution in HsO at 0°C c o n t a i n s 68.85% and at 25°C, 66% H B r . T h e c o n s t a n t - b o i l i n g a c i d at 760 m m . and 126°C c o n t a i n s 47.8% H B r .

C o m p l e t e l y d r y H B r m a y b e s t o r e d for s o m e t i m e o v e r Hg.

A f t e r a w h i l e , d e c o m p o s i t i o n s e t s in, p o s s i b l y p r o m o t e d by light and s t o p c o c k g r e a s e .

IV. A q u e o u s s o l u t i o n s of H B r m a y b e p r e p a r e d u s i n g t h e H B r p r e ­ p a r e d and p u r i f i e d a c c o r d i n g t o I o r II. If a l e s s p u r e p r o d u c t i s suf­

f i c i e n t , it i s p o s s i b l e t o s i m p l i f y t h e p r o c e d u r e in t h e following w a y s : In m e t h o d I: T h e H B r , a f t e r p a s s i n g t h r o u g h t h e w a s h b o t t l e c o n t a i n i n g t e t r a l i n , i s l e d d i r e c t l y into w a t e r c o o l e d w i t h an

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5 . C H L O R I N E , B R O M I N E , I O D I N E 285 i c e - s a l t b a t h . T h e y i e l d in t h i s c a s e i s 94% of t h e o r e t i c a l . When it i s r e m e m b e r e d t h a t half t h e b r o m i n e i s l o s t by c o m b i n i n g with t h e t e t r a l i n , t h e y i e l d b a s e d on t o t a l b r o m i n e r e a c t e d i s 47%.

An e v e n s i m p l e r m e t h o d i s t o m i x e q u a l q u a n t i t i e s of t e t r a l i n and w a t e r and t h e n slowly d r o p B r2 in w i t h c o n t i n u o u s s t i r r i n g . T h e a q u e o u s and n o n a q u e o u s l a y e r s a r e s e p a r a t e d in a s e p a r a t o r y funnel, t h e n o n a q u e o u s l a y e r i s a g a i n w a s h e d w i t h H20 , and t h e w a s h w a t e r i s c o m b i n e d w i t h t h e m a i n H B r s o l u t i o n .

In m e t h o d II: D r y i n g t u b e Η a n d t r a p J a r e r e p l a c e d by one o r m o r e i n t e r c o n n e c t e d w a s h b o t t l e s c o n t a i n i n g w a t e r and c o o l e d by a n i c e - s a l t b a t h . In t h i s c a s e , a p p r o x i m a t e l y 65% H B r s o l u t i o n s a r e o b t a i n e d .

V. H2S 04 + KBr = K H S 04 + HBr 98.1 119 136.2 80.9

A d i r e c t m e t h o d , w h i c h i s s u i t a b l e only f o r t h e p r e p a r a t i o n of c o n s t a n t - b o i l i n g H B r s o l u t i o n s , d e p e n d s on t h e effect of d i l u t e s u l f u r i c a c i d on K B r ( c o n c e n t r a t e d H2S 04 would o x i d i z e t h e H B r t o B r2) .

A m i x t u r e of 120 g. of p u l v e r i z e d K B r a n d 200 m l . of H20 i s c h i l l e d w i t h cold w a t e r and slowly r e a c t e d w i t h 90 m l . of c o n c e n ­ t r a t e d H2S 04. T h e t e m p e r a t u r e should not b e allowed t o r i s e above 75 C t o r e t a r d p o s s i b l e f o r m a t i o n of f r e e b r o m i n e . T h e s o l u t i o n i s t h e n c o o l e d t o r o o m t e m p e r a t u r e and t h e K H S 04 i s f i l t e r e d off t h r o u g h a B u c h n e r funnel ( u s i n g h a r d f i l t e r p a p e r ) . T h e f i l t r a t e i s p l a c e d in a 5 0 0 - m l . d i s t i l l a t i o n f l a s k equipped with a s u i t a b l e c o n d e n s e r and r e c e i v e r and h e a t e d o v e r a w i r e g a u z e . A f t e r d i s t i l l i n g off t h e w a t e r , t h e f r a c t i o n t h a t i s c o l l e c t e d b e g i n s to b o i l 1° below the b o i l i n g p o i n t of the a z e o t r o p e [ b . p . 122.5°C (740 m m . ) , 126°C (760 m m . ) ] and t h e d i s t i l l a t i o n i s s t o p p e d a s s o o n a s t h e t e m p e r a t u r e b e g i n s t o d r o p . T h e y i e l d i s a b o u t 85%.

T h i s a c i d m a y s t i l l c o n t a i n about 0.01% H2S 04. Acid t h a t i s c o m p l e t e l y f r e e of H2S 04— i n t h e h i g h e s t a t t a i n a b l e c o n c e n t r a t i o n - i s o b t a i n e d if c o l l e c t i o n of the d i s t i l l a t e i s b e g u n 5° b e l o w the b o i l i n g point of t h e c o n s t a n t - b o i l i n g a c i d . T h i s d i s t i l l a t e i s t h e n r e d i s t i l l e d , but only t h e f r a c t i o n at t h e b o i l i n g point of t h e a z e o ­ t r o p e i s c o l l e c t e d .

REFERENCES:

I. A. M u l l e r . Mh. C h e m . 4 9 , 29 (1928).

A. K l e m e n c . Die B e h a n d l u n g und R e i n d a r s t e l l u n g von G a s e n [ T r e a t m e n t and P u r i f i c a t i o n of G a s e s ] . 2nd e d . , V i e n n a , 1948, p . 2 3 7 .

II. J . M. S c h n e i d e r and W. C. J o h n s o n in: H. S. Booth. I n o r g , S y n t h e s e s , Vol. I, New Y o r k - L o n d o n , 1939, p . 152.

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Μ . S C H M E I S S E R

Τβ W. R i c h a r d s and Οβ H o n i g s c h m i d . J . A m e r . C h e m . S o c 32^

1581 (1910).

V. G. V„ H e i s i g and E, A m d u r , J . C h e m . Ed. 14, 187 (1938);

C h e m . Z e n t r . 1937 II, 1760.

G. Be H e i s i g and E . A m d u r in: H. S. Booth. I n o r g . S y n t h e s e s , Vol. I. New Y o r k - L o n d o n , 1939, p . 155.

Hydroge n Iodid e

H I

T h e c h o i c e of p r e p a r a t i v e m e t h o d d e p e n d s on w h e t h e r a n h y d r o u s HI o r an HI solution i s r e q u i r e d . Method I ( p r e p a r a t i o n of a n h y ­ d r o u s HI f r o m H3 and I2) i s quite s u i t a b l e f o r t h e p r e p a r a t i o n of HI s o l u t i o n s , while m e t h o d III ( H2S + I2) i s l i m i t e d t o s o l u t i o n s , u n l e s s (in a c c o r d a n c e with II) t h e highly c o n c e n t r a t e d a q u e o u s s o l u t i o n i s d e h y d r a t e d with P205. Since HI s o l u t i o n s soon t u r n b r o w n on s t a n d i n g (due t o t h e f o r m a t i o n of iodine by light and a i r ) , a m e t h o d (IV) for r e g e n e r a t i n g s u c h s o l u t i o n s i s a l s o g i v e n .

I. H2 + I2 = 2 H I

2 253.8 255.8

H y d r o g e n i s p a s s e d o v e r I2 c o n t a i n e d in a 2 5 0 - m l . P y r e x f l a s k A ( s e e F i g . 146) w h i c h c a n be h e a t e d . A P y r e x t u b e B, 90 c m . long and 1.8-2 c m . in d i a m e t e r , i s c o n n e c t e d t o t h e f l a s k . If p o s s i b l e , t h i s t u b e i s fused on d i r e c t l y . If a b s o l u t e l y n e c e s s a r y it m a y b e c o n n e c t e d by a g r o u n d j o i n t . H o w e v e r , in t h i s c a s e t h e joint i s s e a l e d on t h e o u t s i d e with a s b e s t o s - w a t e r g l a s s m i x t u r e . T h e p a r t of t h e t u b e n e a r e s t f l a s k A i s filled for a l e n g t h of 1 0 - 2 0 c m . w i t h p l a t i n i z e d a s b e s t o s o r a m i x t u r e of a s b e s t o s w i t h P t s p o n g e w h i c h i s t h e n h e a t e d to 500°C in a f u r n a c e . T h e t u b e i s followed by a U tube 0 c o n t a i n i n g C a l2 t o d r y t h e HI, a U t u b e Ό w i t h KI t o r e m o v e t h e l a s t t r a c e s of i o d i n e , and a f r e e z i n g t r a p Ε w h i c h i s c o o l e d to

—78°C. A P205 t u b e F s e r v e s a s p r o t e c t i o n 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 . It i s a d v i s a b l e t o p r o v i d e a b y p a s s t u b e for H2. T h e b y p a s s h y d r o g e n s t r e a m m a y t h e n b e u s e d a s a c a r r i e r g a s t o c a r r y u n r e a c t e d iodine, o r iodine f o r m e d by d e c o m p o s i t i o n of HI, f r o m t h e e m p t y p a r t of t u b e Β b a c k t o f l a s k A. In o r d e r to do t h i s , s t o p c o c k Hx i s opened, and t h e t w o - w a y s t o p c o c k i s t u r n e d to a p o s i t i o n 180° f r o m t h a t shown in F i g . 146. After cooling t h e c a t a l y s t , t h e I2 i s h e a t e d with a B u n s e n b u r n e r and s u b l i m e d in a s t r e a m of h y d r o g e n , w h i c h c a r r i e s it i n t o / ! .

Preliminary treatment of starting materials: C y l i n d e r H2 i s , a s u s u a l , p a s s e d o v e r a P t c a t a l y s t and t h r o u g h a s y s t e m of d r y i n g t u b e s . T h e p u r e s t a v a i l a b l e I2 i s u s e d ; it i s d r i e d in a v a c u u m o v e r P205 and, in o r d e r t o r e m o v e any r e m a i n i n g CI and B r , i s i n t i m a t e l y m i x e d with 5% by weight of KI. F o r t h e p l a t i n i z e d

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5 . C H L O R I N E , B R O M I N E , I O D I N E 2 8 7

a s b e s t o s , s e e t h e s e c t i o n on P l a t i n u m M e t a l s ; about 3 g . of a s b e s t o s f i b e r s i s s a t u r a t e d w i t h 7 m l . of 10% H3P t C l6 s o l u t i o n ; t h e d a m p m i x t u r e i s e v a p o r a t e d t o d r y n e s s w i t h c o n t i n u o u s s t i r r i n g and t h e p r o d u c t i s t h e n h e a t e d t o r e d h e a t .

Procedure: After A h a s b e e n c h a r g e d w i t h I2, t h e a i r in t h e a p p a r a t u s i s c a r e f u l l y d i s p l a c e d by N2, following w h i c h H2 i s p a s s e d t h r o u g h . (If H2 w e r e t o b e a d m i t t e d w h i l e t h e a p p a r a t u s s t i l l c o n t a i n e d oxygen, t h e c a t a l y s t c o u l d p r o m o t e a n e x p l o s i v e r e a c t i o n of t h e h y d r o g e n - o x y g e n m i x t u r e . ) T h e c a t a l y s t i s now h e a t e d . T h e I2 in f l a s k >J i s h e a t e d j u s t enough t o p r o d u c e v e r y s m a l l q u a n t i t i e s of I2 v a p o r in t h e p a r t of t u b e Β t h a t e x t e n d s beyond t h e c a t a l y s t . E x p e r i e n c e s h o w s t h a t t h e c o r r e c t t e m p e r a t u r e of t h e I2 i s r e a c h e d w h e n t h e c o n d e n s a t i o n z o n e in t h e iodine f l a s k l i e s s o m e w h a t h i g h e r t h a n t h e s i d e a r m . S o m e I2 a l s o c o n d e n s e s in t h e c o n n e c t i n g t u b e b e t w e e n A and t h e c a t a l y s t and m u s t t h e r e f o r e b e c a r e f u l l y s u b l i m e d f r o m t i m e t o t i m e w i t h a B u n s e n b u r n e r . (In g e n e r a l , c a r e should b e t a k e n d u r i n g t h e e n t i r e r u n t o a s s u r e t h a t t h e r e a r e no s o l i d I2 p l u g s at a n y point of t h e a p p a r a t u s . ) T h e HI p r o d u c t ,

F i g . 146. P r e p a r a t i o n of h y d r o g e n i o d i d e .

a f t e r p a s s i n g t h r o u g h p u r i f i c a t i o n t u b e s 0 and D (which m a y b e o m i t t e d if a h i g h p u r i t y p r o d u c t i s not r e q u i r e d ) , i s f r o z e n in Ε a n d t h e n r e p e a t e d l y f r a c t i o n a t e d . At t h e end of t h e r u n , t h e c a t a l y s t i s c o o l e d in a s t r e a m of H2.

II. A n o t h e r p r e p a r a t i v e m e t h o d for a n h y d r o u s HI c o n s i s t s in d e h y d r a t i o n of highly c o n c e n t r a t e d HI s o l u t i o n s by P2Ob. A r o u n d - b o t t o m f l a s k i s p a r t i a l l y filled w i t h v e r y p u r e P 3 O 5 . T h e HI s o l u t i o n i s t h e n a d d e d in d r o p s f r o m a d r o p p i n g funnel, w h i l e t h e f l a s k i s c o o l e d . T h e g a s e o u s p r o d u c t i s d r i e d in an adjoining t u b e w i t h P205. F u r t h e r p u r i f i c a t i o n of t h e HI p r o d u c t p r o c e e d s in a c c o r d a n c e w i t h m e t h o d I.

PROPERTIES:

F o r m u l a w e i g h t 1 2 7 . 9 3 . C o l o r l e s s g a s . M . p . —50.9°C, b . p .

—35.4°C; d, (0°C) 5.66. Solid o r liquid HI c a n b e s t o r e d at a low t e m p e r a t u r e a w a y f r o m l i g h t . Solubility a t 0°C, 900 g . of H i / 1 0 0 g . of H20 .

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No r u b b e r tubing o r s t o p p e r s should b e u s e d with HI, if at a l l p o s s i b l e . If g r e a s e d s t o p c o c k s m u s t b e u s e d , w h i t e v a s e l i n e i s t h e m o s t s u i t a b l e l u b r i c a n t .

III. Solutions of HI m a y b e o b t a i n e d if t h e p r o d u c t p r e p a r e d a c c o r d i n g t o I, i n s t e a d of b e i n g c o n d e n s e d , i s d i s s o l v e d in w a t e r c o o l e d in an i c e - s a l t b a t h .

T h e following m e t h o d m a y b e u s e d to p r e p a r e a z e o t r o p i c a q u e ­ o u s HI solution:

H2S 4- I2 = 2 HI 4- S

34.1 253.8 255.8 32.1

A s u s p e n s i o n of 120 g. of I2 in 150 m l . of H20 i s v i g o r o u s l y s t i r r e d in a w i d e - n e c k 5 0 0 - m l . v e s s e l w i t h a t h r e e - h o l e s t o p p e r (for a g a s inlet t u b e w h i c h r e a c h e s below t h e s u r f a c e of t h e liquid, a g a s outlet t u b e , and a s t i r r e r ) . T h e s t i r r e r m u s t fit t h e w a l l s of t h e v e s s e l a s c l o s e l y a s p o s s i b l e . A s t r e a m of H2S i s t h e n a b s o r b e d by t h e s u s p e n s i o n , t h e flow r a t e b e i n g c o n t r o l l e d s o a s not t o e x c e e d t h e a b s o r p t i o n r a t e . Any s l i g h t e x c e s s of H2S l e a v e s t h e r e a c t i o n v e s s e l t h r o u g h t h e g a s outlet t u b e and g o e s e i t h e r t o a hood o r i s p a s s e d o v e r t h e s u r f a c e of a s o d i u m h y d r o x i d e s o l u t i o n in a s p e c i a l flask; t h e outlet t u b e should not dip into t h e s o d i u m h y d r o x i d e . After about an h o u r , t h e s o l u t i o n in t h e a b s o r p t i o n f l a s k b e c o m e s p r a c t i c a l l y c o l o r l e s s due t o t h e s e p a r a t i o n of c o n ­

s i d e r a b l e q u a n t i t i e s of s u l f u r . T h e s o l u t i o n i s t h e n s e p a r a t e d f r o m t h e c o a r s e r sulfur p a r t i c l e s by d e c a n t a t i o n and f i l t e r e d t h r o u g h a g l a s s f r i t t o r e m o v e t h e fine s u l f u r . T h e H2S , s t i l l d i s s o l v e d in t h e s o l u t i o n , i s r e m o v e d by a s h o r t p e r i o d of b o i l i n g , a f t e r w h i c h a t e s t of t h e s o l u t i o n should not g i v e a r e a c t i o n for s u l f i d e .

T h e s o l u t i o n i s d i s t i l l e d f r o m a 2 5 0 - m l . d i s t i l l a t i o n f l a s k , u s i n g b o i l i n g c h i p s to avoid b u m p i n g . T h e f r a c t i o n boiling f r o m 125 t o 127°C i s c o l l e c t e d . T h e y i e l d i s about 90% b a s e d on t h e I2 u s e d . T h e a z e t r o p i c a c i d (57% HI) b o i l s at 126°C (760 m m . ) , d 1.70.

It f u m e s s t r o n g l y in a i r . A q u e o u s HI s o l u t i o n s m u s t b e s t o r e d in d a r k , w e l l - s e a l e d f l a s k s . It i s a d v i s a b l e t o s e a l t h e s t o r a g e f l a s k s w i t h p a r a f f i n . A s a f u r t h e r p r e c a u t i o n a g a i n s t o x i d a t i o n , t h e a i r a b o v e t h e s u r f a c e of t h e liquid m a y b e d i s p l a c e d by an i n e r t g a s b e f o r e s e a l i n g t h e f l a s k .

IV. C o n c e n t r a t e d HI s o l u t i o n s t h a t h a v e b e c o m e b r o w n due t o t h e s e p a r a t i o n of iodine m a y be r e g e n e r a t e d a s follows:

I2 + H3P 02 4- H20 = H3PO3 4- 2 HI

253.8 66 18 82 255.8

T h e r e a c t i o n i s c a r r i e d out in a 5 0 0 - m l . g r o u n d g l a s s f l a s k w h i c h i s equipped with an inlet t u b e f o r i n e r t g a s ( N2, H2 o r C 02) and a f r a c t i o n a t i n g c o l u m n . T h e l a t t e r c a r r i e s a d r o p p i n g funnel

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5 . C H L O R I N E , B R O M I N E , I O D I N E 289 ( c o n n e c t e d w i t h a g r o u n d g l a s s joint) on t o p . T h e i o d i n e - c o n t a i n i n g HI s o l u t i o n i s b r o u g h t t o n e a r b o i l i n g w i t h i n e r t g a s s l o w l y p a s s i n g t h r o u g h t h e flask. T h e hot solution i s t h e n r e a c t e d with 50%

H3P 03 s o l u t i o n , added by d r o p s u n t i l d e c o l o r i z a t i o n o c c u r s (only a few m i l l i l i t e r s a r e n e e d e d for t h i s , d e p e n d i n g on t h e iodine c o n t e n t ) . T h e d r o p p i n g funnel i s now r e p l a c e d by a g r o u n d joint t h e r m o m e t e r , and t h e a z e o t r o p i c a c i d i s d i s t i l l e d off at 125-127°C (760 m m . ) .

REFERENCES:

I and III. M. B o d e n s t e i n . Z . p h y s . C h e m . 1 3 , 59 (1894).

M. B o d e n s t e i n and F . L i e n e w e g . Z . p h y s . C h e m . 119, 124 (1926).

R. H. Ogg, J r . J . A m e r . C h e m . Soc. 5 6 , 526 (1934).

A. K l e m e n c . Die B e h a n d l u n g und R e i n d a r s t e l l u n g von G a s e n [ T r e a t m e n t a n d P u r i f i c a t i o n of G a s e s ] , 2nd e d . , V i e n n a , 1948, p . 2 3 9 .

G. B . H e i s i g and O. C . F r y k h o l m in: H. S. Booth, I n o r g . S y n t h e s e s , Vol. I, New Y o r k - L o n d o n , 1939, p . 157.

H, G r u b i t s c h , A n o r g . p r a p . C h e m i e [ P r e p a r a t i v e I n o r g a n i c C h e m . ] , V i e n n a , 1950. p . 2 7 8 .

II. K. F . Bonhoeffer and W. S t e i n e r , Z . p h y s . C h e m . 122, 288 (1926). G. K. R o l l e f s o n and J . E . B o o h e r , J . A m e r . C h e m . Soc.

5 3 , 1728 (1931).

IV. L . S. F o s t e r a n d H. G. N a h a s in: W. C. F e r n e l i u s , I n o r g . S y n t h e s e s , Vol. II, New Y o r k - L o n d o n , 1946, p . 2 1 0 .

Ammoniu m Iodid e NH4I

I. I2 + 2 N H3 + H202 = 2 N H4I + Oz

253.8 34 34 289.8 32

P o w d e r e d iodine (100 g.) i s r e a c t e d w i t h 280 m l . of 10% a m - m o n i a w a t e r ( i . e . , double t h e s t o i c h i o m e t r i c quantity) and 600 m l . of 3% H202( i . e . , 33% e x c e s s ) . T h e I2 d i s s o l v e s and Oa i s e v o l v e d . In s o m e c a s e s , f u r t h e r H2Os s o l u t i o n m u s t b e a d d e d u n t i l t h e r e a c t i o n m i x t u r e b e c o m e s p u r e y e l l o w . T h e s o l u t i o n i s e v a p o r a t e d on a s t e a m b a t h .

T h e c o l o r l e s s c r y s t a l s t h a t s e p a r a t e d e l i q u e s c e r a p i d l y in m o i s t a i r .

n N H3 + HI = N H J

17 127.9 144.9

(NH4)2C03 · H20 + 2 HI = 2 NH4I + 2 H20 + CO,

114.1 255.8 289.9 36 44

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