Carbon a) Elemental Carbon

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SECTION 11

Carbon a) Elemental Carbon

U. HOFMAN N Only p r o c e s s e s of s p e c i a l i m p o r t a n c e t o t h e l a b o r a t o r y will be d i s c u s s e d b e l o w . T h e c o r r e s p o n d i n g i n d u s t r i a l p r o c e s s e s a r e not d e s c r i b e d .

T h e m a n u f a c t u r e of d i a m o n d s [ F . P . Bundy, Η. T . H a l l , Η. M.

S t r o n g and R. H. Wentorf. N a t u r e (London) 176, 51 (1955)], w h i c h i n v o l v e s a g r e a t d e a l of e x p e n s i v e a p p a r a t u s , w i l l not be t r e a t e d .

Pure Carbo n

T h e c a r b o n a v a i l a b l e for i n d u s t r i a l o r l a b o r a t o r y p u r p o s e s i s not p u r e . It c o n t a i n s c a r b o n c o m p o u n d s (with Η, Ο, N, S), a s h - f o r m i n g c o n s t i t u e n t s and a d s o r b e d g a s e s o r v a p o r s . P r e p a r a t i o n of h i g h e s t - p u r i t y c a r b o n , a s well a s i t s u s e in t h e p u r e s t a t e , m a y be a c h i e v e d only in a h i g h - v a c u u m a p p a r a t u s [A. Stock et a l . Z.

a n o r g . a l l g . C h e m . 195, 158 (1931)]. P u r i t y in e x c e s s of 99% i s u s u a l l y sufficient. T h i s m a y be a c h i e v e d by t h e following p r o c e s s e s , w h i c h apply e q u a l l y t o c o k e - t y p e c a r b o n , c a r b o n b l a c k , a c t i v a t e d c h a r c o a l o r g r a p h i t e .

Removal of ash-forming mineral matter. E x h a u s t i v e b o i l i n g w i t h d i l u t e H N O^a o r dilute HC1; ignition t o r e d h e a t at 900 to 1000°C in a s t r e a m of C l²; t r e a t m e n t with h y d r o f l u o r i c a c i d to r e m o v e s i l i c a t e s ; c a l c i n i n g for s e v e r a l h o u r s at 2000 to 3000°C in v a c u u m , in CO o r in i n e r t g a s ( t h i s t r e a t m e n t r e s u l t s in s t r u c t u r a l c h a n g e s , i . e . , g r a p h i t i z a t i o n ) .

Removal of carbon compounds (coking). S o l v e n t s a r e i n c a p a b l e of r e m o v i n g a l l of t h e s e c o n s t i t u e n t s . C o m p l e t e r e m o v a l i s a c h i e v e d by c a l c i n i n g for m a n y h o u r s in v a c u u m o r in H², N² o r i n e r t g a s at 900 t o 1000°C. If m o r e t h a n a few p e r c e n t of c a r b o n c o m p o u n d s a r e p r e s e n t b e f o r e c a l c i n a t i o n , t h e a d d i t i o n a l f o r m a t i o n of C f r o m t h e s e c a r b o n i m p u r i t i e s will r e s u l t in s t r u c t u r a l c h a n g e s . T h e s e s t r u c t u r a l c h a n g e s t e n d chiefly t o r e d u c e a d s o r p t i v e p o w e r . T h i s difficulty c a n be o v e r c o m e by a c t i v a t i o n (q.v,) without affecting t h e p u r i t y of t h e c a r b o n .

6 3 0

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II . CARBON 6 3 1

Surface oxides (q.v.) c a n b e c o m p l e t e l y r e m o v e d a s CO and C 0² at 1000°C.

Removal of adsorbed gases and vapors. It m u s t b e b o r n e in m i n d t h a t a d s o r p t i v e c a r b o n c a n t a k e up a few p e r c e n t by w e i g h t of C 0², H²0 , e t c . , at r o o m t e m p e r a t u r e . P u r i f i c a t i o n i s a c h i e v e d by h e a t i n g for m a n y h o u r s at 300 C in high v a c u u m .

REFERENCES:

O. Ruff et a l . Z . a n o r g . a l l g . C h e m . 148, 313 (1925).

U. Hofmann et a l . Z . a n o r g . a l l g . C h e m . 2 5 5 , 195 (1947).

U. Hofmann and G. O h l e r i c h . Angew. C h e m . 62, 16 (1950).

Specia l Carbo n Preparation s

I. CARBON MONOXIDE BLACK

T h i s c a r b o n b l a c k d e s e r v e s m o r e a t t e n t i o n b e c a u s e m e d i u m - s i z e d g r a p h i t e c r y s t a l s of it u n d e r g o l i t t l e a g g r e g a t i o n . It i s p r e - p a r e d by p a s s i n g CO o v e r finely d i v i d e d , p u r e F e ( e . g . , p u r e i r o n p r e p a r e d by r e d u c t i o n of i r o n c a r b o n y l ) at 4 0 0 - 7 0 0 ° C . D e - p e n d i n g on t h e t e m p e r a t u r e of p r e p a r a t i o n , t h e following a v e r a g e c r y s t a l s i z e s a r e o b t a i n e d : 50 A at 400°C, 100 A at 500 C, 200 A at 700°C. It should b e r e m e m b e r e d t h a t any o c c l u d e d F e c o m p o u n d s c a n be r e m o v e d only by a long p u r i f i c a t i o n p r o c e s s ( s e e P u r e C a r b o n ) .

II. GRAPHITIZED CARBON BLACK

C a l c i n a t i o n in v a c u u m o r p r o t e c t i v e g a s for m a n y h o u r s at 2000-3000°C c a u s e s t h e c r y s t a l l i t e s of t h e individual c a r b o n b l a c k p a r t i c l e s t o g r o w into s l i g h t l y l a r g e r c r y s t a l s , without s i g n i f i c a n t l y affecting t h e s i z e of t h e p a r t i c l e s t h e m s e l v e s ( c h a n n e l b l a c k about 200 A, l a m p b l a c k 5 0 0 - 2 0 0 0 A, T h e r m a t o m i c b l a c k about 3000 A).

T h e p r o d u c t of t h e c a l c i n a t i o n i s a p o l y h e d r o n c o n s i s t i n g of s l i g h t l y p y r a m i d a l g r a p h i t e c r y s t a l s with t h e i r v e r t i c e s d i r e c t e d i n w a r d , with i t s s u r f a c e c o m p o s e d of the b a s a l p l a n e s (001) of g r a p h i t e .

III. GRAPHITE OXIDE BLACK

T h i s b l a c k c o n s i s t s of v e r y t h i n g r a p h i t e f o i l s (about 20 to 50 A thick) t h e d i a m e t e r of w h i c h , h o w e v e r , m a y r a n g e u p t o s o m e h u n - d r e d t h s of a m i l l i m e t e r , d e p e n d i n g on t h e s t a r t i n g g r a p h i t e . It i s p r e p a r e d by m a k i n g g r a p h i t e oxide f r o m g r a p h i t e ( s e e G r a p h i t e O x i d e ) . T h e g r a p h i t e oxide i s d e c o m p o s e d by r a p i d h e a t i n g t o

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632 U . HOFMANN

3 0 0 - 4 0 0 ° C , w h e r e it d e f l a g r a t e s . Since t h e oxygen bound in t h e g r a p h i t e oxide e v o l v e s a s CO and C O^s in t h e d e f l a g r a t i o n , it i s p o s s i b l e t h a t t h e h e x a g o n a l n e t w o r k of t h e c a r b o n b l a c k foils c o n t a i n s h o l e s of a t o m i c d i m e n s i o n s .

A b e t t e r p r o d u c t of o t h e r w i s e i d e n t i c a l p r o p e r t i e s c a n b e p r e p a r e d a s f o l l o w s : An a l k a l i n e s u s p e n s i o n of g r a p h i t e oxide i s r e d u c e d with h y d r o x y l a m i n e at 80°C. T h e a g g l u t i n a t i o n of t h e f o i l s upon f i l t e r i n g and d e s i c c a t i o n c a n b e s u b s t a n t i a l l y inhibited by f r e e z e - d r y i n g of the s a l t - f r e e , d i a l y z e d s u s p e n s i o n .

In both c a s e s t h e c a r b o n b l a c k c o n t a i n s only about 80% c a r b o n . It a l s o c o n t a i n s Ο, H, e t c . , and m u s t be c a r e f u l l y p u r i f i e d by coking and, if n e c e s s a r y , a l s o f r e e d of m i n e r a l m a t t e r .

IV. LUSTROUS CARBON

B r i t t l e foils with p e r f e c t l y r e f l e c t i n g s u r f a c e s b e c a u s e t h e b a s a l p l a n e s of t h e g r a p h i t e c r y s t a l s a r e p a r a l l e l t o t h e foil p l a n e s . S u r f a c e s u p to s e v e r a l c e n t i m e t e r s . T h i c k n e s s e s u p t o s o m e t e n t h s of a m i l l i m e t e r . C o a t i n g s of l u s t r o u s c a r b o n on c e r a m i c m a t e r i a l s s e r v e a s high e l e c t r i c a l r e s i s t a n c e s . T h e c r y s t a l s i z e i s about 25 A.

T h e m a t e r i a l i s p r e p a r e d by c r a c k i n g d i l u t e h y d r o c a r b o n s (e.g., p r o p a n e v a p o r a t about 10 m m . o r N² s a t u r a t e d with g a s o l i n e v a p o r at r o o m t e m p e r a t u r e ) a t 800 t o 1000°C. T h e m a t e r i a l i s d e p o s i t e d on a s m o o t h s u r f a c e s u c h a s p o r c e l a i n o r q u a r t z . It i s d e s i r a b l e t o add s o m e 0² o r w a t e r v a p o r t o t h e h y d r o c a r b o n , s o a s t o avoid s i m u l t a n e o u s p r e c i p i t a t i o n of r e a c t i v e , r o u g h - s u r f a c e c a r b o n . After a t h i c k n e s s of s o m e h u n d r e d t h s of a m i l l i m e t e r h a s b e e n a c h i e v e d , the c a r b o n foils e i t h e r flake off by t h e m s e l v e s o r m a y b e r e a d i l y d e t a c h e d a f t e r c o o l i n g . T h e b e s t t i g h t l y a d h e r i n g c o a t i n g s a r e p r o d u c e d on s u r f a c e s t h a t a r e not c o m p l e t e l y s m o o t h .

V. GRAPHITE FOILS AND FILMS

a) A s o l p r e p a r e d f r o m 1-2 g. of g r a p h i t e oxide (q.v.) in 100 m l . of w a t e r (well s h a k e n o r s t i r r e d ) i s allowed t o e v a p o r a t e . T h e g r a p h i t e oxide s e p a r a t e s a s a foil on t h e b o t t o m of t h e v e s s e l . V e r y c a r e f u l , slow h e a t i n g w i t h g r a d u a l l y r i s i n g t e m p e r a t u r e c a u s e s t h e s h e e t t o give off C O , C 0² and H²0 without d e f l a g r a t i o n u n t i l ,

at 1000°C, a g r a p h i t e l i k e f i l m i s o b t a i n e d . T h i s s t i l l c o n t a i n s a few p e r c e n t of Ο and H. T h e s i z e and t h i c k n e s s of t h e foil i s t h e s a m e a s t h a t of t h e g r a p h i t e oxide and c a n t h e r e f o r e be c o n t r o l l e d by t h e a m o u n t and c o n c e n t r a t i o n of t h e g r a p h i t e oxide s o l and t h e s i z e of t h e v a p o r i z a t i o n v e s s e l . F i l m s w i t h s u r f a c e s a s l a r g e a s 50 cm? c a n be o b t a i n e d in t h i s m a n n e r .

b) V e r y p u r e g r a p h i t e foils c a n be p r o d u c e d by igniting foils of l u s t r o u s c a r b o n for m a n y h o u r s in v a c u u m o r in C O . T h e

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11 . CARBON 633 t e m p e r a t u r e i s 2 0 0 0 - 3 0 0 0 ° C . T h e foils a r e of t h e s a m e s i z e a s t h o s e of l u s t r o u s c a r b o n , i . e . , about 1 c m . in s u r f a c e d i a m e t e r . VI. ADSORPTIVE CARBON (ACTIVATION)

T o a c h i e v e t h e b e s t a d s o r p t i v e p o w e r , it i s helpful t o b r e a k down t h e c r y s t a l l i n e a g g r e g a t i o n s of c a r b o n by c a r e f u l o x i d a t i o n . A c a r b o n i s c o n s i d e r e d h i g h l y a d s o r p t i v e if, for e x a m p l e , it a d s o r b s i t s own w e i g h t of C C 1⁴ a t r o o m t e m p e r a t u r e f r o m half- s a t u r a t e d C C 1⁴ v a p o r .

T h i s b r e a k i n g down of s t r u c t u r e i s effected m o s t s i m p l y by c a l c i n i n g at 950°C in a s t r e a m of C O^s o r H^sO v a p o r and i s c o n t i n u e d u n t i l half t h e c a r b o n h a s b u r n e d off. It s u f f i c e s t o p a s s t h e C O^s s l o w l y o v e r t h e c a r b o n s p r e a d in a thin l a y e r in a b o a t . S u b s e q u e n t r e m o v a l of t h e a d s o r b e d C 0² o r H^sO by h e a t i n g f o r m a n y h o u r s a t 300°C in high v a c u u m i s r e c o m m e n d e d . If s u r f a c e o x i d e s h a v e f o r m e d due t o a d s o r b e d a i r , t h e y m a y b e r e m o v e d by h e a t i n g t o r e d h e a t .

REFERENCES:

I. U. Hofmann. B e r d t s c h . c h e m . G e s . 6 1 , 1180 (1928); Z . E l e k t r o c h e m . 4 2 , 504 (1936).

II. U. Hofmann et a l . K o l l o i d - Z . 96, 231 (1941); A. R a g o s s et a l . K o l l o i d - Z . 105, 118 (1943); H. P . B o e h m . Z . a n o r g . a l l g . C h e m . 297, 315 (1958).

III. G. R u e s s and F . Vogt. Mh. C h e m . 7 8 , 222 (1948).

IV. K. A. Hofmann and U. Hofmann. B e r . d t s c h . c h e m . G e s . 5 9 , 2433 (1926); G. R u e s s . Z . a n o r g . a l l g . C h e m . 2 5 5 , 263 (1947).

V a . H. T h i e l e , F o r s c h u n g e n und F o r t s c h r i t t e 10, 408 (1934);

G e r m a n p a t e n t 600 768.

b . U. Hofmann. G e r m a n p a t e n t 752 734.

VI. O. Ruff and G. R o s s n e r . B e r . d t s c h . c h e m . G e s . 60, 4 1 1 (1927);

U. Hofmann et a l . Z. a n o r g a l l g . C h e m . 2 5 5 , 195 (1947).

Surfac e Compound s o f Carbo n

T h i s s e c t i o n i s d e v o t e d t o c h e m i c a l c o m p o u n d s f o r m e d on t h e s u r f a c e of t h e g r a p h i t e c r y s t a l . * T h e i n t e r n a l s t r u c t u r e of t h e c r y s t a l i s not s i g n i f i c a n t l y c h a n g e d by t h e s u r f a c e c o m p o u n d s , w h i c h i s not t h e c a s e w i t h g r a p h i t e c o m p o u n d s .

* C h l o r i n e i s p r o b a b l y bound not at t h e s u r f a c e of t h e g r a p h i t e c r y s t a l but b y h y d r o c a r b o n i m p u r i t i e s p r e s e n t in t h e m a t e r i a l ( s e e DEGUSSA, N a c h r i c h t e n a u s C h e m i e und T e c h n i k , August 2 1 , 1954).

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6 3 4 U . HOFMANN

I. OXYGEN COMPOUNDS REACTING AS ACIDS IN AQUEOUS SOLUTIONS

P r e p a r a t i o n i n v o l v e s h e a t i n g t h e c a r b o n for m a n y h o u r s in a s t r e a m of 0² at a t e m p e r a t u r e a s n e a r a s p o s s i b l e to t h e ignition point, i . e . , 500°C. D u r i n g o x i d a t i o n , t h e c a r b o n m u s t be v i g o r o u s l y s h a k e n o r , b e t t e r s t i l l , fluidized by t h e 0² s t r e a m . Since oxidation p r o d u c e s C 0², w h i c h i s t h e n a b s o r b e d , it i s r e c o m m e n d e d t h a t t h e oxidation p r o d u c t b e s u b j e c t e d t o long h e a t i n g at 300°C in high v a c u u m . It should b e r e m e m b e r e d t h a t t h e oxidation i s a c c o m p a n i e d b y a c t i v a t i o n w i t h 0².

If a highly a d s o r p t i v e c a r b o n i s u s e d , a s m u c h a s 15 g. of 0² c a n b e t a k e n up by 100 g. of t h e c a r b o n . U n d e r t h e s a m e c o n d i t i o n s , s t e a m p r o d u c e s a c i d g r o u p s w h o s e c o n c e n t r a t i o n m a y r e a c h 700 m e q . of H⁺ i o n s p e r 100 g. of t h e p r e p a r a t i o n . T h e m a t e r i a l i s t e s t e d by s h a k i n g 0.1 g. of t h e c a r b o n with 100 m l . of 0.05N a l c o h o l i c KOH. T h e H⁺ i o n s c a n b e r e p l a c e d by C H³ g r o u p s t h r o u g h m e t h y l a t i o n with d i a z o m e t h a n e . B e c a u s e of t h e a c i d i c s u r f a c e o x i d e s , t h e c a r b o n i s r e a d i l y w e t t e d by w a t e r and p o o r l y by b e n z e n e , a s c o n t r a s t e d w i t h c a r b o n h a v i n g no a c i d s u r f a c e o x i d e s . Above 500°C, 0² i s r e l e a s e d a s CO and C 0².

II. OXYGEN COMPOUNDS REACTING AS BASES IN AQUEOUS SOLUTIONS

T h e s e c o m p o u n d s a r e a l w a y s f o r m e d w h e n c a r b o n c o m e s into c o n t a c t with a i r o r 0² at r o o m t e m p e r a t u r e . T h e i r f o r m a t i o n c a n only b e avoided when c o n t a c t i s p r e v e n t e d . T h e s e b a s i c c o m p o u n d s m a y c o e x i s t on t h e s u r f a c e of t h e c a r b o n w i t h t h e a c i d - f o r m i n g Ο c o m p o u n d s . With highly a d s o r p t i v e c a r b o n t h e s e c o m p o u n d s m a y e x e r t , in a q u e o u s s o l u t i o n , a n effect e q u i v a l e n t t o a c o n c e n t r a t i o n of 100 m e q . of OH" i o n s p e r 100 g. of c a r b o n .

T h e m a t e r i a l i s t e s t e d by s h a k i n g w i t h 0.05 Ν HC1. T h e b a s i c s u r f a c e o x i d e s p r o b a b l y p a r t i c i p a t e in t h e c a t a l y t i c d e c o m p o s i t i o n of H²0² on c a r b o n and when c a r b o n i s u s e d a s an oxygen e l e c t r o d e .

Above 500°C, t h e Ο i s r e l e a s e d a s CO and C O^P, III. SULFUR COMPOUNDS

C a r b o n and e x c e s s S a r e h e a t e d for two d a y s at 600°C in a s e a l e d t u b e . T h e p r o d u c t i s t h e n w a s h e d t h o r o u g h l y in a Soxhlet a p p a r a t u s w i t h C S², t o l u e n e and a l c o h o l . A highly a d s o r p t i v e c a r b o n c a n t a k e u p a s m u c h a s 30 g. of S p e r 100 g. of p r e p a r a t i o n . Above 500°C, the p r e p a r a t i o n s r e l e a s e S, and a s t h e t e m p e r a t u r e r i s e s , C S² i s a l s o g e n e r a t e d .

REFERENCES:

I. H. K r u y t and G. de K a d t . K o l l o i d - Z . 4 7 , 44 (1929); U. Hofmann and G. O h l e r i c h . Angew. C h e m . 62, 16 (1950).

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II . C A R B O N 6 3 5 R e g a r d i n g p r e p a r a t i o n with c o n c e n t r a t e d n i t r i c a c i d , s e e U.

Hofmann and G. O h l e r i c h , a b o v e .

II. A. F r u m k i n . K o l l o i d - Z . 5 1 , 123 (1930); G. B r i n k m a n n . Angew.

C h e m . 6 1 , 378 (1949).

III. J . P . Wibaut and E . J . v.d. K a m . R e c . T r a v . C h i m . 4 9 , 121 (1930); R. J u z a and W. B l a n k e . Z. a n o r g . a l l g . C h e m . 210, 81 (1933); U. Hofmann and G. O h l e r i c h . Angew. C h e m . 62, 16 (1950).

b) Graphite Compounds

W. RUDORFF Alkal i Graphit e Compound s

T h e s e m a y b e p r e p a r e d with m e l t s o r v a p o r of t h e a l k a l i m e t a l s K, Rb and C s . Depending on t h e p r o p o r t i o n s a n d / o r t h e r e a c t i o n t e m p e r a t u r e , t h e c o m p o u n d s r e s u l t i n g h a v e t h e following a p p r o x i m a t e c o m p o s i t i o n s : C⁸M (1st s t a g e ) , C^{2 4}M (2nd s t a g e ) , C^{3 6}M

(3rd s t a g e ) and C^{4 8}M (4th s t a g e ) . C⁸K

T h e a p p a r a t u s i s t h a t of F i g . 207. Section Β of t h e a p p r o x i m a t e l y 22 m m . I.D. g l a s s t u b e i s c h a r g e d w i t h about 1 g . of p o w d e r e d o r g r o u n d g r a p h i t e w h i c h p r i o r t o u s e h a s b e e n t h o r o u g h l y h e a t e d at 900°C in high v a c u u m . An a m p o u l e o r g l a s s t u b e c o n t a i n i n g p u r e Κ m e t a l i s i n t r o d u c e d into A in a s t r e a m of N³, t h e open end facing a. After t h e r e a c t o r t u b e i s s e a l e d off at a, t h e Κ i s d i s t i l l e d into Β in high v a c u u m . T h e n a n e l e c t r i c a l h e a t e r m a i n t a i n e d at 300°C i s p l a c e d o v e r A and B. It i s d e s i r a b l e t o r o t a t e t h e t u b e in g r o u n d joint Ε a f t e r s o m e t i m e s o t h a t e v e n t h e g r a p h i t e p a r t i c l e s a d h e r i n g t o t h e g l a s s at t h e b o t t o m m a y r e a c t a s c o m p l e t e l y a s p o s s i b l e . T h e c o n v e r s i o n i s c o m p l e t e when t h e p r e p a r a t i o n a c q u i r e s a d a r k c o p p e r c o l o r and i s h o m o g e n e o u s . If s o m e b l u e o r b l a c k p a r t i c l e s h a v e f o r m e d , t h e n t h e h e a t i n g p e r i o d w a s too long o r t h e t e m p e r a t u r e t o o high. If t h i s i s t h e c a s e , s o m e Κ i s d i s t i l l e d b a c k f r o m 0 t o Β and t h e h e a t i n g o p e r a t i o n i s r e p e a t e d . After a l l t h e e x c e s s Κ h a s b e e n d i s t i l l e d away f r o m B, t h e m a t e r i a l i s p e r m i t t e d t o c o o l . T h e a p p a r a t u s i s t h e n filled w i t h N² and s e a l e d off a t b and G and t h e t u b e i s r a i s e d t o a v e r t i c a l p o s i t i o n , s o t h a t t h e p r o d u c t i s s e p a r a t e d f r o m t h e K - w e t t e d g l a s s w a l l 0 and c o l l e c t s at Ό.

H e r e the a t t a c h e d s t o r a g e t u b e s (only one of which i s i l l u s t r a t e d ) a r e filled and t h e n t o r c h - s e a l e d .

C04K

T h e p r e p a r a t i o n c o r r e s p o n d s t o t h a t for C⁹K but t h e f u r n a c e i s k e p t at 3 6 0 ° C T h e end of t h e c o n v e r s i o n i s identified by t h e

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6 3 6 W. RUDORFF

15 cm 15 cm 30 cm

F i g . 207. P r e p a r a t i o n of a l k a l i g r a p h i t e c o m p o u n d s .

u n i f o r m l y s t e e l - b l u e c o l o r of t h e p r e p a r a t i o n . P r e c a u t i o n s m u s t b e t a k e n t o e n s u r e t h a t p a r t of t h e p r e p a r a t i o n d o e s not a g a i n t u r n b r o w n by a b s o r b i n g Κ v a p o r w h e n t h e f u r n a c e i s c o o l e d . If t h i s i s t h e c a s e , h e a t i n g m u s t b e c o n t i n u e d . If h e a t i n g i s c o n t i n u e d for t o o l o n g , t h e p r o d u c t s a r e p o o r in K.

C^{3 6}M A N D C^{4 8}M

T h e s e a r e p r e p a r e d f r o m a s t o i c h i o m e t r i c m i x t u r e of g r a p h i t e p o w d e r o r f l a k e s and Κ m e t a l by h e a t i n g f o r 20 h o u r s at 300 t o 400°C in an e v a c u a t e d , s e a l e d t u b e .

R u b i d i u m g r a p h i t e and c e s i u m g r a p h i t e a r e p r e p a r e d in s i m i l a r f a s h i o n .

Analysis. After w e i g h i n g , t h e t u b e s c o n t a i n i n g t h e s u b s t a n c e a r e cut open and t h e c o n t e n t s a r e d i s c h a r g e d into a p r e h e a t e d E r l e n m e y e r f l a s k ( C^QM and C^{2 4}M e i t h e r ignite o r s m o l d e r in t h e f l a s k ) . After c o o l i n g , t h e g r a p h i t e i s b o i l e d w i t h w a t e r , f i l t e r e d and w a s h e d . T h e a l k a l i in t h e f i l t r a t e i s d e t e r m i n e d by v o l u m e t r i c a n a l y s i s . T h e d r i e d g r a p h i t e , w h i c h s t i l l c o n t a i n s a few p e r c e n t of a l k a l i , i s r e p e a t e d l y boiled (until fuming) with c o n c e n t r a t e d H²S 0⁴ and t h e n c a l c i n e d . T h e a s h content of t h e s t a r t i n g g r a p h i t e i s c a l c u l a t e d f r o m t h e weight of t h e a l k a l i sulfate o b t a i n e d .

PROPERTIES:

C⁸K i s d a r k c o p p e r - r e d . L a r g e r c r y s t a l s h a v e a m e t a l l i c b r o n z e c o l o r . C^{2 4}K i s s t e e l b l u e w i t h a m e t a l l i c l u s t e r . T h e c o m p o u n d s p o o r e r in a l k a l i a r e b l u e - b l a c k t o b l a c k . T h e s e m a t e r i a l s a r e v e r y s e n s i t i v e t o 0² and m o i s t u r e . T h e y ignite in a i r .

Structure of CeM : t h e r e i s an e x p a n d e d g r a p h i t e l a t t i c e , in t h e ο d i r e c t i o n , w i t h a l k a l i l a y e r s in e a c h v a c a n c y of t h e C l a t t i c e . In C^{2 4}M , C^{3 6}M , C^{4 8}M , e a c h s e c o n d , t h i r d , o r f o u r t h l a y e r v a c a n c y of the C l a t t i c e i s e x p a n d e d by a n i n t e r c a l a t e d a l k a l i l a y e r .

REFERENCES:

K. F r e d e n h a g e n and G. C a d e n b a c h . Z . a n o r g . a l l g . C h e m . 158, 249 (1926).

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II . CARBON 637 Κ. F r e d e n h a g e n and Κ. Suck. Ζ . a n o r g . a l l g . C h e m . 1 7 8 . 353 (1929).

A. S c h l e e d e and W e l l m a n n . Z . p h y s . C h e m . (B) 1 8 , 1 (1932).

W. Rudorff and E . S c h u l z e . Z . a n o r g . a l l g . C h e m . 2 7 7 , 156 (1954).

Alkal i Ammin e Graphit e Compound s

P r e p a r e d f r o m g r a p h i t e a n d a l k a l i m e t a l d i s s o l v e d in liquid a m m o n i a .

About 2 g . of p o w d e r e d o r flake g r a p h i t e a n d t h e s t i r r i n g b a r of a m a g n e t i c s t i r r e r a r e i n t r o d u c e d into v e s s e l c ,w h i c h h a s a f r i t t e d g l a s s d i s c (Fig. 208). A f t e r c a r e f u l d r y i n g of t h e a p p a r a t u s

F i g . 2 0 8 . P r e p a r a t i o n of a l k a l i a m m i n e g r a p h i t e c o m p o u n d s .

and d i s p l a c e m e n t of t h e a i r w i t h p u r e N^s, N H³ (liquefied o v e r Na in v e s s e l CL) i s c o n d e n s e d in b on t h e a l k a l i m e t a l ( L i , N a , K, Rb o r Cs—at l e a s t 1/30 g r a m - a t o m ) . Stopcock h² i s c l o s e d and t h e solution i s s i p h o n e d f r o m b into ο b y c o o l i n g v e s s e l c. To c o m p l e t e t h e r e a c t i o n in ο t h e c o n t e n t s a r e w e l l s t i r r e d a f t e r r e m o v a l of t h e c o o l i n g b a t h . T h i s m a y c a u s e t h e s o l u t i o n t o boil (if t h i s o c c u r s , s t o p c o c k h² i s o p e n e d ) . T h e s o l u t i o n m u s t s t i l l b e b l u e . If it i s not, a d d i t i o n a l a l k a l i m e t a l m u s t b e a d d e d . F i n a l l y , s t o p c o c k h^s i s opened and t h e s o l u t i o n f o r c e d w i t h N H³ p r e s s u r e t h r o u g h t h e f r i t and into a n o t h e r , w e l l - c o o l e d v e s s e l . T o w a s h t h e g r a p h i t e , N H³ i s c o n d e n s e d in ο o n c e o r t w i c e and f o r c e d out of t h e v e s s e l in t h e s a m e m a n n e r a s b e f o r e . T h e n ο i s b r o u g h t t o r o o m t e m p e r a t u r e . W h e n n o f u r t h e r N H³ e s c a p e s t h r o u g h t h e p r e s s u r e r e l e a s e v a l v e , t h e a p p a r a t u s i s p u r g e d w i t h N² and t h e

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638 W. RUDORFF

p r o d u c t i s p o u r e d into t u b e s d⁹ e a n d / , w h i c h a r e t h e n s e a l e d . Analysis: T h e c o n t e n t s of a weighed a m p o u l e a r e p l a c e d i n a n E r l e n m e y e r f l a s k c o n t a i n i n g 5 0 - 7 0 m l . of i c e - c o l d 2N H²SC>4. T h e d e c o m p o s e d p r o d u c t i s boiled f o r one half h o u r and t h e g r a p h i t e i s f i l t e r e d off a n d w a s h e d . T h e a l k a l i i s d e t e r m i n e d a s sulfate i n a n a l i q u o t of t h e f i l t r a t e ; KOH i s a d d e d to a n o t h e r a l i q u o t , and t h e N H³ i s d i s t i l l e d off a n d d e t e r m i n e d b y v o l u m e t r i c a n a l y s i s . T h e d r i e d g r a p h i t e i s t r e a t e d a s d e s c r i b e d f o r p o t a s s i u m g r a p h i t e c o m p o u n d s .

PROPERTIES:

T h e c o m p o u n d a p p r o x i m a t e s C^{1 2}M ( N H³)². V e r y d a r k b l u e , e n l a r g e d c r y s t a l s . V e r y s e n s i t i v e t o a i r and m o i s t u r e . T h e K, R b and C s c o m p o u n d s c a n b e s t o r e d indefinitely, b u t t h e L i a n d Na c o m p o u n d s d e c o m p o s e i n a few d a y s t o a m i d e s , evolving Η².

REFERENCE:

W. Rudorff, E . Schuize and O. R u b i s c h . Z . a n o r g . a l l g . C h e m . 282, 232 (1955).

Graphit e Oxid e

P r e p a r e d b y o x i d a t i o n of g r a p h i t e with K C 1 0³ i n a m i x t u r e of c o n c e n t r a t e d s u l f u r i c and n i t r i c a c i d s .

G r a p h i t e (10 g . ) , a s a s h - f r e e and u n i f o r m a s p o s s i b l e , i s s u s p e n d e d in a m i x t u r e of 175 m l . of c o n c e n t r a t e d H²S 0⁴a n d 90 m l . of 68% H N 0³. A t o t a l of 110 g, of K C 1 0³ i s added i n s m a l l p o r t i o n s o v e r a p e r i o d of s e v e r a l d a y s t o t h e c o o l e d f l a s k . T h e p r o d u c t i s r e p e a t e d l y s t i r r e d with 6 t o 10 l i t e r s of d i s t i l l e d w a t e r , t h e n s e t t l e d and d e c a n t e d until t h e w a s h w a t e r i s n e u t r a l t o l i t m u s . A s w a s h i n g p r o g r e s s e s t h e b l u e - g r e e n p a r t i c l e s b e c o m e b r o w n a n d s w e l l i n c r e a s i n g l y a s t h e s a l t s a r e r e m o v e d . At t h e end of t h e w a s h i n g t h e s e t t l i n g i s slow and i n c o m p l e t e . ( P u r i f i c a t i o n r e q u i r e s s e v e r a l w e e k s , a n d i s s h o r t e n e d s o m e w h a t b y u s e of a c e n t r i f u g e . ) T h e b r o w n s l u r r y i s s u c t i o n - f i l t e r e d a s m u c h a s p o s s i b l e , s p r e a d o u t to d r y i n a i r , g r o u n d a n d d r i e d t o c o n s t a n t weight i n v a c u u m a t

50°C o v e r P²O^B.

A light, a l m o s t white g r a p h i t e oxide i s o b t a i n e d b y w a s h i n g in t h e d a r k with 5% HC1, c o n t a i n i n g C 1 0². T h i s p r o d u c t c o n t a i n s only about 0.5% a s h , b u t a f t e r v a c u u m - d r y i n g s t i l l s h o w s a v e r y s m a l l a m o u n t of c h l o r i n e .

Good y i e l d s of p r o d u c t s with h i g h e r oxide c o n t e n t s c a n b e a c h i e v e d only when a w e l l - c r y s t a l l i z e d g r a p h i t e i s u s e d a s t h e s t a r t i n g m a t e r i a l , s i n c e o t h e r w i s e t h e r e s u l t i n g o x i d a t i o n p r o d u c t s

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II . C A R B O N 6 3 9 a r e m o s t l y s o l u b l e . It i s a d v i s a b l e t o u s e a g r a p h i t e of u n i f o r m p a r t i c l e s i z e , in t h e r a n g e 0 . 0 1 - 0 . 3 m m . T h e c o a r s e r t h e p a r t i c l e s , t h e l o n g e r t h e t i m e r e q u i r e d f o r o x i d a t i o n .

W a s h i n g of t h e p r e p a r a t i o n w i t h a c e t i c a c i d and e t h e r i s not r e c o m m e n d e d , a s t h i s r e s u l t s not only in a d s o r p t i o n but in a c e t y l a - t i o n of t h e OH g r o u p s of t h e g r a p h i t e o x i d e s ( s e e R e f e r e n c e s , G.

R u e s s ) .

Additional preparative methods: A f a s t e r m e t h o d ( H u m m e r s a n d Offeman) p r o c e e d s a s f o l l o w s : 100 g. of finely m i l l e d g r a p h i t e a n d 50 g. of N a N Oa a r e s t i r r e d t o g e t h e r in 2.3 l i t e r s of i c e - c o o l e d c o n c e n t r a t e d H2S 0 4 . W i t h v i g o r o u s s t i r r i n g , 300 g. of K M n 04

i s a d d e d o v e r a p e r i o d of m a n y h o u r s . T h e r a t e of a d d i t i o n i s g o v e r n e d by t h e p a r t i c l e s i z e of t h e g r a p h i t e . T h e t e m p e r a t u r e of t h e m i x t u r e m u s t not e x c e e d 20°C. T h e m i x t u r e i s t h e n h e a t e d t o 35°C a n d a f t e r 30 m i n u t e s i s s l o w l y r e a c t e d w i t h 4.6 l i t e r s of w a t e r . T h e r e a c t i o n t e m p e r a t u r e m u s t not e x c e e d 70°C. T h e hot s u s p e n s i o n i s t h e n h e l d a t 70°C for a n o t h e r 15 m i n u t e s . After d i l u t i o n to 14 l i t e r s , t h e M n O^s a n d e x c e s s K M n O ^ a r e r e d u c e d w i t h 3%

H202. T h e y e l l o w - b r o w n s u s p e n s i o n i s f i l t e r e d w h i l e s t i l l w a r m a n d w a s h e d a s a b o v e .

Anodic o x i d a t i o n in c o n c e n t r a t e d H N 0³ r e s u l t s in g r a p h i t e w i t h only a low d e g r e e of o x i d a t i o n .

F o r m e t h y l a t i o n of g r a p h i t e o x i d e w i t h d i a z o m e t h a n e in e t h e r o r d i o x a n e s o l u t i o n , s e e r e f e r e n c e s (Hofmann a n d H o i s t ; R u e s s ) .

SYNONYMS:

G r a p h i t e o x y h y d r o x i d e , g r a p h i t i c a c i d .

PROPERTIES:

No definite f o r m u l a . T h e C : 0 a t o m i c r a t i o v a r i e s b e t w e e n 6:1 a n d 6 : 2 . 5 . T h e r a t i o b e t w e e n C a t o m s and OH g r o u p s i s a b o u t 4 : 1 .

T h e d r y m a t e r i a l i s b r o w n t o b l a c k . V e r y h y g r o s c o p i c b e c a u s e of i n t e r c r y s t a l l i n e s w e l l i n g . W i t h c a r e f u l h e a t i n g t o 100°C a n d a b o v e , CO and C 0² a r e s p l i t off. D e f l a g r a t e s on r a p i d h e a t i n g . H y d r o g e n ion c o n t e n t ( g r a p h i t i c acid) a v a i l a b l e f o r e x c h a n g e i s about 600 m e q . / 1 0 0 ge R e a d i l y r e d u c e d t o g r a p h i t e l i k e p r o d u c t s b y S ns +, F e2 +, HI, N2H4, N H2O H , e t c . R e s i s t i v i t y of t h e d r y p r e p a r a t i o n i s , d e p e n d i n g upon t h e Ο c o n t e n t , b e t w e e n 1 03 a n d 10 7 o h m · c m .

Structure: T e t r a h e d r a l l y i n c l i n e d C p l a n e s w i t h m e t a s t a b l e bond at t h e Ο and s i m u l t a n e o u s bonding of t h e OH g r o u p s .

Applications: D e p o l a r i z e r in d r y c e l l s , m e m b r a n e s f o r m e a s  u r e m e n t of t h e p a r t i a l p r e s s u r e of w a t e r v a p o r , m e m b r a n e e l e c t r o d e s .

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6 4 0 W. R U D O R F F

REFERENCES:

U . Hofmann and E . Kbnig. Z . a n o r g . a l l g . C h e m . 234, 311 (1937).

U . Hofmann and R. H o i s t . B e r . d t s c h . c h e m . G e s . 7 2 , 754 (1939).

G. R u e s s . K o l l o i d - Z . 110, 17 (1945); Mh. C h e m . 7 6 , 381 (1946).

A. C l a u s s , R. P l a s s , H. P . B o e h m and U. Hofmann. Z . a n o r g . a l l g . C h e m . 2 9 1 , 205 (1956).

A. C l a u s s and U. Hofman. Angew. C h e m . 6 8 , 522 (1956).

A. C l a u s s , U. Hofmann a n d A. W e i s s . Z . E l e k t r o c h e m . 6 1 , 1284 (1957).

W. S. H u m m e r s and R. E . Offeman. J . A m e r . C h e m . Soc. 80, 1339 (1958).

Carbo n Monofluorid e

P r e p a r e d by f l u o r i n a t i o n of g r a p h i t e at 400 t o 5 0 0 ° C

T h e f l u o r i n a t i o n a p p a r a t u s c o n s i s t s of a Cu t r a p , c o o l e d w i t h liquid n i t r o g e n t o r e m o v e i m p u r i t i e s in t h e F² s t r e a m , and a long Cu r e a c t o r t u b e , about 2 c m . in d i a m e t e r , s c r e w e d onto t h e t r a p . A c a p , opening into a t h i n Cu t u b e 1 t o 2 m m . in d i a m e t e r , i s s c r e w e d to t h e o t h e r end of t h e Cu t u b e .

About 1 g. of g r a p h i t e i s s p r e a d out in a t h i n l a y e r in a Cu b o a t p l a c e d in t h e m i d d l e of t h e r e a c t o r t u b e . T h e t h e r m o c o u p l e i s i n s u l a t e d f r o m t h e t u b e w a l l by a t h i n l a y e r of a s b e s t o s . A t h i c k e r a s b e s t o s l a y e r p r o t e c t s it f r o m c o n t a c t w i t h t h e f u r n a c e w i n d i n g s . T h e hot junction i s , of c o u r s e , e x p o s e d .

T h e g r a p h i t e i s t h o r o u g h l y h e a t e d a t 8 0 0 t o 9 0 0 ° C in high v a c u u m for an h o u r o r two i m m e d i a t e l y b e f o r e t h e f l u o r i n a t i o n . Only a f t e r c o m p l e t e cooling in high v a c u u m i s N² i s a d m i t t e d .

A s l o w F² s t r e a m ( 3 - 6 l i t e r s / h r ) i s p a s s e d t h r o u g h t h e a p p a r a t u s and o v e r t h e g r a p h i t e at r o o m t e m p e r a t u r e for 20 m i n u t e s b e f o r e t h e s t a r t of t h e f l u o r i n a t i o n p r o p e r . Only t h e n i s t h e f u r n a c e t u r n e d on. T h e r e a c t i o n s t a r t s b e t w e e n 420 a n d 500°C, but t h e i n i t i a l c o n v e r s i o n p r o c e e d s q u i e t l y w i t h i n a n a r r o w r a n g e of only about 30°. T h e t e m p e r a t u r e a t t h e o n s e t of t h e r e a c t i o n i s s i g n i f i c a n t l y d e p e n d e n t upon t h e s i z e of t h e g r a p h i t e c r y s t a l s and t h e H F and 0² c o n t e n t of t h e F² s t r e a m . W i t h v e r y finely p o w d e r e d g r a p h i t e of < 0 . 0 1 m m . p a r t i c l e s i z e and w i t h i m p u r e F², c o m b u s t i o n t o v o l a t i l e c a r b o n f l u o r i d e s m a y o c c u r e v e n at 4 0 0 ° C P r e p a r a t i o n s t h a t a r e a l r e a d y w e l l f l u o r i n a t e d will t o l e r a t e t e m p e r a t u r e s a s high a s 520°C t o w a r d t h e end of t h e r e a c t i o n . D e f l a g r a t i o n a l w a y s o c c u r s a b o v e 550°C.

T h e p r o g r e s s of t h e r e a c t i o n i s followed by cooling t h e g r a p h i t e in a s t r e a m of F² and w e i g h i n g . If no w e i g h t g a i n o c c u r s within an h o u r , t h e r e a c t i o n m a y b e p r e s u m e d t o b e o v e r . T h e t o t a l f l u o r i n a - t i o n t i m e i s four t o s e v e n h o u r s .

T h e y i e l d , b a s e d on t h e g r a p h i t e , i s a l m o s t q u a n t i t a t i v e , but w h e n f l u o r i n a t i o n i s c o n t i n u e d f o r l o n g e r p e r i o d s , s l i g h t l o s s e s ,

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II . CARBON 6 4 1

d u e t o c o m b u s t i o n t o v o l a t i l e c a r b o n fluorides, a r e s u s t a i n e d . T h e f l u o r i n e c o n t e n t c o m p u t e d f r o m t h e w e i g h t g a i n i s u s u a l l y 1% l e s s t h a n t h e r e a l c o n t e n t .

A n a l y t i c a l d e t e r m i n a t i o n of F i s a c c o m p l i s h e d by d e c o m p o s i t i o n w i t h m e t a l l i c Na in a s e a l e d i r o n t u b e at 900°C. T h e Na i s r e m o v e d w i t h a l c o h o l , and t h e F p r e c i p i t a t e d a s P b F C l a f t e r f i l t e r i n g off t h e C.

SYNONYM:

G r a p h i t e f l u o r i d e .

PROPERTIES:

D e p e n d i n g on e x p e r i m e n t a l c o n d i t i o n s , t h e f l u o r i n a t i o n p r o d u c t s h a v e c o m p o s i t i o n s v a r y i n g b e t w e e n C F^{0 e 6 8} and C F^{0 # 9 9}. When t h e F c o n t e n t i s low, t h e p r e p a r a t i o n i s g r a y b l a c k , w h i l e at v e r y h i g h F c o n t e n t s it i s s i l v e r w h i t e . D e p e n d i n g upon F c o n t e n t , t h e d e n s i t i e s v a r y b e t w e e n 2.78 a n d 2.50 (in x y l e n e ) . T h e r e s i s t i v i t y i s g r e a t e r t h a n 1 0^e o h m · c m .

T h e p r e p a r a t i o n s a r e not w e t t e d by w a t e r and a r e n e u t r a l t o a c i d s and b a s e s . H y d r o g e n h a s n o effect b e l o w 400°C. R e d u c e d t o g r a p h i t e on b o i l i n g w i t h Zn d u s t and g l a c i a l a c e t i c a c i d . Above 400 C t h e r m a l d e c o m p o s i t i o n t o v o l a t i l e c a r b o n f l u o r i d e s o c c u r s . W h e n h e a t i n g i s r a p i d and t h e t e m p e r a t u r e s high, t h i s i s a c - c o m p a n i e d by d e f l a g r a t i o n and f l a m e .

Structure: T e t r a h e d r a l l y i n c l i n e d C p l a n e s w i t h F a t o m s b o n d e d a b o v e and below t h e C p l a n e s .

REFERENCES:

O. Ruff. O. B r e t t s c h n e i d e r and E . E b e r t . Z . a n o r g . a l l g . C h e m . 2 1 7 , 1 (1934).

W, Rudorff and G. Riidorff. Z . a n o r g . a l l g . a l l g . C h e m . 2 5 3 , 281 (1947).

Tetracarbo n Monofluorid e

P r e p a r e d by f l u o r i n a t i o n of g r a p h i t e a t r o o m t e m p e r a t u r e in t h e p r e s e n c e of H F .

A s t r e a m of F² at 4 - 5 l i t e r s / h r . i s p a s s e d t h r o u g h a c o p p e r w a s h f l a s k h e l d a t 0°C a n d filled w i t h a n h y d r o u s H F , and t h e n t h r o u g h an a t t a c h e d Cu t u b e (about 2 c m . in d i a m e t e r ) . A Cu b o a t c o n t a i n i n g a t h i n l a y e r of about 1 g. of g r a p h i t e i s p l a c e d in t h e t u b e . T h e end of t h e t u b e i s c l o s e d with a s c r e w - o n c a p h a v i n g a n a r r o w o p e n i n g . T h e r e a c t i o n i s f i n i s h e d a f t e r one o r two h o u r s ,

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6 4 2 W. RUDORFF

a s shown by t h e c o n s t a n t w e i g h t of t h e p r o d u c t . T o r e m o v e e x c e s s H F , t h e p r e p a r a t i o n i s w a s h e d w i t h d i l u t e b a s e , w a t e r and a l c o h o l and d r i e d t o r o o m t e m p e r a t u r e o v e r s o d a - l i m e . T h e y i e l d i s q u a n t i t a t i v e .

Q u a n t i t a t i v e d e t e r m i n a t i o n of F i s c a r r i e d out in t h e s a m e m a n n e r a s with c a r b o n m o n o f l u o r i d e .

PROPERTIES:

T h e c o m p o s i t i o n l i e s within t h e r a n g e C^{3 6}F t o C⁴F . T h e c o l o r of t h e p r e p a r a t i o n i s v e l v e t y b l a c k , s o m e t i m e s s o m e w h a t b l u i s h , d ( u n d e r xylene) 2 . 0 5 - 2 . 0 9 . R e s i s t i v i t y 2 - 4 o h m · c m . a t 7 5 0 k g / c m ? Stable t o a c i d s , b a s e s and t h e c o m m o n o r g a n i c r e a g e n t s . Slowly d e c o m p o s e s when h e a t e d f o r a long p e r i o d a b o v e 100°C. D e f l a g r a t e s w h e n r a p i d l y h e a t e d o v e r a f l a m e , f o r m i n g s o o t l i k e f l a k e s .

Structure: F l a t C l a y e r s a s in g r a p h i t e , w i t h F a t o m s bonded above and b e l o w t h e C l a y e r s .

REFERENCE:

W . Rudorff and G. Rudorff. B e r . d t s c h . c h e m . G e s . 80, 417 (1947).

Graphit e Salt s

P r e p a r e d by oxidation of g r a p h i t e in t h e p r e s e n c e of a n h y d r o u s a c i d s .

GRAPHITE BISULFATE

An a g i t a t e d s u s p e n s i o n of about 1 g. of g r a p h i t e ( c o a r s e o r finely c r y s t a l l i n e ) in 10 m l . of c o n c e n t r a t e d H²S 0⁴ i s m i x e d with a s o l u t i o n of C r 0³ o r K²C r²0⁷ in c o n c e n t r a t e d H²S 0⁴. At l e a s t 3 m e q . of a c t i v e oxygen (100 m g . of C r 0³ p e r g. of C) i s r e q u i r e d f o r c o m p l e t e oxidation of t h e g r a p h i t e . After 15 m i n u t e s t h e g r a p h i t e i s u n i f o r m l y d a r k b l u e and c a n b e s u c t i o n - f i l t e r e d t h r o u g h a g l a s s frit and w a s h e d with H²S 0⁴. R e m o v a l of t h e a d h e r i n g H²S 0⁴ m a y b e a c c o m p l i s h e d only by v e r y long w a s h i n g w i t h s i r u p y p y r o - p h o s p h o r i c a c i d o r quick w a s h i n g w i t h i c e - c o l d d i m e t h y l s u l f a t e . T h e r e a c t i o n i s v i r t u a l l y q u a n t i t a t i v e w h e n c o a r s e c r y s t a l l i n e g r a p h i t e i s u s e d , but when fine c r y s t a l l i n e c a r b o n i s e m p l o y e d , b r o w n , c o l l o i d a l oxidation p r o d u c t s a l s o a p p e a r .

When oxidation i s i n c o m p l e t e o r t h e b l u e b i s u l f a t e i s r e d u c e d with F e (II), Sn (II) o r w i t h g r a p h i t e itself, t h e p r o d u c t i s l e s s highly o x i d i z e d and t h e c o l o r i s no l o n g e r b l u e .

T h e a n a l y t i c a l c o m p o s i t i o n m a y b e d e t e r m i n e d f r o m t h e quantity of o x i d a n t s c o n s u m e d in p r e p a r a t i o n , f r o m t h e oxidizing effect

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II. CARBON 6 4 3 upon r e d u c i n g a g e n t s , o r by d e t e r m i n a t i o n of t h e s u l f a t e c o n t e n t a f t e r w a s h i n g w i t h H⁴P²0⁷ o r ( C H³)²S 0⁴.

Additional preparative methods: T h e g r a p h i t e m a y a l s o b e o x i d i z e d w i t h S²O^{e 2}" , P b 0², H I 0³, H I 0⁴, Mn(III) and Mn(IV) c o m p o u n d s , a s w e l l a s a n o d i c a l l y .

PROPERTIES:

T h e c o m p o s i t i o n of t h e b l u e c o m p o u n d c o r r e s p o n d s (in acid) t o about C ^ H S O * · 2 H²S 0 4 .

T h e p r o d u c t i s a s c r y s t a l l i n e a s t h e i n i t i a l g r a p h i t e , but s w o l l e n and v e r y d a r k b l u e . It m a y b e s t o r e d only u n d e r c o n c e n t r a t e d a c i d . D e c o m p o s e d i m m e d i a t e l y by w a t e r , h u m i d a i r , a l c o h o l , e t h e r , a c e t o n e and b e n z e n e .

STRUCTURE:

In t h e b l u e b i s u l f a t e , l a y e r s of a c i d a n i o n s and m o l e c u l e s a r e i n t e r c a l a t e d b e t w e e n t h e C p l a n e s . In t h e l e s s o x i d i z e d b l a c k p r o d u c t s , a c i d l a y e r s a r e i n t e r c a l a t e d in r e g u l a r s e q u e n c e in e a c h s e c o n d , t h i r d , f o u r t h , e t c . , l a y e r v a c a n c y .

GRAPHITE NITRATE, GRAPHITE PERCHLORATE

P r e p a r e d by w a s h i n g g r a p h i t e b i s u l f a t e ( s e e above) with fuming n i t r i c a c i d (d 1.52) o r w i t h 70% H C I O ^ r e s p e c t i v e l y , u n t i l t h e f i l - t r a t e i s f r e e of s u l f a t e i o n s , o r by o x i d a t i o n of g r a p h i t e in t h e c o r r e - s p o n d i n g a c i d s , N²0⁵ b e i n g p r e s e n t in t h e c a s e of n i t r a t e a n d C r 0³ in t h e c a s e of p e r c h l o r a t e . T h e c o n v e r s i o n of t h e b i s u l f a t e i s r e v e r s i b l e .

P r o p e r t i e s and s t r u c t u r e c o r r e s p o n d t o t h o s e of g r a p h i t e b i - s u l f a t e .

F o r o t h e r s a l t - t y p e g r a p h i t e c o m p o u n d s w i t h H F , H²S e 0⁴, H³P 0⁴a n d H³A s 0³, s e e t h e r e f e r e n c e s .

REFERENCES:

W . Rudorff and U. Hofmann. Z . a n o r g . a l l g . C h e m . 2 3 8 , 1 (1938).

W. Rudorff. Z . a n o r g . a l l g . C h e m . 2 5 4 , 319 (1947).

Bromin e Graphit e P r e p a r e d b y a c t i o n of b r o m i n e upon g r a p h i t e .

C o a r s e o r fine c r y s t a l l i n e g r a p h i t e , in a w e i g h i n g b o t t l e , i s a l l o w e d t o s t a n d o v e r b r o m i n e in a d e s i c c a t o r f o r m a n y h o u r s at r o o m t e m p e r a t u r e . T h e m a x i m u m w e i g h t g a i n of t h e g r a p h i t e i s 0 . 8 2 - 0 . 8 4 g. p e r g. of C .

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6 4 4 W. R U D O R F F PROPERTIES:

Meta l Halid e Graphit e Compound s

P r e p a r e d f r o m g r a p h i t e and a n h y d r o u s m e t a l h a l i d e s , e . g . , F e C l³, A 1 C 1³, G a C l³, I n C l³, M o C l⁵, U C 1⁵, e t c . With t h e e x c e p t i o n of F e C l³, t h e s e m e t a l h a l i d e s c a n b e i n t e r c a l a t e d only in t h e p r e s e n c e of f r e e c h l o r i n e .

A) IRON (III) CHLORIDE GRAPHITE

A g l a s s t u b e of about 2 c m . I.D. i s u s e d . At l e a s t 5 g. of a n - h y d r o u s F e C l³ i s s u b l i m e d onto 2 g. of c o a r s e o r fine c r y s t a l - l i n e g r a p h i t e . T h e t u b e i s s e a l e d off on b o t h s i d e s and h e a t e d f o r 24 h o u r s in an e l e c t r i c t u b u l a r f u r n a c e at a c o n s t a n t t e m - p e r a t u r e of 2 0 0 - 3 0 0 ° C . One end of t h e t u b e i s t h e n w i t h d r a w n f r o m t h e f u r n a c e , and t h e h e a t i n g i s c o n t i n u e d at t h e s a m e t e m p e r a - t u r e u n t i l no f u r t h e r u p t a k e of t h e d e s u b l i m e d F e C l³ c a n b e o b s e r v e d .

PROPERTIES:

B l a c k , highly e n l a r g e d c r y s t a l s . T h e F e C l³ c o n t e n t d e p e n d s upon t h e t e m p e r a t u r e of d e s u b l i m a t i o n and i s in t h e r a n g e of 60-70%

F e C l³. When h e a t i n g i s r a p i d , t h e r e i s p r o n o u n c e d s w e l l i n g w i t h e l i m i n a t i o n of F e C l³. T h e c r y s t a l s r e l e a s e F e C l³ in w a t e r , d i l u t e a c i d s , a l c o h o l o r b e n z e n e . D e p e n d i n g on t h e s i z e of t h e c r y s t a l s , t h e w a s h e d p r e p a r a t i o n s c o n t a i n 5 2 - 5 6 % F e C l³.

B) ALUMINUM CHLORIDE GRAPHITE

P r e p a r a t i o n i s s i m i l a r t o t h a t p r e s e n t e d above u n d e r (A).

About 3 - 4 g. of A1C1³ i s s u b l i m e d in a s t r e a m of d r y C l² onto 1 g. of g r a p h i t e . T h e s e a l e d r e a c t i o n t u b e ( c a p a c i t y about 40 c m . ) m u s t T h e c o m p o s i t i o n c o r r e s p o n d s t o an a t o m i c r a t i o C : B r of about 8 : 1 .

B l a c k t o b l u e - g r a y c r y s t a l s , a s in t h e s t a r t i n g g r a p h i t e , but e n l a r g e d . M o s t of t h e B r³ t a k e n u p i s d e s o r b e d in a i r and c a n b e w a s h e d out w i t h w a t e r .

Structure: G r a p h i t e l a t t i c e w i t h a b r o m i n e l a y e r in e v e r y s e c o n d l a y e r v a c a n c y .

REFERENCE:

W . Rudorff. Z . a n o r g . a l l g . C h e m . 2 4 5 , 383 (1941).

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II . C A R B O N 645 b e w e l l filled w i t h C l². T h e h e a t i n g of t h e r e a c t i o n m i x t u r e and s u b l i m i n g of t h e e x c e s s A1C1³ a r e c a r r i e d out at 150 t o 200°C.

PROPERTIES:

V e r y d a r k b l u e , l u s t r o u s , highly e n l a r g e d c r y s t a l s ; r e l e a s e s A1C1³ and C l² when h e a t e d a b o v e 260°C; v e r y h y g r o s c o p i c . W a t e r and o r g a n i c s o l v e n t s d i s s o l v e out m u c h of t h e i n t e r c a l a t e d A 1 C 1³. P r e c i p i t a t e s iodine w h e n a d d e d t o KI s o l u t i o n . T h e c o m p o u n d c o r r e s p o n d s a p p r o x i m a t e l y t o C ^ A l C l " · 2A1C1³.

S t r u c t u r e of A and B. G r a p h i t e l a t t i c e e x p a n d e d in t h e ο d i r e c t i o n w i t h a l a y e r of m e t a l h a l i d e in e a c h l a y e r v a c a n c y .

REFERENCES:

W. Rudorff and H. S c h u l z . Z . a n o r g . a l l g . C h e m . 2 4 5 , 121 (1940).

W. Rudorff a n d R. Z e l l e r . Z . a n o r g . a l l g . C h e m . 279, 182 (1955).

W . Rudorff and A. L a n d e l . Z . a n o r g . a l l g . C h e m . 2 9 3 , 327 (1958).

c) Volatile Carbon Compounds

O . GLEMSER

Carbo n Monoxid e CO

I. FROM FORMIC ACID

HCOOH = CO + H20 46,0 22,4 /

A g a s g e n e r a t o r ( o n e - l i t e r r o u n d - b o t t o m f l a s k w i t h g r o u n d g l a s s d r o p p i n g funnel and g a s o u t l e t tube) t w o - t h i r d s full of c o n c e n t r a t e d p h o s p h o r i c a c i d i s h e a t e d t o 80°C in a w a t e r b a t h . F o r m i c a c i d i s t h e n a d d e d s l o w l y , d r o p - b y - d r o p . R e m o v a l of i m p u r i t i e s ( C 0², a i r , a c i d v a p o r s , w a t e r v a p o r ) i s effected by p a s s i n g t h e g a s s u c c e s s i v e l y t h r o u g h 50% KOH s o l u t i o n and an a l k a l i n e s o l u t i o n of N a²S²0⁴ (25 g. of N a²S²0⁴ in 125 m l . of H²0 , p l u s by 20 m l . of 70% KOH) and o v e r KOH, C a C l² and P²0⁵.

T r a c e s of O^s m a y a l s o b e r e m o v e d w i t h a glowing c a r b o n f i l a m e n t [K. C l u s i u s and W. T e s k e . Z . p h y s . C h e m . (B) 6, 135 (1929)]. L a r g e r q u a n t i t i e s of oxygen a r e r e m o v e d in a p u r i f i c a t i o n t r a i n c o n s i s t i n g of t h r e e w a s h b o t t l e s in s e r i e s , two of w h i c h c o n t a i n 100 g. of s l i g h t l y a m a l g a m a t e d Zn and 100 m l . of 0.1M V O S 0⁴

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6 4 6 O. GLEMSER

s o l u t i o n , while t h e t h i r d c o n t a i n s 100 m l . of H²0 [L. M e i t e s and T . M e i t e s . A n a l . C h e m . 20, 984 (1948)].

V e r y p u r e CO i s o b t a i n e d by liquefaction of t h e g a s and d o u b l e f r a c t i o n a t i o n ( i m p u r i t i e s < 1 0 ~³ m o l e % ) .

II. FROM OXALIC ACID

H²C²0⁴ · 2 H²0 = CO + C 0² + 3 H²0 126.1 22,41 22.31

A m i x t u r e of 100 g. of o x a l i c a c i d d i h y d r a t e and 275 m l . of c o n c e n t r a t e d H²S 0⁴ i s h e a t e d c a r e f u l l y in a r o u n d - b o t t o m f l a s k until t h e o n s e t of g a s g e n e r a t i o n , w h i c h m u s t not b e a l l o w e d to p r o c e e d too v i g o r o u s l y . T h e C 0², f o r m e d in e q u a l a m o u n t s with t h e CO, i s a b s o r b e d in two w a s h b o t t l e s e a c h c o n t a i n i n g 100 m l . of 50% KOH solution. P u r i f i c a t i o n i s t h e s a m e a s in m e t h o d I.

O t h e r p r e p a r a t i v e m e t h o d s : ΙΠ. F r o m f o r m i c a c i d o r b a r i u m f o r m a t e and p h o s p h o r i c a c i d [J. G. T h o m p s o n . Ind. E n g . C h e m . 2 1 , 389 (1929)]. T h i s m e t h o d i s p a r t i c u l a r l y s u i t a b l e for a c o n t i n u o u s p r o c e s s and g i v e s a 92% y i e l d .

IV. F r o m c o n c e n t r a t e d H 2 S 0⁴a n d c y a n i d e s [ j . Wade and L . C.

P a n t i n g . J . C h e m . Soc. (London) 73, 255 (1898)].

V. By d r y h e a t i n g of a m i x t u r e of C a C²Ο⁴ and CaO (A. K l e m e n c . D i e 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 ] , V i e n n a , 1948, p . 159).

P r o c e d u r e s IV and V a r e not a s s a t i s f a c t o r y a s I.

VI. S m a l l a m o u n t s of v e r y p u r e g a s m a y b e p r e p a r e d by t h e r m a l d e c o m p o s i t i o n of N i ( C O )⁴ [A. M i t t a s c h . Z . p h y s . C h e m . 4 0 , 1 (1902);

C. Ε . H, Bawn. T r a n s . F a r a d a y Soc. 3 1 , 440 (1935)].

VII. F r o m C a C O^a p o w d e r and Zn d u s t at 700 to 750°C; v e r y p u r e g a s r e s u l t s [S. W e i n h o u s e . J . A m e r . C h e m . Soc. 7Ό, 442 (1948)].

Purification of tank CO: P o s s i b l e i m p u r i t i e s : C 0², O^s, H³, CH 4, N², Fe(CO)⁵. T h e g a s i s p a s s e d s l o w l y t h r o u g h a tube filled with r e d u c e d c o p p e r w i r e and h e a t e d to 600°C; t h i s r e m o v e s 0² and F e ( C O )⁵. T h e a c t i v a t e d Cu-filled t u b e of M e y e r and Ronge (see s e c t i o n on N i t r o g e n , p . 458) m a y a l s o b e u s e d . T h e CO t h e n flows t h r o u g h a t o w e r filled with m o i s t KOH to a b s o r b t h e C 0². Should f u r t h e r p u r i f i c a t i o n ( p a r t i c u l a r l y r e m o v a l of Η g) b e n e c e s s a r y , t h e CO m u s t b e liquefied and f r a c t i o n a l l y d i s t i l l e d .

PROPERTIES:

F o r m u l a weight 2 8 . 0 1 . P o i s o n o u s , c o l o r l e s s and o d o r l e s s g a s . M . p . - 2 0 5 . 1 ° C , b . p . —191.5°C; c r i t . t. - 1 4 0 . 2 ° C ; c r i t . p . 34.5 a t m . ; t r i p l e pt. p . 115.0 m m . B u r n s with a b l u e f l a m e ; ignition point 700°C in t h e a i r ; l o w e r e x p l o s i o n l i m i t in m o i s t a i r : 12.5% CO.

At e l e v a t e d t e m p e r a t u r e s , d e c o m p o s e s into C O^s and C. Solubility

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II . C A R B O N 647 in H²0 (0°C) 3 . 3 , (20°C) 2 . 3 v o l s , of C O / 1 0 0 g . H²0 . About s e v e n t i m e s a s soluble in m e t h y l and ethyl a l c o h o l s a s in H²0 . R e a d i l y s o l u b l e in a c e t i c a c i d , C H C 1³ and e t h y l a c e t a t e , d (liq., —195°C) 0.814; d (gas, 0°C) 1.250 g . / l i t e r . Heat of f o r m a t i o n —26.39 k c a l . / m o l e .

REFERENCES:

I. E . R u p p . C h e m . - Z . 3 2 , 983 (1908); J . M e y e r . Z . E l e k t r o c h e m . 1 5 , 506 (1929).

II. F . S c h a c h e r l . P u b . F a c . S c . Univ. M a s a r y k 9 9 , 5 (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 ] , V i e n n a , 1948, p . 160.

Carbo n Dioxid e

c o²

PURIFICATION OF TANK CO*

P o s s i b l e i m p u r i t i e s : w a t e r v a p o r , C O , 0² and N², s o m e t i m e s a c c o m p a n i e d by t r a c e s of H²S and S 0².

I. M o d e r a t e l y P u r e C O^s: T h e g a s i s p a s s e d s e q u e n t i a l l y t h r o u g h t h e following v e s s e l s : 1) two w a s h b o t t l e s w i t h Cr(II) a c e t a t e s o l u - t i o n o r V O S 0⁴ s o l u t i o n t o r e m o v e t h e bulk of t h e 0² ( a l s o s e e C O , m e t h o d I); 2) a U t u b e c o n t a i n i n g s m a l l p i e c e s of K H C 0³ (for r e m o v a l of a c i d v a p o r s ) ; 3) a U t u b e with p u m i c e i m p r e g n a t e d w i t h C u S 0⁴ s o l u t i o n , o r a w a s h b o t t l e filled w i t h 1M K M n 0⁴ s o l u t i o n o r 1M K²C r²0⁷ s o l u t i o n ( r e m o v a l of H²S ) ; 4) a w a s h b o t t l e w i t h c o n c e n t r a t e d s u l f u r i c a c i d (for d r y i n g ) ; and 5) a M e y e r and Ronge t u b e filled with a c t i v a t e d Cu and C u^sO h e a t e d t o 200°C ( s e e d e s c r i p - t i o n of t h e p u r i f i c a t i o n of N², p . 458) for r e m o v a l of t h e l a s t t r a c e s of 0² and C O . I n s t e a d of 3 and 4 , R. W e b e r r e c o m m e n d s [Angew.

C h e m . 6 5 , 136 (1953)] t h a t o r g a n i c c o m p o u n d s and H²S b e r e m o v e d by p a s s i n g t h e g a s t h r o u g h a m i x t u r e of 100 v o l u m e s of H²S 0⁴ (d 1.84) and 3.3 v o l u m e s of a q u e o u s f o r m a l d e h y d e (40 v o l . %).

If a g i v e n i m p u r i t y i s not p r e s e n t , t h e c o r r e s p o n d i n g p u r i f i c a - t i o n s t e p m a y b e o m i t t e d .

II. P u r e r C 0²: T h e g a s i s p a s s e d t h r o u g h s a t u r a t e d C u S 0⁴ t h r o u g h K H C 0³ s o l u t i o n , a n d finally t h r o u g h a f r a c t i o n a t o r ( K l e m e n c and B a n k o w s k i ) . T h i s a p p a r a t u s i s a p o r t i o n of t h e e q u i p m e n t p r e s e n t e d in F i g . 153 (p. 345) for t h e p r e p a r a t i o n of v e r y p u r e H²S . T o f r a c t i o n a t e C 0² one e m p l o y s only t h e s e c t i o n t o t h e r i g h t of w a s h b o t t l e 4 , c o n s i s t i n g of e i g h t w e l l - c o o l e d U t u b e s and two l o w - t e m p e r a t u r e t r a p s . I m m e d i a t e l y b e f o r e t h e l a s t c o n d e n s a t i o n t r a p A 2, a m e r c u r y m a n o m e t e r tube i s i n s e r t e d on a s i d e t u b e . T h e C 0² i s f r o z e n out in A¹ a f t e r p a s s i n g t h r o u g h t h e f i r s t f o u r

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648 Ο. GLEMSER

U t u b e s , c o o l e d t o t h e t e m p e r a t u r e s i n d i c a t e d in t h e f i g u r e . When A^x i s sufficiently full, s t o p c o c k a i s o p e n e d , t h e t u b e i s s e a l e d off at point ο, and t h e r e m a i n i n g a p p a r a t u s i s e v a c u a t e d t o a low p r e s s u r e . After t h e r e m a i n i n g f o u r U t u b e s h a v e b e e n c o o l e d t o —78°C ( D r y I c e - a c e t o n e ) , t h e liquid n i t r o g e n i s r e m o v e d f r o m a r o u n d A^l9 t h e f i r s t f r a c t i o n of g a s i s s i p h o n e d off, and c o n d e n s a t i o n v e s s e l

A² i s i m m e r s e d in liquid n i t r o g e n . T h e m i d d l e f r a c t i o n i s c o l l e c t e d in A 2» ^ e r e s i d u e b e i n g left in Α^τ. T h e m a t e r i a l i s s u b  l i m e d t w i c e f r o m A² and t h e p u r i t y of t h e g a s i s c h e c k e d by i t s v a p o r p r e s s u r e at v a r i o u s t e m p e r a t u r e s . T h e g a s i s s t o r e d in 2 5 - l i t e r g l a s s f l a s k s w h i c h h a v e b e e n d e g a s s e d by h e a t i n g in high v a c u u m at 350°C for m a n y h o u r s .

SYNONYM:

C a r b o n i c a c i d a n h y d r i d e .

PROPERTIES:

F o r m u l a w e i g h t 4 4 . 0 1 . C o l o r l e s s , o d o r l e s s g a s . Subl. t . —78.48°C ( a t m o s p h e r i c p r e s s u r e ) ; m . p . —56.7°C (5 a t m . ) ; c r i t . t . 31.3°C;

c r i t . p . 72.9 a t m . ; c r i t . d 0.464; t r i p l e p t . —56.6°C at 5.11 a t m . V a p o r p r e s s u r e ( - 1 2 0 ° C ) 1 0 . 5 ; ( - 1 0 0 ° C ) 1 0 4 . 2 ; ( - 8 2 ° C ) 5 6 9 . 1 m m . Solubility in H²( X (0°C) 1 7 1 ; (20°C) 8 8 ; (60°C) 36 m l . of C O²/ l 0 0 g. of H²0 .

d (vapor, 0°C) 1.977 g . / l i t e r ; d (liq., 0°C) 0.914 (34.4 a t m . ) ; d ( s o l i d , —56.6°C) 1.512. Heat of f o r m a t i o n —94.05 k c a l . / m o l e .

REFERENCES:

I. L . M o s e r . Z . a n o r g . a l l g . C h e m . 110, 125 (1921).

II. A. K l e m e n c and O. B a n k o w s k i . Z . a n o r g . a l l g . C h e m . 2 0 8 , 348 (1932); 209_, 225 (1932).

Tricarbo n Dioxid e

c³o²

I. THERMAL DECOMPOSITION OF MALONIC ACID IN THE PRESENCE OF P²0⁵

C³H⁴0⁴ = C³0² 4- 2 H²0

114.1 68,0

F l a s k a of t h e a p p a r a t u s i l l u s t r a t e d in F i g . 209 i s c h a r g e d w i t h 20 g. of m a l o n i c a c i d , 40 g. of c a l c i n e d s a n d and 200 g. of f r e s h , u n c a k e d and w e l l m i x e d P²O^s, T h e s y s t e m i s e v a c u a t e d t o 0.1 m m . ,

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II . CARBON 649 s t o p c o c k h i s c l o s e d , a n d t h e a p p a r a t u s i s left t o s t a n d f o r s o m e h o u r s t o c o m p l e t e t h e d r y i n g and t o t e s t for l e a k s . T h e p u m p i s t h e n s t a r t e d , s t o p c o c k m i s opened o n c e a g a i n , d i s c o o l e d w i t h liquid n i t r o g e n and a i s h e a t e d on an o i l b a t h t o 140°C. At t h i s t e m p e r a t u r e , d e c o m p o s i t i o n i s c o m p l e t e w i t h i n about an h o u r and i m p u r e C³O^s c o n d e n s e s in d. Now t h e oil b a t h i s r e m o v e d , m i s c l o s e d , t h e p u m p i s s t o p p e d , d r y a i r i s i n t r o d u c e d at h⁹ and a i s r e m o v e d f r o m t h e s y s t e m and s e a l e d off at a. T h e s y s t e m i s a g a i n e v a c u a t e d , m i s c l o s e d , and t h e c o n t e n t s of d a r e s l o w l y d i s t i l l e d into t r a p ft, c o o l e d w i t h liquid n i t r o g e n . P l u g g i n g of ft should not b e a l l o w e d t o o c c u r . A c e t i c a c i d and o t h e r i m p u r i t i e s a r e a b s o r b e d

F i g . 209. P r e p a r a t i o n of t r i c a r b o n d i o x i d e f r o m m a l o n i c a c i d , a) o n e - l i t e r r e a c t i o n f l a s k ; b) r u b b e r s t o p p e r s , l i g h t l y g r e a s e d ; a) c o n n e c t i n g t u b e , 10 m m . I.D. d⁹ h and I) t r a p s ; e) d r y i n g t o w e r c o n t a i n i n g p e a - s i z e d , f r e s h l y c a l c i n e d p i e c e s of C a C O ; p) 8 0 0 - m m . -

in t h e l i m e t o w e r and t h e m a t e r i a l i s f r a c t i o n a t e d in high v a c u u m w i t h s t o p c o c k / c l o s e d . T h i s i s d o n e by p l a c i n g h in an a l c o h o l b a t h (—110°C t o —115°C), w h i l e I i s c o o l e d w i t h liquid n i t r o g e n , s t o p c o c k i i s c l o s e d , and t h e c o n d e n s a t e in h i s m e l t e d . T h e n h i s a g a i n i m m e r s e d in t h e a l c o h o l b a t h , t i s o p e n e d , and d i s t i l l a t i o n into I p r o c e e d s . P r e s s u r e c h a n g e s a r e followed on t h e m a n o m e t e r . W h e n t h e m a n o m e t e r p r e s s u r e i s s t i l l but a few t e n t h s of a m i l l i - m e t e r , t h e v a p o r p r e s s u r e i s d e t e r m i n e d at 0°C and c o m p a r e d w i t h t h a t of t h e p u r e g a s (573.5 m m . ) .

S e p a r a t i o n of t h e C³0²- C 0² m i x t u r e ( C 0² i s a p r o d u c t of t h e s i d e r e a c t i o n C³H⁴0⁴ = C H³C O O H + C O^s) i s difficult. T h e r e f o r e , w h e n t h e s o l i d p h a s e ( C 0²) h a s d i s a p p e a r e d , it i s a d v i s a b l e t o r e d u c e t h e b a t h t e m p e r a t u r e t o —125°C o r —130°C f o r c o m p l e t i o n of t h e s e p a r a t i o n . F r a c t i o n a t i o n t a k e s about 15 h o u r s (A. K l e m e n c , l o c . c i t . ) .

f ^m

long m a n o m e t e r t u b e .