Accelerating Action of Ozone in the Autoxidation Processes

Accelerating Action of Ozone in the Autoxidation Processes E. BRINER

Downloaded by AUBURN UNIV on September 12, 2017 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch028

University of Geneva, Geneva,

Switzerland

Numerous experimental facts have demonstrated the entrainment action of ozone upon oxygen molecules, the latter participating in the autoxidation in which they would have remained inactive if ozone were not present. This entrainment accelerates the reaction rate. The number of molecules entrained by one molecule of consumed ozone increases greatly as the ozone becomes more diluted with oxygen. It a p pears that all these facts are characteristic properties of ozone. The acceleration of the autoxidation by ozone, described in this paper, was applied especially in the ozonization of certain olefins, to prepare their ozonides.

D y t h e t e r m " q u a n t i t a t i v e o z o n i z a t i o n " i s i m p l i e d n o t o n l y t h e y i e l d s of t h e p r o d u c t s f o r m e d b u t also t h e a m o u n t s of ozone c o n s u m e d . P r i o r t o t h e studies d e s c r i b e d i n t h i s paper q u a n t i t a t i v e ozonization h a d n o t been systematically studied. I n a s y s t e m a t i c s t u d y p r o g r a m o n t h e o z o n i z a t i o n of v a r i o u s classes of o r g a n i c c o m p o u n d s , t h e r e a c t i o n of ozone w i t h a l d e h y d e s h a d a p r o m i n e n t p l a c e . T h e b e h a v i o r o f a n energetic o x i d a n t l i k e ozone w i t h respect t o c o m p o u n d s s u c h as a l d e h y d e s , w h i c h are oxidized v e r y easily, was observed. I t h a s l o n g been k n o w n t h a t a l d e h y d e s o x i d i z e s p o n t a n e o u s l y i n t h e presence of o x y g e n , as d o n u m e r o u s o t h e r c o m p o u n d s . T h i s p h e n o m e n o n h a s , t h e r e f o r e , b e e n c a l l e d a u t o x i d a t i o n , a n d t h i s w o r d is u s e d here, i n s p i t e of t h e f a c t t h a t i t i s n o l o n g e r t o be c o n s i d e r e d q u i t e c o r r e c t . T h e first m e a s u r e m e n t s w e r e m a d e i n c o l l a b o r a t i o n w i t h D é m o l i s a n d P a i l l a r d (13). A s o l u t i o n of b e n z a l d e h y d e i n c a r b o n t e t r a c h l o r i d e w a s s u b j e c t e d t o o x y g e n c o n t a i n i n g a k n o w n a m o u n t of ozone. T h e course of t h e r e a c t i o n w a s f o l l o w e d q u a n t i t a t i v e l y w i t h a n a p p a r a t u s n o t d e s c r i b e d h e r e . ( D e t a i l e d d e s c r i p t i o n s of e q u i p m e n t a n d p r o c esses a r e g i v e n i n t h e o r i g i n a l p a p e r s . ) T h e r e s u l t s of t y p i c a l d e t e r m i n a t i o n s a r e d e scribed i n the following paragraphs. I n t h e flask c o n t a i n i n g p o t a s s i u m i o d i d e s o l u t i o n f o r t h e d e t e r m i n a t i o n of u n r e a c t e d ozone a g r e a t d e a l o f l i b e r a t e d i o d i n e w a s f o u n d . T h u s a c o n s i d e r a b l e p r o p o r t i o n of ozone p a s s e d t h r o u g h t h e s o l u t i o n of a l d e h y d e , t h e l a t t e r a p p e a r i n g t o b e o n l y s l i g h t l y s e n s i t i v e t o t h e o x i d i z i n g a c t i o n of ozone. T h e a n a l y s i s of t h e a l d e h y d e s o l u t i o n s h o w e d clearly, however, t h a t i t h a d been h e a v i l y oxidized to benzoic a c i d a n d perbenzoic acid, a n d m u c h more oxygen h a d been t a k e n u p i n this oxidation t h a n corresponded to the a m o u n t of ozone c o n s u m e d . I t w a s , t h e r e f o r e , c o n c l u d e d t h a t t h e ozone h a d c a u s e d c o n s i d e r a b l y m o r e o x y g e n 184

OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

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t o p a r t i c i p a t e i n t h e o x i d a t i o n t h a n w o u l d be e x p e c t e d i n t h e absence of ozone, [ I n a l l these e x p e r i m e n t s o z o n i z e d o x y g e n o r o z o n i z e d a i r w a s b u b b l e d t h r o u g h t h e s o l u t i o n s . R e c e n t l y i t w a s o b s e r v e d t h a t i f a W a r b u r g - t y p e a p p a r a t u s (18) i s u s e d , the same results are obtained b y s i m p l y agitating liquids i n the a p p r o p r i a t e a t m o s p h e r e s . ] T h e ozone f u n c t i o n e d n o t o n l y as a n o x i d i z i n g agent, b u t also as a n o x i d a t i o n catalyst. T h e w o r d " p a t a l y s t " w a s u s e d f r e q u e n t l y i n t h e a u t h o r ' s first p a p e r s . A l t h o u g h i t c o n v e y s t h e i d e a v e r y w e l l , i t is n o t c o r r e c t , as a t least p a r t of t h e ozone i s a c t u a l l y c o n s u m e d i n t h e r e a c t i o n . T h e r e f o r e , i n t h e p r e s e n t p a p e r ozone is r e f e r r e d t o as a n autoxidation-accelerator.


G e n e r a l i t y o f the P h e n o m e n o n F i r s t observations l e d t o speculations o n the possibility t h a t we m i g h t be dealing w i t h a r e a c t i o n affecting n o t o n l y a l d e h y d e s b u t a u t o x i d a t i o n i n g e n e r a l . T o e s t a b l i s h t h i s , t h e a u t h o r u n d e r t o o k , w i t h N i c o l e t a n d P a i l l a r d (16) a n d l a t e r w i t h B i e d e r m a n n ( 7 ) , s e v e r a l series of studies o n a u t o x i d a t i o n , i n c l u d i n g t h e c l a s s i c a l cases of s u l f u r o u s a c i d a n d t h e a l k a l i sulfites a n d b i s u l f i t e s . I n a l l these cases t h e a d d i t i o n of ozone t o o x y g e n o r t o a i r l e d t o a n o x y g e n u p t a k e i n excess of t h a t f o u n d i n t h e absence of ozone, w i t h t h e f o r m a t i o n of s u l f u r i c a c i d , a l k a l i sulfates, o r b i s u l f a t e s , r e s p e c t i v e l y . T h e a u t o x i d a t i o n of s t a n n o u s c h l o r i d e , w h i c h is q u i t e a different c o m p o u n d , w a s s t u d i e d i n c o l l a b o r a t i o n w i t h B e v e r (6), a n d t h e same p h e n o m e n o n w a s f o u n d . A t t h e t i m e of t h e a u t h o r ' s first p u b l i c a t i o n s , i n c o l l a b o r a t i o n w i t h o t h e r s , t h r e e G e r m a n o r g a n i c c h e m i s t s , F i s c h e r , D u l l , a n d V o l z (25), also r e c o g n i z e d t h i s a u t o x i d a t i o n a c c e l e r a t o r effect i n t h e case of a l d e h y d e s u n d e r g o i n g r e a c t i o n w i t h o z o n i z e d o x y g e n , b u t i t is n o t a p p a r e n t t h a t these w o r k e r s v i s u a l i z e d t h e g e n e r a l scope of t h e i r d i s c o v e r y . T h e a c c e l e r a t i n g a c t i o n of ozone w a s also o b s e r v e d i n â h o m o g e n e o u s gaseous s y s t e m — i . e . , i n t h e s l o w o x i d a t i o n of s a t u r a t e d h y d r o c a r b o n s , s u c h as p r o p a n e , b u t a n e , h e x a n e , h e p t a n e , a n d s e v e r a l o c t a n e i s o m e r s (9). T h u s , a c o m p l e t e n e w range of i n v e s t i g a t i o n s w a s u n d e r t a k e n , i n c l u d i n g s t u d i e s o f t h e r e a c t i v i t i e s of t h e v a r i o u s c o m p o u n d s u n d e r g o i n g a u t o x i d a t i o n , t h e influence of t e m p e r a t u r e , t h e influence of t h e v a r i o u s solvents u s e d ( t h e p h e n o m e n o n is i n v e s t i g a t e d c h i e f l y i n s o l u t i o n s ) , a n d t h e a c t i o n of l i g h t . L i g h t accelerates a u t o x i d a t i o n a n d t h e b u b b l e t u b e s m u s t b e k e p t i n t h e d a r k t o isolate t h e role of ozone i n these i n v e s t i g a t i o n s . F u r t h e r , s u c h s o - c a l l e d a n t i o x i d a n t s as h y d r o q u i n o n e , w h i c h slow d o w n a n d even stop the autoxidation completely, act i n a similar w a y i f they are added t o a n a u t o x i d i z a b l e s y s t e m e x p o s e d t o o x y g e n a n d ozone (21). T h u s , ozone d e f i n i t e l y acts u p o n t h e a u t o x i d a t i o n b y m o b i l i z i n g a n a d d i t i o n a l n u m b e r of o x y g e n m o l e c u l e s . Effect of O z o n e i n Autoxidations. T o a p p r e c i a t e t h i s effect w h a t i s c a l l e d t h e o x i d a t i o n y i e l d h a s b e e n d e t e r m i n e d ( a b b r e v i a t e d R O , - f r o m t h e F r e n c h e q u i v a l e n t of oxidation yield, "rendement d'oxydation"). T h i s v a l u e relates t h e a m o u n t of s u p p l e m e n t a r y o x y g e n b o u n d w h e n one passes f r o m t h e o x i d a t i o n w i t h o x y g e n ( o r a i r ) alone t o t h e o x i d a t i o n w i t h o x y g e n ( o r a i r ) c o n t a i n i n g a k n o w n p e r c e n t a g e of ozone, a l l o t h e r c o n d i t i o n s r e m a i n i n g i d e n t i c a l . T h e a m o u n t of r e a c t e d o x y g e n c a n be f o u n d b y a n a l y s i s of t h e o x i d a t i o n p r o d u c t s a f t e r t h e e x p e r i m e n t s . C o n s i d e r i n g , f o r e x a m p l e , t h e a u t o x i d a t i o n of b e n z a l d e h y d e , t h e f o r m a t i o n of one m o l e c u l e of b e n z o i c o r of p e r b e n z o i c a c i d i n v o l v e s c o m b i n a t i o n w i t h one o r t w o a t o m s of o x y g e n , r e s p e c t i v e l y . I n t h e a u t o x i d a t i o n of a n a l k a l i sulfite, e a c h m o l e c u l e of s u l fate f o r m e d u t i l i z e s o n e b o u n d a t o m of o x y g e n . T h u s / f r o m t h e analyses, the o x i d a t i o n y i e l d , R O , is o b t a i n e d a n d is - r e p o r t e d as t h e r a t i o ( m u l t i p l i e d b y 100 i n o r d e r to m a k e t h e c o m p a r i s o n easier) of t h e a m o u n t of r e a c t e d o x y g e n i n excess to t h e a m o u n t of ozone c o n s u m e d . W h e n t h e o x i d a t i o n y i e l d exceeds 100, i t f o l l o w s t h a t t h e o x y g e n molecules h a v e u n d e r g o n e r e a c t i o n b y v i r t u e of t h e presence of ozone. H o w e v e r , i n t h e case of a l d e h y d e s i t is possible t o go one step f u r t h e r a n d s t a t e t h a t t h e o x y g e n h a s a l r e a d y u n d e r -


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gone r e a c t i o n i f t h e o x i d a t i o n y i e l d is g r e a t e r t h a n 3 3 % ; f o r t h i s 3 3 % i s d u e t o t h e d i r e c t o x i d i z i n g a c t i o n of ozone i t s e l f — t h a t i s , t h e a c t i o n of i t s a c t i v e o x y g e n as d e t e r m i n e d b y t h e c l a s s i c a l ozone assay ( t h e l i b e r a t i o n of i o d i n e f r o m a p o t a s s i u m i o d i d e solution). T o e m p h a s i z e t h e significance of t h e role of ozone, use is m a d e of t w o m o r e v a l u e s w h i c h a r e defined b e l o w b a s e d u p o n o x i d a t i o n y i e l d , R O . O n e is t h e u t i l i z a t i o n coeffi c i e n t of ozone c a l l e d « , w h i c h i n d i c a t e s t h e n u m b e r of b o u n d o x y g e n a t o m s i n excess f o r e a c h m o l e c u l e of ozone c o n s u m e d ; i t is a f u n c t i o n of R O :


I f R O = 100, a is e q u a l t o 3. I f « > 3, o x y g e n molecules h a v e c e r t a i n l y t a k e n p a r t i n t h e o x i d a t i o n . T h e o t h e r , N, is t h e n u m b e r of o x y g e n m o l e c u l e s u s e d i n t h e o x i d a t i o n p e r m o l e c u l e of ozone c o n s u m e d . I t is r e l a t e d t o R O a n d t o a b y t h e e q u a t i o n N

3 X RO 2 X 100

=

a 2

=

Ν of course, h a s a c t u a l m e a n i n g o n l y i f R O > 100 a n d Ν a n d a a r e a c t u a l l y average v a l u e s of n u m e r o u s i n d i v i d u a l d e t e r m i n a t i o n s . T a b l e I presents n u m e r i c a l v a l u e s f o r t h e a u t o x i d a t i o n of a l d e h y d e s a n d s o d i u m b i s u l f i t e i n a c u r r e n t of o z o n i z e d o x y g e n . y

Table I.

Autoxidation of Several Aldehydes and Sodium Bisulfite

Molecule undergoing autoxidation Solvent

CeHeCHO Hexane

Temperature, C . Ozone concentration, vol. % RO a

CH (CH )CHO Carbon tetrachloride 0 1.5 580 17.6 8.7 3

0 0.9 370 11 5.5

0

Ν

CHaOCelfcCHO Carbon tetrachloride 0 2.4 240 7.2 3.6

2

NaHSOs Water 0 0.09 450 13.5 6.7

T h e s e v a l u e s s h o w c l e a r l y t h e p r o n o u n c e d a c c e l e r a t i n g a c t i o n of ozone u p o n t h e a u t o x i d a t i o n r a t e ; t h i s a c t i o n b e c o m e s s t i l l m o r e p r o n o u n c e d , i f t h e ozone c o n c e n t r a t i o n i n oxygen o r i n a i r is diminished.

Chemical and

Physicochemical Mechanism

o f the

Autoxidation

Probable Autoxidation M e c h a n i s m under O r d i n a r y Conditions. F o r some t i m e i t was believed t h a t this reaction proceeded i n the following m a n n e r : O x y g e n adds t o t h e a l d e h y d e , f o r m i n g a v e r y u n s t a b l e p e r o x i d e . T h i s p e r o x i d e isomerizes t o a p e r a c i d ( i n t h e p r e s e n t case p e r b e n z o i c a c i d ) , w h i c h is s t a b l e e n o u g h f o r assay. T h e steps a r e r e p r e s e n t e d as f o l l o w s : Ο

C H — C — Η + 0 -> C H — d ^ - H O - » C H — C — Ο — O H 6

6

6

Aldehyde

2

6

S

v

Peroxide

6

a 5

Peracid

T h i s sequence of t r a n s f o r m a t i o n s c o n s t i t u t e s t h e a c t u a l a u t o x i d a t i o n . I n t h e s u b sequent s t e p t h e p e r a c i d reacts w i t h t h e a l d e h y d e , w h i c h r e m a i n s i n s u b s t a n t i a l excess d u r i n g a l a r g e p a r t of t h e r e a c t i o n , t o p r o d u c e t h e a c i d — i . e . , b e n z o i c a c i d .

O H — C — H + C e H s — C — Ο — O H —> e

6

11

ft

2C^—C—Oil

ft Acid


187


P h y s i c a l c h e m i c a l e v i d e n c e suggests t h a t t h e t r a n s f o r m a t i o n o f a l d e h y d e t o t h e peracid proceeds b y a c h a i n reaction i n w h i c h certain s h o r t - l i v e d radicals are i n t e r mediates. T h e n e x t s t e p , i n w h i c h t h e a c i d i s f o r m e d , i s t h e s a m e as t h a t e n v i s a g e d i n t h e c h e m i c a l c o n c e p t of t h i s c h a n g e . A s t h i s r e a c t i o n i s i m p o r t a n t f o r u n d e r s t a n d i n g a u t o x i d a t i o n , t h e a u t h o r s t u d i e d i t s k i n e t i c s i n c o o p e r a t i o n w i t h L a r d o n (15). A t o r d i n a r y t e m p e r a t u r e s t h e r e a c t i o n i s so s l o w t h a t t h e p e r b e n z o i c a c i d p e r s i s t s f o r a short t i m e ; thus, i t m u s t be t a k e n i n t o account w h e n establishing t h e equation f o r the bound oxygen, mentioned above.


A p p l i c a t i o n of Infrared Absorption

Spectroscopy

R e c e n t l y , i n f r a r e d s p e c t r o s c o p y h a s been a p p l i e d t o t h e s t u d y of t h e a u t o x i d a t i o n process. T h e m e t h o d u s e d b y t h e a u t h o r a n d c o w o r k e r s h a s also b e e n a p p l i e d f o r s e v e r a l y e a r s t o s t u d y t h e o z o n i z a t i o n of u n s a t u r a t e d o r g a n i c c o m p o u n d s ; i t does n o t a p p e a r t o h a v e b e e n u t i l i z e d elsewhere. I n p a r t i c u l a r t h e a u t o x i d a t i o n of b e n z a l d e h y d e w a s i n v e s t i g a t e d . I t s c h o i c e as t h e i n i t i a l s u b j e c t f o r s t u d y w a s u n f o r t u n a t e , as t h e use of a n i m p u r e s a m p l e o f p e r b e n z o i c a c i d f o r d e t e r m i n a t i o n of i t s a b s o r p t i o n s p e c t r u m , n o t p r e v i o u s l y r e c o r d e d , l e d t o erroneous c o n c l u s i o n s . T h e s e were l a t e r r e c t i f i e d a f t e r t a k i n g n e w m e a s u r e m e n t s o n a p u r e c r y s t a l l i n e s a m p l e of t h e p e r a c i d (12). F o r t h e p r e s e n t s t u d y t h e t w o m a i n b a n d s a t 1728 t o 1730 a n d a t 1270 c m . - a r e t o b e b o r n e i n m i n d . T h e s e b a n d s m a d e possible a d e m o n s t r a t i o n of t h e a c c e l e r a t i o n of t h e a u t o x i d a t i o n d u e t o ozone a n d t h e influence of s u c h a c c e l e r a t i o n i n o z o n i d e f o r m a t i o n . T h r e e s p e c t r a l series ( F i g u r e s 1, 2, a n d 3 ) , o b t a i n e d i n c o l l a b o r a t i o n w i t h E . D a l l w i g k , a r e discussed b e l o w . I n F i g u r e 1 comparative spectra are shown f o r t h e autoxidation of benzaldehyde i n the presence of e i t h e r p u r e o x y g e n o r o x y g e n w i t h ozone i n t h e i n d i c a t e d c o n c e n t r a tions. A 1-hour r e a c t i o n changes t h e s p e c t r u m of t h e a l d e h y d e ( s p e c t r u m I ) b y m a k i n g t h e t w o b a n d s of p e r b e n z o i c a c i d a p p e a r ( s p e c t r u m I I ) o n e a t 1730 c m . - as a s h o u l d e r o n t h e 1 7 0 7 - c m . - b a n d of t h e a l d e h y d e a n d t h e o t h e r , d i s t i n c t , a t 1270 c m . . After 2 hours the 1 7 3 0 - c m . b a n d i s n i c e l y d e v e l o p e d a n d t h e b a n d a t 1270 c m . is more pronounced (spectrum I I I ) . A f t e r 3 hours b o t h bands (spectrum I V ) have developed still further. S p e c t r u m V shows t h e h i g h l y a c c e l e r a t i n g a c t i o n of ozone u p o n t h e a u t o x i d a t i o n . A c t u a l l y , a l t h o u g h t h e ozone c o n c e n t r a t i o n w a s l o w , C = 0.76% a n d the oxidation l a s t e a f o r o n l y 10 m i n u t e s , t h e t w o p e r a c i d b a n d s a r e s t r o n g e r t h a n i n s p e c t r u m I V , w h i c h i n v o l v e d a 3 - h o u r r e a c t i o n w i t h ozone-free o x y g e n . I n o r d e r t o s h o w t h e d i l u t i o n effect b e t t e r , s t i l l a n o t h e r s p e c t r u m ( s p e c t r u m V I ) is i n c l u d e d i n t h e figure, w h i c h w a s also o b t a i n e d w i t h a r e a c t i o n of o n l y 10 m i n u t e s , b u t i n v o l v e d m u c h h i g h e r ozone c o n c e n t r a t i o n , C = 3.36%. I n comparing spectra V a n d V I , i t i s n o t e d t h a t , i n s p i t e o f t h e h i g h e r ozone c o n c e n t r a t i o n , t h e b a n d s u n d e r c o n s i d e r a t i o n a r e i n b o t h cases a l m o s t e q u a l l y w e l l d e v e l o p e d . 1

1

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- 1

- 1

-

0

0

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3

3

T a b l e II. Cos, % 3.36 0.76

RO 250 840

a 7.5 25

Ν 3.7 12.5

T h i s effect i s also i l l u s t r a t e d b y t h e n u m e r i c a l v a l u e s of T a b l e I I , w h i c h h a v e b e e n calculated for R O , « , a n d Ν according to the formulas given above. I n t h e s p e c i a l case u n d e r d i s c u s s i o n t h e a m o u n t of b o u n d o x y g e n d u e t o t h e ozone a c c e l e r a t o r effect w a s d e t e r m i n e d n o t b y c h e m i c a l a n a l y s i s b u t f r o m s p e c t r o s c o p i c d a t a , b y calculating the perbenzoic acid concentration, C , f r o m t h e w e l l - k n o w n f o r m u l a : l o g / / / = €CZ 0


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Spectra of 0.20M solution of b e n z a l d e h y d e in carbon tetrachloride

Spectra I. Unexposed solution II. Solution after 1-hour exposure to oxygen at 8 liters/hour III. Solution after 2-hour exposure to oxygen at 8 liters/hour IV. Solution after 3-hour exposure to oxygen at 8 liters/hour V. Solution after 10-minute exposure to oxygen containing 0 . 7 6 % ozone VI. Solution after 10-minute exposure to oxygen containing 3.36% ozone


189


BRI Ν ER—AUTOXI DATION PROCESSES

Figure 2.

Spectra of 0.25M solution of stiibene in carbon tetrachloride Spectra I. Nonozonized solution II. 5 0 % ozonized solution III. Superozonized solution IV. More strongly superozonized solution V. Solution 5 days after ozone-oxygen stream shut off

w h e r e I /I is m e a s u r e d a t 1270 c m . , I is t h e t h i c k n e s s of t h e a b s o r b i n g l i q u i d l a y e r , a n d c is t h e m o l e c u l a r e x t i n c t i o n coefficient f o r t h e 1 2 7 0 - c m . b a n d . T h e v a l u e of c w a s p r e v i o u s l y r e p o r t e d t o be 520 {12). T h i s s i m p l i f i e d c a l c u l a t i o n w a s m a d e possible because c o n s i d e r a t i o n of t h e b e n z o i c a c i d w a s o m i t t e d ; u n d e r t h e c o n d i t i o n s e x i s t i n g t h e effect of b e n z o i c a c i d w o u l d h a r d l y b e n o t i c e a b l e o n t h e s p e c t r u m . F o r a d i l u t i o n r o u g h l y fivefold, t h e n u m b e r of o x y g e n m o l e c u l e s p a r t i c i p a t i n g i n t h e o x i d a t i o n i s a l most quadrupled (Table I I ) . T h u s i t w a s e s t a b l i s h e d b y t h e i n f r a r e d s t u d y of a l d e h y d e a u t o x i d a t i o n t h a t t h e first p r o d u c t o b t a i n e d is t h e p e r a c i d . I t does n o t f o l l o w , h o w e v e r , t h a t o t h e r i n t e r mediates are not formed—for example, radicals i n a chain reaction—but their i n s t a b i l i t y is s u c h t h a t t h e y c a n n o t be d e t e c t e d b y i n f r a r e d s p e c t r o g r a p h y . I n F i g u r e 2 t h e a c c e l e r a t e d a u t o x i d a t i o n d u e t o ozone is s h o w n i n t h e s p e c t r o s c o p i c e x a m i n a t i o n of t h e o z o n i z a t i o n of a n olefin, £rans-stilbene, i n c a r b o n t e t r a c h l o r i d e . T h e first d e t e r m i n a t i o n s w e r e m a d e i n these l a b o r a t o r i e s i n 1952 i n c o l l a b o r a t i o n w i t h S u s z 0

- 1

- 1



190


Figure 3.

Spectra of various concentrations of frans-stilbene a n d benzaldehyde in carbon tetrachloride

Spectra I. Nonozonized 0.25M frans-stilbene and 0.025M benzaldehyde solution II. About 9 0 % ozonized 0.25M frans-stilbene and 0.025M benzaldehyde solution III. Superozonized 0.25M frans-stilbene and 0.025Λ4 benzaldehyde solution IV. More strongly superozonized 0.125M frans-stilbene and 0.05M benzaldehyde solution

a n d D a l l w i g k i n t h e course of r e s e a r c h o n i n f r a r e d a b s o r p t i o n s p e c t r a of ozonides (20, 28). S p e c t r u m I shows t h e s t i l b e n e s o l u t i o n ; 5 0 % o z o n i z a t i o n ( s p e c t r u m I I ) p r o d u c e s a s t r o n g b a n d a t 1706 c m . - . I n t h e s p e c t r a d e t e r m i n e d i n 1952, t h e b a n d o b t a i n e d a t 1 0 % ozonization developed regularly u p to 7 0 % ozonization. A t this point i n the i n v e s t i g a t i o n s , t h e p e r f e c t a g r e e m e n t of t h i s f r e q u e n c y w i t h t h e v i b r a t i o n a l b a n d s of t h e C O g r o u p of t h e b e n z a l d e h y d e w a s m o s t s t r i k i n g . B u t i t seemed i m p o s s i b l e t o a t t r i b u t e t h i s b a n d t o t h e a l d e h y d e , i n v i e w of i t s i n s t a b i l i t y i n a s o l u t i o n t h r o u g h w h i c h o x y g e n p l u s ozone a r e c o n s t a n t l y b u b b l e d . C r i e g e e a n d o t h e r s (23) p u b l i s h e d n e w r e s u l t s , w h i c h l e d t o t h e r e s u m p t i o n of these i n v e s t i g a t i o n s . H e p o i n t e d o u t t h a t t h e i n f r a r e d s p e c t r a of r e a l l y p u r e ozonides c o n t a i n e d n o b a n d s i n t h e r a n g e o f s p e c t r a l frequencies of C O g r o u p v i b r a t i o n s . T h i s w a s v e r i f i e d i n these l a b o r a t o r i e s w i t h a s a m p l e of p u r e i r e m s - s t i l b e n e o z o n i d e o b t a i n e d f r o m Criegee. 1


191


T h u s i t was concluded t h a t t h e aldehyde could indeed be protected f r o m t h e action of ozone b y t h e h i g h a f f i n i t y of t h e d o u b l e b o n d f o r ozone. I n d e e d (4, 19), t h e r m o c h e m i c a l m e a s u r e m e n t s h a v e s h o w n t h a t t h e heats o f o z o n i z a t i o n a r e of t h e o r d e r of 8 0 t o 120 k c a l . I n o r d e r t o solve t h i s p r o b l e m , i t w a s o n l y n e c e s s a r y t o effect o z o n i z a t i o n of a s t i l b e n e s o l u t i o n t o w h i c h some b e n z a l d e h y d e h a d b e e n a d d e d . T h e r e s u l t s of these i n v e s t i g a t i o n s were d e f i n i t e l y p o s i t i v e , as s h o w n i n t h e s p e c t r a of F i g u r e 3. F u l l d e t a i l s h a v e b e e n p u b l i s h e d (10, 11, 24) - T h e f o l l o w i n g p o i n t s s h o u l d b e e m p h a s i z e d , w h i c h emerge f r o m a c o n s i d e r a t i o n of t h e s p e c t r a s h o w n i n F i g u r e 2 : first, o n p u r s u i n g t h e o z o n i z a t i o n t h e d e v e l o p m e n t ( s p e c t r a I I I a n d I V ) of t h e t w o b a n d s d u e t o p e r b e n z o i c acid, already referred t o ; a n d secondly the appearance a n d v e r y m a r k e d development ( s p e c t r a I I , I I I , I V , a n d V ) of a b a n d a t 1056 c m . - — i . e . , i n t h e r e g i o n o f t h e o z o n i d e b a n d s a c c o r d i n g t o C r i e g e e a n d o t h e r s (23).


1

I n F i g u r e 3 i t i s seen t h a t , i f a i r c m s - s t i l b e n e s o l u t i o n c o n t a i n i n g b e n z a l d e h y d e ( s p e c t r u m I ) is o z o n i z e d , t h e C O b a n d d u e t o t h e a l d e h y d e a t 1706 c m . does n o t disappear b u t becomes m u c h stronger ( s p e c t r u m I I ) . Therefore, a m a t e r i a l w i t h a C O b a n d m u s t h a v e b e e n p r o d u c e d w h i c h shows t h e same f r e q u e n c y as t h a t o f t h e a l d e h y d e . T h u s a p r o t e c t i v e a c t i o n of t h e d o u b l e b o n d a g a i n s t t h e a u t o x i d a t i o n a c c e l e r a t e d b y ozone i s p l a i n l y m a n i f e s t . I n t h e l a t e s t m e a s u r e m e n t s i t h a s been f o u n d t h a t t h e stilbene double b o n d protects benzaldehyde against a u t o x i d a t i o n due to oxygen a l o n e ; t h u s substances w i t h a d o u b l e b o n d m a y a c t also as a n t i o x i d a n t s . -

1

F u r t h e r m o r e , t h e p r o t e c t i v e a c t i o n of t h e s t i l b e n e d o u b l e b o n d becomes less a n d e v e n ceases as soon as i f t h e d o u b l e b o n d were s a t u r a t e d b y i n c r e a s i n g o z o n i z a t i o n . A t t h i s m o m e n t t h e t w o b a n d s of p e r b e n z o i c a c i d a p p e a r a n d d e v e l o p ( s p e c t r a I I a n d I V ) , i n d i c a t i n g t h a t a u t o x i d a t i o n h a s set i n . T h i s p r o v e s t h a t t h e C O b a n d a t 1706 c m . m u s t b e a s c r i b e d t o b e n z a l d e h y d e , because p e r b e n z o i c a c i d , u n d e r these e x p e r i m e n t a l c o n d i t i o n s , c a n b e d e r i v e d o n l y f r o m t h e a u t o x i d a t i o n of t h i s a l d e h y d e . V e r y s i m i l a r p h e n o m e n a h a v e b e e n s t u d i e d a n d o b s e r v e d w i t h o t h e r olefins, s u c h as a n e t h o l a n d isoeugenol (10, 11, 24). I n these cases t h e C O b a n d s w h i c h a p p e a r a l m o s t a t t h e b e g i n n i n g of t h e o z o n i z a t i o n l i k e w i s e d e v e l o p i n a definite w a y , d e n o t i n g the definite f o r m a t i o n of anisaldehyde a n d v a n i l l i n , respectively. I t seemed d e s i r a b l e t o p o i n t o u t t h e c o n n e c t i o n b e t w e e n these t w o p h e n o m e n a — n a m e l y , a u t o x i d a t i o n a n d p r o d u c t i o n of ozonides, w h i c h a t first glance seem t o h a v e n o t h i n g w h a t s o e v e r t o d o w i t h e a c h o t h e r . T h i s c o n n e c t i o n is of p r a c t i c a l i n t e r e s t , because i t i s u s e f u l t o k n o w t h a t a l d e h y d e s , s u c h as a n i s a l d e h y d e o r v a n i l l i n , a r e a l r e a d y present t o a considerable extent i n t h e " p r e f a b r i c a t e d " s t a t e — t h a t is, before t h e reduc t i v e h y d r o l y s i s t o w h i c h t h e o z o n i z a t i o n p r o d u c t s a r e finally s u b m i t t e d w i t h a v i e w t o scission of t h e ozonides f o r m e d .

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Effect o f O z o n e

Dilution

T h e d i l u t i o n effect seems t o b e f a i r l y c h a r a c t e r i s t i c of t h e ozone a c t i o n u p o n a u t o x i d a t i o n . T h e l o g i c a l m e t h o d of i n v e s t i g a t i o n w o u l d b e t o use o x y g e n - o z o n e m i x t u r e s i n a l l p r o p o r t i o n s , i n c l u d i n g m i x t u r e s h a v i n g e x c e e d i n g l y l o w c o n c e n t r a t i o n s of o x y g e n . A s i t i s n o t possible t o use p u r e ozone as a gas, m i x t u r e s of o x y g e n a n d ozone w e r e u s e d w i t h a n i n e r t gas, n i t r o g e n , i n c o l l a b o r a t i o n w i t h B i e d e r m a n n (7). T h e p r i n c i p a l results are given i n T a b l e I I I . Table III. Mixture composition, % Ozone Oxygen Nitrogen Acid formed, mg. Benzoic acid Perbenzoic acid

a Ν

Effect of O z o n e Dilution 0.9 99

0.8 49-50 49-50

1.0 5 95

1.0 1.2 98-99

361 79 9 4.5

196 71 5.5 2.7

131 33 2 1

107 Traces 1.7 0.8


1

A D V A N C E S IN

192

CHEMISTRY SERIES

T h u s t h e ozone u t i l i z a t i o n b a l a n c e shows t h a t , b y o p e r a t i n g w i t h ozone c o n t a i n i n g less o x y g e n , t h e a m o u n t of p e r b e n z o i c a c i d decreases a n d t e n d s t o r e a c h zero a n d t h a t , parallel to this phenomenon, the values for a n d Ν d r o p so as t o r e a c h a s y m p t o t i c a l l y 1 a n d 0, r e s p e c t i v e l y . T h u s , ozone i n t h e absence of o x y g e n f o r m s a n y a c i d o n l y b y r e a c t i n g w i t h a l d e h y d e ; i t reacts b y m e a n s of i t s a c t i v e o x y g e n o n l y , t h e l i m i t i n g v a l u e f o r b e i n g 1. B u t i f t h e o x y g e n c o n c e n t r a t i o n is v e r y l o w , t h e n u m b e r of m o l e c u l e s m o b i l i z e d f o r a u t o x i d a t i o n c a n also o n l y be l o w . I n c o n t i n u i n g t o p u r s u e i n v e s t i g a t i o n of t h e ozone d i l u t i o n effect, t h e a u t h o r t r i e d t o a s c e r t a i n t h e l i m i t i n g d i l u t i o n f o r w h i c h t h e i n c r e a s e d a u t o x i d a t i o n c o u l d be o b s e r v e d . T a b l e I V is a series of r e s u l t s w h i c h (21) r e f e r t o t h e i n v e s t i g a t i o n of a s o l u t i o n of a

a


Table IV.

Propionaldehyde in C a r b o n Tetrachloride RO 220 380 580 1050 1410 1630

Cos, % 4.2 2.0 1.2 0.43 0.16 0.01

Ν 3.3 5.7 8.7 15.8 21.7 24.4

a 6.6 11.4 17.4 31.6 42.4 48.8

p r o p i o n a l d e h y d e i n c a r b o n t e t r a c h l o r i d e ; t h e r e p r o d u c i b i l i t y of t h e v a l u e s d e t e r m i n e d f o r R O , a, a n d Ν was c o n s i d e r e d s a t i s f a c t o r y . T h e increase i n t h e n u m b e r of m o l e c u l e s m o b i l i z e d f o r a u t o x i d a t i o n p r o c e e d s r e g u l a r l y w i t h ozone d i l u t i o n u n t i l a d i l u t i o n of one v o l u m e ozone i n 10,000 v o l u m e s of o x y g e n — i . e . , C o = 0 . 0 1 % — i s r e a c h e d . I f t h e ozone is d i l u t e d s t i l l f u r t h e r , e s p e c i a l l y b e y o n d 1 v o l u m e of ozone p e r 100,000 v o l u m e s of o x y g e n — C — 0 . 0 0 1 % — s e v e r a l difficulties are e n c o u n t e r e d w h i c h c o u l d n o t be o v e r c o m e c o m p l e t e l y . F i r s t of a l l , t h e a c c u r a t e assay of t h e u n u s e d ozone b e c a m e d i f f i c u l t . I t w a s a s s u m e d , as a first a p p r o x i m a t i o n f o r s i m p l i f i c a t i o n , t h a t a t s u c h s m a l l d i l u t i o n s t h e ozone is u s e d u p c o m p l e t e l y ; t h e r e f o r e , t h e v a l u e s f o r Ν are l o w e r t h a n t h e y s h o u l d be. [This work with v e r y h i g h d i l u t i o n s w a s done i n c o l l a b o r a t i o n w i t h P a p a z i a n (17).1 3

0 3

I n T a b l e V t h e v a l u e s f o r Ν i n t w o series of m e a s u r e m e n t s w i t h b e n z a l d e h y d e i n Table V. Cos in oxygen, % Ν Cos in air, % Ν

Benzaldehyde in C a r b o n Tetrachloride 0.01 180 0.01 70

0.001 980 0.001 500

0.0001 3700 0.0001 1900

0.00001 7000 0.00001 3600

c a r b o n t e t r a c h l o r i d e a r e s h o w n ; t h e first series deals w i t h d i l u t e ozone i n o x y g e n , t h e s e c o n d w i t h d i l u t e ozone i n a i r . T h e s e results s h o w ( e v e n i f o n l y a p p r o x i m a t e l y ) a r e g u l a r p r o g r e s s i o n of t h e d i l u t i o n effect. F u r t h e r m o r e , t h e v a l u e s of Ν o b t a i n e d i n t h e series of e x p e r i m e n t s o n ozone d i l u t e d w i t h a i r are l o w e r t h a n those c o r r e s p o n d i n g t o ozone d i l u t e d w i t h o x y g e n . T h u s , as w a s e x p e c t e d , t h e increase of o x y g e n c o n c e n t r a t i o n is t h e i m p o r t a n t f a c t o r i n t h e d i l u t i o n effects. A t t e m p t s w e r e m a d e t o increase t h e ozone d i l u t i o n f u r t h e r b y u s i n g a i r - o z o n e m i x t u r e s of c o n c e n t r a t i o n s l o w e r t h a n C = 0.00001%. B u t difficulties w e r e e n c o u n t e r e d because of a t m o s p h e r i c o z o n e ; a t t h e a l t i t u d e of G e n e v a (350 t o 400 m e t e r s ) t h e r e is a b o u t 0 . 0 0 0 0 0 1 % of ozone i n t h e a i r . T h u s , t o p r e p a r e s u c h m i x t u r e s of a i r a n d ozone, o r d i n a r y a i r was first d e o z o n i z e d b y p a s s i n g i t t h r o u g h t u b e s h e a t e d t o t e m p e r a t u r e s a b o v e 8 0 0 ° C . F u r t h e r m o r e a n a l d e h y d e reagent w a s u s e d , b u t y r a l d e h y d e d i s s o l v e d i n i s o - o c t a n e , w h i c h is m u c h m o r e s e n s i t i v e t o a u t o x i d a t i o n t h a n b e n z aldehyde i n carbon tetrachloride. 0 3

I n T a b l e V I t h e r e s u l t s of a series of s u c h e x p e r i m e n t s a r e s h o w n ; these e x p e r i -


BRINER—AUTOXIDATION

193

PROCESSES

merits were of a n o r i e n t i n g n a t u r e o n l y , i n v i e w of t h e m a n y e r r o r s t h a t c a n i n t e r v e n e at s u c h e x t r e m e d i l u t i o n s . Table VI.


Cos, % Ν

0.00001 18,000

0.000001 74,000

0.0000001 200,000

T h e o r d e r of increase i n t h e n u m b e r of o x y g e n m o l e c u l e s p a r t i c i p a t i n g i n t h e a u t o x i d a t i o n shows c l e a r l y t h a t t h e d i l u t i o n effect c a n s t i l l be n o t i c e d u n d e r t h e e x t r e m e c o n d i t i o n s a t w h i c h t h e w o r k w a s done. T h e reagent, b u t y r a l d e h y d e i n iso-octane, h a s p r o v e d t o b e e x t r e m e l y s e n s i t i v e t o the a c t i o n of ozone. I t w a s , t h e r e f o r e , u s e d i n studies w i t h P e r r o t t e t (18) f o r ozone measurements i n the atmosphere at various altitudes. A l t h o u g h this m e t h o d is only a p p r o x i m a t e , t h e n u m e r i c a l v a l u e s w i t h i n c r e a s i n g a l t i t u d e a r e of t h e same o r d e r of m a g n i t u d e as those o b t a i n e d b y p h o t o m e t r i c m e a s u r e m e n t s of l i g h t a b s o r p t i o n b y ozone, a r a t h e r exact m e t h o d . A t t h e G o r n e r g r a t , f o r a 3 2 0 0 - m e t e r h e i g h t a n ozone c o n c e n t r a t i o n of 0 . 0 0 0 0 0 3 8 % w a s m e a s u r e d a n d t h e p h o t o m e t r i c g r o u p w o r k i n g a t t h e J u n g f r a u j o c h a t a 3 4 5 0 - m e t e r h e i g h t r e p o r t e d a n ozone c o n c e n t r a t i o n of 0 . 0 0 0 0 0 3 1 % (22). T h i s d i l u t i o n effect i s n o t o n l y f o u n d w i t h a l d e h y d e s . I n e x p e r i m e n t s d o n e w i t h B i e d e r m a n n (8) t h i s r e g u l a r i t y is c o n f i r m e d i n t h e o x i d a t i o n of s o d i u m b i s u l f i t e d o w n to 1 v o l u m e of ozone i n 10,000 v o l u m e s of o x y g e n , C =0.01%. c

Interpretations I n t h i s p a p e r s p e c i a l stress is l a i d o n t h e e x p e r i m e n t a l d a t a , w h i c h c h a r a c t e r i z e t h e a b i l i t y of ozone t o e n t r a i n i t s e l f i n t h e a u t o x i d a t i o n m o l e c u l e s of o x y g e n w h i c h w o u l d h a v e r e m a i n e d i n a c t i v e i f n o ozone w e r e p r e s e n t . T h e f o l l o w i n g i n t e r p r e t a t i o n is b r i e f because t h e h y p o t h e s e s d e v e l o p e d i n t h e a u t h o r ' s l a b o r a t o r y a r e n o t y e t f u l l y satisfactory. I n o r d e r t o e x p l a i n t h e a u t o x i d a t i o n processes, one g e n e r a l l y h a s recourse t o t h e c h a i n - r e a c t i o n m e c h a n i s m , d e p e n d i n g o n t h e existence of h i g h l y u n s t a b l e i n t e r m e d i a t e s often of a h y p o t h e t i c a l n a t u r e o n l y . E x a m p l e s of s u c h u n s t a b l e c o m p o u n d s a r e f o u n d i n t h e p a p e r s b y B o d e n s t e i n o n t h e a u t o x i d a t i o n o f a c e t a l d e h y d e (2) a n d b y H a b e r a n d F r a n c k o n t h e o x i d a t i o n of s o d i u m b i s u l f i t e (26). T h i s m o d e o f e x p l a n a t i o n w a s not p u r s u e d i n t h e p r e s e n t w o r k , as i t w o u l d h a v e n e c e s s i t a t e d t h e a d d i t i o n of n e w h y p o t h e s e s t o e x p l a i n t h e i n c o r p o r a t i o n of t h e ozone m o l e c u l e i n t o t h e p r o p o s e d c h a i n r e a c t i o n s . B u t one m a y c o n s i d e r , i n a s i m p l i f i e d m a n n e r , t h a t ozone s t a r t s t h e c h a i n b y m e a n s of i t s a c t i v e o x y g e n . I t h a s b e e n s t a t e d (27) t h a t p e r o x i d e s , e s p e c i a l l y b e n z o y l p e r o x i d e , a c t as a u t o x i d a t i o n c a t a l y s t s . S i n c e t h e a u t o x i d a t i o n m e c h a n i s m i s so c o m p l e x because of a l l t h e i n t e r v e n i n g f a c t o r s , t h e a u t h o r h a s l i m i t e d h i m s e l f t o c o n s i d e r i n g t h e e n e r g y basis of t h e p r o b l e m (3), w h i c h is m u c h s i m p l e r . O n r e p l a c i n g o x y g e n b y ozone i n t h e o x i d a t i o n one o b t a i n s f o r t h e a c t i v a t i o n e n e r g y of t h e a u t o x i d a t i o n r e a c t i o n a s u p p l e m e n t a r y e n e r g y — n a m e l y , t h e o x i d a t i o n e n e r g y l i b e r a t e d w h e n ozone t r a n s f o r m s i n t o o x y g e n , 3 4 k c a l . p e r g r a m - m o l e of ozone. E x p r e s s e d d i f f e r e n t l y , t h e r e a c t i o n c h a i n s i n d u c e d b y ozone w o u l d t h e n be of a n e n e r g y t y p e . T h i s e n e r g y i n t e r p r e t a t i o n is c o r r o b o r a t e d b y t h e a c c e l e r a t i o n , a l r e a d y r e f e r r e d t o , of t h e a u t o x i d a t i o n b y l i g h t . F o r , as s h o w n b y B a c k s t r o m ( i ) , i t is t h e a b s o r p t i o n of this radiant energy w h i c h initiates the reaction chains. A c c o r d i n g t o this author, h o w ever, t h e a b s o r p t i o n of l i g h t b y t h e a u t o x i d i z a b l e m o l e c u l e t r a n s f o r m s i t i n t o a n u n stable b o d y , a r a d i c a l . T h e m o r e c o m p l e t e l y t h e ozone m o l e c u l e is s u r r o u n d e d b y o x y g e n m o l e c u l e s — i . e . , t h e h i g h e r t h e c o n c e n t r a t i o n of o x y g e n m o l e c u l e s w i t h respect t o ozone m o l e c u l e s — the b e t t e r t h e s u p p l e m e n t a r y e n e r g y is u t i l i z e d . T h i s q u a l i t a t i v e i n t e r p r e t a t i o n of t h e



194

r e a c t i o n p r o b a b l y r e p r e s e n t s t h e l i m i t of o u r p r e s e n t u n d e r s t a n d i n g . T h e r e i s n o d o u b t t h a t other factors enter i n t o p l a y here, especially surface actions w h i c h t h e a u t h o r was l e d t o c o n s i d e r (5) b y o b s e r v i n g t h a t t h e a u t o x i d a t i o n t a k e s p l a c e b e t w e e n gas a n d l i q u i d ; t h i s , a t least i n p a r t , a t t h e s e p a r a t i n g s u r f a c e of these t w o phases.


References (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28)

Bäckström, L., J. Am. Chem. Soc. 49, 1460 (1927). Bodenstein, M., Z. phys. Chem. 12B, 151 (1931). Briner, E., Bull. soc. chim. France 15, 1 (1948). Briner, E., Helv. Chim. Acta 22, 531 (1939). Ibid., 23, 590 (1940). Briner, E., Bever, M. B., Ibid., 19, 369 (1936). Briner, E., Biedermann, E., Ibid., 15, 1227 (1932). Ibid., 16, 548 (1933). Briner, E., Carceller, E., Ibid., 18, 973 (1935). Briner, E., Dallwigk, E., Compt. rend. 243, 630 (1956). Briner, E., Dallwigk, E., Helv. Chim. Acta 39, 1446 (1956). Briner, E., de Chastonay, Ph., Paillard, H., Sper, I., Ibid., 37, 1346 (1954); Compt. rend. 238, 2211 (1954). Briner, E., Demolis, Α., Paillard, H., Helv. Chim. Acta 14, 794 (1931); 15, 201 (1932). Briner, E., Djabri, Ch. el, Paillard, H., Ibid., 21, 95 (1938). Briner, E., Lardon, Α., Ibid., 19, 1062 (1936). Briner, E., Nicolet, S., Paillard, H., Ibid., 14, 804 (1931). Briner, E., Papazian, G., Ibid., 23, 497 (1940). Briner, E., Perrottet, E., Ibid., 20, 294, 458, 1200, 1207 (1937). Briner, E., Ryffel, K., de Nemitz, S., Ibid., 21, 357 (1938). Briner, E., Susz, B., Dallwigk, E., Compt. rend. 234, 1932 (1952). Briner, E., Wenger, P., Helv. Chim. Acta 26, 30 (1943). Chalonge, E., Goetz, P., Vassy, E., Naturwissenschaften, 22, 297 (1934). Criegee, R., Kerckow, Α., Zinke, H., Chem. Ber. 88, 1878 (1955). Dallwigk, E., Briner, E., Helv. Chim. Acta 39, 1926 (1956). Fischer, F., Dull, H., Volz, J., Liebig's Ann. 486, 81 (1931). Haber and Franck, Naturwissenschaften, 19, 450 (1931). Mulcahy, M. R. R., Watt, I. C., Proc. Roy. Soc. 216, 10, 30 (1953). Susz, B., Dallwigk, E., Briner, E., Helv. Chim. Acta 35, 345 (1952). RECEIVED for review June 6, 1957. Accepted June 19, 1957.


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