Preparation of Tertiary Amine Oxides by Ozonization - Advances in

Preparation of Tertiary Amine Oxides by Ozonization ALLISON M A G G I O L O and SIGISMUND J. NIEGOWSKI

Downloaded by UNIV OF MISSOURI COLUMBIA on September 24, 2013 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch031

The Welsbach

Corp., Philadelphia, Pa.

It is reported in the early literature that unsymmetrical amine oxides or those of high molecular weight can not be prepared by the action of ozone on the amine. This study shows that an unsymmetrical amine oxide, such as N-ethylpiperidine oxide, a n d a symmetrical high molecular weight amine oxide, such as tri-n -hexylamine oxide, can be prepared by ozonization in methanol solution.

A l t h o u g h t h e f o r m a t i o n o f t e r t i a r y a m i n e oxides u s i n g s u c h a c t i v e o x y g e n reagents as hydrogen p e r o x i d e a n d p e r a c i d s (2) i s w e l l k n o w n , t h e r e a c t i o n w i t h ozone h a s r e c e i v e d l i t t l e a t t e n t i o n . S t r e c k e r a n d B a l t e s (4) e s t a b l i s h e d t h i s r e a c t i o n b y o z o n a t i n g t r i m e t h y l a m i n e a n d i d e n t i f y i n g t h e p r o d u c t as t r i m e t h y l a m i n e o x i d e . I n o z o n a t i n g s u b s t i t u t i o n p r o d u c t s of a m m o n i a , t h e y observed t h a t oxidation b y a d d i t i o n of oxygen occurs o n l y when the substituents o n the nitrogen are similar a n d have a l o w molecular w e i g h t . T h e y s t a t e d t h a t ozone b e h a v e d l i k e t h e o t h e r o x i d a n t s b y f o r m i n g t e r t i a r y a m i n e oxides, b u t differed b y f o r m i n g o n l y a s y m m e t r i c a l l y s u b s t i t u t e d a m i n e o x i d e of low molecular weight. R e p e a t e d a t t e m p t s t o isolate t h e amine oxide f r o m t h e ( o z o n i z a t i o n ) of d i m e t h y l a n i l i n e w e r e u n s u c c e s s f u l . T h e a u t h o r s e x t e n d t h e k n o w l e d g e o f t h e a c t i o n of ozone o n t e r t i a r y a m i n e s a n d show t h a t b o t h a n u n s y m m e t r i c a l l y substituted amine oxide a n d a h i g h molecular weight amine oxide c a n be p r e p a r e d b y ozonization. N - E t h y l p i p e r i d i n e , a n u n s y m m e t r i c a l t e r t i a r y a m i n e , w a s chosen t o test t h e s t a t e m e n t of S t r e c k e r a n d B a l t e s . A l t h o u g h i t s amine oxide h a d been p r e p a r e d t h r o u g h hydrogen peroxide oxidation b y W e r n e r a n d W o l f f e n s t e i n (6), t h e a u t h o r s o z o n a t e d t h e a m i n e i n m e t h a n o l s o l u t i o n a t d r y ice temperature. I t was n o t isolated b u t w a s converted to the picrate, w h i c h c r y s t a l l i z e d o u t of t h e m e t h a n o l s o l u t i o n . A f t e r p u r i f i c a t i o n , t h e a m i n e o x i d e p i c r a t e was identified b y elemental carbon, hydrogen, a n d nitrogen determinations. Perchloric a c i d t i t r a t i o n , a c c o r d i n g t o t h e p r o c e d u r e of C l a r k a n d W a n g (jf), g a v e t h e m i l l i e q u i v a l e n t w e i g h t of t h e i V - e t h y l p i p e r i d i n e o x i d e p i c r a t e . T h e first t h r e e t e r t i a r y a m i n e s i n t h e a l i p h a t i c series w e r e s t u d i e d b y S t r e c k e r and Baltes. T h e authors studied tri-n-butylamine, tri-n-hexylamine, a n d t r i - n - h e p t y l amine. E a c h amine was ozonated a t d r y ice temperature a n d treated w i t h picric acid. T h e t r i - n - b u t y l a m i n e oxide p i c r a t e r e a d i l y d e p o s i t e d as c r y s t a l s o n s t a n d i n g . A l t h o u g h t h e l a t t e r t w o a m i n e oxides f o r m e d o i l y p r o d u c t s a t first, o n l o n g s t a n d i n g i n t h e r e f r i g e r a t o r t h e y g a v e c r y s t a l s o f t h e a m i n e oxide p i c r a t e s . T h e p u r i f i e d a m i n e oxide p i c r a t e s w e r e a n a l y z e d b y d i r e c t t i t r a t i o n w i t h p e r c h l o r i c acid. T h e s t r u c t u r e o f ozone (ό) m a y b e r e p r e s e n t e d as a resonance h y b r i d of f o u r structures: 202

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

203

M A G G I O L O A N D NIEGOWSKI—TERTIARY AMINE OXIDES

δ

ο

ι

ν

δ

ο II

ο III

ν

ο

V

V

IV

S t r u c t u r e s I a n d I I a r e r e p o r t e d as t h e m a i n c o n t r i b u t i n g f o r m s . M e i n w a l d (8) u s e d these t o e x p l a i n t h e a d d i t i o n of ozone t o c e r t a i n olefins. A s i m i l a r m e c h a n i s m c a n b e p o s t u l a t e d t o e x p l a i n t h e r e a c t i o n of ozone o n t e r t i a r y a m i n e s :


R R—N—R

R—N—R I

ο 0—0 +

—

R R — N — R + O,

é

I 0—0

T h e r e a c t i o n m a y b e e x p l a i n e d as a n e l e c t r o p h i l i c a t t a c k o f t h e t e r m i n a l o x y g e n of ozone o n t h e n u c l e o p h i l i c n i t r o g e n t o f o r m a t r a n s i t o r y i n t e r m e d i a t e w h i c h y i e l d s t h e amine oxide. T h e r e a c t i o n of ozone w i t h these t e r t i a r y a m i n e s i s v e r y r a p i d , b u t t h e a d d i t i o n of ozone i s n o t s t o i c h i o m e t r i c : A b o u t 1.2 t o 1.7 m o l e s o f ozone p e r m o l e o f t h e t e r t i a r y a m i n e w e r e u s e d . T h e y i e l d s of t h e a m i n e oxides, i s o l a t e d as t h e p i c r a t e s , w e r e a b o u t 5 0 % of t h e o r y . Experimental O z o n i z a t i o n . T h e ozone w a s g e n e r a t e d f r o m o x y g e n u s i n g t h e W e l s b a c h T - 2 3 ozonator. T h e o x y g e n flow t h r o u g h t h e o z o n a t o r w a s 0.10 c u b i c f o o t p e r m i n u t e . T h e ozone c o n c e n t r a t i o n w a s a b o u t 4 0 m g . p e r l i t e r . T h e a m i n e s o l u t i o n w a s p l a c e d i n a c y l i n d r i c a l glass t u b e , 2 c m . i n d i a m e t e r a n d 30 c m . i n l e n g t h , e q u i p p e d w i t h a f r i t t e d - g l a s s d i s k a t t h e b o t t o m f o r d i s p e r s i n g t h e gas a n d a s t a n d a r d 2 4 / 4 0 j o i n t a t t h e t o p . T h i s r e a c t o r w a s p l a c e d i n a D e w a r cylinder a n d was cooled w i t h a d r y ice-alcohol m i x t u r e . B y frequent careful a d d i t i o n of s m a l l d r y i c e p a r t i c l e s , t h e d e s i r e d t e m p e r a t u r e w a s m a i n t a i n e d w i t h i n 5 ° C . A f t e r passage t h r o u g h t h e a m i n e s o l u t i o n , a n y u n r e a c t e d ozone w a s a b s o r b e d i n 2 % p o t a s s i u m i o d i d e s o l u t i o n c o n t a i n e d i n a gas w a s h i n g b o t t l e . T h e v o l u m e o f t h e o z o n a t e d o x y g e n , passed t h r o u g h t h e s o l u t i o n a n d s t r i p p e d of ozone b y t h e a m i n e solution or potassium iodide solution, was measured w i t h a wet-test meter. T h e r e a c t i o n of ozone w i t h t e r t i a r y a m i n e s w a s so r a p i d t h a t a t a n ozone flow o f 5 6 m g . p e r m i n u t e n o excess ozone a p p e a r e d i n t h e p o t a s s i u m i o d i d e t r a p d u r i n g t h e r e a c t i o n . T h e a d d i t i o n of ozone w a s s t o p p e d w h e n t h e p o t a s s i u m i o d i d e s h o w e d t h e y e l l o w c o l o r due t o i o d i n e . S e v e r a l a t t e m p t s w e r e m a d e t o i s o l a t e t h e a m i n e o x i d e as a h y d r o c h l o r i d e s a l t . U s u a l l y t h e s a l t d i d n o t c r y s t a l l i z e , b u t a h y g r o s c o p i c o i l r e s u l t e d o n e v a p o r a t i o n of the solvent. Isolation was simplified b y using picric acid, f o r t h e picrates crystallized on standing. T h e e x p e r i m e n t a l t e c h n i q u e c o n s i s t e d of o z o n i z a t i o n a t d r y i c e t e m p e r a t u r e i n a s o l v e n t s u c h as m e t h a n o l , i n w h i c h b o t h t h e p i c r i c a c i d a n d a m i n e o x i d e w e r e s o l u b l e , a n d a d d i t i o n of t h e c o l d s o l u t i o n o f a m i n e o x i d e t o t h e a l c o h o l i c s o l u t i o n o f p i c r i c a c i d . O n s t a n d i n g i n t h e r e f r i g e r a t o r , c r y s t a l s of t h e p i c r a t e s e p a r a t e d f r o m t h e s o l u t i o n . T h e s e c r y s t a l s were f i l t e r e d , d r i e d u n d e r a v a c u u m , a n d w e i g h e d . T h e n t h e y were purified from methanol and analyzed. A n a l y s i s . T h e a m i n e o x i d e p i c r a t e s were d e t e r m i n e d a c c o r d i n g t o t h e p r o c e d u r e of C l a r k a n d W a n g . A s a m p l e of 0.2 t o 0.4 m e q . of t h e p i c r a t e w a s d i s s o l v e d i n 10 m l . of g l a c i a l a c e t i c a c i d . A b o u t 3 d r o p s o f m e t h y l v i o l e t i n d i c a t o r w e r e u s e d . T h e c o l o r c h a n g e f r o m deep t o l i g h t b l u e w a s u s e d as t h e e n d p o i n t . T h e s o l u t i o n s w e r e t i t r a t e d w i t h s t a n d a r d 0ΛΝ p e r c h l o r i c a c i d i n g l a c i a l acetic a c i d w i t h a m i c r o b u r e t .


A D V A N C E S IN

204

CHEMISTRY SERIES

Results T h i s procedure was tested using b o t h amine picrates a n d amine oxide picrates. T h e m i l l i e q u i v a l e n t w e i g h t s of t h e p i c r a t e s d e t e r m i n e d w e r e w i t h i n 1% of t h e t h e o retical value. T h e r e s u l t s of p r e p a r i n g a m i n e oxides are s u m m a r i z e d i n T a b l e I. Table I.

Preparation of Amine O x i d e s Oxide Picrate, Meq. Wt.

Compound Ozonated A -Ethylpiperidine° Tri-n-butylamine Tri-n-hexylamine Tri-n-heptylamine


T

Yield % 57.5 57.1 23.2« 48.2

M . P., ° C . 147-9& 110-1 34-6 44-6

Calculated 358 430 515 557 C

« C7HiBNO.CeH2(N0 ) OH, analyzed by Clark Microanalytical Laboratory. 2

b c

3

Calcd. Found

43.56 43.76

Werner and Wolffenstein reported 142-4° C. as the melting point of the amine oxide picrate. First crop of crystals.

Literature

Found 356,360 429, 434 512, 511 558, 554 Η 5.06 4.98

Ν 15.64 15.58, 15.71

Cited

Clark, J. R., Wang, S. M., Anal. Chem. 26, 1230 (1954). Culvenor, C. C. J., Revs. Pure and Appl. Chem. (Australia) 3, 83-114 (1953). Meinwald, J., Chem. Ber. 88, 1889 (1955). Strecker, W., Baltes, M., Ber. deut. chem. Ges. 54, 2693-2707 (1921). Trambarulo, R., Ghosh, S. N., Burrus, C. Α., Jr., Gordy, W., J. Chem. Phys. 21, 851 (1953). (6) Werner, W., Wolffenstein, R., Ber. deut. chem. Ges. 31, 1553 (1898).

(1) (2) (3) (4) (5)

RECEIVED for review June 6, 1957. on reactions of ozone.

Accepted June 19, 1957.

Number II in a series


Preparation of Tertiary Amine Oxides by Ozonization - Advances in

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