Oxidation of Organic Compounds - ACS Publications - American


Oxidation of Organic Compounds - ACS Publications - American...

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Ozonation of Amines PHILIP S. BAILEY, HAROLD M. WHITE

JOHN

E.

KELLER,

DAVID

A.

MITCHARD,

and

University of Texas at Austin, Austin, Tex. 78712

A review of the literature concerning reactions of ozone with amines has given rise to the working hypothesis that these reactions all involve initially the electrophilic attack of ozone to give an adduct for which at least three different reaction routes are available: loss of molecular oxygen to give an amine oxide or further reaction products thereof, an intramolecular oxidation of a side chain, and dissociation to nitrogen cation radicals and the ozonate anion radical, followed by further reactions of these. Results from ozonations of tert-butylamine and tri-n-butylamine, which furnish additional evidence for the above competitions, are described. >Tphe literature suggests several w a y s i n w h i c h ozone reacts w i t h amines. T h e best k n o w n of these is the o z o n a t i o n of t e r t i a r y amines to a m i n e oxides ( I I )

(I).

H e n b e s t a n d S t r a t f o r d (11)

a n d S h u l m a n (17)

have

s h o w n that c o m p e t i n g w i t h this is an ozone attack o n the a l p h a p o s i t i o n of an a l k y l side c h a i n to p r o d u c e various d e c o m p o s i t i o n p r o d u c t s of III. H e n b e s t (11)

s h o w e d that a m i n e oxide f o r m a t i o n is f a v o r e d i n c h l o r o ­

f o r m a n d m e t h a n o l , w h i l e side c h a i n o x i d a t i o n is p r e d o m i n a n t i n h y d r o ­ c a r b o n solvents.

A l s o of c o n s i d e r a b l e interest are the r e p o r t e d conver­

sions, d u r i n g o z o n a t i o n , of p h e n y l e n e d i a m i n e s to W u r s t e r ' s salts

(VII)

(8, 14), of l i q u i d a m m o n i a to a m m o n i u m ozonate ( V A ) at a l o w t e m ­ perature

(18),

a n d of amines to a m i n e h y d r o c h l o r i d e s ( V B )

n a t e d h y d r o c a r b o n solvents (17, 19). azobenzene

i n chlori­

F i n a l l y , a n e a r l y report states that

a n d q u i n o n e are o b t a i n e d u p o n o z o n a t i o n of a n i l i n e

(i5).

T h e e x p e c t e d i n i t i a l r e a c t i o n b e t w e e n ozone a n d amines w o u l d b e a n e l e c t r o p h i l i c ozone attack to g i v e a d d u c t I ( R e a c t i o n 1) ( I ) .

A similar

a d d u c t has a c t u a l l y b e e n o b s e r v e d i n the r e a c t i o n b e t w e e n the n u c l e o p h i l e t r i p h e n y l p h o s p h i t e a n d ozone (20). the reactions

It o c c u r r e d to us that a l l of

d e s c r i b e d above c o u l d be e x p l a i n e d b y c o m p e t i n g fates 58

In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

64.

BAILEY

ET

Ozonization

AL.

of

59

Amines

of a d d u c t I. R e a c t i o n 2 represents the g e n e r a l l y a c c e p t e d d e c o m p o s i t i o n to a n a m i n e o x i d e a n d o x y g e n ( 1 ) , a n d R e a c t i o n 3 is a possible course of the c o m p e t i n g side c h a i n o x i d a t i o n (12).

R e a c t i o n 4 i n v o l v e s the dis­

s o c i a t i o n of the a m i n e - o z o n e a d d u c t to n i t r o g e n c a t i o n r a d i c a l s

(IV)

a n d the ozonate a n i o n r a d i c a l ( A ) . T h e n i t r o g e n c a t i o n r a d i c a l f r o m a

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p h e n y l e n e d i a m i n e w o u l d be resonance s t a b i l i z e d ( V I I ) ;

+ -

R N:

+

77

(i)

R °o N — O — O — O :

+ :'6=d—6:

3

....

that f r o m a n

i

+ ft f-

+ R N—O + 3

R N—O—O—O 3

0

(2)

2

II

la O—O—OH R N

R N=CHR'

CHR'

2

2

OH

I



R N—CHR + 0 2

lb

(3)

2

III 4-

RoN—O—O—O

3

Ic

+

NHR

3

,

:

IV

* or CHC1, N

R

+

R N'

H

-6-6-6:

Rt 3

O—O—O:

(4)

A

£BU

a

(5)

IV

(6)

OH +

VII

In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

60

OXIDATION

a l i p h a t i c a m i n e or a m m o n i a

(IV),

OF

ORGANIC

COMPOUNDS

III

h o w e v e r , m u s t s t a b i l i z e itself

by

a b s t r a c t i n g a h y d r o g e n a t o m f r o m another a m i n e or a m m o n i a m o l e c u l e , or f r o m the solvent ( R e a c t i o n 5 ) . A p o s s i b l e e x p l a n a t i o n for the r e p o r t e d a n i l i n e results i n v o l v e s c o m p e t i n g reactions of the t w o c a n o n i c a l f o r m s of the a n i l i n e c a t i o n r a d i c a l ( R e a c t i o n 6 ) . I n o r d e r to o b t a i n e v i d e n c e f o r or against these ideas w e h a v e b e g u n a n intensive s t u d y of the reactions of ozone w i t h a v a r i e t y of amines.

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T h i s p a p e r s u m m a r i z e s results f r o m the o z o n a t i o n of

tertf-butylamine

and

of t r i - n - b u t y l a m i n e , w h i c h f u r n i s h e v i d e n c e for the c o m p e t i t i o n s

indi­

c a t e d b y Reactions 2, 3, a n d 4.

A d d i t i o n a l details w i l l b e p u b l i s h e d

elsewhere. I n a t y p i c a l r u n , 5 m m o l e s of

terf-butylamine

i n chloroform reacted

w i t h 4.1 m m o l e s of ozone i n a n o z o n e - n i t r o g e n stream at a b o u t — 6 0 ° C . to g i v e 0.9 m m o l e ( 1 8 % ) ( 1 8 % ) of

terf-butyl

butylammonium

of 2 - m e t h y l - 2 - n i t r o p r o p a n e

( X I ) , 0.9 m m o l e

isocyanate ( X V I ) , a n d 3.0 m m o l e s ( 6 0 % ) of tert-

chloride ( X I V ) .

I n a separate b u t s i m i l a r r u n ,

3.5

m m o l e s of m o l e c u l a r o x y g e n w e r e d e t e r m i n e d as a p r o d u c t . U n d e r the conditions

of

terf-butylamine

the

occurred

between

a n d c h l o r o f o r m i n the absence of ozone or

reaction

no

significant r e a c t i o n

between

ozone a n d c h l o r o f o r m i n the absence of the a m i n e . T h e p r o b a b l e r e a c t i o n course to the n i t r o a l k a n e

(XI),

after

the

f o r m a t i o n of the a m i n e - o z o n e a d d u c t ( R e a c t i o n 1 ) , is s h o w n b y R e a c t i o n s 7 to 9 a n d s u m m e d u p i n R e a c t i o n 10.

A p r i m a r y amine oxide w o u l d

not b e expected to b e stable a n d s h o u l d rearrange to the h y d r o x y l a m i n e ( I X , Reaction 7).

A s i m i l a r set of reactions ( R e a c t i o n 8) s h o u l d result

i n the n i t r o s o a l k a n e ( X ) , w h i c h s h o u l d t h e n be c o n v e r t e d to the n i t r o ­ a l k a n e ( X I ) as s h o w n i n R e a c t i o n 9. E v i d e n c e for this series of reactions was the o b s e r v a t i o n of the b l u e color of the n i t r o s o a l k a n e ( X ) t h r o u g h o u t the o z o n a t i o n a n d the d e m o n s t r a t i o n , i n separate experiments, that the h y d r o x y l a m i n e ( I X ) reacts w i t h t w o m o l e e q u i v a l e n t s of ozone a n d the n i t r o s o a l k a n e ( X ) w i t h one m o l e e q u i v a l e n t of ozone, e a c h to g i v e the nitroalkane

(XI).

T h e most l o g i c a l r o u t e f r o m the i n i t i a l ozone a d d u c t ter£-butylammonium

(VIII)

to

c h l o r i d e ( X I V ) is via n i t r o g e n c a t i o n r a d i c a l X I I ,

p r o d u c e d i n m i n u t e , e q u i l i b r i u m amounts t h r o u g h d i s s o c i a t i o n of V I I I (Reaction 11).

I n the case of c h l o r o f o r m solvent, the p r o p o s e d r e a c t i o n

course is s h o w n b y R e a c t i o n s 11 to 15 a n d is s u m m e d u p , w i t h R e a c t i o n 1, i n R e a c t i o n 16.

N i t r o g e n c a t i o n r a d i c a l X I I a p p a r e n t l y stabilizes itself

b y a b s t r a c t i n g h y d r o g e n f r o m a solvent m o l e c u l e to g i v e a m m o n i u m c a t i o n X l V a a n d solvent r a d i c a l X V ( R e a c t i o n 1 2 ) .

T h e ozonate a n i o n

r a d i c a l ( X I I I ) a n d the solvent r a d i c a l ( X V ) t h e n i n t e r a c t to g i v e the chloride anion

(XlVb)

ter£-butylamine

p r o d u c e tert-butyl

a n d phosgene

(Reaction

13).

Phosgene

isocyanate a n d a d d i t i o n a l salt

In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

and

(XIV)

64.

BAILEY

ET

Ozonization

AL.

+ tert-BuNH 0—O—O

• 0

2

of

+ tert-BuNH —O

+

2

61

Amines

2

— »

tert-BuNHOH

VIII

IX H

H

I

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tert-BuNHOH

(7)

+ O

a

I

— * • fert-BuN*—O—O—O" OH

0

+

2

tert-Bu—N*—O" OH (8)



tert-BuN(OH)

+ O

tert-Bu—N=0'



2

«-

s

+ HOH

tert-Bu—N=0:

tert-Bu—N—O—O—O"

0

II

+

2

° tert-BuNH

2

+ 3 0

3



tert-BuN0

(9)

2

XI

ter*-BuN0

2

+ 3 0

2

+ H 0

(10)

2

XI via

Reactions 14 a n d 15.

ter£-butylamine

It was s h o w n separately that phosgene

and

interact to g i v e the isocyanate at the o z o n a t i o n t e m p e r a ­

ture. R e a c t i o n 17 is a s u m m a t i o n of Reactions 10 a n d 16, a s s u m i n g that the t w o fates of a m i n e - o z o n e a d d u c t V I I I o c c u r e q u a l l y . T h e fact that the e x p e r i m e n t a l results d e s c r i b e d earlier agree w e l l w i t h the s t o i c h i o m e t r y of R e a c t i o n 17 increases confidence i n the v a l i d i t y of the p r o p o s e d mechanisms. I n the

o z o n a t i o n of t r i - n - b u t y l a m i n e at

—40°C.

w i t h an

ozone-

n i t r o g e n stream, 1.2 to 1.6 m o l e e q u i v a l e n t s of ozone w e r e a b s o r b e d , a n d the y i e l d s of t r i - n - b u t y l a m i n e o x i d e w e r e 5 3 % f r o m c h l o r o f o r m a n d 6 % f r o m p e n t a n e solvents. T h e other p r o d u c t s w e r e the side c h a i n o x i d a t i o n p r o d u c t s d e s c r i b e d b y H e n b e s t a n d S t r a t f o r d (11).

T h e s e results e l i m i ­

nate the p o s s i b i l i t y that the s i d e c h a i n o x i d a t i o n is a n o z o n e - i n i t i a t e d autoxidation.

T h e m e c h a n i s m o u t l i n e d b y R e a c t i o n 3 explains n i c e l y

b o t h the r e q u i r e m e n t of ozone itself as the o x i d i z i n g agent

and

the

solvent effect o b s e r v e d . Solvents s u c h as c h l o r o f o r m w o u l d be e x p e c t e d to solvate the o z o n e - a m i n e a d d u c t ( l b ) a n d m a k e the a b s t r a c t i o n of the p r o t o n i n R e a c t i o n 3 difficult. T h u s , loss of m o l e c u l a r o x y g e n to g i v e the a m i n e o x i d e becomes the major r e a c t i o n ( R e a c t i o n 2 ) .

I n pentane s o l u -

In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

62

OXIDATION

O F ORGANIC

COMPOUNDS

III

t i o n , n o s o l v a t i o n of l b occurs, a n d the major r e a c t i o n course is as d e s c r i b e d b y R e a c t i o n 3.

+ ^ r f - B u N H 0 0 0 " Z=±

tert-BuNK

2

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O—0—0:

+

2

XII

(H)

XIII

+ ter*-BuNH

4- C H C 1

+

2

-

3

terf-BuNH

XII

-CC1

XlVa

XIII

2

+

3

XV

XV

terf-BuNH

XlVb

+ C1 C=0

2

(12)

3

- tert-BuN—C=0

2

+

tert-BuNH Cl

(14)

3

I I

H

CI XIV

+

tert-BuNK

2

terf-BuN—C=0

» tert-BuN=C=Q

+

+ _

ter*-BuNH Cl 3

(15)

I I H

CI XVI

4

ter*-BuNH

2

+ 0

+ CHC1

3

-

3

XIV

ter*-BuN=G=0

+ 3

+ -

ter*-BuNH Cl 3

+ 0

2

(16) 5 tert-BuNH

2

+ 40

3

ter*-BuNH Cl-

3

+ CHC1

+

3

-

3

+ 40

2

ter*-BuN0

2

+ tert-BuN=C=Q

+

(17)

+H 0 2

Experimental T h e o z o n a t i o n setup a n d p r o c e d u r e s a n d the m e t h o d of d e t e r m i n i n g m o l e c u l a r o x y g e n y i e l d s are d e s c r i b e d i n earlier p u b l i c a t i o n s ( 2 , 3, 4 5, 16). T h e tert-butylamine, t r i - n - b u t y l a m i n e , a n d solvents w e r e t h e best 9

In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

64.

BAILEY

ET AL.

Ozonizotion

of

Amines

63

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grades a v a i l a b l e c o m m e r c i a l l y ; the amines w e r e f u r t h e r p u r i f i e d b y d i s ­ tillation. ter^Butylhydroxylamine ( I X ) ( 9 ) , 2-methyl-2-nitrosopropane ( X ) (10), 2 - m e t h y l - 2 - n i t r o p r o p a n e ( X I ) (13), a n d tert-butyl isocyanate ( X V I ) (6) w e r e p r e p a r e d b y k n o w n literature p r o c e d u r e s . O z o n a t i o n o f tert-Butylamine. I n a t y p i c a l experiment, a s o l u t i o n of 5.0 m m o l e s of ter£-butylamine i n 50 m l . of c h l o r o f o r m was c o o l e d to — 6 0 ° C . a n d treated w i t h a n o z o n e - n i t r o g e n stream c o n t a i n i n g 6 m m o l e s of o z o n e ; the exit gases w e r e a n a l y z e d f o r m o l e c u l a r o x y g e n (4, 5, 16). F r o m the b e g i n n i n g of the o z o n a t i o n a s l i g h t b l u e c o l o r a r i s i n g f r o m the presence of 2 - m e t h y l - 2 - n i t r o s o p r o p a n e ( X ) a p p e a r e d , b u t it was r e p l a c e d at the e n d b y the p u r p l e c o l o r of u n r e a c t e d ozone. A p r e c i p i t a t e of terf-butylammonium c h l o r i d e f o r m e d d u r i n g the o z o n a t i o n . Excess ozone was p u r g e d w i t h n i t r o g e n , a n d it was f o u n d , b y t i t r a t i n g the i o d i d e t r i p , that 4.1 m m o l e s of ozone h a d r e a c t e d . T h e s o l u t i o n above the p r e c i p i t a t e was a n a l y z e d f o r a l l p r o d u c t s except the £er£-butylammonium c h l o r i d e b y a n F a n d M gas c h r o m a t o g r a p h , u s i n g a 1/4-inch X 20 foot c o l u m n containing C a r b o w a x 2 0 M on Chromosorb P. T h e column temperature was 1 2 5 ° C . f o r a l l p r o d u c t s except tert-butyl isocyanate, f o r w h i c h i t was 7 5 ° C . T h e ter£-butylammonium c h l o r i d e y i e l d was d e t e r m i n e d b y d i s s o l v i n g the p r e c i p i t a t e i n w a t e r a n d t i t r a t i n g for c h l o r i d e i o n . O z o n a ­ tions of terf-butylhydroxylamine ( I X ) and 2-methyl-2-nitrosopropane ( X ) were carried out similarly. A q u a n t i t y of 10 m m o l e s of ozone was passed i n t o 50 m l . of c h l o r o ­ f o r m at — 60 ° C , a n d the exit gases w e r e passed into 1 0 % s o d i u m car­ b o n a t e s o l u t i o n . T h e c h l o r o f o r m was also w a s h e d w i t h the carbonate s o l u t i o n , w h i c h was t h e n a c i d i f i e d w i t h n i t r i c a c i d a n d t r e a t e d w i t h silver nitrate. O n l y a f a i n t t u r b i d i t y was p r o d u c e d . W h e n a s o l u t i o n of 50 m l . of c h l o r o f o r m a n d 20 m m o l e s of ter£-butylamine was a l l o w e d to s t a n d at r o o m t e m p e r a t u r e f o r 3 hours, o n l y 5 m g . of ter£-butylammonium c h l o r i d e were produced. O z o n a t i o n o f T r i - w - b u t y l a m i n e . I n a t y p i c a l experiment, solutions of 4.0 grams (21.6 m m o l e s ) of t r i b u t y l a m i n e i n 40 m l . of p u r e p e n t a n e or c h l o r o f o r m w e r e t r e a t e d w i t h 21.6 m m o l e s of ozone at — 4 5 ° C . T h e ozone a b s o r p t i o n was q u a n t i t a t i v e . F o r pentane solvent, the r e a c t i o n m i x t u r e was extracted w i t h w a t e r ( 3 X 1 5 m l . ) at r o o m t e m p e r a t u r e a n d an a l i q u o t of the w a t e r extract was u s e d to d e t e r m i n e the a m i n e o x i d e b y the t i t a n i u m c h l o r i d e m e t h o d ( 7 ) . F o r the c h l o r o f o r m r e a c t i o n m i x ­ ture, the solvent was r e m o v e d u n d e r r e d u c e d pressure, the r e s i d u e w a s d i s s o l v e d i n pentane, a n d the a m i n e o x i d e was d e t e r m i n e d as just de­ s c r i b e d . T h e u n r e a c t e d s t a r t i n g m a t e r i a l a n d side c h a i n o x i d a t i o n p r o d ­ ucts w e r e d e t e r m i n e d w i t h a n A e r o g r a p h M o d e l 1520B gas c h r o m a t o ­ g r a p h , e q u i p p e d w i t h a h y d r o g e n flame detector a n d a d i s k integrator. A 1/8-inch X 10-foot c o l u m n of 3 0 % silicone g u m r u b b e r S E - 3 0 o n C h r o m o s o r b W was u s e d w i t h t e m p e r a t u r e p r o g r a m m i n g f r o m 7 5 ° to 2 5 0 ° C . T h e p r i n c i p a l side c h a i n o x i d a t i o n p r o d u c t s w e r e , i n d e c r e a s i n g o r d e r of i m p o r t a n c e , d i - n - b u t y l a m i n e , 1 - d i - n - b u t y l a m i n o - l - b u t e n e , N,Nd i b u t y l b u t y r a m i d e , a n d N , N - d i b u t y l f o r m a m i d e . T h e r a t i o of ozone re­ a c t i n g to a m i n e r e a c t i n g was 1.2 to 1.6.

In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

64

OXIDATION

OF ORGANIC

COMPOUNDS

III

Acknowledgment T h i s w o r k w a s s u p p o r t e d b y grants f r o m the N a t i o n a l Science F o u n ­ d a t i o n , the R o b e r t A . W e l c h F o u n d a t i o n , a n d the P e t r o l e u m R e s e a r c h F u n d o f the A m e r i c a n C h e m i c a l Society, f o r w h i c h the authors are v e r y grateful.

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RECEIVED

October 20, 1967.

In Oxidation of Organic Compounds; Mayo, F.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.