Oxidation of Organic Compounds


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69 Photo-Oxygenation of Mono-Olefins Reaction Steps Involving the Olefin FRED

A.

LITT

and

ALEX

NICKON

Enjay Additives Laboratory, L i n d e n , N. J., and T h e Johns Hopkins University, Baltimore, M d .

Early studies on photosensitized oxygenation of mono-olefins have shown the non-involvement of mesomeric allylic intermediates, based on the shifting of the position of the double bond during reaction. In this work, six other intermediates, all involving preliminary formation of the C—O bond are considered. Data from the literature are used to disprove formation of some of these, and data are presented ruling out the others. The reaction steps involving the olefin are thus shown to be concerted.

All p r i m a r y p r o d u c t s i s o l a t e d f r o m olefin photo-oxygenations

contain

the u n s a t u r a t i o n i n a p o s i t i o n adjacent to the o r i g i n a l p o s i t i o n , as i l l u s -

^ C — C p = C

3

^

"

^

l

C

H

=

2 ~ ~ ^

C

HOO

Figure 1. Primary products from olefin photo-oxygenations, showing unsaturation in position adjacent to original position t r a t e d i n F i g u r e 1. M e s o m e r i c a l l y l i c intermediates, s u c h as 1, are there-

C

1

C

2

C —^ 3

1 fore p r e c l u d e d . A p a r t i c u l a r l y elegant e x a m p l e of this r u l e is t h e p h o t o o x y g e n a t i o n of o p t i c a l l y active l i m o n e n e ( 2 ) . O n e p r o d u c t of this 118

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N

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Mono-Olefins

D N I C K O N

r e a c t i o n , after r e d u c t i o n , is trans-carweol

2

(3), w h i c h has the absolute

3

stereochemistry i n d i c a t e d , r u l i n g out i n t e r m e d i a c y of species s u c h as the a l l y l i c free r a d i c a l , 4 (8, 9 ) .

4 T h e p h o t o s e n s i t i z e d o x y g e n a t i o n of t h e c h o l e s t e r o l - 7 - d i

molecules

c o n t a i n i n g e p i m e r i c isotopic labels ( 5 a a n d 5 b ) has d e m o n s t r a t e d t h e c y c l i c n a t u r e of t h e r e a c t i o n ; the C — H or C — D b o n d b r o k e n w a s a l w a y s

5a: R = H , R = D 5b: R = D, R = H t

2

x

2

6a: = H 6b: R = D x

the b o n d o n t h e a side of the steroid skeleton, cis to t h e C — O b o n d f o r m e d (11).

A t the time, h o w e v e r , n o conclusions r e g a r d i n g the t i m i n g

of t h e f o r m a t i o n of the C — O a n d O — H b o n d s c o u l d b e d r a w n . T h e species that reacts w i t h the olefin has b e e n v a r i o u s l y c i t e d as singlet o x y g e n a n d as a c o m p l e x b e t w e e n o x y g e n a n d sensitizer. W e find o n l y six reasonable w a y s to c o m b i n e a n olefin w i t h singlet o x y g e n . T h e s e

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possible intermediates are s h o w n i n F i g u r e 2. T h e sensitizer, i f still present, c o u l d b e c o n s i d e r e d b o u n d to the o x y g e n i n some m a n n e r . W h i l e t h e first five intermediates, 7 t h r o u g h 11, c o u l d b e c o n s i d e r e d extreme forms of a resonance h y b r i d , w e are o b l i g e d to consider these structures separately, l a c k i n g a priori i n f o r m a t i o n o n t h e relative c o n t r i ­ b u t i o n s of these forms.

7

10

Figure 2.

8

11

Possible intermediates olefin

9

12

in photo-oxygenation

of

Intermediate 7 w a s first p r o p o s e d b y D . B . S h a r p (14) a n d n a m e d b y h i m a " p e r e p o x i d e . " T h e f o l l o w i n g discussion, r e g a r d i n g the p h o t o o x y g e n a t i o n of a s i m p l e t r i s u b s t i t u t e d olefin, shows that the l i k e l i h o o d of i n v o l v e m e n t of this i n t e r m e d i a t e is s m a l l . I n the p h o t o - o x y g e n a t i o n of a t r i s u b s t i t u t e d olefin, s u c h as t r i m e t h y l ethylene ( 1 3 ) , t w o perepoxides are p o s s i b l e — a si/n-perepoxide ( 1 4 ) , a n d a n a n f i - p e r e p o x i d e ( 1 5 ) — a s s h o w n i n F i g u r e 3. W h i l e 14 c o u l d give either the tertiary h y d r o p e r o x i d e 16 or the secondary h y d r o p e r o x i d e 17, p e r e p o x i d e 15 c o u l d o n l y y i e l d 17. Statistically, therefore, o n l y onef o u r t h of the olefin u n d e r g o i n g r e a c t i o n w o u l d g i v e 16. I n r e a c t i o n of 13, t h e p r e d o m i n a t i n g p e r e p o x i d e s h o u l d b e 15, f o r steric reasons. F u r ­ thermore, i n the r e a c t i o n of 14, i f there is a n y p a r t i a l p o s i t i v e charge o n the oxirane c a r b o n , 17 w o u l d p r e d o m i n a t e since t h e p a r t i a l positive c h a r g e w o u l d b e at a tertiary center rather t h a n a secondary one, as f o r the f o r m a t i o n of 16. T h e r e f o r e the statistical result above is the u p p e r l i m i t r e q u i r e d b y this m e c h a n i s m . T h e o b s e r v e d result w a s that t h e t w o h y d r o p e r o x i d e s w e r e f o r m e d i n e q u a l y i e l d s (8, 9 ) . T h e p h o t o - o x y g e n a ­ t i o n of t r i s u b s t i t u t e d olefins other t h a n 13 t y p i c a l l y also gives n e a r l y

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Mono-Olefins 0" 00H

Figure 3.

Mechanism for photo-oxygenation

of a trisubstituted

e q u a l y i e l d s of secondary a n d tertiary h y d r o p e r o x i d e s ( 1 ) .

olefin

Involvement

of p e r e p o x i d e intermediates is not, therefore, l i k e l y . A n u m b e r of studies h a v e s h o w n that i n c r e a s i n g a l k y l s u b s t i t u t i o n of the d o u b l e b o n d facilitates the r e a c t i o n (9, 10, 14).

I n t e r m e d i a c y of

10 is, therefore, p r e c l u d e d since it requires the opposite substituent effect. N o r b o r n e n e ( 1 8 ) p r o v e d to b e a u s e f u l substrate i n testing for inter­ mediates 8 a n d 9. T h e b r i d g e h e a d h y d r o g e n s are k e p t f r o m p a r t i c i p a t i n g b y the consequent r u l e ) (7).

i n t r o d u c t i o n of a b r i d g e h e a d d o u b l e b o n d

(Bredt's

T h e olefinic l i n k a g e i n n o r b o r n e n e has b e e n s h o w n to b e at

least as reactive to a v a r i e t y of reagents as that of a n a c y c y l i c or m o n o ­ c y c l i c olefins (6).

T h e dioxetane i n t e r m e d i a t e , 19, if f o r m e d w o u l d b e

c a p a b l e of g i v i n g d s - l , 3 - d i f o r m y l c y c l o p e n t a n e , 20.

T h e z w i t t e r i o n inter­

m e d i a t e , 2 1 , if f o r m e d , w o u l d be c a p a b l e of g i v i n g a n y of a host

of

u l t i m a t e p r o d u c t s , t h r o u g h skeletal rearrangements c u s t o m a r i l y associated w i t h the 2 - n o r b o r n o n i u m i o n system

(12).

T h e s e r e a c t i o n paths

are

s h o w n i n F i g u r e 4. W i t h these possibilities i n m i n d w e a t t e m p t e d the p h o t o - o x y g e n a t i o n of n o r b o r n e n e .

W i t h either m e t h y l e n e b l u e or h e m a t o p o r p h y r i n as sen­

sitizer a n d m e t h a n o l or p y r i d i n e as solvent, w e o b t a i n e d no e v i d e n c e of a n y r e a c t i o n b y i n f r a r e d or N M R s p e c t r u m , b y gas c h r o m a t o g r a p h y , or b y spot test for h y d r o p e r o x i d e ( p o t a s s i u m i o d i d e / s t a r c h i n 2 - p r o p a n o l / acetic a c i d ) or p e r o x i d e ( h y d r i o d i c a c i d / s t a r c h i n 2 - p r o p a n o l ) .

While

the h a l f - l i f e of r e a c t i o n of cyclohexene was o n l y a b o u t one d a y u n d e r our r e a c t i o n c o n d i t i o n s , no e v i d e n c e of r e a c t i o n of n o r b o r n e n e w a s o b ­ t a i n e d i n a p e r i o d of one m o n t h . A s s a y of n o r b o r n e n e b y gas c h r o m a ­ t o g r a p h y w i t h b e n z e n e as i n t e r n a l s t a n d a r d f a i l e d to s h o w a n y d e p l e t i o n of n o r b o r n e n e over the a t t e m p t e d r e a c t i o n i n t e r v a l . W h i l e w e f o u n d no e v i d e n c e of a n y r e a c t i v i t y of n o r b o r n e n e ,

the

relevant p o i n t is that the r e a c t i v i t y , if existent, is at least f o u r orders of m a g n i t u d e l o w e r t h a n that of cyclohexene, a s i m i l a r l y s u b s t i t u t e d olefin c o n t a i n i n g reactive

allylic hydrogens.

W e therefore

find

that the d i -

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OOH

Figure 4.

Reaction paths in the photo-oxygenation

oxetane a n d z w i t t e r i o n intermediates

III

OOH

of

norbornene

8 a n d 9, d o not c o n t r i b u t e signifi­

c a n t l y to the p h o t o - o x y g e n a t i o n p a t h of " r e a c t i v e "

olefins.

T h e possible i n v o l v e m e n t of singlet d i r a d i c a l 11 o r triplet d i r a d i c a l 12 w a s tested b y s t u d y i n g t h e p h o t o - o x y g e n a t i o n

of various

cis-trans

olefin pairs as f o l l o w s . F i g u r e 5 indicates a p o t e n t i a l scheme f o r p h o t o -

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A N D NICKON

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Mono-Olefins

o x y g e n a t i o n of a 1,2-disubstituted

olefin.

( T h e scheme w o u l d a p p l y to

r e a c t i o n of a n u n s y m m e t r i c a l t r i - or tetrasubstituted olefin as w e l l . )

The

i m p o r t a n t feature of this sequence is t h e presence of a single b o n d i n the p o s i t i o n of the o r i g i n a l d o u b l e b o n d .

R o t a t i o n a r o u n d this

single

b o n d converts d i r a d i c a l 2 2 , p r o d u c e d b y a d d i t i o n of o x y g e n to t h e cis olefin, to 2 3 , that p r o d u c e d f r o m the trans olefin. If these intermediates w e r e f o r m e d r e v e r s i b l y , the geometric isomers of the olefin w o u l d interconvert d u r i n g r e a c t i o n . W e felt it best to select a n u n r e a c t i v e olefin p a i r f o r this s t u d y since the r e d u c e d r e a c t i v i t y c o u l d reflect the slowness of the final step a n d m a x i m i z e the i s o m e r i z a t i o n p o s s i b i l i t y . T h e c y c l o d o d e c e n e isomers w e r e

Figure 5.

Potential scheme for photo-oxygenation olefin

of a

1,2-disubstituted

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OF ORGANIC

COMPOUNDS

H I

U n d e r the c o n d i t i o n s i n w h i c h cyclohexene r e a c t e d w i t h

a o n e - d a y h a l f - l i f e , t h e h a l f - l i f e o f Jrans-cyclododecene

photo-oxygenation

was about 3 weeks. T h e trans isomer, 24, w a s a b o u t three times as reactive as t h e cis isomer 2 5 . Samples of the c y c l o d o d e c e n e s , separated f r o m a

24

25

c o m m e r c i a l m i x t u r e b y p r e p a r a t i v e gas c h r o m a t o g r a p h y , w e r e separately p h o t o - o x y g e n a t e d w i t h m e t h y l e n e b l u e as sensitizer. A l t h o u g h t h e detec­ t i o n l i m i t of t h e isomer of the starting o l e f i n w a s less t h a n 1 % , r e l a t i v e to the starting isomer, i n n o case w a s i s o m e r i z a t i o n detected. Since i t w a s d e s i r a b l e to i n c l u d e a n o l e f i n w i t h a p a r t i c u l a r l y large d r i v i n g force t o w a r d i s o m e r i z a t i o n w e chose c a r y o p h y l l e n e ( 2 6 ) .

The

frans-cyclononene l i n k a g e of c a r y o p h y l l e n e is r e a d i l y i s o m e r i z e d b y r a d i ­ cals s u c h as t h e n i t r o g e n oxides ( 4 ) . isomerization was apparent. w o u l d have been detected

E v e n i n this case, h o w e v e r , n o

W e c o n f i r m e d that i s o c a r y o p h y l l e n e

26 formed.

(27)

under the reaction conditions h a d it been

27

W e f u r t h e r f o u n d that c a r y o p h y l l e n e w a s a b o u t five times as

reactive as i s o c a r y o p h y l l e n e , a n d therefore, i f i s o c a r y o p h y l l e n e h a d b e e n f o r m e d , i t w o u l d h a v e persisted f o r d e t e c t i o n . T o extend the g e n e r a l i t y of these results, w e e x a m i n e d the p h o t o oxygenation

of trans,

trans,

£rans-l,5,9-cyclododecatriene

28

29

(28).

The

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m o n o i s o m e r i z e d m a t e r i a l ( 2 9 ) f a i l e d to a p p e a r d u r i n g reactions.

Exami­

n a t i o n of the p h o t o - o x y g e n a t i o n of b o t h g e o m e t r i c a l isomers of 4 - m e t h y l 2-pentene a n d 2-octene ( 3 0 t h r o u g h 3 3 ) f a i l e d to s h o w i s o m e r i z a t i o n i n these cases.

30

31

32

33

Q u a n t i t a t i v e l y , unless the p h o t o - o x y g e n a t i o n rate of the isomer n o t i n i t i a l l y present is n e g l i g i b l e c o m p a r e d w i t h t h e p h o t o - o x y g e n a t i o n rate of t h e starting isomer, the d e t e c t i o n l i m i t of t h e i s o m e r i z a t i o n rate constant (as a f r a c t i o n of t h e rate constant f o r p r o d u c t f o r m a t i o n ) is greater t h a n that f o r the isomer i n i t i a l l y absent since, i f f o r m e d , some of the latter w o u l d react b e f o r e detection.

T o evaluate

the d e t e c t i o n l i m i t of the

i s o m e r i z a t i o n rate constant, the d e t a i l e d scheme of F i g u r e 5 is s i m p l i f i e d to give t h e scheme o f F i g u r e 6.

Figure 6.

Simplified scheme for photo-oxygenation a 1,2-disubstituted olefin

of

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R a t e constants i n F i g u r e 6 are r e l a t e d to those i n F i g u r e 5 b y t h e following equations:

* i = j ^ - J [*.*»(*. +

**=

(i)

[*.*-.*.,]

* [i]

k

+ **) + hk.M

=

+

(2)

»)

k

W » ]

+

(4)

where T h e details of this d e r i v a t i o n , b a s e d o n the steady-state a p p r o x i m a t i o n f o r the d i r a d i c a l intermediates, are f o u n d i n the A p p e n d i x . T h e d e r i v a t i o n of the i s o m e r i z a t i o n rate constant u p p e r l i m i t expres­ s i o n is as f o l l o w s . F o r definiteness, assume the starting isomer to h a v e the trans c o n f i g u r a t i o n . U n d e r the h i g h d i l u t i o n c o n d i t i o n s w i t h these r e l a t i v e l y u n r e a c t i v e d i s u b s t i t u t e d olefins w e f o u n d the p h o t o - o x y g e n a t i o n to p r o c e e d b y pseudo-first-order kinetics.

T h e rates of change

concentrations of t h e t w o isomers are g i v e n b y E q u a t i o n s 5 a n d 6. dT/dt=-(k + fc )T + k C 4

s

dC/dt=-(k

2

+ k )C

1

(5) (6)

+ hj

2

of t h e

w h e r e C a n d T represent the concentrations of the cis a n d trans isomers, r e s p e c t i v e l y , a n d t is t i m e . Since t h e experiment shows that fc

4

c o m p a r a b l e w i t h fc , it f o l l o w s that k C 4

2

>> >

x

2

T since C < <

T, and

E q u a t i o n 5 reduces to E q u a t i o n 7, w h i c h integrates to E q u a t i o n 8, i n w h i c h the s u b s c r i p t o indicates the i n i t i a l v a l u e . dT/dt

= -kJ

T

=

(7)

T exp

(8)

0

E q u a t i o n 8 is s u b s t i t u t e d i n t o E q u a t i o n 6, a n d w i t h k

x

> > k , the latter 2

d i f f e r e n t i a l e q u a t i o n is s o l v e d w i t h the i n i t i a l c o n d i t i o n C

0

=

0 to give

E q u a t i o n 9. C =

[exp

(-M)

- exp

(-M)]

(9)

O n e u n f o r t u n a t e aspect of these l o n g - d u r a t i o n photo-oxygenations is that the sensitizer b l e a c h e d at a significant rate d u r i n g the r e a c t i o n a n d h a d to b e r e p l e n i s h e d at intervals. It w a s desirable, therefore, to e l i m i -

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nate t i m e as a v a r i a b l e i n E q u a t i o n 9. I n v e r s i o n of E q u a t i o n 8 expresses the t i m e as a f u n c t i o n of t h e c o n c e n t r a t i o n of the trans olefin, a n d E q u a ­ t i o n 10 results f r o m thus s u b s t i t u t i n g E q u a t i o n 8 i n t o E q u a t i o n 9. C = ^ [ ( T / T

0

)

-

(T/T ) 10

F o r frans-cyclododecene t u m y i e l d m a y b e estimated c o n d i t i o n s , photo-oxygenates

1 1

2 1

^

2

mole/

for 0 ( % ) . +

2

( 2 4 ) , t h e o r d e r of m a g n i t u d e o f t h e q u a n ­ as f o l l o w s .

Cholesterol, under identical

100-200 times as fast as 2 4 . E i s f e l d has

s h o w n that cholesterol photo-oxygenates

at about 1/40 t h e rate of 2,5-

d i m e t h y l f u r a n ( 5 ) , w h i c h i n t u r n has b e e n s h o w n t o photo-oxygenate w i t h a q u a n t u m y i e l d of t h e order of 0.5 ( 9 ) . T h e q u a n t u m y i e l d of frarw-cyclododecene p h o t o - o x y g e n a t i o n is thus about 10" at t h e c o n c e n ­ 4

t r a t i o n s t u d i e d , a b o u t 10~ moles/liter. 2

Schenck a n d K o c h have shown

that t h e species that reacts w i t h t h e olefins decays w i t h a rate constant of a b o u t 1 0 s e c . (13). 8

liters/mole-sec.

1

T h e v a l u e of h

f o r 2 4 therefore is a b o u t 1 0

T h e r e f o r e , f o r t h e *A a n d g

states of o x y g e n , k

s

6

^

130 10

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and 10

sec." , respectively.

1 8

1

O F ORGANIC

COMPOUNDS

T h e s e are, of course,

E y r i n g ' s transition-state v i b r a t i o n a l f r e q u e n c y kT/h. t i o n o f d i r a d i c a l s is, therefore, i m p o s s i b l e .

III

greater t h a n

Irreversible f o r m a ­

W e therefore c o n c l u d e that

the r e a c t i o n of the olefin is c o n c e r t e d . S u p p o r t i n g e v i d e n c e against i r r e v e r s i b l e i n t e r m e d i a t e f o r m a t i o n is f o u n d i n some u n p u b l i s h e d studies b y H . G . V i l h u b e r ( 1 5 ) , E . W e r s t i u k (16), a n d V . C h u a n g ( 3 ) o n the p r i m a r y d e u t e r i u m isotope effect. P r i m a r y isotope effects of 1.2 t o 2.1 w e r e d e t e r m i n e d f o r d e u t e r a t e d olefins 3 4 - 3 6 . D

D

H ) 2

D*

D

2

2

34

i

k

C H

H

CH

3

3

CD

CH

H

3

CD

3

3

CD ^

3

CH

CH

H

3

3

CD CD -v-

35

3

3

CD

3

C H CH

3

36

P a r t i c i p a t i o n o f t h e h y d r o g e n ( o r d e u t e r i u m ) d u r i n g the r a t e - d e t e r m i n i n g r e a c t i o n is thus i n d i c a t e d since, as s h o w n earlier, the O — H b o n d c o u l d not b e f o r m e d p r i o r to f o r m a t i o n of t h e C — O b o n d .

Experimental Photo-oxygenations w e r e p e r f o r m e d i n a t u b u l a r apparatus p r e v i o u s l y r e p o r t e d ( 4 ) . I n t h e p h o t o - o x y g e n a t i o n of the m o r e v o l a t i l e olefins ( 3 0 t h r o u g h 3 3 ) , the solvent w a s saturated w i t h o x y g e n b e f o r e d i s s o l u t i o n of the olefin, a n d n o o x y g e n w a s a d m i t t e d d u r i n g i r r a d i a t i o n . I n the p h o t o o x y g e n a t i o n of t h e slower olefins ( 2 4 , 2 5 , 2 8 ) a 500-watt slide projector was u s e d i n c o n j u n c t i o n w i t h a flat-sided c e l l a n d a c a p i l l a r y b u b b l e r . P r e p a r a t i v e gas c h r o m a t o g r a p h y w a s u s e d to separate the c y c l o d o d e c e n e isomers. A n A e r o g r a p h A - 7 0 0 i n s t r u m e n t w i t h a 20-foot X 3/8 i n c h d i e t h y l e n e g l y c o l succinate polyester c o l u m n at 160 ° C . w a s u s e d . T h e c r u d e fractions w e r e r e c h r o m a t o g r a p h e d to o b t a i n samples of ca. 99.8% purity. cis-2-Octene ( 3 3 ) w a s p u r i f i e d b y p r e p a r a t i v e gas c h r o m a t o g r a p h y i n the same i n s t r u m e n t w i t h a 12 foot X 1/4 i n c h silver n i t r a t e / d i e t h y l e n e g l y c o l c o l u m n at r o o m temperature. T h e p u r i t y of the p r o d u c t w a s ca. 99.9%. trans, trans, tfrans-l,5,9-Cyclododecatriene ( 2 8 ) was isolated b y par­ t i a l f r e e z i n g of the c o m m e r c i a l m i x t u r e of isomers a n d r e c r y s t a l l i z i n g the solid product from methanol. T h e c a r y o p h y l l e n e ( 2 6 ) u s e d c o n t a i n e d about 3 % i s o c a r y o p h y l l e n e ( 2 7 ) ( w e are i n d e b t e d to D r . J . R o b e r t s f o r s u p p l y i n g this s a m p l e ) . A t t e m p t s to r e m o v e this i m p u r i t y b y p r e p a r a t i v e gas c h r o m a t o g r a p h y l e d to n o i m p r o v e m e n t . O t h e r olefins w e r e c o m m e r c i a l samples of > 9 9 % purity. Reactions w e r e m o n i t o r e d b y gas c h r o m a t o g r a p h y . C y c l o d o d e c a n e w a s u s e d as i n t e r n a l s t a n d a r d f o r olefins 2 4 t h r o u g h 29 o n a P e r k i n - E l m e r m o d e l 226 i n s t r u m e n t w i t h a 9 foot X 1 / 8 i n c h d i e t h y l e n e g l y c o l succinate

69.

LITT

Mono-Olefins

A N D NICKON

131

polyester c o l u m n at 150 ° C . B e n z e n e w a s u s e d as i n t e r n a l s t a n d a r d i n t h e p h o t o - o x y g e n a t i o n of 18 a n d 30 t h r o u g h 33 o n a n A e r o g r a p h i n s t r u m e n t w i t h a 10 foot X 1/8 i n c h silver n i t r a t e / d i e t h y l e n e g l y c o l c o l u m n at r o o m temperature.

Acknowledgments W e gratefully acknowledge

financial

tutes of H e a l t h ( G r a n t G M 0 9 6 9 3 ) .

support b y the N a t i o n a l Insti­

T h e w o r k w a s c o n d u c t e d at T h e

Johns H o p k i n s U n i v e r s i t y .

Literature Cited

(1) Benson, S. W., J. Am. Chem. Soc. 87, 972 (1965). (2) Calvett, J. G., Pitts, Jr., J. N., "Photochemistry," p. 91, Wiley, New York, 1966. (3) Chuang, V., Nickon, A., unpublished results. (4) Deussen, E., Lewinsohn, A., Ann. 356, 20 (1907). (5) Eisfeld, W., Ph.D. Dissertation, Göttingen, 1965. (6) Eliel, E. L., "Stereochemistry of Carbon Compounds," p. 303, McGrawHill, New York, 1962. (7) Fawcett, F. S., Chem. Rev. 47, 219 (1950). (8) Foote, C. S., Wexler, R., Ando, W., Tetrahedron Letters 46, 4111 (1965). (9) Gollnick, K., Schenck, G. O., Pure Appl. Chem. 9, 507 (1964). (10) Kopecky, K. R., Reich, H. J., Can. J. Chem. 43, 2265 (1965). (11) Nickon, A., Bagli, J. F., J. Am. Chem. Soc. 83, 1498 (1961). (12) Sargent, G. D., Quart. Rev. 20, 301 (1966). (13) Schenck, G. O., Koch, E., Z. Electrochem. 64, 170 (1960). (14) Sharp, D. B., "Abstracts of Papers," 138th Meeting, ACS, Sept. 1960, 79P. (15) Vilhuber, H. G., Nickon, A., unpublished results. (16) Werstiuk, E., Nickon, A., unpublished results. RECEIVED

February 5, 1968.

Appendix Simplification of isomerization kinetics: T h e c o m p l e t e k i n e t i c scheme f o r i s o m e r i z a t i o n a n d r e a c t i o n is s h o w n i n F i g u r e 5. A s s u m i n g l a n d I* are at steady-state c o n c e n t r a t i o n s : 0

d(l )/dt

= 0=k C

d(l )/dt

= 0 = kT + k\

c

t

a

c

+ kl e

e

- k l

t

a

c

- k l c

- k l

c

e

t

- kl e

t

c

- kl

c

(A-l)

- k l,

(A-2)

b

d

t

w h e r e t is t i m e , C a n d T represent cis a n d trans olefins, I a n d I* represent the intermediates, a n d a l l k's are pseudo-first-order rate constants. c

132

OXIDATION

O F ORGANIC

COMPOUNDS

III

Rearranging Equations A - l and A - 2 U*-a +

+ h) + (-k )I e

t

0

9

d

e

(A-3)

= k T.

(A-4)

a

I (k_ + k + k ) + (-k_ )I t

= k C. c

c

S o l v i n g E q u a t i o n s A - 3 a n d A - 4 s i m u l t a n e o u s l y f o r I a n d I* c

kaP(k_ + k c

+

e

+ &&T c

,

e

^

(*_ +fc_ + * )(fc + *-c + *d) - M . a

e

j

&

c

e

+ fc. + fc ) + k k_ C

k T(k.

e

a

b

a

(A6)

e

+ * ) - M-e

^' '

k k (k +fc_ + k ) + (k k_ k ) (k_ + &_ + (fc_ + fc + — k k.

^ ^^

' ~ (*.. +

+ * ) (* + k. 6

e

d

c

Defining ^

a

b

c

e

d

e

a

a

c

e

d

e

e

e

k k_ k_ n

e

a

*» =

6

c

e

k k.

d

e

kj^ek., , ? r ^ (k_ + k_ + & ) (fc_ + k + a

^

k k (k_ ^-e c

(^-a

&

e

d

e

(A-8)

P

(k_ + &_ + fc ) (fc. + & + k )

c

e

— & fc_ e

e

(A-9) e

H~fc_ + + (k k k ) k ) (k_ -\- k -\- k ) — k k_ a

b

c

c

e

e

d

(A-10)

b

e

e

T h e d e t a i l e d system is k i n e t i c a l l y e q u i v a l e n t t o t h e s i m p l i f i e d system o f F i g u r e 6, dQ/dt=-(k + k )C + fc T (A-ll) x

3

2

+ fc )T +

dT/dt=-(k

4

s

fc C 2

(A-12)

as m a y b e v e r i f i e d b y s u b s t i t u t i n g E q u a t i o n s A - 5 t h r o u g h A - 1 0 into t h e k i n e t i c l a w f o r F i g u r e 5, w h i c h is dC/dt=-k C

+ kI

a

a

dT/dt = -k T c

+ kl

c

c

t