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2 Discovery, Chemistry, and Application of Hindered Amines 1

2

3

3

E. G. R O Z A N T S E V , E. SH. K A G A N , V. D. S H O L L E , V. B. IVANOV and V. A. SMIRNOV

2

1

2

3

Department of Biochemistry, M T I M M P , Moscow, USSR Polytechnic Institute of Novocherkassk, Novocherkassk, USSR Institute of Chemical Physics of the Academy of Science of the USSR, Moscow, USSR

This chapter i s a comprehensive overview of the progress in the f i e l d of generation, chemistry, and application of nitroxyl radicals and their precursors, for example, hindered amines of the 2,2,6,6-tetramethylpiperidine series. Because of the impor tance of nitroxyl radicals to polymer stabi l i z a t i o n , this application i s discussed at length, while the others are touched upon briefly.

Discovery It is well known from chemical history that the discoveries of the first stable organic radicals, such as triphenylmethyl, diphenylpicrylhydrazyl, tri-tert-butylphenoxyl, and nitroxides are very significant contributions to theoretical chemistry. The relative stabilities of these radicals were attributed by chemists to the participation of an unpaired electron in conjugated 7r-electron systems. Classical stable radicals can thus be thought of as a superposition of many resonance structures with different localizations of an unpaired electron. The first stable radical obtained by Pilotti and Schwerin in 1901 in the pure state can be described by a variety of tautomeric and resonance structures as shown in Scheme 1. The development of the physical organic chemistry of stable radicals stimulated the investigation of relationships between their structures and reactivity. As a result, there developed the widely held concept that organic free radicals which do not possess a system of conjugated multiple bonds, such as 0097-6156/ 85/ 0280-0011 $07.50/ 0 © 1985 American Chemical Society Klemchuk; Polymer Stabilization and Degradation ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

12

POLYMER STABILIZATION AND DEGRADATION

CH

^

3

CH3 — C — CH3

CH

/^N ***

3

CH3—C—CH

3

0' (1)

(2)

(3)

cannot e x i s t under o r d i n a r y c o n d i t i o n s i n a c h e m i c a l l y pure s t a t e . Due t o t h e i r h i g h r e a c t i v i t y , the c o n c e n t r a t i o n s o f such r a d i c a l s d i m i n i s h v e r y r a p i d l y , and t h e i r l i f e t i m e s at room temperature do not o f t e n exceed f r a c t i o n s o f a s e c o n d . Y e t , p a r a d o x i c a l l y enough, i n t h e l a t e F i f t i e s and e a r l y S i x t i e s , the f i r s t f r e e r a d i c a l s i n a c h e m i c a l l y pure s t a t e were o b t a i n e d and though they d i d not p o s s e s s c o n j u g a t e d m u l t i p l e b o n d s , t h e y were e x t r e m e l y s t a b l e under o r d i n a r y c o n d i t i o n s . These b r i g h t l y c o l o r e d c r y s t a l l i n e r a d i c a l s d i d not change t h e i r p h y s i c a l and c h e m i c a l c h a r a c t e r i s t i c s f o r months, even when s t o r e d i n a i r at room temperature. In t h e s e new r a d i c a l s , t h e u n p a i r e d e l e c t r o n does not p a r t i c i p a t e i n m u l t i p l e bond systems a n d , t h e r e f o r e , i t i s e s s e n t i a l l y l o c a l i z e d at the n i t r o g e n - o x y g e n bond ( 1 , 2 ) .

C0NH

2

A-

(A)

(5)

(6)

(7)

T h u s , i t was e x p e r i m e n t a l l y demonstrated t h a t a whole c l a s s o f s t a b l e f r e e r a d i c a l s does e x i s t , even though " t h e o r e t i c a l l y " t h e y are u n l i k e l y t o e x i s t under o r d i n a r y c o n d i t i o n s . From t h e S i x t i e s the i n t e r e s t i n the new r a d i c a l s by c h e m i s t s , p h y s i c i s t s and b i o l o g i s t s has been r a p i d l y i n c r e a s i n g . A f t e r t h e f i r s t p u b l i c a t i o n o f h i s p a p e r , one o f the a u t h o r s o f the p r e s e n t communication r e c e i v e d more t h a n a thousand i n q u i r i e s from many European c o u n t r i e s and A m e r i c a , and i n 1965 s e v e r a l independent r e s e a r c h groups and l a b o r a t o r i e s d e a l i n g w i t h d i f f e r e n t a s p e c t s o f the new r a d i c a l c h e m i s t r y a p p e a r e d . U n l i k e t h e c l a s s i c a l n i t r o x i d e s such as p o r p h y r e x i d e and o t h e r d e r i v a t i v e s o f q u a d r i v a l e n t n i t r o g e n , t h e new r a d i c a l s , c a l l e d n i t r o x y l s ( o r i m i n o x y l s ) c o u l d undergo r e a c t i o n s w i t h o u t involvement of the r a d i c a l s i t e . In 1961, E . G . Rozantsev and Y u . G . Mamedova were t h e f i r s t t o r e a l i z e t h e " n o n - r a d i c a l r e a c t i o n s o f f r e e r a d i c a l s " ( 3 , 4 ) ; e . g . , the formation of 2 , 2 , 6 , 6 - t e t r a m e t h y l - 4 o x o p i p e r i d i n e - l - o x y l oxime w i t h o u t c h e m i c a l involvement o f t h e f r e e

Klemchuk; Polymer Stabilization and Degradation ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

2.

ROZANTSEV ET AL.

radical

Hindered Amines: Discovery, Chemistry, and Application 13

site: 0

N-OH

(8) T h i s and some o t h e r n o n - r a d i c a l r e a c t i o n s o f r a d i c a l s were t h e o r e t i c a l l y p r e d i c t e d by Neiman back i n t h e f i f t i e s . B u t , to o b t a i n t h e s t a r t i n g s t a b l e r a d i c a l s ( 5 , 6 ) , i t was n e c e s s a r y above a l l to o b t a i n v a r i o u s s t e r i c a l l y h i n d e r e d a m i n e s . Consequently, the development o f s t a b l e n i t r o x y l c h e m i s t r y i n s p i r e d g r e a t i n t e r e s t i n hindered amines. It i s i n t e r e s t i n g t o note t h a t t h e f i r s t s t e r i c a l l y h i n d e r e d amine, c a l l e d " t r i a c e t o n a m i n e , was d e s c r i b e d as f a r back as 1874 b y two R u s s i a n c h e m i s t s , S o k o l o f f and L a c h i n o f f (7) and by a German c h e m i s t , H e i n t z ( 8 ) , whose works were p u b l i s h e d almost s i m u l t a n e o u s ly. The f i r s t s y n t h e s e s o f t r i a c e t o n a m i n e were based on t h e r e a c t i o n o f acetone w i t h ammonia. T h u s , t r i a c e t o n a m i n e became a c c e s s i b l e even though the y i e l d d i d not exceed 8%. At p r e s e n t , along w i t h a c e t o n e , some o t h e r s t a r t i n g m a t e r i a l s (9) such as d i acetone a l c o h o l , 2,2,4,4,6-pentamethyl-2,3,4,5-tetrahydropyrimidine and phorone a r e used f o r t h e s y n t h e s i s o f t r i a c e t o n a m i n e . I t i s not s u r p r i s i n g t h a t at the o u t s e t almost a l l h i n d e r e d amines n e c e s s a r y f o r t h e s y n t h e s i s o f v a r i o u s h i n d e r e d n i t r o x y l r a d i c a l s were o b t a i n e d from t r i a c e t o n a m i n e ( 1 0 - 1 2 ) . In 1962, u t i l i z a t i o n o f the new n i t r o x y l r a d i c a l s was suggested f o r i n h i b i t i o n o f o x i d a t i v e d e g r a d a t i o n o f t h e r m o p l a s t i c polymers (13). In 1965, M c C o n n e l l p u b l i s h e d h i s e a r l y work which l a i d t h e f o u n d a t i o n f o r a p p l i c a t i o n o f t h e new r a d i c a l s and t h e i r n o n - r a d i c a l r e a c t i o n s i n t h e s p i n - l a b e l method ( 1 4 ) . 1 1

Synthesis A c t u a l l y , t r i a c e t o n a m i n e s t i l l remains t h e o n l y s t a r t i n g compound f o r t h e s y n t h e s i s o f 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e d e r i v a t i v e s . The main methods o f i t s p r e p a r a t i o n a r e g i v e n i n Scheme 2. A summary o f methods o f s y n t h e s i s f o r t r i a c e t o n a m i n e and o t h e r h i n d e r e d p i p e r i d i n e s a r e summarized i n ( 1 5 ) . A h i g h l y e f f i c i e n t method o f p r o d u c i n g t r i a c e t o n a m i n e from acetone and ammonia t h r o u g h E q u a t i o n (4) was d e v e l o p e d i n the USSR (16). The c o s t o f t r i a c e t o n a m i n e produced on t h e b a s i s o f t h i s t e c h n o l o g y on a p i l o t p l a n t s c a l e i s a p p r o x i m a t e l y $10 p e r k i l o g r a m which i s s i g n i f i c a n t l y lower t h a n t h a t i n t h e A l d r i c h c a t a l o g (1982) o f c h e m i c a l s and i n t e r m e d i a t e s . By now a l a r g e number o f 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e d e r i v a t i v e s has been p r e p a r e d . These a r e m o s t l y compounds h a v i n g s u b s t i t u e n t s i n t h e f o u r - p o s i t i o n o f a p i p e r i d i n e r i n g , and t h e i r



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3

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(1)

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Scheme 2 .

R e a c t i o n s f o r the s y n t h e s i s

(5)

of

triacetonamine.


2.

ROZANTSEV ET AL.


s t r u c t u r e s show t h e i r c l o s e s t r u c t u r a l r e l a t i o n s h i p t o triacetonamine. A l t h o u g h t r i a c e t o n a m i n e has some s t r u c t u r a l p e c u l i a r i t i e s , i t undergoes many r e a c t i o n s t y p i c a l o f o r d i n a r y p i p e r i d i n e s (17) . D e t a i l e d i n f o r m a t i o n on t r i a c e t o n a m i n e c h e m i s t r y and s y n t h e s i s methods f o r 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e d e r i v a t i v e s can be found elsewhere ( 1 8 , 1 9 ) . The most important 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e d e r i v a t i v e s (Scheme 3) were s y n t h e s i z e d from t r i acetonamine (9) o r k e t o n e - r a d i c a l (5) i n one o r more s t e p s t h r o u g h t y p i c a l t r a n s f o r m a t i o n s o f the ketone c a r b o n y l g r o u p . The m a j o r i t y o f t h e w e l l known compounds i n t h e 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e s e r i e s was g e n e r a t e d from ( 1 0 , 11, 14). The most numerous ones a r e a l c o h o l e s t e r s ( 1 0 ) , amides and o t h e r amine d e r i v a t i v e s ( 1 1 ) . E l e c t r o c h e m i c a l methods f o r t h e s y n t h e s i s o f s e v e r a l i m p o r t a n t t r i a c e t o n a m i n e d e r i v a t i v e s have been e l a b o r a t e d r e c e n t l y ; e . g . , t h e e l e c t r o d e r e a c t i o n s shown b e l o w :

E l e c t r o c h e m i c a l methods f o r o b t a i n i n g t h e s i m p l e s t 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e d e r i v a t i v e s shown i n t h e scheme were a d v a n t a g e o u s l y used b y t h e a u t h o r s . E l e c t r o c h e m i c a l methods o f 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e p r e p a r a t i o n have u n d e n i a b l e advantages over t h e method based on t h e r e d u c t i o n o f t r i a c e t o n a m i n e by h y d r a z i n e at 150 - 200°C ( 2 5 ) . The r e a c t i o n s o f t h e a - m e t h y l e n e group ( p o s i t i o n s 3 and 5 ) , u n l i k e t h e r e a c t i o n s o f t h e c a r b o n y l g r o u p , a r e u n u s u a l and o c c u r under f o r c i n g c o n d i t i o n s . Some o f t h e s e r e a c t i o n s at p o s i t i o n 3 a r e g i v e n i n Scheme 4 . More d e t a i l e d i n f o r m a t i o n i s g i v e n i n ( 2 6 , 2 7 ) . R e a c t i o n s o f enamine (20) w i t h Mannich b a s e s , w i t h e s t e r s o f a, ) 8 - u n s a t u r a t e d a c i d s and w i t h a c r y l o n i t r i l e t a k e p l a c e under more s e v e r e c o n d i t i o n s as compared t o t h e s i m i l a r r e a c t i o n s o f c y c l o h e x a n e enamines. Enamines (20) do not undergo t h e r e a c t i o n s o f a c y l a t i o n and a l k y l a t i o n ; but t h e Mannich r e a c t i o n , t h a t o f b r o m i n a t i o n and t h e F a v o r s k i i rearrangement a r e u n e x p e c t e d l y e a s y . No o t h e r methods f o r i n t r o d u c i n g s u b s t i t u e n t s i n t o p o s i t i o n 3 o f t r i a c e t o n a m i n e , but those i n d i c a t e d i n Scheme 4, a r e known.



Scheme 3 . Most i m p o r t a n t h i n d e r e d amine s t r u c t u r e s from t r i a c e t o n a m i n e .

derived


ROZANTSEV ET AL.

Hindered Amines: Discovery, Chemistry, and Application


18


3 - F o r m y l - 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e - l - o x y l o b t a i n e d by t h e r e a c t i o n g i v e n below c o u l d have been o f g r e a t importance f o r t h e synthesis chemistry of 2 , 2 , 6 , 6 - t e t r a m e t h y l p i p e r i d i n e derivatives. B u t , a f t e r i t s s y n t h e s i s had been r e p o r t e d , t h e r e i s no e v i d e n c e o f its u t i l i z a t i o n (28).

0

0

I. 0 Chemistry o f N i t r o x y l Radicals There i s no need t o g i v e a thorough d e s c r i p t i o n o f t h e c h e m i s t r y o f h i n d e r e d n i t r o x y l r a d i c a l s as i t has been f u l l y d i s c u s s e d i n a number o f summaries i n c l u d i n g t h e papers w r i t t e n by t h e a u t h o r s o f the p r e s e n t communication (18,19 , 2 9 - 3 7 ) . T h i s paper i s aimed at g i v i n g some g e n e r a l c h a r a c t e r i s t i c s o f the c h e m i c a l p r o p e r t i e s o f n i t r o x y l r a d i c a l s and the methods f o r t h e i r s y n t h e s i s . N i t r o x y l r a d i c a l s have e x t r a o r d i n a r i l y h i g h s t a b i l i t y . N e v e r t h e l e s s , under some c o n d i t i o n s they behave as f r e e r a d i c a l s . H i n d e r e d n i t r o x y l r a d i c a l s recombine w i t h a c t i v e a l k y l r a d i c a l s to^givg hydroxylamine e t h e r s . The r a t e o f t h i s r e a c t i o n amounts t o 10 - 1 0 L / m o l . s e C . ; i . e . , n i t r o x y l s are e f f i c i e n t acceptors of a l k y l r a d i c a l s ; they a l s o react v i g o r o u s l y with h y d r o x y l r a d i c a l s (37-38). >N'-0

+

R-

>N-0

+

'OH

>N-0R

N

>N^ OH

The most c h a r a c t e r i s t i c r e a c t i o n o f h i n d e r e d n i t r o x y l s i s t h e i r r e d u c t i o n which r e s u l t s e i t h e r i n the c o r r e s p o n d i n g h y d r o x y l a m i n e o r amine. H y d r o x y l a m i n e s , as a r u l e , a r e r e a d i l y o x i d i z e d t o t h e c o r responding r a d i c a l s . O x i d a t i o n c a n be a c c o m p l i s h e d w i t h atmospheric oxygen i n t h e p r e s e n c e o f c a t a l y t i c amounts o f heavy m e t a l s a l t s ; e . g . , cupric s a l t s . PbC^ and K^[Fe(CN)^] c a n a l s o be used as o x i d i z i n g agents. This e a s i l y occuring t r a n s f o r m a t i o n - r a d i c a l —> h y d r o x y l a m i n e —> r a d i c a l - i s the b a s i s f o r s e v e r a l i m p o r t a n t s y n t h e s e s , i n p a r t i c u l a r , e l e c t r o c h e m i c a l s y n t h e s e s o f the n i t r o x y l r a d i c a l s (4) and (6) ( 3 9 , 4 0 ) :

OH 2e, 2 H

I OH

+

[0] N I • 0 (6)


2.

ROZANTSEV ET AL.


(4) Photoexcitation increases n i t r o x y l r e a c t i v i t y appreciably. The p h o t o c h e m i c a l r e a c t i o n o f the r a d i c a l (6) w i t h t o l u e n e y i e l d s q u a n t i t a t i v e l y t h e c o r r e s p o n d i n g h y d r o x y l a m i n e and i t s b e n z y l e t h e r (41). T h i s r e a c t i o n s i m u l a t e s t o a c e r t a i n e x t e n t the p r o c e s s o f polymer s t a b i l i z a t i o n by n i t r o x y l r a d i c a l s .

(5)

Though r e d u c t i o n o f t h e n i t r o x y l group o c c u r s q u i t e r e a d i l y , t h e r e are agents which a c h i e v e r e d u c t i o n o f o t h e r groups w i t h o u t i n v o l v i n g paramagnetic c e n t e r s . Examples o f such r e a c t i o n s are g i v e n below:

OH NaBH,

0*

•a

NaBELCN


19

20


In a c i d medium, n i t r o x y l r a d i c a l s d i s p r o p o r t i o n a t e h y d r o x y l a m i n e s and oxoammonium s a l t s .

2

>N-0

+

2 HX

>>N^O*X"

to

+ >1*

produce

• x" ^DH

The mechanism o f t h i s r e a c t i o n i s c o n s i d e r e d i n (42) . At pH 1, t h e e q u i l i b r i u m o f t h i s r e a c t i o n i s s h i f t e d t o t h e r i g h t ; at pH 3, t o the l e f t . T h i s means t h a t n i t r o x y l r a d i c a l s a r e weak b a s e s , much weaker t h a n t h e c o r r e s p o n d i n g a m i n e s . This p r o p e r t y f a c i l i t a t e s the s e p a r a t i o n o f amines from r a d i c a l s b y e x t r a c t i n g an amine w i t h d i l u t e h y d r o g e n c h l o r i d e (pH 2-3) . T h i s method o f r a d i c a l p u r i f i c a t i o n i s used f o r p r e p a r a t o r y p u r p o s e s . Oxoammonium s a l t s a r e s t r o n g o x i d i z i n g agents; i n f a c t , the o x i d i z i n g p r o p e r t i e s of n i t r o x y l r a d i c a l s i n a c i d medium a r e a s s o c i a t e d w i t h oxoammonium s a l t s . For example, i n a c i d medium, r a d i c a l s o x i d i z e a l c o h o l s t o t h e corresponding aldehydes.

S t r o n g o x i d a n t s such as c h l o r i n e and bromine o x i d i z e r a d i c a l s t o c o r r e s p o n d i n g oxoammonium s a l t s (30):

2

Developments

>N*-0

+

CI

2

i n Nitroxyl Radical

>

;>N=O

nitroxyl

CI

Synthesis

The u n u s u a l c h a r a c t e r i s t i c s o f t h e n i t r o x y l group d e t e r m i n e t h e methods o f n i t r o x y l r a d i c a l s y n t h e s i s . Here a r e t h e major ways o f their synthesis. 1.

O x i d a t i o n o f the corresponding hindered p i p e r i d i n e s . This s y n t h e s i s t e c h n i q u e c a n be used o n l y when t h e s t a r t i n g p i p e r i d i n e c o n t a i n s an H-atom on n i t r o g e n . This c o n d i t i o n r e s t r i c t s the a p p l i c a t i o n o f the method t o t h e most s i m p l e n i t r o x y l r a d i c a l s of the p i p e r i d i n e s e r i e s . The h y d r o g e n p e r o x i d e - s o d i u m t u n g s t a t e system i s most o f t e n used f o r p i p e r i d i n e o x i d a t i o n . The mechanism and k i n e t i c s o f t h i s r e a c t i o n a r e d e s c r i b e d i n (43). The t e c h n i q u e s o f h i n d e r e d p i p e r i d i n e s y n t h e s i s a r e constantly improving. T a k e , f o r example t h e method o f 2 , 2 , 6 , 6 -


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ROZANTSEV ET AL.


t e t r a m e t h y l - 4 - p i p e r i d i n o l o x i d a t i o n which makes i t p o s s i b l e t o o b t a i n the c o r r e s p o n d i n g r a d i c a l w i t h 98% y i e l d i n two h o u r s (44). T r i a c e t o n a m i n e and 2 , 2 , 6 , 6 - t e t r a m e t h y l - 4 - p i p e r i d i n o l are o x i d i z e d by the hydrogen p e r o x i d e - s o d i u m c a r b o n a t e system v e r y s e l e c t i v e l y , g i v i n g p r a c t i c a l l y a q u a n t i t a t i v e y i e l d (45). For amine o x i d a t i o n , the hydrogen p e r o x i d e - a c e t o n i t r i l e system i s o f t e n e f f e c t i v e enough ( 4 6 , 4 7 ) , w h i l e f o r h i n d e r e d p i p e r i d i n e o x i d a t i o n , p e r a c i d s can be a l s o u s e d . 2.

R e a c t i o n s which do not i n v o l v e the r a d i c a l s i t e . T h i s i s the most s i g n i f i c a n t c l a s s o f h i n d e r e d n i t r o x y l r e a c t i o n s . These r e a c t i o n s r e p r e s e n t a c h e m i c a l b a s i s f o r the s p i n - l a b e l method. The s i m p l e s t h i n d e r e d n i t r o x y l s , such as those i n d i c a t e d i n Scheme 3, a r e commonly used as the s t a r t i n g compounds. Some o f t h e s e r a d i c a l s are c o m m e r c i a l l y a v a i l a b l e i n s e v e r a l c o u n t r i e s . Many s e l e c t i v e r e a g e n t s are known at p r e s e n t which do not i n t e r act with a n i t r o x y l group. So, t o c a r r y out a new s y n t h e s i s , you have o n l y t o choose a p r o p e r reagent f o r the g i v e n r e a c t i o n u s i n g recommendations r e p o r t e d i n the s c i e n t i f i c l i t e r a t u r e and c a r r y out t h e r e a c t i o n .

3.

Hydroxylamine u t i l i z a t i o n . In t h o s e c a s e s where i t i s i m p o s s i b l e t o p r e s e r v e the r a d i c a l c e n t e r t h r o u g h a l l the s t a g e s o f s y n t h e s i s , i t can be c o n v e r t e d to the c o r r e s p o n d i n g h y d r o x y l amine. The l a t t e r as mentioned e a r l i e r , u n l i k e n i t r o x y l r a d i c a l s , i s s t a b l e i n a c i d i c medium and i s reduced at a h i g h e r potential. S e v e r a l examples o f h y d r o x y l a m i n e u t i l i z a t i o n f o r r a d i c a l s y n t h e s i s from the a u t h o r s ' e x p e r i e n c e a r e g i v e n on p. 18 and below ( 4 8 ) .

H 2 CI

NaOH

Application The i n v e s t i g a t i o n s u n d e r t a k e n w i t h the purpose o f s t u d y i n g the c h a r a c t e r i s t i c s o f r a d i c a l s r e s u l t e d i n wide p r a c t i c a l a p p l i c a t i o n o f the l a t t e r . N i t r o x y l r a d i c a l s are used i n b i o c h e m i s t r y , o r g a n i c


22


c h e m i s t r y , h i g h m o l e c u l a r weight compound c h e m i s t r y , a n a l y t i c a l c h e m i s t r y and m e d i c i n e , and t h e range o f t h e i r a p p l i c a t i o n i s steadily increasing. H i n d e r e d n i t r o x y l s have found t h e i r w i d e s t a p p l i c a t i o n i n t h e s p i n - l a b e l method w i d e l y used i n b i o p h y s i c a l r e s e a r c h . As has a l r e a d y been m e n t i o n e d , t h i s method was d e v i s e d i n t h e c o u r s e o f n i t r o x y l c h e m i s t r y development when t h e r e a c t i o n s o f t h e r a d i c a l s o f t h i s c l a s s , not i n v o l v i n g a n i t r o x y l g r o u p , were d i s c o v e r e d . S e v e r a l monographs and many r e v i e w papers w i t h a t o t a l number o f more t h a n one thousand pages a r e devoted t o t h e s p i n - l a b e l method (35-39,49,50). These communications c o v e r a l l t h e a s p e c t s o f h i n d e r e d n i t r o x y l a p p l i c a t i o n i n t h i s method. T h e r e f o r e , the s p i n - l a b e l method i s not d i s c u s s e d h e r e at l e n g t h . Another important f i e l d o f the a p p l i c a t i o n o f n i t r o x y l r a d i c a l s and t h e i r p r e c u r s o r s , h i n d e r e d a m i n e s , i s t h e p r o t e c t i o n o f polymers and o t h e r o r g a n i c compounds a g a i n s t t h e f a c t o r s c a u s i n g t h e i r t h e r m o - and p h o t o - d e s t r u c t i o n . In t h e p r e s e n t work, an attempt has been made t o d e s c r i b e b r i e f l y t h e main achievements i n t h i s f i e l d . In c o n c l u s i o n , we s h a l l c o n s i d e r some o t h e r f i e l d s o f n i t r o x y l radical application. Polymer S t a b i l i z a t i o n " H i n d e r e d amine s t a b i l i z e r s have been the s i n g l e most important development o f t h e l a s t decade i n polymer s t a b i l i z a t i o n " P e t e r P . Klemchuk. The p o s s i b i l i t y o f s t a b i l i z i n g polymers w i t h h i n d e r e d n i t r o x y l r a d i c a l s i s based on t h e i r r e a c t i o n w i t h polymer r a d i c a l s which a r e engaged i n p r o p a g a t i n g polymer o x i d a t i o n . It was e s t a b l i s h e d t h a t hindered amines, the p r e c u r s o r s of n i t r o x y l r a d i c a l s , are a l s o e f f e c t i v e p h o t o s t a b i l i z e r s a n d , as s u c h , t h e y a r e more e f f e c t i v e t h a n most o f t h e common p h o t o s t a b i l i z e r s f o r p o l y m e r s . Complete i n f o r m a t i o n on s t r u c t u r e and a c t i o n mechanisms o f s t a b i l i z e r s based on h i n d e r e d amines c a n be found i n ( 3 8 , 5 2 - 5 6 ) . Here a r e p r e s e n t e d o n l y modern t r e n d s i n t h e c h e m i s t r y o f p h o t o - and t h e r m o s t a b i l i z e r s based on h i n d e r e d a m i n e s , t h e mechanisms o f t h e i r a c t i o n and t h e methods o f s e l e c t i n g s t a b i l i z i n g c o m p o s i t i o n s , i n c l u d i n g m i x t u r e s o f h i n d e r e d amines w i t h o t h e r c l a s s e s o f stabilizers. In Scheme 5 a r e g i v e n t h e s t r u c t u r e s o f some 2,2,6,6-tetramethylpiperidine d e r i v a t i v e s which a r e e f f e c t i v e p o l y mer s t a b i l i z e r s . The a n a l y s i s o f t h e s t r u c t u r e s o f t h e s e compounds a l l o w s t h e f o r m u l a t i o n o f t h e d e s i g n p r i n c i p l e s o f polymer s t a b i l i z e r s based on h i n d e r e d amines i n g e n e r a l and h i n d e r e d p i p e r i d i n e s i n p a r t i c u l a r (38,51) . Data on h i n d e r e d amine s t r u c t u r e s as polymer s t a b i l i z e r s l e a d t o the f o l l o w i n g c o n c l u s i o n s about the development o f r e s e a r c h i n t h i s field: 1.

Methods a r e b e i n g e l a b o r a t e d f o r s y n t h e s i z i n g m u l t i f u n c t i o n a l s t a b i l i z e r s c o m p r i s i n g i n one m o l e c u l e the fragments o f e i t h e r h i n d e r e d amine o r a n i t r o x y l r a d i c a l and UV a b s o r b e r , o r g a n i c p h o s p h i t e , hindered p h e n o l , t h i o e t h e r , metal d e r i v a t i v e , e s p e c i a l l y those of n i c k e l , e t c . The i n t r o d u c t i o n o f a UV a b s o r b e r fragment u s u a l l y r e s u l t s i n i n c r e a s e d e f f e c t i v e n e s s o f p h o t o p r o t e c t i v e a c t i o n because a


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d i f f e r e n t s y n e r g i s t i c mechanism o p e r a t e s between UV a b s o r b e r and a n t i o x i d a n t , and the UV a b s o r b e r fragment can quench the e x c i t e d s t a t e o f the n i t r o x y l r e s p o n s i b l e f o r p h o t o c h e m i c a l t r a n s f o r m a tion. I n t r o d u c t i o n o f an a d d i t i o n a l a n t i o x i d a n t group i s connected m a i n l y w i t h the n e c e s s i t y t o i n c r e a s e the s t a b i l i t y o f the m a t e r i a l i n the p r o c e s s o f i t s u t i l i z a t i o n . Among such s t a b i l i z e r s is Tinuvin 144, a C i b a - G e i g y s t a b i l i z e r ( 2 1 ) . At 1 1 0 ° - 1 2 0 ° C , i t performs comparably t o t h e r m o s t a b i l i z e r s such as Irganox 1010 (22).

2.

3.

Work i s c a r r i e d out t o o b t a i n compounds c o m p r i s i n g s e v e r a l h i n d e r e d amine or n i t r o x y l f r a g m e n t s . The mechanism by which the e f f e c t i v e n e s s o f p h o t o s t a b i l i z e r s w i t h two o r more h i n d e r e d amine fragments i s i n c r e a s e d i s not e s t a b l i s h e d . It was e m p i r i c a l l y o b s e r v e d t h a t n i t r o x y l e f f e c t i v e n e s s d u r i n g the i n h i b i t i o n o f p o l y p r o p y l e n e t h e r m o o x i d a t i o n i n c r e a s e s w i t h an i n c r e a s e i n the number o f paramagnetic c e n t e r s i n a m o l e c u l e . The e f f e c t i v e n e s s o f t h e r m o s t a b i l i z e r s o f the b i - r a d i c a l type i n c r e a s e s

when the d i s t a n c e between paramagnetic c e n t e r s d e c r e a s e s . This phenomenon may be due t o a cage r e a c t i o n o f the a l k y l r a d i c a l , which i s formed d u r i n g the i n t e r a c t i o n o f a polymer w i t h n i t r o x y l with another n i t r o x y l g r o u p . T h i s r e a c t i o n h i n d e r s the s i d e i n i t i a t i o n o f o x i d a t i o n by t h e n i t r o x y l r a d i c a l . There i s n ' t a s a t i s f a c t o r y e x p l a n a t i o n t o the i n c r e a s e i n p h o t o s t a b i l i z e r e f f e c t i v i t y w i t h the i n c r e a s e i n the number o f NH groups because mono- r a t h e r t h a n p o l y r a d i c a l s are formed d u r i n g p h o t o o x i d a t i o n of hindered amines. S t a b i l i z e r s o f h i g h c o m p a t i b i l i t y w i t h polymers are b e i n g s y n thesized. To improve t h e i r c o m p a t i b i l i t y w i t h p o l y m e r s , some fragments are i n t r o d u c e d i n t o the s t a b i l i z e r . F o r example, a l k y l s u b s t i t u e n t s p r o v i d e h i g h e f f e c t i v e n e s s to p h o t o s t a b i l i -



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770

TINUVIN

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292

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HO-T COOR

Bu

TINUVIN

1

N-0

II 0

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1

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8

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R-0C-fCH -V- C-OR II 0

2

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Scheme 5 . S t r u c t u r e s o f h i n d e r e d amine s t a b i l i z e r s f o r polymers. Continued on next page.


ROZANTSEV ET AL.


Scheme 5 .

Continued.


26


zers f o r p o l y o l e f i n s . Some c h a r a c t e r i s t i c s o f s t a b i l i z e r s s t r u c t u r e s appear t o c o n t r i b u t e t o t h e i r a c c u m u l a t i o n i n t h o s e s i t e s where p h o t o o x i d a t i o n o c c u r s . T h i s seems t o be p a r t i c u l a r l y a p p l i e d t o p o l y p r o p y l e n e which i s n o n u n i f o r m l y o x i d i z e d . 4. Methods o f h i n d e r e d amine s t a b i l i z e r s y n t h e s i s are b e i n g d e v e l oped w i t h t h e purpose o f r e d u c i n g c o s t and u s i n g a v a i l a b l e raw materials. The a c t i o n mechanism o f polymer p h o t o s t a b i l i z e r s based on h i n d e r e d amines a t t r a c t e d g r e a t a t t e n t i o n a f t e r numerous r e p o r t s on t h e i r h i g h e f f e c t i v e n e s s had a p p e a r e d . The main c o n c l u s i o n s from t h e s c i e n t i f i c l i t e r a t u r e on t h e mechanisms o f h i n d e r e d amine a c t i o n a r e offered below. More d e t a i l e d i n f o r m a t i o n c a n be found i n numerous r e v i e w s , t h e ones c o m p i l e d by t h e a u t h o r s o f t h e p r e s e n t a r t i c l e including (38,51-56). 1

The f o l l o w i n g methods a r e used at p r e s e n t t o p r o t e c t polymers against photooxidation (59): a. The use i n polymer c o m p o s i t i o n o f s u b s t a n c e s which at f i r s t absorb UV r a d i a t i o n and t h e n r e l e a s e t h e absorbed energy i n a form which i s not h a r m f u l t o t h e p o l y m e r . These compounds, c a l l e d UV a b s o r b e r s , p r o t e c t t h e polymer a g a i n s t UV r a d i a t i o n by d i r e c t a b s o r p t i o n . b. I n c o r p o r a t i o n i n t o polymer o f compounds which c a n d e a c t i v a t e photo e x c i t e d s t a t e s ( e i t h e r s i n g l e t o r t r i p l e t ) . c. I n c o r p o r a t i o n i n t o polymers o f s u b s t a n c e s c a p a b l e o f c a t a l y z i n g the n o n - r a d i c a l d e c o m p o s i t i o n o f h y d r o p e r o x i d e s . d. Make u s e o f compounds ( a n t i o x i d a n t s ) which a r e c a p a b l e o f trapping oxidation-propagating free r a d i c a l s thereby breaking the o x i d a t i o n c h a i n s . H i n d e r e d a m i n e s , n i t r o x y l r a d i c a l s , and t h e i r t r a n s f o r m a t i o n p r o d u c t s cannot a c t by t h e mechanisms o f UV l i g h t s c r e e n i n g o r q u e n c h i n g o f photo e x c i t e d s t a t e s . T h e i r a c t i o n i s due m a i n l y t o t h e i r involvement w i t h t h e o x i d a t i o n p r o p a g a t i n g c h e m i c a l r e a c t i o n s t a k i n g p l a c e d u r i n g polymer p h o t o o x i d a t i o n ; s o , t h e y a c t as r a d i c a l trapping antioxidants. But a number o f important f e a t u r e s e s s e n t i a l l y d i s t i n g u i s h them from common a r o m a t i c a n t i o x i d a n t s ( p h e n o l s and amines) which a r e poor polymer p h o t o s t a b i l i z e r s . S e v e r a l r e a c t i o n s may be i n v o l v e d i n p r o v i d i n g p r o t e c t i o n t o polymers a g a i n s t p h o t o d e c o m p o s i t i o n d e s t r u c t i o n . The c o n t r i b u t i o n of each o f t h e p r o c e s s e s depends on t h e n a t u r e o f t h e polymer and the o x i d a t i o n c o n d i t i o n s . The time d u r i n g which a h i n d e r e d amine i s t r a n s f o r m e d i n t o n i t r o x y l i n p o l y p r o p y l e n e i s s h o r t compared t o the i n d u c t i o n p e r i o d . T h e r e f o r e , p i p e r i d i n e s and c o r r e s p o n d i n g n i t r o x y l r a d i c a l s a r e almost e q u a l l y e f f e c t i v e f o r polymer s t a b i l ization. In r u b b e r , which i s more r a p i d l y o x i d i z e d t h a n p o l y p r o p y l e n e , n i t r o x y l r a d i c a l s a r e f a i r l y more e f f e c t i v e t h a n h i n d e r e d amines. Subsequent t r a n s f o r m a t i o n s o f n i t r o x y l r a d i c a l s , formed t h r o u g h R e a c t i o n s 6-8 a r e shown i n Scheme 6 ( 5 3 ) . The a n t i o x i d a n t a c t i o n o f n i t r o x y l r a d i c a l s i s due t o t h e i r a b i l i t y t o r e a c t w i t h a l k y l r a d i c a l s as i n R e a c t i o n 9 . Because o f t h e i r r e a c t i v i t y with a l k y l r a d i c a l s , n i t r o x y l s are b e t t e r photoo x i d a t i o n i n h i b i t o r s t h a n t h e i n h i b i t o r s o f o t h e r c l a s s e s . The r a t e c o n s t a n t f o r t{je r e a c t i o n o f n i t r o x y l s w i t h h y d r o x y l r a d i c a l ( E q u a t i o n 10) i s 10 L / m o l . s e c . T h i s r e a c t i o n c a n be o f p a r t i c u l a r importance f o r t h e i n h i b i t i o n o f polymer p h o t o o x i d a t i o n . R e a c t i o n s 11-13 i n i t i a t e polymer p h o t o o x i d a t i o n . However,


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ROZANTSEV ET AL.


t h e y do not have an a p p r e c i a b l e i n f l u e n c e on h i n d e r e d amine e f f i c i e n c y because R e a c t i o n s 11 and 12 o c c u r o n l y at e l e v a t e d tempera t u r e s , and R e a c t i o n 13 o c c u r s o n l y under t h e a c t i o n o f l i g h t i n a narrow w a v e l e n g t h band, c o r r e s p o n d i n g t o n i t r o x y l r a d i c a l a b s o r p t i o n , and t h i s i s t h e r e g i o n where n i t r o x y l s absorb l i g h t more p o o r l y t h a n p h e n o l s and a r o m a t i c amines. Moreover, h y d r o x y l a m i n e s formed from R e a c t i o n s 11-13 a r e e f f i c i e n t a n t i o x i d a n t s w h i l e t h e products of the p h o t o o x i d a t i o n of aromatic a n t i o x i d a n t s (phenols and amines) o f t e n f u n c t i o n as s e n s i t i z e r s f o r i n i t i a t i n g polymer photooxidat ion. R e a c t i o n 13 was s t u d i e d w i t h model compounds. R a d i c a l (6) undergoes t h e f o l l o w i n g p h o t o l y t i c r e a c t i o n :

50$ Under s i m i l a r c o n d i t i o n s , the five-membered n i t r o x y l (7) decomposes to e l i m i n a t e NO. Poor s t a b i l i t y o f five-membered n i t r o x y l s i s p r o b a b l y one o f the reasons why examples o f t h a t type a r e not o f f e r e d c o m m e r c i a l l y as polymer s t a b i l i z e r s . Hydroxylamines and t h e i r e t h e r s , formed d u r i n g the a f o r e s a i d R e a c t i o n s 9-13 a l s o i n h i b i t p h o t o o x i d a t i o n (Scheme 7 ) . Hydroxylamine s , u n l i k e n i t r o x y l r a d i c a l s , r e a c t w i t h p e r o x i d e r a d i c a l s (Reaction 11). The r a t e c o n s t a n t o f t h i s r e a c t i o n i s c l o s e to the c o r r e s p o n d i n g c o n s t a n t s e s t i m a t e d f o r most a c t i v e p h e n o l s . Hydroxylamine e t h e r s are p o o r e r i n h i b i t o r s t h a n commonly used phenols and a r o m a t i c amines ( r a t e c o n s t a n t f o r t h e i r r e a c t i o n w i t h Me2CNC00 r a d i c a l i n c h l o r o b e n z e n e at 65° i s 1-20 L / m o l . s e c . ) Under t h e r m a l c o n d i t i o n s , h y d r o x y l a m i n e e t h e r s c a n r e v e r s i b l y decompose ( R e a c t i o n 1 5 ) . The r a d i c a l s formed d i s p r o p o r t i o n a t e t o e l i m i n a t e o l e f i n s and y i e l d h y d r o x y l a m i n e ( R e a c t i o n 1 6 ) . In the presence of s u f f i c i e n t l y e f f e c t i v e acceptors of a l k y l r a d i c a l s ( e . g . , o x y g e n ) , the r e a c t i o n r a t e o f peroxy r a d i c a l f o r m a t i o n i s much h i g h e r t h a n t h a t o f h y d r o x y l a m i n e f o r m a t i o n . T h u s , i n the p r o c e s s o f polymer p h o t o o x i d a t i o n , n i t r o x y l r a d i c a l s r e g e n e r a t e and can b r e a k m u l t i p l e o x i d a t i v e c h a i n s . A n a l y s i s o f r e a c t i o n r a t e c o n s t a n t s i n model systems shows t h a t at room t e m p e r a t u r e , the main r e a c t i o n l e a d i n g t o r e g e n e r a t i o n of n i t r o x y l r a d i c a l s i s t h e i r i n t e r a c t i o n with peroxide r a d i c a l s , ( R e a c t i o n 11) and at e l e v a t e d t e m p e r a t u r e s (more t h a n 8 0 ° ) the main r e a c t i o n i s t h a t o f h y d r o x y l a m i n e e t h e r d e c o m p o s i t i o n ( R e a c t i o n 15) (53). It has been p r o p o s e d , m a i n l y i n the p a t e n t l i t e r a t u r e , to use h i n d e r e d amines i n m i x t u r e s w i t h o t h e r c l a s s e s o f s t a b i l i z e r s . A short survey of l i t e r a t u r e data along these l i n e s i s given i n (38). The m i x t u r e s c o n t a i n i n g h i n d e r e d amines and UV a b s o r b e r s 2-(hydroxy-


27


>N-0

+

P-

>

>N -0

+

-OH ^

>N-OP

(6)

OH #

N

>N

(7) 0

>N-0

+

PH

N

>N-0

+

POOH

>N10

+

PH

^

Scheme 6 .

h i / >

>N-OH

+

P.

(8)

^

>N-OH

+

P0

^

>N-OH

+

P.

(9)

2

(10)

T r a n s f o r m a t i o n s of n i t r o x y l

radicals.

>N-OH

+

P0 -

>

>N-0

+

POOH

>N-OH

+

POOH

>

>N-0

+

PO.

>N-OP

+

P'0

>

>N-0

+

P'OOH

+>C=CN-0P

+

P 0 .

>

>N-0

+

P'OOP

(14)

^

>K-0

+

P.

(15)

>

>N-0H

2

!

>N-OP >N-0

+

P-

2

2

cheme 7 . R e a c t i o n s of hydroxylamines n polymer s t a b i l i z a t i o n .

(11) +

H 0

(12)

2

+ >C=C

R-N-R' 0

0

C(CH ) 3

CN


2

32


Complete information on application of the spin-trap method is given in summaries (70-72). Geophysics. Utilization of dynamic proton polarization phenomenon in nitroxyl radical solutions facilitated the improvement of spinprecision magnetometers by synchronizing the processes of nuclear polarization and precision measurement. Deuterated radical solutions serve as sensors in such instruments. Instruments of this type have already been produced in France. They find application in geophysical research, geological explorations and in searches for metallic objects under water. Oil Recovery. Nitroxyl radicals have found significant application in the oil production industry to control the rate of water encroachment of an oil pool. The method consists of the following: nitroxyl radicals are introduced into the water-injection well together with water, and water encroachment of the oil pool is followed by sampling and determining the nitroxyl radical content by EPR. Introduction of this method will permit increases in o i l recovery (73). Diamond Quality Assessment. The physical-chemical characteristics of nitroxyl radicals make it possible to evaluate crystal quality of diamonds, for example, with high sensitivity and reliability. It is possible to detect cracks on the crystal surface, to introduce quantitative criteria for estimation of the quality of diamonds, and to carry out defect differentiation (74). Antiwear. It has been shown that the addition of nitroxyl radicals of the 2,2,6,6-tetramethylpiperidine series to lubricating compositions consisting of mineral oil and alkyl adipates (20%) considerably improves their lubricating properties (75). When utilizing the suggested compositions, the maximum load can be increased by 1.2-1.6 times for the same and sometimes even smaller friction factor. At the same time, the weight wearout rate is reduced by 1.2-2.0 times for bronze samples and by 2-8 times for steel samples. In conclusion, it is worth noting that nitroxyl radical applications have been limited heretofore by unjustifiably high prices. The prices of the simplest radicals in the Aldrich chemical catalog of 1982 were in the range of $1,000-$15,000 a kilogram. At present, they are being steadily reduced. In the authors opinion, the prices can be reduced even for small volumes of production at least by 1/50. This will lead to a wider investigation of their properties and, naturally, will extend the range of their application. 1

Literature Cited 1.

2. 3. 4.

Rozantsev, E. G.; Lebedev, O. L . ; Kararnovsky. S. N. "The Discovery of the Phenomenon of Stable Localized Free-Radical Center Formation," Otkrytie SSSR N 246 August 6, 1981. Otkrytiya SSSR, 18, Moscow. Rozantsev, E. G. "Free Iminoxyl Radicals," Khimiya, Moscow, 1970. Rozantsev, E. G. Izv. Akad. Nauk SSSR, Ser. Khim. 1963, 1669. Neiman, M. B.; Rozantsev, E. G.; Mamedova, Yu. G. Nature 1963, 200, 256.


2.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35.

ROZANTSEV ET AL.


USSR Patent 166 032, 1962. Rozantsev, E. G. Izv. Akad. Nauk SSSR, Ser. Khim. 1964, 2218. Sokoloff, N.; Latschinoff, P. Ber. 1874, 7, 1384. Heintz, W. Ann. 1874, 175, 133. Rozantsev, E. G. Ivanov, V. P. Khim.-Pharm. Zh. 1971, 47. Rozantsev, E. G. Izv. Akad. Nauk SSSR, Ser. Khim. 1964, 2187. Rozantsev, E. G.; Krinitzkaya, L. A. Tetrahedron 1965, 21, 491. Rozantsev, E. G.; Neiman, M. F. Tetrahedron 1964, 20, 131. USSR Patent 166 133, 1964. Ohnishi, S.; McConnell, H. M. J. Am. Chem. Soc. 1965, 87, 2293. Sosnovsky, G.; Konieczny, M. Z. Naturforsch. 1977, 32B, 328. Kedik, S. A.; Rozantsev. E. G.; Usvyatsov, A. A. Dokl. Akad. Nauk SSSR 1981, 257, N 6, 1382. Prostakov, N. S.; Gayvaronskaya, L. A. Usp. Khim. 1978, 47, 859. Rozantsev. E. G.; Kagan. E. Sh.; Sholle, V. D. in "Paramagnetic Models of Drugs and Biochemicals," Ed. Zdanov, R. I., C.R.C. Press Boca Raton, Florida 1985. Rozantsev, E. G.; Dagonneau, M.; Kagan, E. Sh.; Sholle, V. D.; Michailov, V. I. Synthesis 1984. Kagan, E. Sh.; Avrutskaya, I. A.; Kondrashov, S. V.; Novikov, V. T.; Fioshin, M. Ya.; Smirnov, V. A. Electrochemical Synthesis of 2,2,6,6-tetramethylpiperidine, Khimiya geterociclicheskih soedinenii 1984, 3, 358-359. Tomilov, A. P.; Smirnov, V. A.; Kagan, E. Sh. "Electrochemical Synthesis of Organic Compounds," Rostov University Ed. 1981, 59-61. USSR Patent 908.017, 1982. Surov, I. I.; Avrutskaya, I. A.; Fioshin, M. Ya. Electrochimia 1983, 19, 1561-1565. Tsarkova, T. G.; Avrutskaya, I. A.; Fioshin, M. Ya. Electrochimia 1984, 20, N3, 404-407. Rubtsov, M. V.; Baichikov, A. G. "Synthetic Pharmaceutical Chemicals, Meditsina," Moscow, 1971, 194. Rozantsev, E. G.; Dagonneau, M.; Kagan, E. Sh.; Mikhailov, V. I. J. Chem. Res. (S) 1979, 260; J. Chem. Res. 1979, 2901. Mikhailov, V. D. "Enamines in the Synthesis of Nitroxyl Radicals of the 2,2,6,6-tetramethylpiperidine Series," Cand. Dis. RGU, Rostov-on-the-Don, 1975. Briere, R.; Espil, J. C.; Ramasseul, R.; Rassat, A.; Rey, P. Tetrahedron Let. 1979, 941. Rozantsev, E. G. "Free Nitroxyl Radicals," Plenum Press, New York, London, 1970. Rosantsev, E. G.; Sholle, V. D. Organitscheskaya Khimia Svobodnych Radicalov, Khimia, Moscow 1979. Rozantsev, E. G.; Sholle, V. D. Synthesis 1971, 190-202. Rozantsev, E. G.; Sholle, V. D. Synthesis 1971, 401-414. "Spin-Labelling, Theory and Application," Ed. by L. Bezlinez, Academic Press, New York, London, 1976. Keana, I. F. W. Chem. Rev. 1978, 78, 37-63. Zhdanov, R. I. "Paramagnitnye Modeli Biologitscheski Aktivnych Soedinenii," Nauka, Moscow, 1981.


33

34


36.

Forrester, A. K.; Hay, G. M.; Thomson, R. H. "Organic Chemistry of Stable Free Radical," Academic Press, London, 1967, 405. 37. Buchachenko, A. L . ; Vasserman, A. M. "Stabilnye Radicaly," Khimia, Moscow, 1973. 38. Dagonneau, M.; Ivanov, V. B.; Rozantsev, E. G.; Sholle, V. D.; Kagan, E. Sh. "Sterically Hindered Amines," J . M. S.-Rev. Macromol. Chem. Phys. 1982-1983, c. 22(2), 169-202. 39. Kagan, E. Sh.; Kondrashov, S. V.; Selivanov, V. N. in " A l l Union Conference on Electrochemistry" June 21-25, 1982, Moscow, 1982, 208. 40. Bogdanova, N. N.; Surov, I. I.; Avrutskaya, I. A.; Fioshin, M. Ya. Electrochimia 1983, 19, 1286. 41. Keana, I. F. W.; Dinerstein, R. I.; Baitis, F. J . Org. Chem. 1970, 36, 209-211. 42. Golubev, V. A.; Zhdanov, R. I.; Gida, V. M.; Rozantsev, E. G. Izv. Akad. Nauk SSSR Ser. Khim. 1971, 853-855. 43. Sen, V. D.; Golubev, V. A.; Efremova, N. M. Izv. Akad. Nauk SSSR, Ser. Khim. 1982, 61-72. 44. Sosnovsky, G.; Konieczny, M. Z. Naturforshc. 1976, Teil B., 31, 1376-1378. 45. Levina, T. M.; Rozantsev, E. G. A. S. Chegolya. Dokl. Akad. Nauk SSSR 1981, 261, 109-110. 46. USSR Patent 391 137, 1973. 47. Raucman, E. I.; Rosen, G. M.; Abon-Donia, M. B. Synth. Comm. 1975, 5, 409-413. 48. Kagan, E. Sh.; Mikhailov, V. I.; Sholle, V. D.; Rozynov, B. V.; Rozantsev, E. G. Izv. Akad. Nauk SSSR, Ser. Khim. 1977. 49. Likhtenshtein, G. I. "Spin-Labelling Methods in Molecular Biology," Nauka, Moscow, 1977. 50. Kuznetsov, L. N. "The Spin-Probe Method," Nauka, Moscow, 1976. 51. Toda, T.; Kurumada, T. Sankyo Kenkyosho Nempo "Research and Development of Hindered Amine Light Stabilizers," Ann. Rep. Sankyo Res. Lab. 1983, 35, c. 1-37. 52. Shlyapintokh, V. Ya. "Photochemical Transformations and Polymer Stabilization," Khimia, Moscow, 1979. 53. Shlyapintokh, V. Ya.; Ivanov, V. B. "Developments in Polymer Stab.," Ed. G. Scott, Appl. Sci. Publ. London, 1982, 5, 41. 54. Allen, N. S. "Developments in Polym. Photochemistry," Ed. N. S. Allen. Appl. Sci. Publ., London, 1981, 239. 55. Carlsson, D. J . ; et. a l . "Developments in Polymer Stabilization," Ed. G. Scott, Appl. Sci. Publ., London, 1979, 1, 219. 56. Gugumus, F . , "Developments in Polymer Stabilization," Ed. G. Scott, Appl. Sci. Publ., London, 1979, 1, 261. 57. Shlyapintokh, V. Ya.; Bystritskaya, E. B.; Shapiro, A. B.; Smirnov, V. A.; Rozantsev, E. G.; Izv. Akad. Nauk SSSR, Ser. Khim. 1973, 1915. 58. Shlyapintokh, V. Ya.; Ivanov, V. B.; Hvostach, D. M.; Shapiro, A. B.; Rozantsev, E. G. Dokl. Akad. Nauk SSSR, 1975, 225, 1132.


2.

ROZANTSEV ET AL.

59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75.


Randy, B.; Rabek, J. F. "Photodegradation, Photooxidation and Photostabilization of Polymers," Wiley-Interscience, New York, 1975. Allen, N. S.; McKeller, I. F.; Wilson, D. Chem. Ind. 1978, 887-889. Rozantsev, E. G.; Krinitskaya, L. A.; Troitskaya, L. S. Khim. Prom. 1964, 20, 180. Vakula, V. A.; Pritykin, L. H. "Foundation of Physical Chemistry of Polymer Adhesion," Khimia, Moscow, 1984. USSR Patent 600 162, 1978. Pritykin, L. M.; Genel, L. S.; Gerenrot, V. G.; Shapiro, A. B.; Bakula, V. L. Plastics 1981, 36-39. USSR Patent 732 405, 1980. Danjushina, G. A.; Kagan, E. Sh.; Smirnov, V. A.; Pritykin, L. M. Plasticheskie Massy 1982, 83. Pritykin, L. M. Biofisika 1976, 21, 1059. Pelevina, I. I.; Afanasjev, G. G.; Gotlib, V. Ya. "Klectochnye Faktory Reaktsii Opukholei na Obluchenie i Khimikoterapevticheskie Vozdeistvija," Nauka, Moscow, 1978, 304. All-Union Conference on Nitroxyl Radicals, Chernogolovka, May 12-14, 1982, Tezisy Dokladov. Pedersen, I. A.; Torssel, K. Acta. Chem. Scand. 1971, 25, 3151-62. Yansen, E. G. Acc. Chem. Res. 1971, 4, 31-40. Lagercrantz, C. J. Phys. Chem. 1971, 75, 3466. Bukin, I. I.; Rozantsev, E. G. et. al. Neftyanoe Khozyaistvo 1978, 46. Bukin, I. I.; Kagarmanov, N. F. et al. Sverkhtverdye Materialy 1983, 27, 23. USSR Patent 802 358, 1981.

RECEIVED January 31, 1985


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