Notizen 543 Push-Pull Nitrogen Free Radicals from Benzene*

Notizen 543 Push-Pull Nitrogen Free Radicals from Benzene*

sulphonanilides or Benzanilides with Donor

p a r a -Substituents

R o d i c a I s t r a t o i u , I a n c u P a s c a r u , a n d A l e x a n d r u T. B a l a b a n *

In s titu te of Atom ic Physics, B ucharest, R oum ania

(Z. Naturforsch. 2M>, 543-544 [1973];

received April S, 1973)

ESR spectra, phenyiogy

It was pointed out1 that nitrogen free radicals have enhanced stability if they are sterically shielded and possess push-pull electronic effects.

Combination of electron-donor groups X (such as alkoxy, dialkyl- or diarylamino) w ith acceptor groups Z (such as arenesulphonyl, aroyl, 2,4,6-tri-, 2,4-di- or 2,6-dinitrophenyl, 2,4,6-tricyano- or -tricarbomethoxyphenyl) yields nitrogen free radi­

cals 1 which do not react with oxygen and can be observed in solution by ESR spectroscopy in sta­

tionary systems; in some cases they can even be isolated in crystalline state. In addition to nitrogen free radicals with structures resulted from the above combinations, their ^-phenylogues 2 are also stable. Thus />-phenylogues of diphenylpicryl- hydrazyl2 or of picrylalkoxyaminyl3 were prepared.

Recently, the preparation and ESR spectra of l,l-diphenyl-2-arenesulphonylhydrazyls (3) were reported,4 whereas l,l-diphenyl-2-aroylhydrazyls

(4)

sent paper we report the preparation and ESR spectra of ^-phenylogues 5 and 6 of free radicals 3 and

4,

X —N —Z ^ X —N = Z ^ * X —N —Z

© © © ©

« -> X —N = Z<— X = N —Z

© " © © ©

1

/ > - X - C6H4- N - Z Ph2N —N — S 0 2—Ar

2 3

Ph2N —N - C O - A r

4

Requests for reprints should be sent to Prof. Dr. A.

T. Ba l a b a n, Institut of Atomic Physics, P.O.B. 35, Bucharest, Roumania.

p - X - C6H4 - N - S 02 - Ar 5

/>—X —C6H 4—N - C O - Ar

6

Arenesulphonanilides were prepared from arene­

sulphonyl chlorides and substituted anilines in py­

ridine. Their oxidation with lead tetraacetate in benzene, dioxane or dichloromethane afforded co­

loured solutions of 5 (Ar = C6H 6, ^>-C6H4CH3, />-C6H4N 0 2, X = Me2N, Ph2N, MeO) giving well- resolved E SR spectra in stationary systems at room or lower temperatures. Thus 5 (X = Me2N), irres­

pective of the Ar group, presents an ESR spectrum w ith 31 lines at -4 0 °C (Figure); at room tempera­

ture the half-life is about one min. excepting the /»-nitrobenzenesulphonyl derivative which is stable for a longer time. The g-value is 2.0031+0.0001.

This value rules out a nitroxidic structure which would require a g-factor of approx. 2.006. Coupling constants determined with a computer program6 are : 6.2 G (one aminyl nitrogen), 6.2 G (two o-hy- drogens), 4.2 G (one /»-amino nitrogen), 4.2 G (six m ethyl hydrogens), 2.1 G (two ra-hydrogens).

Figure. First-derivative ESR spectrum of 5, Ar =

£-CaH5N 0 2, X = NMe2, in methylene dichloride at -40 °C.

Radicals 5 (X = Ph2N, irrespective of the Ar group) are even more stable. At -4 0 °C they present an E SR spectrum with a large number of lines which make the interpretation difficult; at -2 0 °C to + 3 0 °C, however, six lines are obtained (g-factor 2.0032), w ith coupling constants 8 .8 G (one hydro­

gen), 4.4 G (one hydrogen) and 4.4 G (one nitrogen), passing gradually during approx. 1 0 min. into a five-line E SR spectrum (g-factor 2.0034) with coupling constant 4.9 G (two nitrogen nuclei).

These complex transformations m ay involve7 loss of S 02 from the radical 5 and are under study.

Similar oxidation of benzanilide (6) (Ar = Ph, X = Ph2N) in dichlorometane at -3 0 °C affords a five-line ESR spectrum with coupling constant 6.2 G due to two nitrogen nuclei and g-factor 2.0031.

544

Notizen

[1971].

2 A .T . B a l a b a n , P .T . F r a n g o p o l , M. F r a n g o p o l ,

and N . N e g o i ' J ’Ä, Tetrahedron, [London] 23, 4661 [1967].

3 A .T . B a l a b a n , M . F r a n g o p o l , N . N e g o i j ä , P . T . F r a n g o p o l , and M . P a r a s c h i v , R ev. R oum aine Chim. 14, 971 [1969].

4 A .T . B a l a b a n and N . N E G o rp Ä , R ev. R oum aine Chim. 17, 1227 [1972],

5 I . S . C i c c a r e l l o , T. G a r o f a n o , and M . S a n t a n - g e l o , N u ovo Cim ento 12, 389 [1959]; 17, 881 [I960];

Y u . M . R y z h m a n o v , Y u . V. Y a b l o k o v , B .M . K o z y ­ r e v , and R . D. M a t e v o s y a n , D okl. Akad. N auk.

S S S R 162, 116 [1965]; A. E. A r b u z o v and F. G. V a ­ l i t o v a , ibid. 147,99 [1962]; A . E. A r b u z o v and S. Y u . B a i g i l d i n a , I z v . Akad. N auk. Ser. Khim . 1966, 1547; D. B r a u n , G. P e s c h k , and E. H e c h l e r ,

Chem iker Ztg. 94, 703 [1970],

8 A .T . B a l a b a n , R ev. R oum aine Chim. 17, 9 [1972];

C. P o m p o n i u a n d A . T . B a l a b a n , ib id ., in press.

7 D .M . L e m a l , T . W . R a v e , a n d S . D . M c G r e g o r , J.

A m e r . c h e m . S o c . 85, 1944 [1963]; L . A . C a r p i n o , J.

o r g . C h e m is t r y 30, 736 [1965]; W . v. E c k a r t a n d R . P ü t t e r , A n g e w . C h e m . 84, 822 [1972]; J.K. K i c e , T h e C h e m is t r y o f O r g a n ic S u lfu r C o m p o u n d s , N.

K h a r a s c h a n d C. Y . M e y e r s , Vol. 2, p . 115, A c a d e ­ m ic P r e s s , O x f o r d 1966.