Chemistry of pyrrole

It is one of the part of heterocycle chemistry.

1. P Y RROLE P r e s e n t e d b y M i n a l s a i n i M . S c . p r e v ious 1 8 7 1 4 7 1

2. P Y RROLE - INTRODUCTION STRUCTURE OF PYRROLE A R O M ATIC CHA R A C T E R O F PYRROLE P R E P A R A TION O F P Y RROLE PHYSICAL PROPERTIES C H E M I C A L P R O P ERT I E S A P P L I C A TION S O F P YRROLE C O N C L USION R E F E R ENCE S 2 C o n tent s

3. I N T R O D U C T I O N 3 P Y R R O L E i s a f i v e m e m b e r e d h e t e r o c y c l i c c o m p o u n d .

4. S T R U C T U R E O F P Y R R O L E ▪ A l l t h e f o u r C a t o m a s well as N a t o m i s s p ^ 2 h y b r i d i z e d . ▪ S h o u ld h a v e D i e n e l i k e s t r u c t u r e , s o m u s t u n d e r g o a d d i t i o n r e a c t i o n s . ▪ B u t u n d e r g o e s e l e c t r o p h i l l i c substitutio n . ▪ Resonance energy is a b out 1 k J / m o l , w h i l e c o n j u g a t e d D i e ne h a v e R E only 1 2 . 5 k J / m o l . ▪ E x h i b i t s c o n s i d e r a b l e a r o m a t i c c h a r a c ter . M o l e c ular F o r m u la : C 4 H 5 N 4

5. A R O M A T I C C H A R A C T E R • T h e h y bridized o r b i tals o f C a n d N a t o m a r e in v o lved in a x i a l o v e r l a p forming s i g m a b o n d s . • E a c h unh y b r i d i z i e d o r b i t a l o f C a t o m h a s o n e e l e c t r o n w h i l e N a t om h a s a p a i r o f e l e c t r o n s . • T h e s i d e w i s e o v e r l a p o f t h e u n - h y b r i d i z e d o r b i t a l s r e s u l t s i n a de l ocalised l l e l e c t r o n c l o u d w h i c h a c c o u n t s f o r the a r o m a t i c c h a r a c t e r o f p y r r o l e . 5 ☆ C y c l i c a n d p l a n a r s t r u cture ☆ D e l o c a l i s e d l l - e l e c t r o n s ☆ O b e y s H U C K L E ' s R u l e , ( 4 n + 2 ) l l e l e c t r o n r u l e

6. 6

7. Preparation o f p y r r o l e 7

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11. P H Y S I C A L P R O P E R T I E S I t is colorless v o l a tile l i q uid t h at darken s readily upon e x p o sure t o a i r . I t i s s p a r i n g l y s o l u b l e in w a t e r b u t r e a d i l y s o l u b l e in a l c o h o l a n d e t h e r . I t h a s d i p o l e i n w h i c h p o s i t i v e e n d l i e s t o w a r d s n i t r o g e n w i t h a d i p o l e m o m e n t o f 1 . 5 8 D W e a k l y b a s i c , w i t h a c o n j u g a t e a c i d w i t h a P k a o f - 3 . 8 A l s o w e a k l y a c i d i c a t N - H p o s i t i o n , w i t h a P k a o f 1 7 . 5 1 1

12. C H E M I C A L P R O P E R TIES W e a k b a s e . L o n e p a i r o f e lectrons o n t h e N a t o m i s not r e a d i l y a v a i l a b l e f o r p r o t o n a t i o n a n d h e n c e p y r r ole b e h a v e a s a w e a k b a s e . M u c h w e a k e r b a s e t h a n pyridine b e c ause l o n e p a i r o f e l ectron i s in volved in f o r m i n g a r o m a t i c s e x t e t . 1 2 B a s i c c h a r a cter :

13. A c i d i c character : P y rrole is w e a k l y a c i dic c o m p o u nd d u e t o t h e p r e s e n c e of i m i n o h y d r o g e n a t o m . A c i d i c c h a r a c t e r c a n b e explained b y t w o f a c t o rs : D u e t o g r e a t e r s - c h a r a cter i n t h e N - H b o n d i n p y r r o l e t h e b o n d i n g e l e c t r o n s a r e h e l d m o r e strongly t o t h e p y r r o l e n i t r o g e n . s o , h y d r o g e n is e l i minate d a s a p r o t o n . O n c e t h e p y r r y l a n i o n i s f o r m e d , i t i s stabili z ed d u e t o r e s o n ance . 1 3

14. T h e s t a b i l ity of h y b r i d f o r a n i o n is e v e n m o r e because u n l i k e p y r r o l e , t h e r e is n o c h a r g e s e p a r a t i on in a n y c o n t r i b u t i n g structures o f a n i o n . T h u s , p y r r o l e c h a n g e s t o t h e a n i o n b y l o s i n g p r o t o n w h i c h a c c o u n t s f o r it s a c i d i c c h a r a c t e r . 1 4

15. E L E C T R O P H I L L I C SUBSTITUTION R E A C T I O N : P y r r o l e i s v e r y r e a c t i v e t o w a r d s e l e c t r o p h i l e d u e t o | | - e l e c t r o n d e n s i t y a t t h e c a r b o n a t o m o f t h e p y rrole r i n g is h i g h b e c a use o f r e s o n a n c e . E l e c t r o p h i llic s u bstitution o f p y rrole p r e f e r a bly o c c u rred a t 2 & 5 t h p o s i t i on . 1 5

16. G 1 6

17. R E D U C T I O N : 1 7

18. O X I D A T I O N : 1 8

19. ☆ APPLICATIONS O F P Y RROLE : P y rrole a n d it s d e r i v a tives a r e w i d ely used a s a n intermediate in s y n t h esis o f p h a r maceutical s , m e d i c ine s , a g r o c hemicals , d y e s , p h o t o g r a p h i c c h e m i c a l s , p e r f u mes a n d o t h e r o r g a n i c compounds . T h e y a re u sed a s c a t a l y st s f o r p o l y m e r i z a tion process , c o r r o s i o n inhibitor , p r e s e r v a t ives a n d a s s o l v e nt s f o r r e s i n a n d t e r p e ne s . T h e y a r e u s e d a s t h e s t a ndard o f c h r o m a t o g r a p h i c a n a l y s i s . T h e y a r e u s e d a l s o i n m a n y o r g a n i c s y n t h e s i s . 1 9

20. ☆ C O N C L USION : P Y R ROLE I S AROMATIC H E T E R OCYCLIC C O M P O UND . I T B E H A V E S A S A W E A K A C I D A N D A S A W E A K B A S E . R E D UCTION O F P Y R R OLE Y I E L D S P Y R R O L I D I N E W H I C H I S I M P O R T A N T NUCLEUS I N M A N Y N A T U R A L P R O D U C T S . I T U N D E R G O E S ELECTROPHILLIC S U B S TITUTION R E A C T I O N S L I K E HALOGEN ATI O N , S U L P H O N A T I O N , N I T R A T I O N , C O U P L I N G R E A C T I O N , A C E T Y L A T I O N E T C . P Y R R OLE C A N U N D E R GO R I N G E X P A N S I O N A N D R I N G O P E NING M E C H A N I S M S . 2

21. ☆ R E F ERENCES : h t t p s : / / e n . m . Wikipedia . o r g / w i k i / p y r r ole h t t ps : / / w w w . n a t u r e . com / a r t i cles / p j 2 8 1 2 6 h t t ps : / / w w w . r e s e a rch g a t e . n e t / p u b l i c a tion / 2 2 4008257 2 1