Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

368 MECHANISM OF SKKAUP'S KBACTION
The first quinoline derivative obtained by the process (a) was the
dye alizarin blue (Prud'homme, 1877). /3-Nitroalizarin was heated
with glycerol and sulphuric acid. The constitution of the product was
established by Graebe :
CO OH CO OH
D u r i n g t h e p r o c e s s t h e N O 2 - g r o u p i s r e d u c e d t o N H 2 .
--»•
S k r a u p ' s s y n t h e s i s i n v o l v e s t h e e l i m i n a t i o n o f w a t e r . T h u s a c r o l e i n
w i l l b e f o r m e d . I t m a y r e a c t w i t h a n i l i n e t o f o r m a n a z o m e t h i n e
( S c h i f l ' s b a s e ) ( I ) , b u t m o r e p r o b a b l y t h e b a s e a d d s i t s e l f t o t h e O = C
d o u b l e b o n d ( I I ) :
. N H
N N
O n e i t h e r h y p o t h e s i s a d i h y d r o q u i n o l i n e i s f o r m e d . T h e e x t r a
h y d r o g e n i s r e m o v e d b y t h e n i t r o b e n z e n e p r e s e n t .
A s e c o n d s i m i l a r s y n t h e s i s , d u e t o D o e b n e r a n d M i l l e r , l e a d s t o t h e
f o r m a t i o n o f s u b s t i t u t e d q u i n o l i n e s . T h e s i m p l e s t e x a m p l e i s t h e p r o -
d u c t i o n o f q u i n a l d i n e f r o m a n i l i n e a n d p a r a l d e h y d e b y h e a t i n g w i t h
c o n c e n t r a t e d h y d r o c h l o r i c a c i d . T h e c o u r s e o f t h e r e a c t i o n i s c l o s e l y
r e l a t e d t o t h a t o f t h e S k r a u p s y n t h e s i s b y r o u t e I I . T h e r e t h e a n i l i n e
r e a c t s w i t h a c r o l e i n , h e r e w i t h c r o t o n a l d e h y d e , w h i c h i s e a s i l y f o r m e d
u n d e r t h e c o n d i t i o n s w h i c h p r e v a i l :
N H , N H N H
i C H . C H 3
j i C H
H O C O H
H e r e a l s o t h e r e a r e t w o h y d r o g e n a t o m s i n e x c e s s , b u t t h e y a r e
r e m o v e d b y s e c o n d a r y r e a c t i o n s ( l e a d i n g t o t h e f o r m a t i o n o f h y d r o -
g e n a t e d p r o d u c t s ) . T h e w e l l - k n o w n d r u g a t o p h a n ( u s e d i n g o u t ) ,