Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

A K Y L H Y D K O X Y L A M I N E S 1 7 5
s h o u l d n o t b e c o m b i n e d . P h e n y l h y d r o x y l a m i n e , w h i c h h a s n o t b e e n
r e c r y s t a l l i s e d , c a n o n l y b e p r e s e r v e d u n d e c o m p o s e d f o r a f e w d a y s a t
t h e m o s t .
C a r e s h o u l d b e t a k e n n o t t o a l l o w p h e n y l h y d r o x y l a m i n e , e s p e c i a l l y
w h e n i n s o l u t i o n , t o c o m e i n t o c o n t a c t w i t h t h e s k i n . I n m a n y i n d i -
v i d u a l s i t p r o d u c e s s e v e r e e c z e m a , w h i l s t o t h e r s a r e q u i t e u n a f f e c t e d .
A m m o n i u m h y d r o g e n s u l p h i d e is a l s o a v e r y s u i t a b l e r e a g e n t f o r
t h e r e d u c t i o n of n i t r o c o m p o u n d s t o a r y l h y d r o x y l a m i n e s ; i t is u s e d i n
a l c o h o l i c s o l u t i o n i n t h e c o l d . 1
A n a l u m i n i u m - m e r c u r y c o u p l e a c t s i n t h e s a m e w a y a s z i n c d u s t .
T h i s a l u m i n i u m a m a l g a m , p r e p a r e d b y t h e a c t i o n of m e r c u r i c c h l o r i d e
o n a l u m i n i u m ( p r e f e r a b l y g r a n u l a t e d ) , is a l s o s u i t a b l e f o r r e d u c i n g s u b -
s t a n c e s d i s s o l v e d i n e t h e r o r a l c o h o l ; t h e w a t e r w h i c h is r e q u i r e d is
s l o w l y a d d e d d r o p b y d r o p . ( T h e m e t h o d is t h a t of H . W i s l i c e n u s . )
T h e e x t e n t of t h e r e d u c t i o n v a r i e s a c c o r d i n g t o t h e n i t r o - c o m p o u n d c o n -
c e r n e d , b u t c o r r e s p o n d s a p p r o x i m a t e l y t o t h e e f f e c t of z i n c d u s t i n a
n e u t r a l m e d i u m . C o n s e q u e n t l y r e d u c t i o n u s u a l l y d o e s n o t p r o c e e d
b e y o n d t h e h y d r o x y l a m i n e s t a g e .
P h e n y l h y d r o x y l a m i n e , e s p e c i a l l y w h e n i m p u r e , is v e r y u n s t a b l e . I t
d a r k e n s a n d d e c o m p o s e s e v e n i n a c l o s e d c o n t a i n e r w h e n k e p t f o r a
s h o r t t i m e . T h e p u r e m a t e r i a l c a n b e k e p t f o r a c o n s i d e r a b l e t i m e i n
a d e s i c c a t o r .
I n c o n t r a s t t o t h e p a r e n t s u b s t a n c e of t h e s e r i e s , y - t o l y l h y d r o x y l
a m i n e , w h i c h is p r e p a r e d b y t h e r e d u c t i o n w i t h z i n c d u s t of y - n i t r o -
t o l u e n e i n b o i l i n g a l c o h o l , is a q u i t e s t a b l e c o m p o u n d .
T h e a r y l h y d r o x y l a m i n e s a r e w e a k b a s e s w h i c h d i s s o l v e i n d i l u t e a c i d s
t o f o r m s a l t s . T h e i n s t a b i l i t y of p h e n y l h y d r o x y l a m i n e h a s t h r e e c a u s e s :
t h e e f f e c t of a t m o s p h e r i c o x y g e n , of a l k a l i s , a n d of a c i d s . O n e x p o s u r e
t o a i r t h e c o m p o u n d , e s p e c i a l l y if i m p u r e , is o x i d i s e d t o n i t r o s o b e n z e n e ,
w h i c h c a n b e d e t e c t e d i n d e c o m p o s i n g p h e n y l h y d r o x y l a m i n e b y i t s
p u n g e n t o d o u r . A s is o f t e n t h e c a s e , t h e v e l o c i t y of t h i s p r o c e s s , w h i c h
is k n o w n a s a u t o x i d a t i o n , is i n c r e a s e d b y a l k a l i s ; it is a c c o m p a n i e d b y
t h e p r o d u c t i o n of h y d r o g e n p e r o x i d e a c c o r d i n g t o t h e e q u a t i o n :
C 6 H 5 . N H O H + O 2 — > C 6 H 5 . N O + H 2 O 2
Since nitrosobenzene condenses with phenylhydroxylamine forming
azoxybenzene, the latter substance occurs amongst the decomposition
products of phenylhydroxylamine. Also, by the action of alkalis, water
is eliminated and azobenzene is produced. The action of acids will be
discussed below.
ATT
L i k e h y d r o x y l a m i n e itself, all its d e r i v a t i v e s of t h e f o r m R . N < T T
a r e r e d u c i n g a g e n t s .
1 Willstfttter, Ber., 1908, 4 1 , 1936.