Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

MOLBCULAK ASYMMBTKY 231
The amygdalin of bitter almonds and of other stone-fruits is the
glucoside formed by the combination of 2-mandelic nitrile and gentiobiose
(see p. 398). This glucoside belongs to the class of jS-glucosides,
since it is hydrolysed by the enzyme emulsin yielding two molecules
of dextrose, benzaldehyde, and hydrocyanic acid. Natural 2-mandelic
acid was first obtained by Liebig, who subjected amygdalin to acid
hydrolysis.
The cyanohydrin synthesis has been applied in the study of the
sugars by H. Kiliani, who used it in the synthesis of higher members of
the class. The carboxylic acids which result from the hydrolysis of
the nitriles can be reduced, in the form of their lactones, to the corresponding
aldehydes.
C N
HC=O
HC=O
HCOH
HOGH
HCOH
HCOH
CH2OH
«!-Glucose
H C O H
H C O H
— > H O C H
1
!OH
HCOH
CH OH
H 2 O H
HCOH
HCOH
--»• H O C H
H O O H
H C O H
C H 2 O H
« ! - G l u c o h e p t o s e
I n t h e s y n t h e s i s o f m a n d e l i c n i t r i l e d e s c r i b e d a b o v e a s y m m e t r y i s
p r o d u c e d i n o n e c a r b o n a t o m , b u t e x a c t l y e q u a l n u m b e r s o f m o l e c u l e s
o f t h e t w o a n t i p o d e s a r e f o r m e d , s i n c e t h e r e i s j u s t a s m u c h c h a n c e t h a t
o n e s h o u l d b e f o r m e d a s t h e o t h e r .
P h
> C = O <
P h x
T h e d - a n d I - v a r i e t i e s d i f f e r o n l y i n c r y s t a l f o r m a n d i n d i r e c t i o n o f
t h e r o t a t i o n ; i n a l l o t h e r p h y s i c a l a n d i n a l l c h e m i c a l p r o p e r t i e s t h e y
b e h a v e e x a c t l y a l i k e . T h e s a l t s w h i c h t h e t w o f o r m s y i e l d w i t h a n
1 T h e c o m p o u n d h a v i n g t h e o p p o s i t e c o n f i g u r a t i o n H O C H i s p r o d u c e d a t t h e
s a m e t i m e , b u t n o t , a s i n t h e p r o d u c t i o n o f a s i m p l e r a c e m i c s u b s t a n c e , i n e q u a l
a m o u n t . T h e a s y m m e t r y a l r e a d y p r e s e n t e x e r t s a d i r e c t i n g i n f l u e n c e w h i c h
f a v o u r s o n e o f t h e t w o c o n f i g u r a t i o n s .
O H
) H
C N