54 
Camphor — Natural  and  Synthetic.  { 
Am.  Jour.  Pharm. 
February,  1915. 
Bredt  later  modified  his  formula  to  that  shown  by  (VI). 
The  oxidation  of  camphor  to  camphoronic  acid  is  then  formulated 
as  follows : 
CHi 
-CH 
-CH5 
CHj-C-CH, 
I 
CH2  C  
I 
CO 
CH2  CH— COOH 
CH3-C-CH3 
CH2  C— COOH 
CH3 
(VII)  Camphoric  acid 
COOH 
COOH 
CH3-C-CH3 
I 
CH2  C— COOH 
CH3 
(VIII)  Camphoronic  acid 
CH3 
(VI)  Camphor  (Bredt,  1893) 
Camphoronic  acid  has  been  synthesized  and  is  of  known  con- 
stitution (a-a-/?-trimethyl  tricarballylic  acid).  Lastly,  two  other 
points  may  be  mentioned  in  connection  with  this  complicated  question 
of  the  structure  of  camphor. 
The  first  is  the  partial  synthesis  of  camphor  by  the  distillation  of 
the  calcium  salt  of  homocamphoric  acid  9  (IX). 
This  reaction  is  shown  thus — 
COO 
CH, 
-CH2 
CH3-C-CH3 
CHS 
+CaC03 
-CO 
CH3 
(IX)  Calcium  homocamphorate 
CH3 
Camphor 
The  second  point  is  the  evidence  derived  from  stereochemical 
considerations.  From  Formula  (VI)  it  will  be  seen  that  camphor 
contains  two  asymmetric  carbon  atoms  (printed  in  heavy  type).  To 
these  asymmetric  atoms  camphor  owes  its  optical  activity.  If  now 
the  carbonyl  (CO)  group  be  reduced  to  (CH2),  the  asymmetry  of 
both  carbon  atoms  is  destroyed,  and  the  resulting  compound  must  be 
inactive.  This  is  entirely  supported  by  the  experimental  results. 
Bredt's  formula  for  camphor  is  the  only  one  to  interpret  satisfactorily 
all  the  reactions  discussed  above,  and  his  formula  is  now  generally 
accepted. 
Synthetic  Camphor. 
The  raw  material  for  the  synthesis  of  camphor  is  turpentine,  the 
resinous  liquid  exuding  from  various  Coniferce.  American  turpentine 
is  mostly  obtained  from  Pinus  palustris,  the  French  variety  from 
9  Bredt  and  Rosenberg,  Annalen  der  Chemie,  289. 
