CAMPHOR, NATURAL AND SYNTHETIC 65 



Camphoronic acid is of known structure. It is a-a-/3- 

 trimethyl-tricarballylic acid, for on dry distillation it is broken 

 down to trimethyl-succinic acid, isobutyric acid, and carbon 

 dioxide. It has, moreover, been prepared synthetically with 

 the aid of acetoacetic-ether. All these reactions find a satis- 

 factory explanation in Bredt's formula for camphor, which is 

 therefore now generally accepted. Lastly, two other points 

 may be mentioned in connection with this difficult question of 

 the structure of the camphor molecule. The first is the partial 

 synthesis of camphor by the distillation of the calcium salt of 

 homocamphoric acid (IX.), 1 which is shown thus — 



CH, CH CH, 



I 



CH3 — C — CHa 



COO CH, CH CH, 



Ca 



CH, C CO 



I 

 CH 3 



(IX.) Calcium homocamphorate. 



CH 3 — C— CH 3 

 O CH 2 C CO 



CH 3 



CaCO s 



The second is the support derived from stereo-chemical 

 evidence. It will be seen by reference to formula VI. that 

 camphor contains two asymmetric carbon atoms (printed in 

 heavy type) — i.e. two carbon atoms, each of which is combined 

 to four different groups. To these asymmetric carbon atoms 

 camphor owes its property of optical activity. If now the 

 carbonyl (CO) group be reduced to CH 2 , the asymmetry of both 

 carbon atoms is destroyed. If therefore the structure for 

 camphor assumed by Bredt be the correct one, the optically 

 active camphor must become inactive upon substituting CH 2 

 for CO. This is entirely supported by the facts. 



Synthetic Camphor 



Synthetic camphor is identical with the naturally occurring 

 product in all its properties, chemical and physical, with the 

 exception that it has no rotatory action on the plane of polarised 

 light. The "inactive" camphor which is obtained synthetically 

 is a mixture of the dextro- and lsevo-forms, and has not yet 

 been resolved into its optically active components, although 

 Pickard and Littlebury 2 have recently accomplished the resolu- 

 tion of inactive borneol into its dextro- and laevo- modifications 



1 Bredt and Rosenberg, Annalen der Chemie, 289, I. 



2 Trans. Chem. Soc. 91 (1907), 1973. 



