CAMPHOR, NATURAL AND SYNTHETIC 



67 



4. Heating with anhydrous acetates of lead, zinc, or alkaline 

 earth metals in glacial acetic acid solution. 



These methods, and many others, yield camphene of varying 

 degrees of purity ; method 3 gives a very pure camphene, while 

 the use of metallic acetates yields a mixture of camphene with 

 bornyl acetate and other bodies. 



CH.,- 



CH 3 - 

 :h„ — 



-C— CH ; 



— C 



I 

 CH 3 



(X.) Pinene. 



H 



CH CH 2 C CH— CI 



I 



CH 3 — C— CH 



I 

 CH., CH.. C — ^— CH— — H 



I 

 CH 3 



(XI.) Pinene hydrochloride. 



CH, 



-CH- 



-CH 



CH 



CH 3 — C— CH 3 



I 

 -C 



CH 



I 



CH 3 



(XII.) Camphene. 



The next stage in the process is the so-called " esterification " 

 — the conversion of camphene into bornyl acetate (XIII.). 

 Bertram and Walbaum l found that when camphene is dissolved 

 in about its own volume of glacial acetic acid and allowed to 

 stand at slightly elevated temperature with about 5 per cent, 

 of sulphuric acid, it adds on the elements of acetic acid and is 

 converted into bornyl acetate. 2 Bornyl acetate is an oil boiling 

 with some decomposition at about 225 C. ; it distils at 107 C. 

 at a pressure of 13 mm. ; it is readily volatile in steam. 



The bornyl acetate is now saponified, whereby borneol (XIV.) 

 is obtained. This is accomplished by treatment with alcoholic 

 caustic soda, sodium acetate resulting as a by-product. The 

 resultant borneol is, with the exception of its optical inactivity, 

 identical with the naturally occurring Borneo camphor. 



The final operation in the synthesis consists in the oxidation 

 of the borneol to camphor. 



CH 2 CH CH 2 CH 2 CH CH 2 



CH 2 



-CH- 



-CH, 



CH 3 -C- 

 CH 2 C 



-CH 3 



CHOOC.CH, 



CH 3 — C- 



I 

 CH, C 



-CH, 



CHOH CH 



CH3 C CH; 



I 



-c 



CO 



CH 3 



(XIII.) Bornyl acetate. 



CH, 



(XIV.) Borneol. 



CH 3 



(XV.) Camphor. 



1 Jour.f.prak. C/iem., N.F. 49, I. 



2 In the synthesis of camphor it is really zVo-bornyl acetate and z'^-borneol 

 that are obtained. The differences between the ordinary and iso-compounds are 

 slight. The nature of the isomerism is not clear. It is not one of position, for 

 both borneol and isoborneol result from the reduction of camphor. Moreover, 

 isoborneol yields ordinary camphor on oxidation. For simplicity, therefore, the 

 terms "bornyl acetate" and " borneol" are employed throughout this article. 



