Terpenes Di-cyclic

Similarly pinane, the saturated di-cyclic terpene containing a telra-methylene group, is not a natural product but the corresponding unsaturated terpene with one double bond analogous to menthene is the chief constituent of turpentine. It is known as pinene and has the following constitution. 

The most important di-cyclic terpenes belong to the camphane group in which a penta-methylene ring is present. This five carbon... 

The most important of all of the oxygen derivatives of the terpene hydrocarbons are those of the di-cyclic group. Of these the most common is the well-known substance camphor, also termed Japan camphor. It is a ketone derivative of a di-cyclic terpene of the cam-phane type known as Bomylene. The corresponding alcohol derivative is known as Bomeol, or Borneo camphor. 

They are derivatives of saturated di-cyclic terpenes which in turn are related to the unsaturated di-cyclic terpenes thujene and fenchene which we have previously discussed (p.p. 822, 824). 

Camphor and Bomeol are therefore derived from a camphane di-cyclic terpene in which the isopropyl group joins the para carbons. The unsaturated di-cyclic terpene corresponding to camphor was at first supposed to be camphene but later work has proven that it is not camphene but Bornylene which has the structure corresponding to camphor. The constitution of camphene is still unestablished. 

Synthesis of Camphor.— The relationship of camphor to pinene, the terpene present in turpentine, is of especial interest and importance in connection with its synthesis. Pinene is the unsaturated di-cyclic terpene related to the saturated di-cyclic terpene pinane (p. 823). In both of these terpenes the di-cyclic arrangement is different from that in camphane and Bornylene in that the isopropyl group in forming the secondary cycle joins the meta carbons instead of the para. Now pinene, by addition of hydrogen chloride, forms a hydrochloride which has been referred to as artificial camphor. This hydrochloride is identical with the hydrochloric acid ester of Bomeol and may be converted into Bomeol by hydrolysis. Now as Bomeol can be oxidized to camphor we may thus obtain true synthetic camphor from pinene. The reactions, involving an intermediate product and then rearrangement of the secondary cycle in pinene, are as follows ... 

The most important group of the mono-cyclic terpenes is the dihydro cymene group the members of which are known as terpa-di-enes or mentha-di-enes with the composition CioHie which has been mentioned before as the unit terpene formula. Several of the hydrocarbons of this group are natural products in essential oils. 

Cyclic terpenes monocyclic (dipentene) di-cyclic (pinene). 

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