52 SCIENCE PROGRESS 



Pinene is thus represented as a bicyclic compound which 

 includes a dimethylated tetramethylene ring. 



The applicability of this formula in other directions may now 

 be considered. 



The production of crystals in moist specimens of oil of 

 turpentine has long been known and the composition of the 

 substance thus formed was established by Dumas and Peligot 

 in 1834. 1 The compound terpin hydrate contains the elements 

 of the hydrocarbon united with two molecules of water and a 

 molecule of water of crystallisation, C ]0 H 2 o0 2 . H 2 0. It is a 

 glycol which loses the elements of water very readily and 

 yields terpineol, an unsaturated monohydric alcohol C 10 H 17 OH. 

 Terpineol in its turn yields, by loss of water, dipentene (racemic 

 limonene) Ci H 16 , a hydrocarbon isomeric with pinene which is 

 freely converted into it by contact with dilute aqueous acids. 

 Terpineol and dipentene (limonene) are now known to have the 

 constitution assigned to them by Wagner 2 and these formulae 

 result from the hydrolytic disruption of the tetramethylene ring. 



Terpineol. Dipentene. 



HO . CMe 2 CH 2 : CMe 



CH CH 



CH„/^\CH 2 CH 2 f-^CH 2 



chL^/CH 2 ch1^ch 2 



CMe CMe 



That these formulae have been for some years generally accepted 

 by chemists is largely due to the timely support given to 

 Wagner's views by the researches of Baeyer. 



By the oxidation of terpineol Baeyer showed in 1896 3 that a 

 product is obtained, namely the methyl ketone of homoterpenylic 

 acid, which is identical with the product of hydrolysis of a pinonic 

 acid, and that acid is produced by the direct oxidation of pinene by 

 means of neutral permanganate. Starting from pinene in both 

 cases, therefore, the operations required are either hydrolysis 

 and subsequent oxidation (A) or oxidation and subsequent 

 hydrolysis (B). 



These processes are represented by the Wagner formulae 

 as follows : 



1 Annates Chim. Phys. 57, 334. 



2 Loc. cit. 3 Ber. 29, 2775. 



