— 174 — 



that this body in particular contains a larger proportion of Wallach's 

 a-terpinene than of the y- compound. The terpinenes which are 

 obtained from phosphate of carvenylamine by dry distillation, from 

 chlorinated ketone and from chloro-carvenene, behave in a similar 

 manner. 



In all these instances, therefore, the terpinene preparations show 

 the optical behaviour which is to be expected on the basis of their 

 probable constitution, and of Bruhl's rules for the optical activity of 

 conjugated double -linkings. The synthesis of terpinene from sabina- 

 ketone apparently contradicts the above findings. Auwers, however, 

 is of opinion that these contradistinctions are entirely cleared up if 

 we assume that the hydrocarbon which is formed consists of 5O°/ 

 each of either a-terpinene and of a hydrocarbon with the formula 



CH 9 -( X ^—-> — C Q H, 



or of mixture of a- and y-terpinene and the hydrocarbon in question. 



It results from these investigations that all the processes which 

 lead via terpin produce terpinene-derivatives in which a-terpinene can 

 not be regarded as the characteristic constituent. From the terpinene 

 hydrohaloids, the a -terpinene- content cannot be expected to exceed 

 50 °/ in the most favourable case. For obtaining a-terpinene-prepar- 

 ations which, although not pure, are of a comparatively high percentage, 

 Auwers regards the method from carvone via dihydrocarveol as the 

 best, on account of its ease and cheapness. Semmler regards car- 

 venene as a particularly pure a-terpinene, but Auwers cannot agree 

 with this view, because by this process also, the action of nascent 

 hydrochloric acid produces conditions which afford no guarantee of 

 a uniform final product. The optical investigation of chloro-carvenene 

 and of carvenene, which has been repeated by Auwers, showed some 

 slight discrepancies with the results of Klages and of Semmler, but it 

 agreed in respect of the divergencies such as have been observed in 

 the case of numerous other bodies with conjugated double linkings. 

 Carvenene does not appear to be identical with a-terpinene from 

 o-cresol. The latter possesses the lowest b. p. and the least density 

 of all terpinenes known. It also differs from the others in its behaviour 

 towards the action of sulphuric acid. 



These results lead Auwers to regard it as beyond question that 

 optically the terpinenes are no exception to Bruhl's rules, and that in 

 determining their constitution, the physical, and especially the optical, 

 behaviour should occupy an important place, together with the 

 chemical tests. 



