50 BACON. 



Tlie terpeiies jDresent a difficult field for investigation. The usual 

 methods of organic synthesis often fail in working with them and general 

 methods of passing from one class of compounds to another are not only 

 not well developed, but they frequently fail even with the greatest precau- 

 tions. The terjjenes, being, hydrocyclic bodies, partially unsaturated, are 

 very sensitive to reactions which would present conditions where poly- 

 merization is possible, while oxidation and many other reactions often 

 involve their complete destruction or the formation of noncr5rstalline 

 derivatives and smears. Nevertheless, it appears as if an intimate con- 

 nection between the terpenes and the essential oils and perfume substances, 

 as well as between them and the plant alkaloids exists structurally, and 

 therefore the investigation of synthetic methods among the terpenes be- 

 comes of vital imi^ortance. The great need is to discover methods gen- 

 erally applicable of passing smoothly from the terpenes to their deriva- 

 tives and the means of obtaining the latter in the pure state. The Grig- 

 nard reaction, which in the last few years has developed so many other 

 fields of organic chemistry, naturally suggests itself, for the hydrogen 

 halides of the terpenes are in almost all cases compounds easily prepared. 

 It was therefore decided in this laboratory to take up the study of the 

 Grignard reaction in its application to the terpene series and although 

 the work is not by any means completed, the results obtained seem to be so 

 promising that it was deemed advisable to i^ublish this preliminary notice 

 so as to reserve the field. 



It has definitely been proved that limonene hydrochloride reacts with 

 magnesium in the presence of absolute ether to form a magnesium-halogen 

 compound, and that the latter, when decomposed by -water, gives a hydro- 

 carbon Ci„His, this takes up hydrogen chloride in the cold and, after 

 the action of magnesium and then of water, gives CI^oH^o. The reaction of 

 benzaldehyde on the mixed compound of ethyl ether and magnesium 

 hydro-limonene chloride is extraordinary ; the carbinol which is to be ex- 

 j)ected, is not formed, but instead the benzaldehyde Ijehaves as if it con- 

 tained hydroxyl, decomposing the Grignard body in the same manner 

 as water or an alcohol would. It is at first thought very surprising that 

 lienzaldehyde should he capable of reacting as if it possessed a tautomeric 



form -p-n"-^^" However, Freer' showed some 3'ears ago that aldehj^les 



react with sodium as if thej^ contained hydroxyl groups, and 'Net * and 

 his students have recently proved that aldehydes, in many cases, do assume 

 the enol form liefore reacting, so that an equilibrium between enol and 

 keto structure is to be expected in these bodies. It is more difficult to 

 believe in such a structure in the case of benzaldehyde, in which body, if 

 we refer to our ordinary conceptions of organic chemistry, we will need 



"Am. Ghem. Jour. (1896), 18, 552. 

 ^Ann. Ghem. [Liehig) (1907), 357, 258. 



