TERPENES AND ESSENTIAL OILS, I. 61 



Ea'periment 11. — Tliere were employeed 20 grams of limonene liydrocliloride, 

 100 cubic centimeters of absolute ether and 10 grams of magnesium prepared with 

 iodine according to the method of Von Baej^er." This means of. rendering the 

 magnesium active was finally found to be the most satisfactorj^, as with the metal 

 so prepared the Grignard reaction starts immediately withoiit the aid of any otlier 

 catalyzer and continues to completion with great vigour. The reaction was 

 carried out in the apparatus used for Experiment 10, 24 grams of benzaldehyde 

 (free from benzoic acid) being added to flask No. 2. The contents of all flasks 

 were worked up in the usual manner. 



Flask No. 1 gave 5.2 grams of an oil, principally C'n.His, representing the por- 

 tion of CioHijMgCl which was insoluble in the quantitj' of absolute ether used. 

 The precipitate with benzaldehj'de formed in flask No. 2 was very thoroughly 

 washed with absolute ether and immediately worked up; the total oil being 

 10.6 grams. The following analytical data were obtained: 



15.56 grams substance (calculated) gave 1.93 grams magnesium and 3.03 grams 



chlorine. 





Found 



Calculated 





(percent). 



(percent). 



Mg 



12.4 



14.7 



CI 



19.48 



21.5 



From the 10.0 grams of total oil tliere were isolated 0.2 gram benzoic acid, 

 9.1 grams of an oil boiling between 177° and 182°, the latter was converted into 

 16.5 grams benzaldehyde phenylhydrazone melting at 154°, and 1 gram of a 

 tarry residue remained in the distilling flask. 



Flask No. 3 contained only a trace of magnesium and yielded a total of 21 

 grams of oil boiling between 170° and 183°; from the latter a quantity of 

 benzaldehyde plienyldrazone corresponding to 12.96 grams benzaldehyde was 

 isolated. The remaining liquid which in amount was 10.8 grams, after removing 

 the excess of phenylhydrazine, was the dihydro-terpene Ci„His. The calculated 

 amount of pure CioHu which would be set free from CjoH^MgCl by 9 grams of 

 benzaldehyde (formed by decomposing this magnesium compound in flask No. 2) 

 is 12.4 grams, if the course of the reaction is that which has been assumed in 

 this paper. This agreement is a close one when the inevitable losses in frac- 

 tionation are considered. In this experiment, therefore, the reaction has been 

 shown to proceed qnantitatively according to our assumptions. 



The combination of magnesium chloride and benzaldehyde which has 

 been so fully discussed^ when freshly prepared is exceedingly unstable 

 in the air, oxidizing upon exposure with a marked evolution of heat and 

 with reddening. When left standing under absolute ether it is fairly 

 stable, especially if present in a thick layer, so that if such a thick layer 

 is allowed to stand over night in the open air but little benzoic acid is 

 obtained, the benzaldehyde on acidifying being in greater part recovered 

 as such. Oxidation is rapid if the solid is suspended in ether and a 

 stream of air or of oxygen is passed in, but under these circmnstances 

 peroxide formation takes place, and for this reason Ijenzene was chosen 

 instead of ether. 



It is entirely premature at the present time to enter into a discussion of 



^-Ber. d. Oliem. Ges. (1905), 38, 2759. 



