— 131 — 



The ready conversion of the corresponding methyl-group of p-cymene 

 into a carboxyl group has already been known for a long time: formation 

 of cuminic acid 1 ). The dibasic acid formed after administering citral 

 in the organism, has most probably the following constitution: — 



CH 



)C:CH.CH 2 .CH:C.CH 2 COOH 



^^ COOH 



i. e., 7-methyl octadiene-3,6-dicarboxylic-i,3 acid. 



On the zinc dust distillation of the ammonium salt it yielded a 

 pyrrol derivative which gave an intense colour reaction with pine- 

 wood; for this reason, it belongs to the succinic acid series. When 

 treated with sodium amalgam, the acid remained unchanged. Attempts 

 of abstracting water by means of acetyl chloride were unsuccessful 2 ). 

 Besides this crystalline acid, citral yields in the organism an isomeric 

 amorphous acid 3 ), of which the product of inversion was obtained in 

 crystalline form; it is probably formed by oxidation of one of the 

 methyl-groups in the end-position. The dibasic acid is also formed in 

 the organism after administration of geraniol, the alcohol corresponding 

 to citral, whilst after giving nerol, only insignificant quantities can be 

 detected in the urine. This shows either that nerol contains small 

 quantities of geraniol, or that in the organism a partial conversion by 

 displacement of a double linking takes place. Geranic acid 4 ), on the 

 other hand, which is formed by oxidation of citral, yields abundant 

 quantities of the dibasic acid after administering it to a rabbit. 



Likewise as the aliphatic citral can be converted into two stereo- 

 isomeric cyclic derivatives a- and fi - cyclocitral , geranic acid also 

 can be converted into two corresponding cyclic products. Dilute 

 acids act on aliphatic terpene compounds in such manner, that they 

 dissolve the double linkings present by attaching the elements of water; 

 the hydroxyl- groups then attach themselves preferably to the carbon 

 atoms which carry methyl-groups 5 ). On hydrolysis of geranic acid there 

 is formed first of all: — 



(CH 3 ) 2 • C(OH) • CH 2 • CH 2 • CH 2 • C(OH) • CH 2 • COOH 



CH 3 



The closing of the ring takes place in the first instance in the 

 sense of formula I; according to the direction in which water is split 

 off, a- and /?-cyclogeranic acids are formed: — 



*) Ziegler, Arch. f. exper. Pharmakol. 1 (1873). 



2 ) H. Hildebrandt and C. Harries, Beitr. zur Chemie u. Physiol. 4: (1903). 



3 ) H. Hildebrandt, Arch. f. exper. Pharmakol. 46 (1901). 



4 ) Berl. Berichte 26 (1893), 2717. 



5 ) Tiemann, Berl. Berichte 28 (1895), 2137, and 31 (1898), 882. 



9* 



