Notes on scientific research. 149 



the reaction giving rise to acetic acid and to several other acids, among which in all 

 probability, is butyric acid. 



On the reduction of cinnamic acid see p. 134. 



Dihydrocarvenolide. Some time ago we recorded the reduction, by Wallach, of 

 the lactone i-carvenolide Ci Hi 4 O 2 to dihydrocarvenolide by Paal's method 1 ). Since that 

 time Wallach has continued his investigations 2 ) and has discovered that it is possible 

 to reduce the D-£-carvenolide obtained from d-carvone to D-Z-dihydrocarvenolide (m. p. 50 

 to 51°), a body which is identical with dihydropulegenolide of the same m. p. 1 ). Seeing 

 that the presence of a pentacyclic ring in pulegenolide, or rather in its parent-substance, 

 pulegenic acid, is a proved fact, it follows that carvenolide must likewise contain a 

 pentacyclic modification, that is to say, that when carvone tribromide is converted into 

 carvenolide, a ring-displacement occurs. Wallach has furthermore observed that pule- 

 genolide is not inactive, as was formerly believed to be the case, but faintly active, it 

 is remarkable that the activity becomes more pronounced after the reduction of the body. 



In the course of the preparation of ^-carvenolic acid (m. p. 135 to 136°) from 

 i-carvenolide by boiling with alkali, an isomeric acid, m. p. 104 to 105°, was detected 

 as a by-product. Wallach differentiates between this compound ^-i-carvenolic acid, 

 and that with a higher b. p. (a-^-carvenolic acid.) When melted wit potash, carvenolic 

 acid yields an acid with 7 carbon-atoms, probably a J^methylpentene carboxylic acid. 

 There is an easier way of preparing pulegenolic acid than from pulegenolide, namely 

 from the brominated lactone of pulegenic acid by boiling with sodium methylate. 

 Dihydrocarvenolic acid was prepared from i-, d- and ^-dihydrocarvenolide by saponi- 

 fication with potash-liquor. It is identical with the acid obtained from dihydropulegenolide. 

 When subjected to slow dry distillation it yields a hydrocarbon and an acid, which 

 may perhaps be identical with pulegene and pulegenic acid. An acid of the same 

 constitution as pulegenic acid is also formed when ^-dihydrocarvenolic acid is melted 

 with caustic potash at about 130°, but this acid does not appear to be identical with 

 pulegenic acid. Its amide has m. p. 115° and is lasvorotatory, whereas the amide of 

 pulegenic acid (m. p. 121°) is dextrorotatory. The amide of pulegenic acid ([«] D +29,05°) 

 is very difficult to reduce, which may be explained on the assumption that it contains 

 a semicyclic double-bond. This bond appears to unite with hydrogen with difficulty, 

 as has, for instance, been demonstrated already in the case of /3-fencholenic acid 3 ), 

 and as applies also to /?-campholenic acid. The saturated amide C 9 Hi 7 CONH 2 which 

 is obtained from pulegenic acid amide is only very faintly dextrorotatory ([«] D -f- 4,847°). 



CH-CH 3 



H 2 C 

 H 2 C 



CHCOO 



/ 

 CH-C(CH 8 ) 



Dihydropulegenolide = Dihydrocarvenolide. 



Bergaptene and xanthotoxin. It will be remembered that H. Thorns 4 ) has 

 ascertained the presence, in the peel of Fagara xanthoxyloides, of bergaptene and 

 xanthotoxin. Recently, in collaboration with E. Bastcke 5 ), Thorns has elucidated the 

 constitution of bergaptene. At an earlier date Pomeranz had been led to the belief, 



l ) Comp. Report October 1911, 126. — 2 ) Liebigs Annalen 392 (1912), 49. — 3 ) Comp. Report April 1911. 

 165. — *) Berl. Berichte 44 (1911), 3325; Report April 1912, 80. — 5 ) Berl. Berichte 45 (1912), 3705. 



