- 138 - 



however, had to be determined still, has now been recognized as A 1 - 

 acetylcycl opentene. This statement has been made in a joint paper 

 by O. Wallach and W. H. Perkin jun. 1 ). Perkin, when oxidising the 

 ethyl ester of the zl 1 -cyclohexene acetic acid with ozone 2 ), had obtained 

 an aldehydo ketonic ester (I) which, when boiled with sulphuric acid, was 

 converted into z( 1 -acetyl cyclopentene (II) which could be identified 

 with the ketone C 7 H 10 O obtained from the acid itself. 



7 CH 2 - CHO CH 2 — CH 2X 



I. H C< y CO.CH 2 .COOR II. | J>C.CO.CH 3 



x ch 2 — ch/ ch 2 — ch y 



By condensing cyclopentanone with bromo-propionic ester accord- 

 ing to the series of reactions generally used for the preparation of 

 tetrahydrated extracyclic ring ketones 3 ), Wallach had also succeeded 

 in producing zl 1 -acetyl cyclopentene and had also recognized its identity 

 with the ketone obtained from cyclohexene acetic acid, because the 

 derivatives of the two ketones possessed the same properties (oxime 

 m. p. 90 to 9 1 °, benzoyl oxime m. p. 1 1 6 to 1 1 7 ; semicarbazone m. p. 203 

 to 204 ). According to Perkin's experiments it is to be assumed that 

 A ^cyclohexene acetic acid produces in the first place a ketonic aldehyde 

 which is immediately converted, by internal condensation, into acetyl 

 cyclopentene. Such an unlooked-for result of an oxidation with per- 

 manganate shows the extreme caution which must be exercised in for- 

 ming theories regarding the constitution of a body from oxidative analysis. 



Cinnamic acid. With regard to the complicated isomerism of 

 the different cinnamic acids, new and far-reaching researches have 

 been published, the main features of which we will briefly pass in review. 



E. Erlenmeyer jun. 4 ) has made investigations into the problem 

 as to what is the origin of the difference between synthetic cinnamic 

 acid and natural cinnamic acid from storax. The two acids differ, 

 for instance, in the manner in which they crystallise from ether, as 

 well as in regard to solubility. The synthetic acid melts at 132 to 

 1 33 , the acid from storax at 134 to 13 5 . It was shown that syn- 

 thetic cinnamic acid is a uniformly crystallising mixture made up of 

 about equal parts of storax-a-acid and an isomeric combination termed 

 hetero - a - cinnamic acid. It is very difficult to split up the mixture 

 by crystallisation, as the two component parts evidently exert mutual 

 molecular attraction. No admixture of other products could be detected. 



*) Berl. Berichte 42 (1909), 145. 



2 ) Journ. chem. Soc. 93 (1908), 1946. 



3 ) Report November 1908, 166. 



4 ) Berl. Berichte 42 (1909), 502. 



