— 194 — 



nucleus to exist under conditions of different stability which are sus- j 

 ceptible of inter-conversion. 



According to Erlenmeyer the esters of cinnamic acid and the benz- 

 aldehydes may be differentiated by their odour by those who have acquired 

 some experience in this field of investigation. Of the two benzaldehydes, 

 for instance, hetero-benzaldehyde has a much more acrid odour than storacic 

 benzaldehyde, of which the odour is bland. 



The detection of the differences in the properties of the cinnamic acids 

 and benzaldehydes to which reference is made above has induced the 

 authors to extend their research to the investigation of benzene and stil- 

 bene, and here they discovered similar differences as in the benzaldehydes. 

 Other differences, such as the formation of various derivatives and dif- 

 ferences in the rates of velocity of reaction cannot, according to Erlenmeyer, 

 be expected in isomerides of identical atomic structure. These isomerides 

 however, must be distinguished by differences in energy. 



In order to discover whether the peculiar behaviour of the cinnamic 

 acids may perhaps be due to impurities arising from derivatives, Erlenmeyer 

 and Hilgendorff 1 ) have prepared mixtures of storacic cinnamic acid with 

 various such derivatives. They examined mixtures with p-, o-, and m-chloro- 

 cinnamic acid, with p-, m-, and o-hydroxycinnamic acid, with o- and £>-methoxy- 

 cinnamic acid and with methylcinnamic acids. Among all the mixtures 

 which were prepared by the authors that consisting of 1 part ^-methyl- 

 cinnamic acid and 99 parts storacic cinnamic acid resembles synthetic 

 cinnamic acid to a quite extraordinary degree, but the presence of this 

 acid may be proved beyond doubt by oxidation and separation of the 

 terephthalic acid. Attempts at oxidation with heterocinnamic acid afforded 

 no trace of terephthalic acid. When a mixture contains 10% methyl- 

 cinnamic acid^that body may be removed by fractional precipitation, but 

 a 20°/o content of methylcinnamic acid cannot be detected by combustion. 

 The result of the crystallographic examination of the various mixtures was 

 that of all the admixtures recorded above only that with methylcinnamic 

 acid makes a mixture with any resemblance to synthetic cinnamic acid. 



So far it had not been established whether the two constituents, 

 storacic and hetero-cinnamic acids, which have been separated out from 

 synthetic cinnamic acid could be further split up. The results of investig- 

 ations into this subject which have been carried out by Erlenmeyer and 

 G. Hilgendorff 2 ) agree that synthetic cinnamic acid prepared from chlorine- 

 free benzaldehyde or from natural bitter almond oil free from hydrocyanic 

 acid, does not owe such of its properties as differ from those of storacic 

 cinnamic acid to any impurity, but that it consists of a mixture of storacic 

 cinnamic acid and hetero-cinnamic acid which crystallise together. 



*) Biochem. Zeitschr. 34 (1912), 405. 

 2 ) Biochem. Zeitschr. 34 (1912), 417. 



