iéi 



ühemistry. — "Action of sun-light on the cinnamic acids". By 

 Dr. A. W. K. DE Jong. 



The conliimed investigation has sliown that the peculiar behavionr 

 of cinnamic acid in the solid condition nnder the influence of sun- 

 light must be attributed to the ease with which it passes into the 

 metastable form. This metastable condition has been described first 

 by 0. Lehmann ') in 1885. Erlenmeyer Jr. has communicated a very 

 lengthy investigation as to the existence of different forms of cinnamic 

 acid in the Ber. D. Ch. G. and further in the Biochem. Zeitschr. 

 He comes to the conclusion tluxt of the normal cinnamic acid 

 there exist four different modifications, namely a- and (J-Storax cinnamic 

 acid and a- and /?-Hetero ciuiuxmic acid. Cinnamic acid derived from 

 plants consists of Storax cinnamic acid with but 0,57o of the Hetero- 

 acid whilst synthetic cinnamic acid is a mixture of about equal parts 

 of those acids. On heating their aqueous or dilute-alcoholic solutions 

 the «-acids are converted into the /J-acids. In Ber. 39 p. 158J, Ber. 

 42 p. 509 and Biochem. Zeitschr. 34 p. 355 some further convei'sions 

 of the a- into the (?-acids, and the reverse phenomenon, are commu- 

 nicated. The cinnamic acid used in my experiments was Storax 

 cinnamic acid (probably derived from hydrolysed coca-acids ; see 

 previous communication) as it was deposited from alcohol in the 

 well-formed, thick prismatic cryslals of Storax cinnamic acid (in 

 Ber. 42, p. 504 are found the photographs of the various forms). 

 On repeatedly recrystallising from warm 95"/^ alcohol which took 

 place in the said experiments the n-Storax cimiamic acid is converted 

 more or less into the /?-acid. This mixture "when illuminated always 

 yielded u- and /i-truxiilic acid. The transformation into /i-acid was 

 much promoted, because after dissolving the cinnamic acid in alcohol 

 the solution was made to evaporate rapidly by the shaking of the 

 dish. For it was noticed tiiat when an alcoholic solution of «-Storax 

 cinnamic acid is poured on to a glass plate and the alcohol allowed 

 to evaporate rapidly by blowing, only crystals of ("^-Storax cinnamic 

 acid are formed. These cryslals when illuminated gave only ^-truxillic 

 acid whereas the prismatic crystals of the «-Storax cinnamic acid 

 gave only «-truxillic acid. The crushing of the crystals caused no 

 change in the action of the light. 



From the research is thus shown that «-Storax cinnamic acid gives 

 «-truxillic acid when illuminated in the solid condition, whilst under 

 the same circumstances, ^-truxillic acid is formed from the /?-Storax acid. 



n Ber. 43, 4fil (1910); Graham Otto's Lehrbuch der Chemie Bd. I, 3e 

 Ablh., p. 57. 



13 

 Proceedings Royal Acad. Amsterdam. Vol. XVllI. 



