— 179 — 



Graziani and Padoa 1 ) have furthermore investigated the relations 

 which exist between molecular structure and phototropy. In the course 

 of these it was found that the hydrazones of formula I, in which the methyl 

 occupies a position adjacent to the nitrogen-atom, exhibit no phototropy. 

 Of the 1 , 3, 5-xylylhydrazones (II) which have so far been examined, in 

 which two methyl-groups stand in the meta-position towards the nitrogen- 

 atom, only one was faintly phototropic. 



CH 3 CH 3 



I <^~ \— NHNrCHR II / \— NHNrCHR 



CH 3 CH 3 



The authors describe: benzaldehyde-1, 4, 5-xylylhydrazone, small, deep- 

 yellow needles, m. p. 89° (from glacial acetic acid). Anisic aldehyde- 

 1,4, 5-xylylhydrazone, yellowish leaflets, m. p. 117° (from alcohol). Cinna- 

 mic aldehyde-1, 4, 5-xylylhydrazone, yellow leaflets, m. p. 121° (from alcohol), 

 cuminol-1, 4, 5-xylylhydrazone, small yellow needles, m. p. 85° (from alcohol), 

 piperonal-1, 4, 5-xylylhydrazone, yellow scales, m. p. 85° (from alcohol), 

 vanillin-1, 4, 5-xylylhydrazone, white needles, m. p. 158° (from alcohol), 

 salicylic aldehyde-1, 4, 5-xylylhydrazone, yellowish scales, m. p. 134° (from 

 alcohol), cinnamic aldehyde-1, 3, 5-xylylhydrazone, yellow, phototropic 

 crystals, m. p. 142 to 143° (from alcohol), acquiring a more intense brown 

 colour when exposed to sunlight for 2 to 3 minutes, but resuming their 

 original colour at from 75 to 78°, piperonal-1, 3, 5-xylylhydrazone, small 

 yellow needles, m. p. 135 to 136° (from alcohol), and anisic aldehyde- 

 1,3, 5-xylylhydrazone, deep yellow needles, m. p. 144 to 145° (from alcohol). 



On the occurrence of benzaldehyde in parts of plants, see p. 161. 



It appears from the results of the investigations recently published 

 by Bloch, Hohn, and Bugge 2 ), Hohn and Bloch 3 ), and Bugge and Bloch 4 ), 

 that many cyclic aldehydes combine with hydrogen persulphides into 

 condensation- or additive -compounds which are partly tolerably stable 

 and are mostly capable of giving reactions. A whole series of such com- 

 pounds with their derivatives are described, but we can only refer briefly 

 to a few. 



In certain conditions benzaldehyde condenses with hydrogen persul- 

 phide, forming dithiobenzoic acid (phenyl carbithio acid) (I). In a similar manner 

 salicylic aldehyde yields o-hydroxyphenyl- carbithio acid (II), and anisic 

 aldehyde gives rise to dithioanisic acid (p-methoxyphenylcarbithio acid) (III). 



*) Atti R. Accad. dei Lincei, Roma V. 19 (1910), II. 193. Quoted from Chem. Zentralbt. 

 1910, II. 1213. 



2 ) Journ. f. prakt. Chem. II. 82 (1910), 473. 

 8 ) Ihidem 4S6. 

 *) Ibidem 512. 



12* 



