2 6o SCIENCE PROGRESS 



There is no evidence by which the question can yet be decided. 

 In view, however, of the relationship of this change with the 

 interaction of benzaldehyde and nitrobenzene discussed above it 

 will be considered in this section. 



The transformation of nitrobenzaldehyde differs from the 

 photochemical changes hitherto discussed on account of the 

 extreme rapidity with which it takes place : whereas the majority 

 of the interactions considered need several weeks or even 

 months for completion and in most cases are very incomplete, 

 the rate at which 0-nitrobenzaldehyde undergoes change is more 

 nearly comparable with that of ordinary photographic changes. 

 The nitroaldehyde is converted into the nitroso-acid even when 

 in the solid state, the colourless crystals becoming first green 

 but retaining their transparency and finally white and opaque 

 (Bruni and Callegari 1 ); in solution the transformation of the 

 aldehyde takes place so rapidly that, in a few hours, the tube 

 containing the liquid is full of crystals of the nitroso-acid. 



A solution of o-nitrobenzaldehyde in ethylic alcohol gives at 

 first ethylic nitrosobenzoate : as an alcoholic solution of o-nitroso- 

 benzoic acid does not esterify on exposure to light, the action 

 probably takes place as follows : 2 



C s U t <CHO + 2Et0H -* C ' H '<CH<gf; ■* C « H <<?O.OEt + EtOH 



Some o-nitrosobenzoic acid, however, is always formed, as in 

 the case of indifferent solvents. Methylic alcohol gives methylic 

 nitrosobenzoate but isopropylic alcohol gives only o-nitroso- 

 benzoic acid. The influence of structure is also strikingly shown 

 in the fact that meta-and para-nitrobenzaldehyde do not undergo 

 a similar transformation. Moreover, no such change occurs in the 

 case of o-nitrocinnamic aldehyde, N0 2 . C 6 H 4 . CH :CH . CHO ; 

 but most other ortho-nitro-aldehydes behave like o-nitro- 

 benzaldehyde. o-Nitropiperonal, 3 for example, gives o-nitroso- 

 piperonylic acid : 



CH -> < \o) C|iH;! \N0 2 ~* CH,( >C 6 H 2 ( NO ' 



2 :4-Dinitrobenzaldehyde gives o-nitroso-^-nitrobenzoic acid* 



1 Atti R. Accad. Lined, 1904, 13, i. 567. 



2 Bamberger and Elger, Ber. 1903, 36, 3645. 

 s Atti R. Accad. Lincei, 1902, 11, i. 277. 



4 Cohn and Friedlander, Ber. 1902, 35, 1265. 



