THE CHEMICAL ACTION OF LIGHT 259 



Azoxybenzene is derived from nitrosobenzene in the manner 

 experimentally demonstrated by Bamberger : in this case by the 

 intervention of benzoylphenylhydroxylamine : 



C 6 H 5 NO + C 6 H 5 N <£q C H = C « H 5 C0 ■ 0H + C 6 H s NO : NQHs 1 



Finally it has been shown by Knipscheer 2 that azoxybenzene 

 is transformed under the influence of light into its isomeride 

 o-hydroxyazobenzene : 



;> N:N / } 



•S N x -> n,oh 



u 



(no ^-hydroxyazobenzene being formed in this case). 



Very few other aldehydes are as active as benzaldehyde 

 in reducing nitrobenzene ; anisaldehyde alone produces a 

 similar series of changes. Salicylic, cinnamic and vanillic 

 aldehydes, piperonal and furfural are without action on nitro- 

 benzene and the same is true of the ketones, acetone and 

 acetophenone. A similar series of changes, giving rise to an 

 even more complex set of products, has been observed in the 

 case of nitrobenzene and benzaldehydephenylhydrazone. 3 



Intramolecular Oxidation 



Several remarkable instances have been discovered in which 

 one group in a molecule is oxidised at the expense of another 

 under the influence of light. One of the most striking is 

 afforded by 0-nitrobenzaldehyde, 4 which is rapidly changed on 

 exposure to light into o-nitrosobenzoic acid. The change may 

 be regarded either as a case of intramolecular rearrangement 

 falling under Class V. ; or as an intermodular action in which 

 two molecules of the same kind take part, thus : 



/N0 2 CHO\ /NO 



QH / + >C 6 H 4 = 2C 6 H 4 < 



\CHO N0 2 / \CO.OH 



1 Angeli's formula for azoxybenzene. 



' Proc. K. Akad. Wetensch. Amsterdam, 1902, 5, 51. 



1 Ciusa, Gazzetta, 36, ii. 94. 



4 Atti R. Accad. Lincei., 1901, 10, i. 228 ; Ber. 1901, 34, 2040. 



