THE CHEMICAL ACTION OF LIGHT 253 



takes place much more slowly than in the case of either of 

 the other alcohols. 



Perhaps the most interesting of the oxidations effected by 

 quinone under the influence of light is that of the polyhydric 

 alcohols, such as glycerol, erythrol, af-mannitol and dulcitol, 

 each of which loses two atoms of hydrogen and is converted 

 into the corresponding aldehyde. 



These changes are striking in so far as previously they 

 were known to occur only under the influence of relatively 

 powerful oxidising agents, such as nitric acid or an alkaline 

 hypobromite. A particularly interesting case is the oxidation 

 of glucose by quinone in sunlight to glucosone, as follows : 

 CH 2 (OH) . CH(OH) . CH(OH) . CH(OH) . CH(OH) . CHO -> 



Glucose. 



CH./OH). [CH(OH)l . CO . CHO 



Glucosone. 



Other quinones behave with alcohols in the same way as 

 benzoquinone ; this is especially true of thymoquinone, which 

 in ordinary alcoholic solution gives thymoquinol and aldehyde. 

 The action of phenanthraquinone or isatin on alcohol takes 

 place, however, very slowly. 



Formic acid is fairly rapidly oxidised by quinone in sun- 

 light to carbon dioxide, quinol being the other product. 1 The 

 fatty acids (acetic and propionic acid) are only very slowly 

 affected and the nature of the products (other than quin- 

 hydrone) could not be ascertained. Hydroxy-acids (lactic, 

 malic and tartaric) are oxidised by quinone to carbon dioxide ; 

 the corresponding keto-acid could not be isolated. 



But quinones are not the only compounds which are capable 

 of being reduced by alcohols under the influence of sunlight : 

 ketones and aldehydes are similarly affected, albeit, as a rule, 

 much more slowly and incompletely. In the case of the 

 paraffinoid ketones, the action is of a complex character (see 

 Section VII.) but is relatively simple in the case of benzenoid 

 ketones : thus, benzophenone (4 grm.), in presence of alcohol 

 (20 cc), is transformed in eight days almost completely into 

 benzopinacone : 2 



C 6 H 5 C 6 H 5 C 6 H5 



2 CO + C 2 H c O = HO . C C . OH + C.H.O 



C 6 H 5 C,iH 5 C 6 H 5 



Benzopinacone. 



1 Atti R. Accad. Lincei, 1901, 10, i. 92. 2 Ber. 1900, 33, 291 1 



