254 SCIENCE PROGRESS 



Acetophenone, in a similar manner, gives acetopinacone : 



QHj C 6 H 5 



I I 



HO — C C — OH 



I I 



CH 3 CH 3 



In these cases, the simple reduction to secondary alcohol is 

 masked by the tendency of two molecules of the latter to 

 undergo oxidation to form a pinacone. Benzopinacone is also 

 largely formed when benzophenone is exposed to sunlight in 

 certain hydrocarbon solvents, such as toluene, ethylbenzene 

 and the xylenes but other changes also occur in such cases 

 (see Section VII.)- 1 



Benzoin in alcoholic solution is reduced to hydrobenzoin 

 (its stereo-isomeride z'sohydrobenzoin being formed at the same 

 time) but a quantity of resin is also produced. 2 The main 

 action, however, is that expressed by the equation : 



C S H 5 . CO . CH(OH) . C 6 H 5 + C,H 6 = C 6 H 5 CH(OH) . CH(OH) . CH S + C 2 H,0 



When the diketone benzil, C 6 H 5 . CO. CO . C 6 H 5 is exposed 

 to light 3 in alcoholic or ethereal solution during a few hours, it 

 is partly reduced to benzoin, which combines with unchanged 

 benzil to form benzilbenzoin, 



2(C B H 5 . CO . CO . C 8 H 5 ) C 6 H 5 . CH(OH) . CO . C 6 H 5) 



a loose molecular compound which is resolved into its components 

 when melted or when boiled with benzene or alcohol. If the 

 action of light be prolonged, the benzilbenzoin which has 

 separated redissolves and a quantity of resin is formed together 

 with benzoin, benzil, benzoic acid and ethylic benzoate. 4 



The action of light on benzaldehyde is particularly striking 

 on account of the variety of products. The simplest product, 5 

 obtained in alcoholic solution, is a mixture of the two 

 stereoisomeric hydrobenzoins formed by reduction, thus : 



2C 6 H 5 . CHO + C 2 H e O = C 6 H 5 . CH(OH) . CH(OH) . C 6 H 5 + C 2 H 4 



Hydrobenzoin. 



A complex, polymerised form, (C U H 14 2 )4, of hydrobenzoin is 

 also produced. The polymerisation of benzaldehyde alone under 



1 Atti R. Accad. Lincei, 1910, 19, i. 645. 2 Ibid. 1901, 10, i. 92. 



3 Klinger, Ber. 1886, 19, 1862. 



4 Ciamician and Silber, Atti Lincei, 1903, 12, i. 235 ; Ber. 1903, 36, 1575. 



5 Atti R. Accad. Lincei, 1901, 10, i. 92. 



