96 



When we disregard the formation of diphenylmethane it is be- 

 yond all doid^t that the formation of pinacone or benzhydrole is in 

 the first instance dependent on the reaction of the medium. 



The nature of the metal is apparently of secondary importance 

 and can only exert an influence in so far as it yields OH-ions. 

 (Magnesium, sodium). 



So long as the reaction is acid, even ever so feeble, pinacone is 

 exclusively formed ; but no sooner do OH-ions occur than we notice 

 the appearance of the hydrole. 



This even takes place with aluminium-amalgam in 80 7o alcohol 

 where we may take it for granted tiuit the liquid is practically 

 neutral, although the possibility is not excluded that at the boundary 

 layer of the metal a very small excess of OH is temporarily present. 



If the excess of OH-ions is small w^e can still detect the pinacone 

 in the presence of hydrole, but when it becomes more considerable 

 pinacone is soon no longer present. 



The cause of the non-occurrence of i)inacone in strongly alkaline 

 solutions is now very easy to explain. If we boil a solution of 

 pinacone with sodium ethoxide it gets converted into a mixture of 

 benzophenone and hydrole. 



During the reduction in an alkaline medium the pinacone gene- 

 rated will be contiiuiously converted into the above mixture of which 

 the keton will be again reduced, so that finally all will have been 

 converted into hydrole. 



Apparently the latter, in strongly alkaline liquids, becomes the 

 only direct reduction product. 



That this, however, cannot be the case is shown from the course 

 of the reduction in a feebly alkaline medium where also pinacone 

 may be retained. 



In a neutral solution much larger quantities of pinacone may be 

 retained and owing to the fact that they are not reduced any further 

 we have already come to the conclusion that pinacone cannot be 

 an intermediate reaction product as the following scheme might express: 



2 C.H^COCeH, ^ [(C,H3),C0H], ^ 2 (C.HJ.CHOH. 



In an alkaline solution, pinacone can be. incidentally, an inter- 

 mediate product owing to a secondary reaction : 



2 C.H^COC.H, ^ [(G^HJ^COH], -^ (C.HJ.CHOH -f (C,HJ,C(), etc. 

 We might assume that, apart from this secondary hydrole for- 

 mation, a direct addition of an entire molecule of hydrogen to the 

 ketone takes place under the influence of the OH-iqns. Then howe- 

 ver it would be strange that in presence of an excess of OH-ions, 



