B.— CHEMISTRY 



47 



^ra«j-elimination of radicals takes place as a rule more readily than 

 m-elimination, and more recently evidence has accumulated that this is 

 also the case with the aldoximes and their derivatives. 



The assumption which was formerly made that, in a pair of stereo- 

 isomeric aldoximes, the isomer which was the less easily dehydrated had 

 the hydrogen and hydroxyl on opposite sides of the CN group is almost 

 certainly wrong. 



Of the different methods of converting p-benzaldoximes into the cor- 

 responding benzonitriles, that which proceeds most smoothly, and is 

 probably least obscure in its mechanism, consists in the conversion of 

 the oxime into its acetyl derivative and the treatment of this with aqueous 

 sodium carbonate. 



. H OH 



H2O 



Ac • •• 



Before reaction. 



After reaction. 



Fig. 6. 



The elimination of acetic acid from the oxime acetate is a reaction 

 which can be very clearly represented with the aid of the tetrahedral 

 octet, and with this method of representation it is indicated plainly that 

 /raws-elimination should take place more readily than f?V-elimination. 



When the acetyl derivative of the p-oxime is treated with sodium 

 carbonate the products are water, benzonitrile, and the acet-ion. The 

 components of benzonitrile and of the acet-ion are already present in the 

 acetyl derivative, and since both are indifferent towards sodium carbonate 

 solution their liberation must take place as a secondary consequence of 

 some direct action of the solution on the molecule of the acetyl derivative. 

 This is clearly the removal of a proton by union with a hydroxyl ion 

 from the alkaline solution to form water. The elimination of acetic 

 acid thus consists of a chain of three events, each dependent on the next. 

 The first is the removal of the proton. The second is the movement of 

 the nitrogen nucleus to bring it into alignment with the phenyl-carbon 



