84 Biological Chemistry. 



Conversely, when a ketone is treated with nascent 

 hydrogen, a secondary alcohol is regenerated 



R, R ' 



>CO-fH 2 = >CHOH 

 R'/ R'< 



From these reactions a considerable analogy between the 

 ketones and aldehydes may be predicted. Their relation- 

 ship may be expressed by the following formulae : 



>co >co 



H/ ,. R'/ 



Their reactions are in many respects similar. Thus, 

 they react with phosphorus pentachloride to yield dichloro 

 derivatives, in which both chlorine atoms are attached to 

 the same carbon atom of the general formula 



R-CC1 2 R' or 



They also form similar addition products with sodium (bi) 

 hydrogen sulphite and hydrocyanic acid (but not with 

 ammonia), and they form similar " condensation " products 

 with phenylhydrazine, hydroxylamine, and semicarbazide. 

 The constitution of the products thus formed can be readily 

 derived by substituting R' for H in the aldehyde group 

 in the equations given above. 



The ketones differ from the aldehydes, however, in 

 certain particulars. They are not oxidized nearly so 

 readily, and when oxidation does takes place they yield a 

 mixture of acids with a smaller number of carbon atoms 

 than the ketone. Thus acetone, CH 3 CO CH 8 , on oxida- 

 tion yields a mixture of acetic (C 2 H 4 O 2 ) and carbonic acids. 

 The chemical analogy between the ketones and the alde- 

 hydes is so close that a further detailed discussion of the 

 chemical properties of the former is unnecessary. 



The ketones are generally named after the alkyl 



