86 Biological Chemistry. 



distinction to the aldehydes, acids with a smaller number 



of carbon atoms. They can be represented by the general 



z> 

 formula ^>00, where R and R' may be the same or 



different alkyl radicles. 



ADDENDUM TO PARTS IV. AND V. SUBSTITUTED 

 ALDEHYDES AND KETONES. 



Aldehydes and ketones are also known in which the 

 hydrogen of the alkyl radicle is substituted by a halo- 

 gen atom. Certain of these compounds are of techno- 

 logical importance by virtue of their powerful narcotic 

 action. 



Chloral The chief of these is chloral, CC1 3 CHO, 

 which may be regarded as acetaldehyde in which three 

 of the hydrogen atoms of the methyl group are substituted 

 by chlorine. It is formed by the action of chlorine on 

 alcohol by a series of somewhat complex reactions, and 

 was originally isolated by Liebig. It is an oily liquid, 

 boiling point 20, which readily forms a crystalline addition 



product with water, to which the formula CC1 3 CH^_~,. 



may be assigned. The crystals, which melt at 57, are 

 soluble in water; it is in the form of the hydrate that 

 it is generally employed as a drug. Chloral hydrate 

 exhibits most of the characteristic aldehyde reactions, and 

 is readily oxidized to trichloracetic acid that is, acetic 

 acid in which three of the hydrogen atoms are replaced 

 by chlorine (see p. 90). 



2CC1 3 CHO + 2 = 2CC1 3 - C0 2 H 



Other analogous more complex substances are known, 

 such as butyl chloral, which find a limited application in 

 medicine as narcotics or hypnotics. 



