5 6 ALDEHYDES 



9. The aldehydes are able to react with alcohols with the 

 formation of condensation compounds known as acetals ; thus, 

 for example, acetic aldehyde reacts with ethyl alcohol as fol- 

 lows : 



CH 3 CH 3 



I HOC 2 H 6 OC 2 H 8 



O + = \/ + H a 



t/ HOC 2 H 5 c OC 2 H. 



Acetic Ethyl Acetal 



aldehyde alcohol 



By analogy, acetic aldehyde should also be able to react 

 with water as follows : 



CH 3 CH 3 



HOH I OH 



O + = / + H 8 



HOH _ OH 



This substance does not, however, actually exist, since a 

 compound having two or more hydroxyl groups attached to 

 the same carbon atom is, as a rule, unstable, and at once loses 

 water. Exceptions to this rule are, however, occasionally met 

 with; for example, chloral CC1 3 CHO forms a stable com- 

 pound, chloral hydrate, of the formula 



OH 



CC1 8 C OH 



10. Aldehydes exhibit a tendency to polymerize, that is, 

 for two or more molecules to combine together to form new 

 compounds of higher molecular weight. 



Thus two molecules of formaldehyde will combine together, 

 forming a compound known as paraformaldehyde (CH 2 O) 2 ; 

 this substance, which is a white solid, is obtained by evaporat- 

 ing an aqueous solution of formaldehyde. 



A second polymer formed from three molecules of formal- 

 dehyde is known as metaformaldehyde or trioxymethylene 

 (CH 2 O) 3 . This substance is produced by the spontaneous 

 polymerization of anhydrous formaldehyde. 



In the case of both the above polymers the molecules of 



