Tri-chlor Aldehyde—Chloral

It will be recalled that this compound is the intermediate product in the formation of chloroform from alcohol. The alcohol is first oxidized to aldehyde by means of chlorine, (p. 115), the substitution of chlorine in the aldehyde then taking place as above. 

It is possible that this oxidation takes place by the loss of hydrogen through the direct action of chlorine without the action of oxygen (p. 222). 

In the preparation of chloroform the tri-chlor acet-aldehyde then reacts with an alkali present yielding chloroform and the alkali-metal salt of formic acid, as follows  

Chloral.—Chloral, or tri-chlor acet-aldehyde, was first prepared by Liebig in 1832 by the chlorination of alcohol as above. It may also be obtained by the direct action of chlorine upon acet-aldehyde. It is an oily liquid with a sweet suffocating odor. It boils at 97.7°. It does not mix with water but on boiling with water it forms a hydrated compound which crystallizes in large clear crystals, readily soluble in water. This is known as chloral hydrate. The structure of chloral hydrate is probably that of an addition product, viz., a, chlorinated di-hydroxy alcohol. In this compound we have an exception to the general rule that two hydroxyl groups can not be linked to the same carbon atom. 

This constitution of the hydrate is indicated by the fact that it does not give the aldehyde reaction with fuchsine as does both acet-aldehyde and chloral. Also by the fact that the ethyl ester of such a di-hydroxy alcohol is known and is formed from chloral by reaction with alcohol. 

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