136 GLYCOLS. 



FOURTH GROUP. 

 A. DIATOMIC ALCOHOLS, C n II 2n + 2 2 (GLYCOLS). 



The diatomic alcohols are derived from the hydro 

 carbons of the marsh gas series by the replacement of 

 two hydrogen atoms by means of two hydroxyl-groups. 

 They are formed from the chlorides, bromides, and 

 iodides of the hydrocarbons C n H 2n by the exchange of 

 the chlorine, bromine, or iodine atoms for hydroxyl. 



The first member of this series, methylene alcohol 

 CH 2 (OH) 2 , is not known and can probably not exist. 

 Methylene iodide (p. 36), when treated with silver 

 acetate, yields, besides silver iodide, methylene acetate 



CH 2 * a li( l uid that boils at 170 * If &amp;gt; how &quot; 



ever, the attempt is made to isolate the alcohol from 

 this ether by means of heating with water or alkalies, 

 formic aldehyde (oxymethylene) is obtained instead. 

 It appears to be a general fact, that such diatomic alco 

 hols as contain both hydroxyl groups in combination 

 with the same carbon atom, cannot exist. Two dia 

 tomic alcohols can theoretically be derived from ethyl 



hydride CIP.CIR, viz., jp OH and CH3 - CH j OH 

 Only the first of these can, however, be isolated ; the 

 second, the acetic ether CH 3 .CH SJS of which 



can readily be prepared (p. 104), is resolved into 

 aldehyde and water when the attempt is made to iso 

 late it. 



1. Ethylene Alcohol (Ethylglycol). 



Preparation. Ethylene bromide is boiled for a few 

 hours with potassium acetate and alcohol, then dis 

 tilled ; that portion of the distillate boiling between 140- 

 200 (which consists mainly of monacetic glycol ether), 



