136 GLYCOLS. 



FOURTH GROUP. 

 A. DIATOMIC ALCOHOLS, C W H 2W + 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 271 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 | Q Q2H3Q a liquid, that boils at 170. If, how- 



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 CH 3 .CIR, viz., Q^QH and CH3 - CH j OH 



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



( O O 2 TT 3 O 

 second, the acetic ether CH 3 .CH ! 'TTS f 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). 



9 H2 ' OH 

 CH 2 .OH. 



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), 



