GLYCOLS, in organic chemistry, the generic name given to the aliphatic dihydric alcohols.
The tertiary glycols are known as pinacones and are formed on the reduction of ketones with sodium amalgam.
The glycols are somewhat thick liquids, of high boiling point, the pinacones only being crystalline solids; they are readily soluble in water and alcohol, but are insoluble in ether.
Two propylene glycols, C3H302, are known, viz.
As a useful preliminary it is convenient to divide heterocyclic ring systems into two leading groups: (I) systems resulting from simple internal dehydration (or similar condensations) of saturated aliphatic compounds - such compounds are: the internal anhydrides or cyclic ethers of the glycols and thioglycols (ethylene oxide, &c.); the cyclic alkyleneimides resulting from the splitting off of ammonia between the amino groups of diaminoparaffins (pyrrolidine, piperazine, &c.); the cyclic esters of oxycarboxylic acids (lactones, lactides); the internal anhydrides of aminocarboxylic acids (lactams, betaines); cyclic derivatives of dicarboxylic acids (anhydrides, imides, alkylen-esters, alkylenamides, &c.).
Diamines.-The diamines contain two amino groups and bear the same relation to the glycols that the primary monamines bear to the primary alcohols.
In 1855, reviewing the various substances that had been obtained from glycerin, he reached the conclusion that glycerin is a body of alcoholic nature formed on the type of three molecules of water, as common alcohol is on that of one, and was thus led (1856) to the discovery of the glycols or diatomic alcohols, bodies similarly related to the double water type.
The oxidation of the glycols led him to homologues of lactic acid, and a controversy about the constitution of the latter with H.
Alcohols are classified on two distinct principles, one depending upon the number of hydroxyl groups present, the other on the nature of the remaining groups attached to the carbon atom which carries the hydroxyl group. Monatomic or monohydric alcohols contain only one hydroxyl group; diatomic, two, known as glycols; triatomic, three, known as glycerols; and so on.
He observed that aldehydes and ketones may suffer reduction in neutral, alkaline, and sometimes acid solution to secondary and tertiary glycols, substances which he named pinacones; and also that certain pinacones when distilled with dilute sulphuric acid gave compounds, which he named pinacolines.