SUBSTITUTION PRODUCTS OF THE HYDROCARBONS 4 1 



prefix " glyc " and is an alcohol as the termination " ol " sig- 

 nifies. It is also termed ethylene glycol because as a sym- 

 metrical disubstituted ethane it is related to ethylene (see p. 

 132). It is a thick liquid soluble in water. Its application in 

 our study is as an introduction to the polyhydroxy alcohols. 

 The dihydroxy products of the hydrocarbons above ethane 

 will not be mentioned. 



Trihydroxy Alcohols. — The simplest trihydroxy product is 

 the symmetrical trihydroxy substitution product of propane : 



CH3CH2CH3 -> CH2OH - CHOH - CH2OH 



Propane Trihydroxy propane 



Glycerol (Glycerin) . — This trihydroxy propane is the well- 

 known compound glycerin. Its better name is glycerol, which 

 signifies its alcohol character. It is important to remember 

 that these compounds are true alcohols in their chemical char- 

 acter and also in many of their physical properties, such as 

 solubility. Glycerol is a thick, clear liquid, of sweet taste, solu- 

 ble in water. The importance of glycerol in agricultural chem- 

 istry is in its relation to the fats and oils as we shall explain 

 later. 



Higher Polyhydroxy Alcohols. — The higher polyhydroxy 

 alcohols are known in the tetra (4), penta (5) and hexa (6) hy- 

 droxyl compounds. The tetrahydroxy alcohols are represented 

 by erythritol or erythrite, the penta by arabitol or arabite and 

 the hexa by dulcitol or dulcite, sorbitol or sorbite and mannitol 

 or mannite. The striking fact which has already been referred 

 to is that as the number of hydroxyl groups increases the com- 

 pounds possess a sweeter taste. Glycol, glycerol, erythritol, 

 mannitol, each is sweeter than the one preceding it. We shall 

 find when we study the carbohydrates (sugars) that these poly- 

 hydroxy alcohols are directly related to them. 



