FATS AND OILS, WAXES, AND LIPOIDS 131 



for the extraction of oils from plant tissues are of very great 

 economic importance. 



CHEMICAL CONSTITUTION 



The fats (of either plant or animal origin) are glycerides, i.e., 

 glycerol esters of organic acids. As has been pointed out, esters 

 are derived from organic acids and alcohols in exactly the same way 

 that mineral salts are derived from inorganic acids and metallic 

 bases. 



Thus, 



Base Acid Salt 



and, C 2 H 5 |OH + HjOOC H = C 2 H 5 OOC - H+H 2 O 



Alcohol Acid Ester 



or, R- OH + H|OOC-R = R-OOC-R+H 2 O 



Any alcohol Any acid Any ester 



Glycerol is, however, a trihydric alcohol, i.e., it contains three 

 replaceable (OH) groups. Its formula is C3H 5 (OH) 3 , or 

 CH 2 OH-CHOH-CH 2 OH. Hence, three molecules of a mono- 

 basic acid are required to replace all of its (OH) groups. 



For example, 



CH 2 OH + HOOC-Ci 7 H 35 = CH 2 OOC Ci 7 H 3 5 



CHOH + HOOC-Ci 7 H 35 = CHOOC-Ci 7 H 35 +3H 2 O 



I I 



CH 2 OH + HOOC-Ci 7 H 35 = CH 2 OOC-Ci 7 H 35 



Glycerol 3 mols. stearic acid Stearin a fat 



It is theoretically possible, of course, to replace either one, two, 

 or three of the (OH) groups in the glycerol with acid radicals, thus 

 producing either mono-, di-, or triglycerides. If the primary 

 alcohol groups in the glycerine molecule are designated by (1) 



(1) (2) (1) 



and the secondary one by (2), thus, CH 2 OH CHOH CH 2 OH, it is 

 conceivable that there may be either (1) or (2) monoglycerides, 

 either (1, 1) or (1, 2) diglycerides, or a triglyceride, depending upon 

 which of the (OH) groups are replaced. Compounds of all of 

 these types have been produced by combinations of glycerol with 

 varying proportions of organic acids under carefully controlled 

 conditions; and all of them found to possess fat-like properties, 



