CHEMir.VL PROPERTIES OF F.VTTY .VOIDS AND REL.\TED COMPOUNDS 121 



excellent solvents for various types of lipids, especially the cellulose-type 

 lacquers. 



The esters composed of the lower acids and alcohols are liquids which 

 possess a fruity, aromatic odor. They are present as such in the fruits; 

 the synthetic products are widely employed in the manufacture of artificial 

 fruit essences. The esters composed of longer chain acids and alcohols are 

 no longer liquid, but are hard, brittle, lustrous solids, which possess a 

 crystalline structure. These higher molecular weight esters are usually 

 mixtures which are not readily separable into pure compounds. The solid 

 esters of higher molecular weight are known as waxes. They are dis- 

 cussed in Chapter IV. Some esters having an unsaturated acid or alcohol 

 component have been reported to occur in natural plant or animal products. 



Table 42 shows the physical constants of the common methyl and ethyl 

 esters, while Table 43 lists the melting and boiling points of the mono- and 

 dimethyl and -ethyl esters of some of the dicarboxylic acids. For more de- 

 tails the reader is referred to the monograph of Ralston.^ 



Table 43 



Melting Points and Boiling Points of Mono- and Dimethyl and Ethyl Esters of 



Some Dicarboxylic Acids" 



" Adapted from A. W. Ralston, Fatty Acids and Their Derivatives, Wiley, New York, 

 1948, p. 512. 



'' Freezing point. 



" Superior number indicates barometric pressure in millimeters of mercury at which 

 boiling point was determined. 



b'. Esters of Polyhydric Alcohols : Most of the esters of the polyhydric 

 alcohols are solids which melt at higher temperatures than is the case with 

 the corresponding monoesters. In the case of ethylene and propylene gly- 

 cols, the diesters melt at appreciably higher temperatures than do the 

 monoesters. On the other hand, this relationship is completely reversed 

 with glycerol. 



The sugars and the sugar alcohols form a wide variety of esters. Glu- 

 cose esters having 5 fatty acid residues have been prepared, as well as the 

 sucrose octa-ester. Many partially esterified products are kno^Ti. Prob- 

 ably the most important of the carbohydrate esters are those of cellulose. 

 Such an inorganic ester as cellulose nitrate has been recognized for a long 

 while. This polysaccharide forms esters not only with acetic acid but also 



