276 III. CHEMISTRY OF NEUTRAL FATS 



alkoxy group of an alcohol is one type, known as alcoholysis. A second re- 

 action involves interchange of alkoxy groups between different esters. 

 Such a process is most properly spoken of as an inter esterification. The 

 third class of reactions included under this category is acidolysis. This 

 last interchange involves the replacement of an acid group of an ester with 

 another acid. 



a. Alcoholysis. This type of reaction is the one which has been known 

 for the longest time. Duffy*"^ reported, almost one hundred years ago, 

 that ethyl stearate originates when ethyl alcohol and glyceryl stearate are 

 caused to react. 



Several types of reactions can be classified under alcoholysis. These in- 

 clude the reactions between: (1) monoesters and monohydric alcohols, (2) 

 monoesters and polyhydric alcohols, (5) polyesters and monohydric alco- 

 hols, and finally (4) polyesters and polyhydric alcohols. When the reac- 

 tion is carried out with a specific alcohol, it is frequently identified by the 

 name of that alcohol. Thus, methanolysis, ethanolysis, and propanolysis 

 refer to alcoholysis reactions carried out with methyl, ethyl, or propyl alco- 

 hol, respectively. 



Alcoholysis is usually carried out by heating an excess of the alcohol 

 with the ester in the presence of a catalyst. The catalysts usually employed 

 are the mineral acids, such as hydrochloric or sulfuric acid, in 1-2% con- 

 centration. Benzenesulfonic acid"'' may also be used in that capacity, 

 while alkaline hydroxides likewise exert a catalytic action. ^"^ All glyc- 

 erides react with alcohols, but those of low molecular weight are the most 

 reactive. Substrates soluble in alcohol are attacked most readily, while 

 the use of alkali solvents for the fat also improves the rate of reaction. 

 An alcohol group of lower weight usually replaces one of higher weight.*^" 



Alcoholysis, when employed with triglycerides, is a stepwise process. 

 Thus, when tristearin and ethyl alcohol react, not only is ethyl stearate 

 formed, but di- and monoglycerides as well. Thus, when 3000 g. of tri- 

 stearin was treated with an excess of ethanol in the presence of hydrochloric 

 acid, Griin et aZ.^" isolated, in addition to 1200 g. of ethyl stearate, 300 g. 

 of distearin and 200 g. of monostearin, while 400 g. of the original tristearin 

 were foimd at the end of the reaction. A similar stepwise process occurs 

 when a hydroxide is used as the catalytic agent. ^"^ 



The interaction of most triglycerides and alcohol takes place slowly, due 

 to the insolubility of the fat in alcohol. As the reaction proceeds, an in- 

 creasing solubility results. When an homogenous solution is obtained, it is 

 complete. Due to the ready solubility of castor oil in alcohol resulting from 



«8 P. Duffv, J. Chem. Soc, 5, 303-316 (1853). 



«9 Y. Toyama and T. Tsuchiya, /. Soc. Chem. Ind. Japan, 36, suppl., 232-233B (1933). 

 "0 E. M. Bellet, Compt. rend., 193, 1020-1023 (1931). 



411 A. Grun, F. Wittka, and E. Kunze, Chem. Umschau, U, 15-16 (1917); Chem. AbsL, 

 13, 2768-2769 (1919). 



