CHEMICAL PROPERTIES OF FATS AND OILS 279 



b. Ester-Ester Interchange. Rearrangements of the acid components 

 in esters may take place when several esters are mixed and the conditions 

 are adjusted to render such interchange possible. There are a number of 

 procedures which may be used. 



(a) Undirected Interesterification. The usual method may be referred to 

 as undirected interesterification which, as carried out in the past, involves 

 the use of high temperatures without a catalyst to accomplish the change. 

 Under these conditions all reactants are molten and in a single phase. 

 This method is slow, and the yields are poor. In 1865, Friedel and Crafts^^^ 

 demonstrated that, when ethyl benzoate and amyl acetate were heated, the 

 best production of amyl benzoate and ethyl acetate occurred at 300°C. 

 Normann^^' reported that a mixture of 10 parts tristearin and 90 parts soy- 

 bean oil having a melting point of 130. 1°F, was changed to one melting at 

 110.7°F., after heating for 17 hours at 250°C. ; after 24 hours of such treat- 

 ment the melting point of the interesterified mixture was reduced to 

 93.7°F. Van Loon*^^ reported that the melting point of a mixture of 20 

 parts of beef stearin and 80 parts of soybean oil dropped from 108. 5°F. to 

 97.0°F. after heating for 16 hours at 275°C. It is therefore evident that a 

 rearrangement of the fatty acids in the triglycerides occurs during inter- 

 esterification, with the result that the melting point is lowered in the new 

 mixed triglycerides. Under conditions of undirected interesterification, 

 the fatty acids are arranged entirely in a random distribution in the tri- 

 glycerides. 



A second procedure for carrying out ester-ester interchange involves the 

 use of a catalyst. Under such conditions the reaction may take place at 

 room temperature ; the high degree of heating required to bring about the 

 ester interchange in the absence of a catalyst is not needed, nor is it de- 

 sirable. Alkali metal alkoxides have been shown to be extremely ef- 

 fective catalysts. Sodium ethylate can be used at room temperature 

 satisfactorily, 2*^ when prepared and employed under favorable conditions. 

 Although sodium ethylate or methylate has previously been used as a 

 catalyst where the reaction mixture was heated at 275-400 ^F.,*'^*"^^^ 

 reactions other than ester interchange are brought about, and these may be 

 undesirable. 



Sodium ethylate can be employed in amounts as low as 0.1% at tempera- 

 tures below 120°C., provided the medium is dry, peroxide-free, and the 

 catalyst is immediately dispersed in the oil mixture. It is necessary to ex- 

 clude air and moisture rigidly. Sodium methoxide may also be used in a 



«* C. Friedel and J. R. Crafts, Ann., 133, 207-211 (1865). 



<" Firma Oelwerke Germania G.M.B.H. and W, Normann, German Patent No. 417,215 

 (June 2G, 1920). 



^2* C. Van Loon, U. S. Patent No. 1,873,513 (Aug. 23, 1932). 



*25 E. W. Eckey (to Procter & GamWle), U. S. Patent No. 2,378,005 (June 12, 1945). 



*26 M. Naudet and P. Dcsnucllc, BuU. soc. chiin. [5], IS, 595-598 (1946). 



