116 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



reactive, secondary alcohols have less than 50% of the activity of the prim- 

 ary alcohols, while tertiary alcohols present almost no ester formation. 

 In a standardized test in which the alcohol was treated with acetic acid at 

 155°C. for one hour, the following percentages of esterification were ob- 

 served by Menschutkin^^*^^^^ with primary alcohols: methanol, 55.6; 

 ethanol, 46.9; propanol, 46.9; n-butanol, 46.8; and n-octyl alcohol, 46.6. 

 Tn the case of the secondary alcohols under identical conditions, the results 

 were as follows : dimethylcarbinol, 26.5; methylethylcarbinol, 22.6; meth- 

 ylhexylcarbinol, 21.2; methylisopropylcarbinol, 18.9; and diethylcarbinol, 

 16.9. The values for ester formation obtained with the tertiary alcohols 

 under the same conditions were: trimethylcarbinol, 1.4; dimethylethyl- 

 carbinol, 0.8; methyldiethylcarbinol, 1.0; dimethylpropylcarbinol, 2.1; 

 and dimethylisopropylcarbinol, 0.9. In the absence of an added catalyst, 

 equilibrium was reached with primary alcohols at 65-70% of ester formed, 

 with secondary alcohols at 50-60%, and with tertiary alcohols at only 5% 

 completion. 



The nature of the acid component has a corresponding effect on the 

 esterification reaction. However, in the tests with different fatty acids, 

 the results are less clear-cut, since the rate of esterification without added 

 catalyst is a function of the amount of the acid plus the effect of the fatty 

 acid as a catalyst. In spite of this difficulty, marked variations between 

 different acids have been noted. The rate of reaction is lowered as the 

 length of the aliphatic chain increases, and especially in relation to the 

 extent to which the fatty-acid chain is branched. Menschutkin,^-^^^"'^^ 

 has reported that ester is formed in the following percentages when several 

 acids are treated for one hour with isobutanol at 155°C.: formic, 61.7; 

 acetic, 44.4; propionic, 41.2; butyric, 33.3; caprylic, 30.9; isobutyric, 

 29.0; a-methylethylacetic, 21.5; trimethylacetic, 8.3; and dimethyl- 

 ethylacetic, 3.5. 



The speed of reaction between methanol or ethanol and a large number 

 of fatty acids has been reported by the Sudborough group. ^*^~^^^ When 

 these values were recalculated by SkrabaP^^ on the basis of ^mbOh using 

 HCl as one, the following were the results with the aliphatic acids: formic. 

 2568; acetic, 239; propionic, 211.7; butyric, 115.2; valeric, 123.2; ca 

 proic, 118.7; heptanoic, 120.9; caprylic, 125.8; nonanoic, 123.5; capric, 

 119.3; lauric, 121.9; myristic, 120.9; palmitic, 114.4; and stearic, 123.7. 

 The value for k was shown to be reduced markedly in a series of mono- 

 ethenoid acids, particularly when the point of unsaturation was approxi- 

 mate to that of the carboxyl group. The values for /c of the several mono- 

 unsaturated acids investigated were as follows: undecenoic, 53.0; oleic, 



'8^ A. Ski-abal, "Chemical Kinetics," in International Critical Tables, Vol. VII, Mc- 

 Graw-Hill, pp. 113-152, New York, 1938, p. 138. 



