610 E. W. Dean — Hydrolysis of Esters. 



some of the other esters in our list are probably too low for 

 the work at twenty -five degrees. The ratios obtained from the 

 constants for zero degrees have been considered of more weight 

 in the study of the results. 



After a fairly close examination of the above figures we have 

 been unsuccessful in an attempt to obtain conclusions of very 

 general value. The one thing most apparent is that the velocity 

 of saponification of the ester is closely connected with the 

 strength of the acid from which it is derived. This is in 

 accord with the theory set forth by both Hjelt* and Sudbor- 

 ough,f that the velocity of saponification is controlled by two 

 factors, the strength of the acid and steric influences in the 

 molecule. At present we are unable to obtain any mathemat- 

 ical expression which w T ill be of value in predicting the magni- 

 tude or direction of these steric influences. 



Two or three points brought out by the tables deserve men- 

 tion. The effect of alkyloxy groups is very varied. Extreme 

 cases are those of the esters of methyloxy acetic and beta ethy- 

 loxy propionic acids, which have respectively the greatest and 

 least velocities of all the series. The effect of the hydroxyl 

 group is nearly the same in the cases of glycollate and lactate, 

 but is decidedly less in the case of ethyl mandelate. In ethyl gly- 

 cerate steric influences prevent any logical comparison. Finally 

 it is to be noted that the ratios of saponification of these esters 

 are entirely different from those of their velocity of hydrolysis 

 in acid solution. 



Summary. 



1. The presence of a hydroxyl group in aliphatic esters 

 seems to produce an acceleration in the velocity of saponifi- 

 cation, although this effect is variable in its magnitude. 



2. (a) Alkyloxy groups may cause an effect varying from a 

 tremendous acceleration to a slight retardation in different cases. 



(b) The velocity of saponification of alkyloxy esters of 

 similar constitution decreases with the size of the substituted 

 group. 



3. Beta substituted esters seem to decompose less rapidly 

 than isomeric alpha products, a single point of resemblance to 

 effects produced in acid hydrolysis. 



4. The velocity of saponification is very largely controlled 

 by the strength of the acid from which the ester is derived. 



It is our intention to continue this study on the velocities of 

 several other esters and obtain if possible data which will enable 

 us to draw more general conclusions on the subject. 



*Loe. cit. 1 Proc. Chem. Soc, xiii, 241. 



