E. W. Dean — Esters of Substituted Aliphatic Acids. 335 



Discussion of Results. 



Perhaps the most noticeable fact set forth by the above 

 figures is the marked and varying retardation caused by the 

 hydroxyl group in esters of this series. The irregularity in 

 effect of this group was indicated in the previous experiments 

 with acetates and propionates and is now definitely established. 

 The comparison of velocities of corresponding hydroxy and 

 unsubstituted esters shows that the hydroxyl group may pro- 

 duce effects varying in different cases from a slight accelera- 

 tion to a considerable retardation. Thus it seems to be defi- 

 nitely proven that the effect of the hydroxyl group upon the 

 velocity of ester hydrolysis is not in any sense an additive 

 property. 



A second fact of interest is that substituted and unsubstituted 

 iso-butyrates decompose more slowly than the corresponding 

 normal esters. The difference here measured appears to be 

 somewhat greater than that found by De Hemptinne* between 

 the unsubstituted esters but is in the same direction. 



The beta hydroxy ester hydrolyzes more slowly than the 

 alpha, which is in accord with the rule indicated by all pre- 

 vious experiments. f 



All the esters decompose more slowly than analogous ones 

 of the propionic and acetic series. Temperature coefficients 

 seem to be rather irregular, perhaps on account of experimental 

 error. There are at least no conclusions to be drawn from 

 their variations. 



Alkaline Hydrolysis. 



In connection with the experiments recorded in the first half 

 of this paper it was thought desirable to make measurements 

 upon the reaction velocities of esters of the above list in alka- 

 line solution. Previous work* has indicated that this velocity 

 is controlled by the strength of the acid from which the ester 

 is derived and by another factor called steric influence. JSTo 

 mathematical relation for the latter has yet been worked out, 

 but it seems to be closely related to that which controls the 

 velocity of acid hydrolysis. The strength of the acid in the 

 latter case has at most only a minor influence. 



Procedure. 



Part of the measurements were made by the use of the titra- 

 tion method which has been carefully described in an earlier 

 papery of this series. Experiments were also made by a modi- 



* Loc. cit. 



f This Journal, xxxiv, 69 ; xxxv, 486. 



i This Journal, xxxv, 605. 



