722 



h. For Iso and n butyric acid the proportion of tlie hjdratation 

 constants =1:1,04, and J : 1,07 respectively; that of the dissocia- 

 tion constants 1 :1,01, and 1:1,02 respectively. Tlie branching of 

 a saturated group, appears therefore to exert but little intluence on 

 the velocity of hydratatiou. This is in accordance with the fact that 

 the hydratation constants of the two isomerics- diuiethylsuccinic an- 

 hydrides are proportional to the dissociation constants of the correlated 

 acids. ^) 



c. If now we assume provisional!}' that, other influences being 

 ecpial, the hydratation constant is proportional to the dissociation 

 constant, the specific intluence of the saturated group may then bo 

 expressed in figures. 



Therefore we have only got to divide the hydratation constants 

 by the dissociation constants; we tiien obtain, for the intluence of 

 this group, for instance at 25°: 



For acetic acid 3.92 X 10-3 



For propionic „ 2.89 X 10-3 



„ u butyric „ 1.65 X 10-3 



„ isobutyric „ 1.58 X 10-3 



Proportion 

 1.36 

 1.75 



From the corresponding values for butyric acid and isobutyric 

 anhydride follows that the influence of the configuration of the group 

 in regard to other influences must be trifling (see b). 



The influence of the mass must be, however, ^'ery great as the 

 retardation that occurs by the introduction of two methyl groups in 

 the acetic anhydride (^1.36) is less than that observed by intro- 

 ducing those same groups into the propionic anhydride (= 1.75). 



This stronger retarding influence of the ethyl than that of the 

 methyl group also appears from what has been found in the case 

 of the mixed acetic propionic anhydride. The constant thereof lies 

 between the two constants of the acetic and propionic anhydride, 

 but slightly more towards the constant of propionic anhydride. 



In the case of the isovaleric anhydride we have met with very 

 great difficulties; the solubility of this substance in water is exceed- 

 ingly small so that we could not get solutions containing more 

 than 0,005 raol. V». 



Owing, however, to the very small velocity with which the 

 hydratation took place and the fairly great conductivity of the iso- 

 valeric acid the process could be traced very accurately. 



1) Rec. 31, 80 (1912). 



