76 Dritshel and Jlill — Esters of Halogen Sitbstituted Acids. 



cold distilled water in a 300*^'"° flask. Tiie j^ipette was allowed 

 to drain 40 seconds and the time at the end of this period was 

 recorded. As soon as possible the mixture was titrated with 

 N/10 Ba(OII)„ with ])henolphthalein as an indicator. The 

 end titrations were made on the contents of ane of the flasks, 

 usually after the lapse of a week. In the case of the less 

 soluble esters a longer period was necessary before equilibrium 

 was reached. Where K/20 solutions of the esters could not be 

 prepared, saturated solutions were used. These were prepared 

 by adding an excess of ester to the acid solution previously 

 brought to the required temperature in the thermostat. After 

 shaking vigorously for a few seconds the solution was rapidly 

 filtered through a dry filter paper into pressure flasks and 

 placed in the thermostat. This method was adopted to give 

 a homogeneous mixture during hydrolysis. 



In Table I are given results of individual experiments. Table 

 II is a summary of the results obtained; the values of K 

 given are averages of values for each experiment. Lowen- 

 herz's and deHemptinne's results calculated for 25° and N/20 

 acid are also found in Table II. Both used the formula 



1 A 



K = — X log -7— — where t represents time in 5-minute units, 



t A. — CC 



A represents initial concentration of the ester and A— a? is 



concentration at the end of # X 5 minutes. Lowenherz worked 



at 40° an( 



acid as 



results 



formula was used 



;ration at the end of # X 5 minutes. Lowenherz worked j 



and dellemptinne at 25°; both used N/10 hydrochloric ■ 



a catalyzer. Therefore in calculating the former's I 



for 25° and N/20 hydrochloric acid, the following \ 



,. K X 2-3 



K = 



3-8X5X2 



where K is the velocity constant for 25° and N/20 acid with 



one-minute time units, 2"3 is the factor to transform to natural 



logarithms, 3'8 is the coefficient for the temperature change 



25° to 40° N/10 acid as found by Lowenherz. Throughout 



2'3 

 our work the formula K= — X log (T^^ — t^) - log (T4.- To), 



z 



which is the same formula expressed in terms of titrations, has 

 been used. We have, however, expressed time in one-minute 

 units and multiplied by 2"3 to convert ordinary logarithms to 

 natural logarithms. 



Lowenherz found experimentally that the temperature 

 coefficient of N/10 hydrochloric acid for the change from 25° to 

 40° is 3'8. To obtain this he determined the reaction velocity 

 constant for the same ester at 25° and at 40° and divided the 



