Substituted Aliphatic Acids. 71 



50 per cent acetone or alcohol the solubility of this ester is no 

 greater than that of the monohalogen propionic acid esters in 

 water. The presence of this amount of acetone or alcohol was 

 found to retard the velocity of the hydrolysis so that no satis- 

 factory results could be obtained. In the case of the mono^ 

 halogen propionic esters l cm8 of each ester was dissolved in 250 cmS 

 of decinormal hydrochloric or hydrobromic acid previously 

 warmed in the thermostat to the required temperature. As 

 soon as the ester was completely dissolved 25 cmS of the reaction 

 mixture were titrated with decinormal barium hydroxide, using 

 phenolphthalein as an indicator. Subsequent titrations were 

 made at the time intervals indicated in the tables, and the final 

 titrations usually after the lapse of 12 to 14 days. In order to 

 ascertain if any halogen was liberated in the form of free 

 halogen acids from the esters or the halogen propionic acids 

 resulting from the hydrolysis of the esters, titrations were made 

 with decinormal silver nitrate at the time when the equilibrium 

 was apparently reached. It was found that at 25° C. and 35° C. 

 there was no apparent decomposition in this direction in the 

 time required for all except the final titrations, and in these 

 there was only a little decomposition observed at 35° C. and 

 none at all at 25° C. The necessary correction was applied 

 where there appeared an appreciable increase in the concentra- 

 tion of the halogen acid. At 50° C. the last titration, preced- 

 ing the equilibrium titration, was made in each case within 10 

 hours of the beginning of the reaction. In the ethyl /3-chlor- 

 propionate and the ethyl a- and /S-brom propionates as much as 

 2 per cent or 3 per cent of the halogen was set free as halogen 

 acid, for which corrections were made accordingly. From 

 these titrations the velocity constants recorded in Table I were 

 calculated by using the well-known titration formula for mono- 

 molecular reactions : K = -^r [log (T^ - T ) - log (T^ - T n ) ], 



u 



where T is the initial titration, T^ the final titration, and T n the 

 intermediate titrations, all expressed in cubic centimeters of 

 decinormal barium hydroxide, and t is time in minutes between 

 the titrations T and T n . 



It was thought desirable also to make hydrolysis measure- 

 ments in the absence of any added catalyzing acid. In this 

 case the reactions proceed very slowly at first but with increas- 

 ing velocity as the concentration of the acid liberated becomes 

 greater. The velocity of the hydrolytic decomposition of the 

 esters is accelerated by the halogen substituted propionic acids 

 resulting from the hydrolysis of the esters and by the halogen 

 acids subsequently set free by the hydrolysis of the halogen 

 substituted propionic acids. This second accelerating effect 

 becomes very prominent after the hydrolysis has proceeded for 



