Phelps and Eddy — Hydrohromic Acid. 287 



merit (1) of Table I seventy-five per cent of the hydrobromic 

 acid has reacted in this way. Further, the efficiency in ester 

 formation of hydrobromic acid with or without zinc bromide 

 was shown in Tables I and II to be dependent in large measure 

 upon the temperature. The difference in the amount of ethyl 

 chloride formed at the different temperatures, the large amount 

 of ethyl bromide formed under similar conditions of tempera- 

 ture with hydrobromic acid, and the variability in the effi- 

 ciency of zinc bromide at different temperatures, would indicate 

 that the failure of zinc bromide to act as an efficient catalyzer 

 at higher temperature is due to the almost complete action 

 of hydrobromic acid on alcohol at that temperature to form 

 ethyl bromide and water. The same difference in the effect of 

 temperature is evident with hydrochloric acid, as is shown by 

 experiments (1) and (2) of Table III, but. in these cases the 

 action to form ethyl chloride and water makes itself markedly 

 evident only at temperatures that are most unsuited for esteri- 

 fication. And it seems fair to assume that it is this fact that 

 makes hydrochloric acid more advantageous than hydrobromic 

 for use as a catalyzer in esterification. 



Presumably it is this difference in catalytic action at differ- 

 ent temperatures of " hydrobromic acid that explains the differ- 

 ence in the results given by Goldschmidt and those recorded 

 here. Goldschmidt, measuring the rate of esterification at 25°, 

 found hydrochloric and hydrobromic acids equally efficient as 

 catalyzers. In our experiments at higher temperatures they 

 are never equally efficient. In dilute solutions the hydro- 

 chloric acid as catalyzer is much more efficient, while with the 

 highest concentrations the hydrobromic acid is more efficient 

 if the esterification is carried on at a temperature of 85°-90°. 

 At 100°-110° the hydrochloric acid is much more efficient, 

 and markedly more so than the hydrobromic acid at a temper- 

 ature of 125°-150°. While the presence of zinc chloride or 

 zinc bromine as the second catalyzer increases the amount of 

 ester formed, it yet remains true, as shown by the results given, 

 that raising the temperature above the point where alcohol will 

 just distil from the esterification flask will decrease the amount 

 of benzoic ester produced in the case of either zinc chloride or 

 zinc bromide, except where the zinc bromide is present in 

 amount almost equal to the weight of benzoic acid taken. 

 Zinc chloride in presence of hydrochloric acid is, however, a 

 more efficient catalytic agent, both the hydrobromic acid and 

 the zinc bromide being especially sensitive to any rise in tem- 

 perature. 



The amount of ethyl benzoate produced in experiments (1) 

 and (3) of Table III is in the opposite ratio to the quantity of 

 the ethyl chloride formed. Hence, the statement found in the 



