288 Phelps and Eddy — Hydrobromic Acid. 



literature that the efficiency of hydrochloric acid as a catalyzer is 

 dependent upon the formation of nascent ethyl chloride would 

 not seem to be borne out by these experiments. 



It is to be noted, on the other hand, that zinc chloride, 

 known to be one of the best catalyzers* in the formation of 

 ethyl chloride from alcohol and hydrochloric acid, helps the 

 esteriiication of benzoic acid. The extent to which hydro- 

 chloric acid has reacted to form ethyl chloride, either with or 

 without zinc chloride, is seen on comparing (1) and (3) of 

 Table III. The acid found in the esteriiication flasks in (1) 

 and (2) of Table III shows a tendency to the accumulation of 

 mineral acid in that flask. This accumulation is greater, 

 naturally, at the lower temperatures. A similar tendency 

 was observed at the temperature of 85°-90° in experiment (1) 

 of Table I with hydrobromic acid. Since in (1) and (2) of 

 Table III the same amount of alcoholic hydrochloric acid was 

 employed, the temperature being the only marked difference, 

 the results are directly comparable. It would seem possible 

 that the accumulation of hydrochloric acid at the lower tem- 

 perature might explain the greater yield of ester obtained. 

 That is to say, the catalytic effect of hydrochloric acid to give 

 ideal yields of ester depends upon a certain concentration of 

 acid or of positive hydrogen ions, other conditions remaining 

 the same. It would seem from these experiments that neither 

 the concentration of the hydrochloric acid nor the concentra- 

 tion of the positive hydrogen ions can be the determining 

 factor in esterih* cation in the presence of zinc chloride, since 

 it has been shown that alcoholic hydrochloric acid gives a 

 much higher yield of ester in the presence of zinc chloride 

 than when acting under precisely the same conditions without 

 zinc chloride. The well known catalytic effect of zinc chloride 

 on ethyl alcohol and hydrochloric acid to form ethyl chloride 

 must have taken place and thus have diminished the concen- 

 tration of the hydrochloric acid. Not only this, but in this 

 action of alcohol and hydrochloric acid water has been pro- 

 duced, which would also be a hindrance to esteriiication. Yet 

 the fact remains that in the presence of the lower concentra- 

 tion of hydrochloric acid, even with the water formed by 

 alcohol and hydrochloric acid in the presence of zinc chloride, 

 the zinc chloride is a most efficient catalytic agent in esteriiica- 

 tion. 



Another proof that the amount of ester produced is not pro- 

 portional to the concentration of the positive hydrogen ions 

 present has been mentioned earlier in this paper, when it was 

 noted that, under otherwise similar conditions, a small amount 

 of sulphuric acid, which ionizes to a smaller extent than hydro- 

 * Groves, Ann., clxxiv, 372. 



