viii, a, i Gibbs and Pratt: Hydroxyl and Carboxyl 35 



a beneficial rather than a prejudicial action. The effect of the 

 alkali is to reduce the phenolic condition, which we will show 

 can be practically eliminated. 



This is actually the case in phenol, o-cresol, o-hydroxybenzyl 

 alcohol, and sodium salicylate. The primary effect of the alkali 

 upon salicylic acid is the formation of the sodium salt, and this 

 is manifested in the absorption spectrum by a shift of the band 

 toward the shorter wave length, a position nearer the character- 

 istic band of phenol. 



It is evident that the carboxylic C=0 group has not the effect 

 in the di-sodium salt of salicylic acid that it has in the sodium 

 salt of the ester. 



The above representation for sodium methyl salicylate indi- 

 cates that the free affinities of this compound are so bound that 

 in effect its equilibrium more closely resembles that of an ether 

 than of an ester. By this assumption the greatly decreased rate 

 of saponification of sodium methyl salicylate is capable of ex- 

 planation. Salicylic acid, on the other hand, shows no similar be- 

 havior in the presence of alkalies, and presents no corresponding 

 analogies to acetoacetic ether, although the absorption spectra 

 of the free acid and ester are identical. When methyl is em- 

 ployed instead of sodium to replace the hydroxylic hydrogen of 

 methyl salicylate forming the methyl ether of methyl salicylate, 

 the equilibrium is disturbed in a different manner due to the 

 fixation of the labile hydrogen atom, and this is manifested by a 

 shift in the absorption band toward the shorter wave lengths 

 and a decrease in its persistence, indicating decreased activity. 

 This decreased activity cannot be attributed to the phenol portion 

 of the molecule, for the absorption spectrum of phenol is not 

 altered in this way by its change to anisole, but is due to the 

 reduction of the influence upon the >C=0 group. 



The strength of salicylic acid is diminished by the change of 

 the hydroxyl group to methoxyl. This is shown in the absorption 

 spectra of these compounds by a decided shift in the absorption 

 band of the former toward the shorter wave lengths. The ab- 

 sorption bands of neither of these compounds are altered by the 

 change of the carbonyl group to its methyl ester. It is evident 

 that the strength of the acid is affected by any neighboring 

 group which will influence the potential activity of the >C=0 

 group of the carboxyl. The absorption spectra of salicylic acid, 

 methyl ether of salicylic acid, and benzoic acid indicate the 

 strength of these acids to be in the order named, a fact which 

 is in accord with their affinity constants. 



