METHYL SALICYLATE III. 83 
still the compound is colored in the light, probably due to the 
formation of the o-toluquinone. In this respect the behavior of 
this compound is different from that of p-hydroxy benzoic acid. 
The fixation of the labile hydrogen increases the stability of the 
compound and prevents the catalytic oxidation in the sunlight. 
Anisole and the dimethyl ethers of the dihydroxy benzenes show 
no labile hydrogen atom while the mono-methyl] esters present 
this condition. 
Concerning the comparative rates of the reaction in sunlight, 
in general it can be stated that the greater the number of 
hydroxyl groups, the more rapid the reaction. In the di-sub- 
stituted benzenes containing one hydroxyl group the meta com- 
pound is most easily oxidized, the ortho next, and the para 
compound has the slowest reaction rate. The hydroxyl com- 
pounds which we have investigated" are the three cresols, the 
methyl ester of para-cresol, the three hydroxy benzoic acids and 
their methyl, and in some cases the ethyl esters, gentisic acid 
[C,H,,COOH (1) OH (2) OH (5)] and its methyl and ethyl 
ester. 
The esters of the phenol-carboxylic acids are all more sen- 
sitive to the action of light in the presence of oxygen than are 
the free acids themselves. All of the compounds, of the classes 
mentioned, which are colored in the sunlight are also colored 
by hydrogen peroxide in the dark at room temperature, and at 
a more rapid rate at higher temperatures. 
As would naturally be expected, other oxidizing agents such 
as dilute nitric, chromic, and persulphuric acids, ozone and oxy- 
gen liberated at the anode produce the same effect. 
Concerning the products of the oxidations there is little doubt 
but that the first colored compound formed is in every case a 
quinone. Some of these quinones are transitory products and in 
the case of the oxidation of salicylic acid, meta hydroxy benzoic 
acid, and gentisic acid, the first product of the oxidation is 
in each of these cases the same, the p-quinone of benzoic acid. 
Rakowski and Leppert” obtained what they presumed to be this com- 
pound by treating hydroquinone carboxylic acid with weak oxidizing 
agents. 
* Baly and Eubank, Jbid., 1349. 
* Previous papers described the investigation of phenol, anisole, and 
aniline. Gibbs, This Journal, Sec. A (1908), 3, 361; (1909), 4, 188; 
(1910), 5, 9, and 419. 
“ Ber. d. deutschen chem. Ges. (1875), 8, 788. 
