84 GIBBS, WILLIAMS, AND PRATT. 
Brunner“ failed to isolate the corresponding quinone from toluhydro- 
quinone carboxylic acid. ; 
Nef," who studied the former compound, states that it is not possible 
to isolate this product of the oxidation of gentisic acid or its ethyl ester. 
The former decomposes, on warming with ferric chloride, into quinone 
and carbon dioxide and the latter is difficult of oxidation and immediately 
decomposes. In durylhydroquinone carboxylic acid, C.(CHs):.(OH).COOH, 
there is a more stable condition which admits of easy oxidation to the 
corresponding quinone. 
The oxidation of the hydroxy benzoic acids, by means of powerful oxi- 
dizing agents such as persulphuric acid or the electric current, gives com- 
plicated condensation products. Perkin and Nierstein” produced catellagic 
acid by the oxidation of p-hydroxy benzoic acid or pyrocatechuic acid with 
persulphuric acid, and metallagie acid from m-hydroxy benzoic acid. 
Perkin and Perkin™ state that the electrolytic oxidation of p- and m- 
hydroxy benzoic acids gave disappointing results and they believe the 
persulphate method more advantageous. 
Nef’s statement that the ester of hydroquinone carboxylic acid 
is difficultly oxidizable we have found to be rather misleading. 
This compound colors very rapidly in the sunlight in presence 
of water and oxygen, and in the laboratory is easily oxidized by 
dilute hydrogen peroxide, amylnitrite, potassium dichromate in 
very dilute sulphuric acid solution cooled by ice, very dilute solu- 
tions of persulphuric acid at 0°, and by other oxidizing agents. 
Decomposition does not appear to take place, at least not in the 
initial stages of the reaction. In all cases, the quinone color 
appears at once. 
In alkaline solutions these oxidations are usually much more 
rapid and accompanied by secondary reactions and decomposi- 
tions which yield, in many cases, products that have never been 
satisfactorily identified, a condition quite characteristic of the 
polyhydroxy benzenes. 
Ridenour * states that hydrogen peroxide in 2.3 per cent solutions forms 
with salicylic acid in presence of ammonium carbonate a Congo-red color. 
Heyl™ observes that salicylic acid in sodium hydroxide solution gives 
an intense red color on shaking with hydrogen peroxide, while o-phenyl 
COOH 
salieylie acid, CoH CHa , gives no color. He offers no explanation, 
OH 
* Monatsh. f. Chem. (1881), 2, 464. 
* Ber. d. deutschen chem. Ges. (1883), 18, 3499. 
> Journ. Chem. Soc. London (1905), 87, 1418. 
*t Tbid. (1908), 93, 1196. 
2 Am. Journ. Pharm., 71, 414, through Dammer (1903), 4, 148. 
* Ber. d. deutschen chem. Ges. (1899), 31, 3035. 
