DIETHYL-PROTOCATECHUIC ACID,ETC. 357 



phuric acid. Fine lustrous needles ; gives no reaction 

 with iron chloride ; fusing point, 170-171. 



Diethyl-protocatechuic acid, C 6 H 3 j 



prepared in the same way as the preceding acid, forms 

 lustrous, white' needles, which give no reaction with 

 iron chloride, and fuse at 149. 



Piperonylic acid (Methylen- protocatechuic 



> 



acid). C 6 H 3 < CK Is produced by further oxidation 



( CO.OH. 



of piperonal (p. 324) by means of potassium hyperman- 

 ganate; and boiling piperonal with alcoholic potassa. 

 Is prepared artificially by heating protocatechuic acid, 

 methylene iodide, and potassium hydroxide together in 

 sealed tubes; boiling the product with potassa-ley, and 

 acidifying the solution. Colorless needles; fusing point, 

 228 ; sublimable without decomposition ; insoluble in 

 cold water, difficultly soluble in boiling water and cold 

 alcohol, more easily soluble in hot alcohol. Monobasic 

 acid. "When heated with dilute hydrochloric acid, it 

 is resolved into carbon and protocatechuic acid. 



] 



Ethylene-protocatechuic acid, C 6 H 3 



( CO.OH, 



is prepared by heating protocatechuic acid, ethylene 

 bromide, and potassium hydroxide together, and treat- 

 ing the mass thus obtained as in the previous case. 

 This acid resembles the preceding one. 



A substance called carbohydroquinonic acid, which is 

 obtained by the action of bromine on an aqueous solu- 

 tion of quinic acid (p. 361) ; and by fusing quinic acid 

 with caustic potassa, is in all probability identical with 

 protocatechuic acid. 



3. Dioxybenzoic acid. Obtained by fusing the 

 potassium salt of disulphobenzoic acid (p. 334) with 

 caustic potassa. Crystallizes from water with 1 J mole- 



