356 PROTOCATECHUIC ACID, ETC. 



moderately difficultly soluble in cold water (in 58 parts 

 at 21), easily soluble in hot water, alcohol, and ether ; 

 contains no water of crystallization ; fuses at 183, and 

 is decomposed at 210-212 into carbonic anhydride 

 and a mixture of hydroquinone and pyrocatechin. 

 Iron chloride turns its solution deep blue, which be 

 comes blood-red on a subsequent addition of a little 

 ammonia. The salts are very unstable, and are decom 

 posed, when left in aqueous solution in contact with 

 the air. 



2. Protocatechuic acid. Is formed by the action 

 of melting caustic potassa on iodoparaoxybenzoic acid, 

 bromanisic acid, para- and ortho-cresol sulphuric acids, 

 piperic acid, catechin and a great many resins (guaia- 

 cum, gum-benzoin, dragonsblood, assafcetida, myrrh, 

 acaroid, etc) ; the production from resins is usually ac 

 companied by the formation of paraoxybenzoic acid. 

 Crystallizes from water in colorless laminae or needles 

 with one molecule of water of crystallization. Diffi 

 cultly soluble in cold water, more easily in hot water, 

 in alcohol, and ether. Fuses at 199, and decomposes 

 at a higher temperature into carbonic anhydride and 

 pyrocatechin. Its solution is turned dark green by 

 iron chloride ; this color changes to a beautiful blue on 

 the addition of a small quantity of a dilute solution of 

 sodium carbonate, the addition of more of the latter 

 solution giving rise to a dark red. The solutions of its 

 salts turn violet on the addition of salts of iron sub- 

 oxide. &quot;When mixed with bromine it is converted into 

 monobromprotocatechuic acid, C 7 H 5 BrO, which crystal 

 lizes in fine rhombic needles. 



Dimethyl-protocatechuic acid, C 6 IP j 



Is obtained by heating 1 part of protocatechuic acid, 4 

 parts of methyl iodide, and 1 part of potassium hydrox 

 ide with methyl alcohol in sealed tubes at 140 about 

 three hours. The mass thus obtained is boiled with 

 caustic soda ; and the acid precipitated by means of sul- 



