326 TETRABR* (MQ-DIPHENOQU I N( IN E. 



equal proportions. The free quinhydrone is obtained by acidi- 

 fying the blue substance and washing out. Stable on drying, it 

 forms minute greenish-brown needles, with bright-green metallic 

 lustre, giving the violet coloration in sulphuric acid. Found 

 Br=62.35 and 62.20, so that it is apparently hydrated. Theory 

 for c'.H^Br.A + ?H, 0=61.65% Br. The potassium- 

 derivative, made from di-potassium tetrabromo-diphenol and 

 potassium ferricyanide, is less soluble in water, and has less 

 lustre ( specimen dried at 8o° in bath after extinguishing the 

 light) : found K=7.oo and Br=56.55 (averages). Theory for 

 C J4 H,Br 8 4 K,, +2H,() is K=6.oo\and Br=56.;o. 



E. Action of strong hydrobromic acid on the quinone.— 

 ( )n the analogy of the work on coerulignone, this was expected 

 to give penta-bromo-diphenol ( see Liebermann and others on 

 2 — bromo-hydro-coerulignone). Experiment showed, however, 

 that bromine was liberated freely, and the only organic product 

 was tetrabromo-diphenol, reduction thus having occurred. 



When the quinhydrone or its blue salts are warmed with 

 acetic anhydride, it is split into tetrabromo-diphenol-diacetate and 

 a red quinonoid body. This latter appears to be identical with 

 tetrabromo-dipheno-quinone, but on analysis gives too low results 

 for bromine: found 60.3, 60.45 an d 60.34% Br instead of 64. A 

 similar product is obtained by treating alkaline tetrabromo-diphe- 

 nol with a large excess of alkaline oxidant, and then acidifying 

 This specimen, after thorough percolation with alcohol and water, 

 gave Bn=6o.o and 59.2. The reduction-product melted at 238 

 only and seemed quite oxidizable. Prolonged boiling of tetra- 

 bromo-dipheno-quinone itself, with acetic anhydride, causes the 

 whole to react, and the products are the above diacetate, and a 

 more soluble substance melting at 190 , apparently tri-acetoxy- 

 tribromodiphenol. 



An attempt to make a mixed quinhydrone from dipheno- 

 quinone and tetrabromo-diphenol gave only diphenoquinhydrone, 



F. Reduction of tetrabromo-diphenoquinone. — This was done 

 quantitatively by moistening with alcohol, covering with normal 

 stannous chloride (in 1IC1) in a weigh-bottle nearly tilled with 

 the mixture and digesting on water-bath until the solid was white: 

 by back-titration with iodine, the amount of SnCl 2 used in the 

 reduction was found to be 0.396% calculated as hydrogen. The 

 theory is 0.400. The crude reduction-product was free from tin 

 and melted at 260-264 , and was therefore pure tetrabromo- 

 diphenol. 



(i. Reduction of the quinone with bisulphite. — This gives 

 about 80% of the tetrabromo-diphenol, the rest having been con- 

 verted into 3-3'-5- tribromo-diphenol-sulphonic acid, since from 6 

 to 8% of ionic bromine was found in the liquors. The above acid 

 could not be isolated: on concentration in presence of the HNO3 

 (from double decomposition with AgNC>3 to determine free bro- 

 mide) it reacted, giving a yellow nitro-compound melting at 210 . 

 The potassium salt of this, brick-red, sparingly soluble, gave on 



