324 TETRA15ROMO-D1PHENO-QUINONE. 



From the foregoing evidence tetrabromo-diphenol is- 



Br Br 



HO< X 7 OH 



C. Methods of preparation of tetrabromo-dipheno-quinone. 

 — The author has been unable, following Magatti's method (use 

 of fuming nitric acid), to obtain a pure product, although the 

 latter corresponds exactly with Magatti's description (Ber. 1880, 

 226). Seven determinations gave values for Br. varying between 

 60.8 and 62.5, whereas the theory is 63.97%. Magatti published 

 an analysis giving 64.44% Br., but since he has miscalculated 

 the theory as 64.60, I believe his analysis to have been fictitious. 

 He has contributed also two other miscalculations to Science, 

 namely, the theoretical figures for tetrachloro-diphenol and tetra- 

 chloro-dipheno-quinone, which are wrong in nearly all the items.* 

 My best product is obtained by first dissolving diphenol in 

 caustic soda and reprecipitating with dilute acid. It then forms 

 a remarkable semi-transparent jelly ( which becomes opaque on 

 heating). Excess of FeCl3 is then added, when the jelly gradu- 

 ally oxidises, through the dark-olive quinhydrone described 

 below, to the quinone. The mixture is kept at about 50 for 

 eight hours, becoming brick-red and finally microcrystalline ; 

 after washing and drying, it is repeatedly extracted with warm 

 alcohol and benzene to remove soluble impurities, such as dibromo- 

 quinone. Found 0=29.05, H=i.io 3 Br. =63.0 and 63.9. Theory 

 C u H i BT i O, : — C=28.8, H=o.8. Crystals of a less microscopic 

 size are obtained by using dilute HN< ) 3 and Fe (N0 3 ) 3 for the 

 oxidation: found Br .=64.1%. 



Fairly large crystals, like those given by Magatti's method, 

 can be got by adding the theoretical quantity of Cr03 in cold 

 acetic acid to a saturated solution of tetrabromo-diphenol in 

 acetic acid at 50 °. At lower temperatures the quinhydrone is 

 obtained, and at higher temperatures the whole is oxidised, 

 apparently to dibromo-quinone. 



A fairly pure product is also obtainable by digesting the 

 above-mentioned jelly with 50% nitric acid until the product is 

 red with a violet lustre, washing with a large quantity of dilute 

 ammonia to remove nitro-compounds, and then with warm alcohol 

 and finally with water. It should not be dried in presence of 

 alcohol. Other methods giving apparently satisfactory products 

 (but with Br 1% low) consist in heating the acid jelly ( 1) with 

 aqueous Cr0 3 and a little FeCl 3 , (2) with gradual addition of 

 KBr+KBr0 3 . 



All attempts to perform the synthesis of this substance from 



* For examples of other fictitious German analyses the interested 

 reader >hould consult Trans. Clicin. Sac. 1900, p. 632. 



