^54 DERIVATIVES OF DIPIIENOOUIXOXE. 



to dicresol. The latter, obtained in this way, melted at 157" 

 without purihcation, and was therefore the sole ])roduct. 

 0.0567 when treated with a weighed quantity of normal tin 

 solution till white, and then titrated back with .iodine, used 

 0.0314 tin: hydrogen used in reduction — - 0.93%. Theory 

 calculated from formula C^^ Hjg Og = 0.945%. The needles of 

 trans-dicresoquinone possess " straight-extinction." 



Tlie cis-form is obtained by treating a solution of dicresol 

 in excess of glacial acetic acid at 40° with solution of half its 

 weight of CrC ) ^ The solutions must be suddenly mixed, when 

 the quinone comes out at once, in fairly stout deep-red needles. 

 It is washed with acetic acid in which it is practically insoluble, 

 and then with water to remove the latter, which would other- 

 wise cause partial decomposition during drying. Cis-dicreso- 

 quinone thus prepared is brick-red like phenanthraquinone, and 

 in bulk has an extremely faint pink lustre, much fainter than 

 that of Willstaetter's dark variety of diphcnoquinone. The 

 author suspects that this substance of Willstaetter's owes its lustre 

 to a trace of its quinhydrone ; Willstaetter publishes no reduction- 

 analysis of it. 



Under the microscope the needles are seen to be complex 

 and do not exhibit any consistent extinction to polarised light, 

 even in intense illumination. 



The acetic acid method is rather tricky, as when the tem- 

 perature is too low the product contains the quinhydrone and is 

 greenish-brown, and when too hot the product is impure and 

 the yield bad. Under the right conditions the yield is 97%. 

 When the red variety was reduced by stannous chloride (not 

 instantaneous) the product, washed with the minimum quantity 

 of water in a Gooch crucible, amounted to 97% of the quinone 

 taken, melted at 157°, and was therefore pure dicresol. 



Both varieties resist sodium hydrate, thus dififering from 

 coerulignone and the allied substances. 



The third method of preparation yields a mixture of the two 

 varieties, the yellow predominating. Dicresol is dissolved in hot 

 water with a little alcohol and treated at a'bout 80° with 

 excess of a ferric salt in acid solution, and digested till the 

 olive colour of the quinhydrone changes to orange and the whole 

 precipitate is microcrystalline. The yield is theoretical : the crude 

 IDroduct melts indistinctly at about 152°. 0.1302 used 0.0695 

 tin. Hydrogen for reduction = 0.96%, and the dicresol 

 obtained melted correctly. The mixture is dark-orange in bulk. 



All three preparations give the same reaction with concen- 

 trated sulphuric acid, namely, a deep brown-orange coloration, 

 similar to that given by diphcnoquinone (see end). 



Some success was met with in the attempt to change the 

 modifications into each other, but as they are sensitive to heat 

 and very sparingly soluble, it was not possible to perform the 

 experiments on a large scale. When boiled with chloroform, the 

 red variety decomposed, and only a black '' mess " was obtain- 



