( 513 ) 



bv making sure of the absolute purity of his toluene ami bioniine 

 bv means of special methods of purifying : for details his dissertation 

 and his paper in the ••Recueil' (next appearing should be consulted. 



As the composition of the reaction mixture consisting of ortho- 

 /}'j7vjbromotoluene ïind benzyl bromide had to be determined, but as 

 no method for this was available, it was necessary to work out a 

 suitable process : in order to do this it was necessary to tirst possess 

 the thi-ee said substances in a chemically pure state so as to be able 

 to make artificial mixtures for testing the analytici\l methods. 



The preparation of /></;virbromotoluene and of benzyl chloride presented 

 no difficulties. The first substance was obtained from />rt;v/toluidine 

 by diazotation, and as this is a solid it could be readily freed JVom 

 any adhering traces of its isomers by i-ecrystallisation from ligroin 

 and thus yield a parabromotoluene also free from its isomers. Benzyl 

 bromide was made from benzyl alcohol and hydrobromic acid. On 

 the other hand the preparation of pure t>r//i(?bromotoluene was not 

 so easy. This was also prepared from the corresponding toluidine, 

 but the difficulty was to obtain the latter in a pure condition. This 

 was overcome in the manner i)re\ iously communicated (These Proc. 

 VII p. 395]. 



In the actual ijivestigation a large excess of toluene was always 

 taken (8 mols. toluene to 1 mol. of bromine) so as to avoid for certain 

 the formation of liigher substitution products. Besides the three above 

 mentioned substances the reaction mixture contains, therefore, a lai'ge 

 quantity of toluene: hydrogen bromide is also, present and often 

 iUso a small quantity of free bromine, especially in the reactions 

 which were executed in the dark. This reaction product was now 

 iuiaiysed quïuiritatively as follows : A slow current of air removed 

 almost quantitatively the hydrogen bromide, which was absorbed in 

 water and titrated : the quantity thus found is equivalent to iuid 

 serves as a measui-e for the brominated products. In order to free 

 the liquid from any free bromine, and to determine the amount of 

 the same, it is poured into a solution of potassium iodide and the 

 liberated iodine titrated with thiosulphate. The liquid is now washed 

 with water, dried, and the toluene is distilled off in an airbath 

 heated by boiling amyl alcohol. On taking the sp. gr. of the di&tilled 

 toluene it appeared that this had not carried over any brominated 

 products to speak of. 



After these operations the liquid now only consisted ofthebromo- 

 toluenes and benzyl bromide besides also a small quantify of toluene. 

 In this mixtni-e the benzyl bromide can be estimated by means of 

 alcoholic silver nitrate which yields silver bromide quantitatively. 



36* 



