126 



Dr. T. E. Thorpe on the 



[Dec. 16, 



coholic solution of potash or ammonia without giving up the least trace of 

 bromine. It is evident, therefore, that the two bromides, although pre- 

 pared under circumstances apparently exactly similar, are not identical. In 

 all probability the bromide we obtained is identical with that recently pre- 

 pared by Berthelot by acting upon boiling ethylbenzol with the vapour of 

 bromine. To this compound the formula C 6 H 5 {C 2 H 4 Br is assigned; it 

 cannot be distilled without a considerable portion undergoing decomposition 

 into styrol and hydrobromic acid, and loses easily its bromine by double 

 decomposition. 



It remained now to discover the cause of the variation in the position of 

 the bromine atom. In the preparation of the two products the conditions 

 were apparently identical; why, then, should the substitution have occurred 

 in the phenyl group in the bromide obtained by Fittig, and in the ethyl 

 group in our own ? The cause of the difference was soon found to reside 

 in the bromine emplo}^ed. The bromine used by Fittig doubtless contained 

 iodine. By digesting a few grains of the bromine employed in our expe- 

 riments with water and granulated zinc, and, on the complete disappear- 

 ance of all colour, filtering the solution, adding a small quantity of chlorine- 

 water, and then shaking the mixture with a few drops of benzol, the absence 

 of even a trace of iodine was shown by the benzol remaining perfectly 

 colourless. By adding about 0-5 °/ 0 iodine to the bromine before allowing 

 it to act upon the ethylbenzol, I easily succeeded in obtaining monobrom- 

 ethylbenzol with the properties described by Fittig. It distilled constantly 

 without decomposition at 203° C, and completely resisted the action of 

 boiling alcoholic potash. A similar series of comparative experiments on 

 cymol obtained from camphor was attended with like results. We have 

 thus a ready method of effecting at will the kind of substitution required 

 without the employment of heat, the presence or absence of iodine deter- 

 mines the position of the substituting bromine ; in the one case substitution 

 occurs in the phenyl group, in the other in the lateral group. The bro- 

 mine obtained by Berthelot is described as boiling between 200° and 210°, 

 whilst the bromide which I obtained distilled at 190°. I am disposed, 

 however, to consider the higher number to be a nearer approximation to 

 the truth. The difference observed in my case is probably due to the fact 

 that in distilling the substance I operated on a larger scale than did Ber- 

 thelot, and kept the liquid exposed to the influence of the high temperature 

 for a comparatively longer time, thus working under conditions more 

 favourable to the production of styrol and hydrobromic acid, the formation 

 of which would necessarily tend to lower the boiling-point. 



Nearly seven years ago Dr. Hugo Miiller drew attention to the remark- 

 able effect of iodine in facilitating the action of chlorine upon organic 

 compounds. He showed that many substances which were acted upon 

 with great difficulty by chlorine alone, and some of them only with the aid 

 of direct sunlight, yield chlorine products with great ease when acted upon 

 by chlorine in the presence of iodine. He failed, however, to point out 



