218 SCIENCE PROGRESS 



cular proportions of bromine) bromination takes place in the 

 a-position, first one and then the other a-hydrogen atom being- 

 displaced. 



/CH, /CHBr /CBr., 



CO x CO \CO 



/ a 6^1x100311^110^ 

 { a'-Bromocamphor 



Camphor f a Bromocamphor 1 aa'-Dibromocaraphor 



Bromination proceeds with the utmost readiness, but it is 

 noteworthy that whereas the first bromine atom can only be 

 removed by drastic methods of reduction, the second can be 

 removed very easily by mild reducing agents such as alcoholic 

 potash. If the bromination be carried out in a sealed tube 

 at temperatures above ioo°, bromine enters the nucleus, the 



CHBr 

 products being an a/3-dibromocamphor, C 8 H 13 Br< , and 



X CO 



XBr a 



sometimes an aa'/3-tribromocamphor, C 8 H, 3 Br\ . It is 



X CO 



also possible to start from the aa'-dibromocamphor and con- 

 vert it into the a/3-isomeride by heating it in a sealed tube 

 with concentrated hydrobromic acid. There can be little doubt 

 that this change depends on a process of simultaneous bro- 

 mination and reduction, the transference of the halogen being 

 due to the tendency to form the tribromo-derivative coupled 

 with the reducing action of the hydrogen bromide on the 

 easily displaced a'-halogen atom. It is therefore not necessary 

 in this case to postulate the existence of any special mechanism 

 for effecting isomeric change, beyond that which is involved 

 in the processes of bromination and reduction. 



The conversion of propyl into isopropyl bromide in presence 

 of aluminium bromide might be explained in a similar manner 

 as depending on simultaneous bromination and reduction, but 

 it appears more probable that in this case there is a rever- 

 sible removal of hydrogen bromide, an olefine being formed at 

 an intermediate stage as in the case of Butlerow's isomeric 

 alcohols : 



CH 3 CH 3 CH, 



