ON ISOMERIC NAPHTHALENE DERIVATIVES. 191 



Sixth Report of the Cotiimittee, consisting of Professor W, A. 

 TiLDEN and Professor H. E. Armstrong (Secretary), appointed 

 for the purpose of investigating Isomeric Naphthalene Deriva- 

 tives. {Drawn up by Professor Armstrong.) 



It was stated in the last report that Mr. Rossiter and the writer had 

 devoted much time to the study of the dibromonaphthalenes, but that the 

 results were not sufficiently complete to render their publication desirable ; 

 an account of the work contemplated in this passage was communicated 

 to the Chemical Society late in the year (cf. ' C.S. Proceedins's,' 1891 

 p. 182). 



In this communication data were given which suffice to characterise 

 and diffisrentiate^/ii;e of the isomeric dibromonaphthalenes, i.e., the 1 : 4, 

 1 : 4', 1 : 3, 1 : 2', and 1 : .3' modifications. The action of bromine on 

 a- and ^-dibromonaphthalene was also described, and the nature of the 

 complex product formed on c/i-brominating naphthalene, which has occu- 

 pied the attention of so many observers, was finally determined, it being 

 shown to consist of 1 : 4 dibromonaphthalene (m.p. 82-83°) mixed 

 with the 1 : 4' isomeride (m.p. 132°). 



When naphthalene is dibrominated, 1 : 4 dibromonaphthalene is the 

 major product, so much so that this modification crystallises out in an 

 almost pni-e state from the solution of the crude product in alcohol. It 

 has been stated by Darmstaedter and Wichelhaus that when naphthalene- 

 a-sulphonic acid is bromiuated a product is obtained which on crystal- 

 lisation from alcohol first affords 1 : 4' dibromonaphthalene, the remainder 

 of the product melting at 68-70°, and resembling that obtained from 

 naphthalene. It therefore seemed probable that, whereas naphthalene 

 yields chiefly 1 : 4 dibromonaphthalene, the a-snlphonic acid yields chiefly 

 the 1 : 4' derivative, and that consequently the acid radicle exercises a 

 marked influence in determining the entrance of bromine into the un- 

 substituted nucleus (cf Report for 1886), an influence much greater 

 than that of bromine towards sulphuric acid, as bromonaphthalene yields 

 little but the 1 : 4 acid when sulphonated. Darmstaedter and Wichelhaus' 

 experiments have been repeated by the writer, and the accuracy of this 

 conclusion confirmed ; a very considerable amount of 1:4' bromosul- 

 phonic acid is formed on brominating naphthalene-sulphonic acid, 1 : 4 

 dibromonaphthalene being quite a minor product. 



On comparing the dibromo-products obtained from naphthalene with 

 the dichloro-products, an nnusual divei^gence is apparent ; there can be 

 no doubt, however, that this is attributable to the extreme instability of 

 bromine addition compounds of naphthalene. The dichloronaphthalenes 

 are, in fact, products of the withdrawal of 2HC1 from the tetrachloride, 

 while the dibromonaphthalenes are products of the action of bromine on 

 bromonaphthalene, and hence it is that the 1 : 3 modification, which is 

 the chief product of chlorination, is absent from the product of bromination. 

 When the conditions are similar the difference in behaviour of naphtha- 

 lene towards chlorine and bromine is of the ordinary character, and such 

 as was to be expected ; thus when a-chloronaphthalene is chlorinated by 

 means of SOoCl., at such a temperature (100-180°) as to prevent the 

 persistence of an addition compound, it yields pure 1 : 4 dichloronaph- 

 thalene and no trace of the 1 : 3 isomeride, which is the principal pro- 



