ON ISOMERIC NAPTHALENE DERIVATIVES. 269 



better results are obtained in many cases by merely distilling the sulpho- 

 bromide, although the formation of higher bromo-derivatives is not 

 entirely avoided. During the year Mr. Jenks and the writer have 

 made considerable progress in completing the series of bromonaphtha- 

 lenes (di- and tri-derivatives), and in determining the nature of the 

 sulphonic acids prepared from the dibromonaphthalenes by Mr. Rossiter 

 and the writer. 



One result of which mention may be made relates to the tribromo- 

 naphthalene obtained by Jolin by distilling nitro-l : 4-dibromonaph- 

 thalene with phosphorus pentabromide, which hitherto has always been 

 represented as the 1 : 4 : 1' derivative, apparently because it is supposed 

 that, as a rule, o-nitro-compounds are formed on nitrating naphthalene 

 derivatives. Judging from the low melting-point of the tribromonaph- 

 thalene in question, it is improbable that it is a tri-a-derivative, as such 

 a tribromonaphthalene should melt at a much higher temperature. The 

 accuracy of this conclusion is established by the observation that 1 : 4- 

 dibromonaphthalene /(etero-/?-sulphonic bromide is converted by distilla- 

 tion into a tribromonaphthalene which is undoubtedly identical with that 

 prepared from nitro-l : 4-dibromonaphthalene. 



Attempts to devise a satisfactory method of preparing 1 : I'dibromo- 

 naphthalene had been made by Mr. Jenks and the writer prior to 

 Meldola's discovery of this modification, and as these have been continued 

 to a successful issue reference may be made to the subject. The first 

 method devised involved brominating the acetyl derivative of Guareschi's 

 1 : 4' bromonaphthylamine, prepared by brominating nitronaphthalene, 

 &c. ; this readily a0"ords what appears to be a 1 : I'-dibromacetnaphthalide, 

 but the greatest difiiculty has been experienced in hydrolysing this 

 compound. 



A second method consists in nitrating 1 : 4-bromonaphthalene sulpho- 

 chloride. A 1 : r-nitrobromosulphochloride is readily obtained, but, 

 although the chief product, it is by no means the only one. 



A third and far simpler method consists in heating 1 : 4-bromonaph- 

 thalene sulphochloride with bromine and subsequently hydrolysing the 

 1 : 1-dibromosulphochloride, which is almost the exclusive product when 

 the operation is properly carried out. 



Although it is known that naphthalene-p-sulphonic acid is very readily 

 converted into 1 : 4-dibromonaphthalene /;e?ero-/j-sulphonic acid, the order 

 in which the bromine atoms enter has not been determined ; and it is, in fact, 

 difficult to arrest the action at an intermediate stage, the tendency to form 

 the dibromo-derivative being very great. Mr. Stallard, however, having 

 kindly placed a quantity of monobrominated /3-sulphonate at the writer's 

 disposal, it has been ascertained that it is an «,-bromo-/33'-derivative. 

 By heating naphthalene-/J-sulphochloride with a molecular proportion of 

 bromine a very satisfactory amount of 1 : 3'-bromosulphochloride is readily 

 obtained. The ' repellent ' influence of an acid radicle is clearly brought 

 out by these results, as /3-bromonaphtlialene yields 1 : 2 -dibromonaph- 

 thalene when brominated. 



It is well known that there is often great difficulty, especially in the 

 case of o-naphthol and d-naphthylamine, in obtaining satisfactory yields 

 of bromo-derivatives, a considerable amount of by-product being formed, 

 the nature of which has not been understood hitherto. Some light has 

 been thrown on the nature of these products by observations made by Mr. 

 Jenks and the writer. 



