ON ISOMERIC NAPHTHALENE DERIVATIVES. 



173 



Constitution of the isomeric dichloronaphthalenes. — A list of the twelve 

 reputed dichloronaphthalenes was given in the last report, and their 

 constitution was provisionally discussed. The results since obtained 

 render it possible to finally assign the proper formulae to the several 

 modifications, the method adopted affording almost if not quite as 

 absolute a determination of their constitution as that employed by 

 Korner in the case of the dibromobenzenes : an account thereof is given 

 in the ' Proceedings of the Chemical Society,' 1888, pp. 104-1 07 ; 1889, pp. 

 34-37 ; pp. 48-64. The conclusions arrived at by Erdmann and Kirch- 

 hoff are confirmed ; as the synthetic method which these chemists had 

 adopted was one which did not exclude the possibility of the occurrence 

 of isomeric change, objection was taken to their proof in the last report, 

 but it is now clear that they had correctly interpreted their results. 



The so-called a-dichloronaphthalene, m.p. 38", obtained by the 

 action of alcoholic potash on naphthalene tetrachloride, has been proved 

 to be a mixture of 1 : 4 (/S) dichloronaphthalene, m.p. 68°, and 1 : 3 (^) 

 dichloronaphthalene (m.p. 61°). (Cf. 'Chem. Soc. Proceedings,' 1888, 

 106.) It has previously been pointed out that the so-called K-dichloro- 

 naphthalene of Glaus has no claim to recognition, and that it is doubtful 

 whether the t-dichloronaphthalene described as melting at 120° was 

 a pure substance : consequently at present but nine of the ten possible 

 dichloronaphthalenes are to be regarded as beyond doubt existent ; their 

 constitution is as follows : 



The alpha-law. Spontaneous ocairrence of isomeric change on stdphona- 

 tion. — In previous reports attention has frequently been directed to the 

 circumstance that, as a rule, aZp7m-derivatives are formed, and that beta- 

 derivatives are only obtained either when a group is present in an alpha 

 position which determines the entry of the new group into the contiguous 

 beta position, or owing to the occurrence of secondary change : it has in 

 fact been argued that an isolated beta position is never directly attacked. 

 Further evidence tending to strengthen this conclusion has recently been 

 obtained. When either ;8-chloro- or /3-bromouaphthalene is sulphonated, 

 the chief product is the 2 : V a-acid ; and a relatively very small amount of 

 the isomeric 2 : 3' /8-acid is also obtained, and it was suggested that this 

 was formed by spontaneous isomeric change from the 2 : 1' acid, as it 

 was found possible to convert the a- into the ^-acid by heating. /8-iodo- 

 naphthalene in like manner was found to yield two sulpho-acids, but it was 

 pointed out in the second of these reports that the melting point of the 

 Bulphochloride of the acid found in small quantity was remarkably low. 



