ON ISOMERIC NAPHTHALENE DERIVATIVES. 



97 



melting-point of the sulpho-cliloride of the chloro-acid, and the designation 

 and melting-point of the dichloronaphthalene are as follows : — 



Sulphochloride Dichloronaphthalene 



betanaphthylaminesulphonic acid (a) ( Badische) . 

 „ „ (0) (Bronner) . 



„ (7)(Dahl). 

 „ „ (5) (Bayer and 



Duisberg) 



Isomeric dicMoronapMJialenes. — No less than 12 isomeric dichloro- 

 naphthalenes have now been described. The conventional plane symbol of 

 naphthalene serves to exhibit only ten, but a geometrical symbol may be 

 constructed in accordance with the method followed by Herrmann in the 

 case of benzene ('Berichte,' 1888, 1949), which foreshadows no less than 

 sixteen. The following is a list of the reputed dichloronaphtbalenes : — 



(1) 

 (^) • 



(3) . 



(4) . 



(5) . 



(6) . 



• V 



. m.p, 

 . . . m.p. 

 0'. . . m.p 

 /8 . . . m.p. 



m.p. = 34° 

 m.p. = 38° 

 = 48° 

 = 61°-5 

 = 65° 

 = 68° 



(7) 



m.p. 



8.3° 



a-a-dichloronapJdhalenes. Nos. 6, 7, and 9 in the list belong to this 

 category and represent the three possible a-a-derivatives : ft-dicMoro- 

 najplithalene is undoubtedly the u^:a^homonudeal modification, being 

 obtainable from naphthalene tetrachloride and from naphthionic acid ; 

 7- and ci-dichloronapMhalenes are heteronucleal compounds, and if no other 

 evidence -were forthcoming, the fact that the y- compound has the higher 

 melting-point would alone justify us in regarding it as the symmetri- 

 cal o^K^'derivative; since, however, it is obtainable from the nitro- 

 sulphonic acid isomeric with the a-a-acid known as the Scholkopf acid, 

 which -taking Bamberger's researches into account — is a so-called peri or 

 hetero-ortho derivative, there cannot be any doubt that y- is 1 : 4' and 

 that 4 is 1 : 1' dichloronaphthalene. 



p-ly-dicMoronapJithalenes. — Of the three possible /3-/3- modifications, 

 c. and (- dichloronaphthaleve are the two possible hetero-compounds ; and. 

 from the high melting-point of the latter there can be practically no 

 doubt that it is the symmetrical 2 : 3' modification, the c-componnd being 

 therefore the 2 : 2' derivative. 



a-ij-dicJdoronaphfhaJenes. — Four are possible, two hetero- and two 

 homonucleal. rj- and 6' (m.p. 6.3°'5) dichloronaphthahnes may be prepared 

 as above stated from Dahl's and the Badische modification of Z)etenaphthyla- 

 minesulphonic acid respectively, and also from two n-nitro-acids obtained, 

 by Cleve by nitrating naphthaleneZ/e/asulphonic acid ; they are therefore 

 undoubtedly a- ft- compounds, and are probably both heteronucleal. If these 

 arguments be correct, the one is 1 : 2', the other 1 : 3' dichloronaphtha- 

 lene, 



Q-dichloronaplitlialene (m.p. 61°-5) is either the 1 : 2 or the 1 : 3 modi-- 

 fication. u-dicMoronaplitlialene, the product of the action of alkali on 

 naphthalene tetrachloride, is undoubtedly a homonucleal compound. The 

 modification melting at 34°, prepared by Cleve from chlorobetanaphthol 

 and chlorobetanaphthylamine, is also homonucleal ; this latter is an alpha- 

 chloronaphthalene derivative (Cleve), so that the dichloronaphthalene 

 melting at 34° if not the 1 : 2 is the 1 : 3 variety. By exclusion, it 



1888. H 



