232 REPORT — 1887. 



at once displaces the snlpho-group in the acid, forming 1:4 iodobromo- 

 naphthalene (m.p. 88°). 



a-Cyanonaphthalene yields an acid which forms well-characterised 

 salts, &c. : this is undoubtedly an a-sulphonic derivative, as it is con- 

 verted by fusion with potash into an hydroxycarhoxylic acid, from which 

 a-naphthol may be obtained by removal of carbon dioxide. The hy- 

 droxy acid appears not to be identical with the a-hydroxy acid pre- 

 pared from a-naphtoic acid ; if this be the case it is to be anticipated 

 that, although the sulphonic acids prepared from a-naphtoic acid and from 

 a-cyanonaphthaleue are both o-a-derivatives, the one will prove to be the 

 1:1' and the other (probably the cyano-compound) the 1:4' derivative. 

 In any case, however, the behaviour of a-cyanonaphthalene aflfords another 

 example of the modification of the ' meta-law ' which prevails in the 

 benzene series in favour of the ' alpha-law ' to which reference was made 

 in the previous report. These experiments on o-derivatives have been 

 made by Mr. S. Williamson. 



Dlcldoronaijlilhalenesulfhonic acids. — With the object of characterising 

 the dichloronaphthalenes and in order to obtain more material for the 

 detei'mination of the laws of substitution, a systematic study of the 

 sulpho-acids obtainable from the dichloronaphthalenes has been com- 

 menced and already extended to five of them by Mr. W. P. Wynne and 

 myself; the examination of the dichloronaphthalenes melting at about 

 61°, obtained from various sources, has afibrded results of special interest, 

 which serve to throw light on the constitution of several of the com- 

 pounds referred to in the previous report, and has also led to the dis- 

 covery that two distinct dichloronaphthalenes have hitherto been con- 

 founded together. 



1. It was suggested in the former report that the sulpho-acid formed 

 from a-CidHyCl in small quantity together with the 1:4 acid was an 

 a-a-derivative ; if so, it should give either the 1:1' or 1:4' dichloro- 

 naphthalene on treatment with PCI5. Actually, however, it is found to 

 yield a dichloronaphthaleue melting at about 61° — the melting-point of 

 Cleve's (^-modification — thus proving it to be an o-/3-derivative. 



Now there is reason to believe that, as a rule, if a /3-hydrogen atom 

 become displaced it is one contiguous to an o-position which is already 

 occupied ; it is therefore probable that the dichloronaphthalene in question 

 and the parent sulphonic acid are 1:2 derivatives. The acid obtained on sul- 

 phonating the dichloronaphthalene gave a sulphochloride melting at 113°. 



2. The chloro-acid obtained as chief product on sulphonating 

 /S-CjoHyCl was said by Arnell to yield a dichloronaj^hthalene melting 

 at about 61° when distilled with PCI 5 : on re'^eating the experiment, it 

 was found that the product fused sharply at 65°. The sulpho-acid pre- 

 pared from this dichloronaphthalene gave salts similar to those obtained 

 from the acid prepared from the dichloronaphthaleue discussed in the 

 preceding paragraph, and its sulpho-chloride fused at 119°. Avery small 

 quantity of the products from a-CioH^Cl was at disposal, but a very con- 

 siderable quantity of those from /S-CjoH^Cl, which could therefore be 

 carefully purified ; and as the formation of a 1 : 2 derivative on sulpho- 

 nating /3-C10H7CI appears highly pi'obable, it is believed that the slight 

 diflferences observed were due to impurity in the products from a-CioHyCl. 

 It is thought desirable provisionally to term the dichloronaphthalene 

 melting at 65° liomo-Q-dicliloronaplitlialene = 0-CioHeCl2, as it is probably 

 a homonucleal compound. 



