ON ISOMERIC NAPHTHALENE DERIVATIVES. 



217 



law ; but an interesting modification of the meta-law, exemplified by the 

 behaviour of nitronaphthalene to bromine, nitric acid, and sulphuric 

 acid, is to be noted : nitrobenzene under such circumstances would yield 

 chiefly the meta-derivative, but in the case of nitronaphthalene the 

 attack becomes shifted to the other nucleus, an a -a -derivative being 

 formed as represented by the formulae : — 



NO,, 



NO, 



NOo 



NO., 



SO,H 



It would appear from our knowledge of the naphthalene derivatives 

 generally that, as a rule, the a-hydrogen atoms (see figure) are those 

 which become displaced, and that the /5-atoms are aff'ected only under 

 somewhat exceptional conditions — as in the formation of /3-sulphonic 

 acids at high temperatures in presence of an excess of sulphuric acid — 

 and when an amidogen or hydroxyl group is present. Hence the beha- 

 viour of nitronaphthalene above referred to — the absence of similarity in 

 the behaviour of the corresponding nitro-derivatives of naphthalene and 

 benzene — is not improbably due to the existence in the case of naphthalene 

 of a higher law, which it may be permitted to term the ' alpha-law.' 



As naphthalene-/3-sulphonic acid is the only /3-derivative obtainable 

 •directly from naphthalene, it appeared to be specially important to study 

 the behaviour of the sulphonic derivatives in order to throw light on the 

 formation of the /3-mou(isulphonic acid ; and it was to be expected that 

 their investigation would furnish results of value in determining the laws 

 ■of substitution in the naphthalene series : moreover the ease with which 

 the sulphonic radicle may be removed by hydrolysis renders the sulphonic 

 derivatives especially suitable subjects of study.' 



It will suffice to indicate briefly the character of the results hitherto 

 •obtained, reserving a full account for one of the chemical journals. 



The action of sulphuric acid in excess on naphthalene at a tempera- 

 ture of 160°-180° has been studied by Ebert and Merz, who isolated 

 two distinct acids — an a- and a ji-disuljph.onic acid ; Armstrong and 

 Graham (' Chem. Soc. Trans.' 1881, p. 133 ; ' Berichte,' 1882, p. 204) on re- 

 examining the product obtained evidence of the presence of other disul- 

 phonic acids, but after numerous trials the attempt to separate these was 

 for the time abandoned, and attention directed to the preparation of disul- 

 phonic acids by other methods less likely to give rise to secondary changes, 

 such as readily occur on heating in presence of sulphuric acid. The result 

 has been to establish the existence of two acids isomeric with the a- and 

 /3-acid of Ebert and Merz. 



y-Naphthalenedisulplionic Acid. — This appears to be the sole pro- 

 duct of the action of chlorosulphonic acid, CISO3H, on naphthalene in 

 accordance with the equation : CioHg-f 2SO3HCI = C,oB[5(S03H)2 

 -f- 2HC1. On distilling its chloride (m. p. 184°) with phosphorus penta- 

 chloride, y-dichloronaphthalene is produced : therefore it may be con- 

 cluded that y-naphthalenedisulphonic acid is an a-n-derivative of the 

 same constitution as the nitronaphthalene derivatives formulated above. 



