a 34 KEPOKT— 1902. ■ 



of the aromatic series ; and also to point out, as far as our present some- 

 what scanty knowledge regarding hydro-aromatic bodies will permit, the 

 resemblances and diSerences in the properties and reactions of these three 

 series of bodies. 



Many instances have already been quoted of the ring formation of 

 hydro-aromatic substances from open-chain compounds : e.g.. 



The preparation of hexahydrobeuzene by method (i.), p. 120. 



J, „ ketohexahydrobenzene by method (ii.), p. 125, 



„ „ substituted dihydroresorcins by methods (i.) and 



(ii.), p. 127. 

 „ ,, substituted ketotetrahydrobenzenes, p 128. 



■ '■ „ „ hexahydrobeuzene dicarboxylic acid, p. 132. 



Two examples have also been given of the passage of hydro-aromatic 

 into aromatic bodies (p. 129), in which cases bromine is first added on 

 at a double bond and then illuminated as hydrogen bromide. Other 

 similar examples are the conversion of 3-chloro-l -methyl- A, . 3-dihydro- 

 benzene into metachlortoluene ' 



CCl = CH CCl = CH 



/ \ • / \ 



CH CHj -^ CH CH 



C(CHg)-CH2 C(CH3)-CH 



and of 3-chloro-l : 5-dimethy'l-A, . .(-dihydrobenzene into chlorxylenc.'^ 

 From the author's experience it would seem that this action of bromine on' 

 derivatives of dihydrobenzene appears to be of a general nature, but the 

 work is not sufficiently far advanced to permit of a more definite state- 

 ment being made. 



Bromine acts on hexahydrobeuzene, giving rise to tetrabromol>enzene.' 



In some cases oxidising agents convert hydro-aromatic into aromatic 

 bodies, as the three following examples show : — 



1 : 3-Dimethyldihydrobenzene gives with nitric and sulphuric acids 

 nitro-, dinitro-, and trinitro-xy lanes. ^ 



Nitric acid converts 3 : 5-dichloro-l : l-dimethyl-:l2:4"dihydrobenzene 

 into 3:5- dichlorobenzoic acid.'' 



.CH = CC1 .CH = CC1 



(CH3%.0 \CH ->. HOOC.C \CH 



V^H.,-CC1 ^CH-CCl 



■1 : 4-Dihydroxyhexahydrobenzene (quinite) on oxidation with chro- 

 mic acid gives quinone,'' which, however, may itself be regarded as a 

 hydro -aromatic substance. 



In the following tables there will be found a comparison of some 

 of the physical properties of benzene with those of the three typical 

 hydro-aromatic hydrocarbons, dihydrobenzene^ tetrahydrobenzene, and 



' Klages and Knoevenagel, Ber., 1894, 27, 3022. 



= Ihid., p. 3024. 



=< Zelinsky, Ber., IDOl, 34, 2803. 



* VVallach, ^l«7irt/m, 1890, 258, 319. 



" Crossley and Le Sueur, J.C.S., 1902, 81, 831. 



« Bur., 1892, 25, 1037. 



