ON HYDRO-AROMATIC COMPOUNDS WITH SINGLE NUCLEUS. 121 



as the reducing agent ; but MarkownikofF ' has proved that this reagent 

 acts on derivatives of hexahydrobeuzene to produce the isomeric methyl- 

 cyclopentane 



^CHj • CHo 

 CH3.CH/ I 



\CHj . CHj 



although hexahydrobenzene itself is not acted on in this manner.^ 



(iii.) From a mixture of benzene and hydrogen under the influence of 

 reduced nickel.^ 



The properties of hexahydrobenzene are typical of its homologues in 

 so far as the latter have been studied. It is a liquid smelling like benzene ; 

 on cooling it solidifies, forming crystals (M.P. 6° -4) which, belong to the 

 cubic system, and therefore have no action on polarised light, thus differ- 

 ing from benzene.* Concentrated nitric acid has no action on it even 

 after long standing, and a mixture of nitric and sulphuric acids acts very 

 slowly at ordinary temperatures, but violently on warming, producing some 

 nitro products, but principally adipic acid. Chlorine substitutes, but 

 bromine has no action at ordinary temperatures, and at 100° gives rise to 

 polybromides of methylcyclopentane.^ 



Physical 2)roperties *^ :— In an interesting paper on the molecular 

 volumes and refractive constants of benzene, hydrobenzenes, and six carbon 

 open-chain hydrocarbons Bruhl ^ shows that there is no great change in 

 these constants in passing from benzene to di-, tetra-, or hexa-hydro- 

 benzenes, as would be expected if the molecular structure of these bodies 

 differed materially, whereas considerable diflTerences are noticed in passing 

 from hexahydrobenzene to the open-chain hydrocarbon hexane." 



Substituted hexahydrobenzenes have been synthetised as follows : — 



(i.) From substituted hydroxyhexahydrobenzenes by method (ii.) 

 above.^ 



(ii.) From chlorhexahydrobenzene by the action of zinc alkyl com- 

 pounds.'" 



(iii.) From substituted benzenes by method (iii.) above. Pure products 

 are only obtained from benzene and toluene, the reaction being more 

 complicated in the case of higher homologues. 



2Wrahydrobenzene, CqH^q. — "When hydroxyhexahydrobenzene (p. 123) 

 is treated with hydrogen bromide, bromohexahydrobenzene is obtained, 

 from which quinoline removes the elements of hydrogen bromide, giving 

 tetrahydrobenzene.'' 



.CHj . CHj .CHj . CH^ .CH2 . CH 



CHj \cHOH CHj \cHBr CH^ ScH 

 "^CHj . CHj \cHj . CH„ \CH„ . CH„ 



' Annahn, 1898, 302, 1. 



- See also Ber., 1895, 28, 1022, 1234, and 1897, 30, 387, 1225; J.C.S., 1898, 73, 

 932. 



' Sabatier and Senderens, Compt. Rend., 1901, 132, 1254. 



* 5er., 1901, 34, 2799. » ^/iwaZew, 1898, 302, 1. 



« J.C.S., 1898, 73, 932, and 1900, 77, 372, 846. 



' Ber., 1894, 27. 1065. » See also Stohmann, J.pr. Chem. [2],''48, 447. 



» Zelinsky, Ber., 1895, 28, 781, 1343 ; 1896, 29, 214 ; 1897, 30, 1532 ; 1898, 31, 

 3206 ; Knoevenagel, Annalen, 1897, 297, 123. 



'» KursanofF, Ber., 1899, 32, 2972. " Baeyer, Annalen, 1894, 278, 107. 



