120 HEPORf— 1902. 



Hydro-aromcdic Gom'pounds ivith Single Nucleus, 

 By Arthur W. Crossley, D.Sc, Fh.D. 



[Ordered by the General Committee to be printed in extenso.'] 



When hydrogen is added on to benzene, di-, tetra-, and hexa-hydrobenzene 

 are obtained, and it has become customary to consider all homologues and 

 derivatives of the three above-mentioned hydrocarbons under the name 

 ' hydro-aromatic compounds.' ^ It is only of comparatively recent years 

 that these bodies have been much investigated, stimulus to research being 

 found in a knowledge of the fact that many groups of naturally occurring 

 substances stand in the closest relationship to the hydro-aromatic bodies, 

 notably, the terpenes and camphors, and the hydrocarbons of petroleum. 



Strictly speaking, hydro-aromatic bodies do not come under the heading 

 'aromatic compounds ' ; for as soon as two hydrogen atoms are added on 

 to the benzene ring the peculiar system of linkage which provides the 

 characteristic aromatic properties is destroyed, and the resulting bodies 

 exhibit the chemical behaviour of unsaturated aliphatic compounds (com- 

 pare p. 131). This remains true when four hydrogen atoms are added 

 to benzene, and when six hydrogen atoms are added there result 

 hexahydrobenzene derivatives, which are almost identical in chemical 

 deportment with the saturated aliphatic compounds. 



In such a brief communication as the present it has been found 

 impossible to deal with the enormous amount of recent work on the 

 terpenes and camphors, and therefore the subject has been avoided ; 

 but in this report an attempt is made to refer to all the most important 

 memoirs on the subject of hydro-aromatic compounds containing a single 

 nucleus, and it is hoped that the result may prove useful to intending 

 workers in this attractive field of research. 



Hydrocarbons. 



Hexahydrobenzene, C(,H,2, and its homologues (naphthenes) occur in 

 various kinds of petroleum,'' in the oil from bituminous shales,^ and are 

 produced during the ' cracking process.' ■* 



Hexahydrobenzene has been synthesised as follows : — 



(i.) From hexamethylene dibromide and metallic sodium.^ 

 (ii.) From hydroxyhexahydrobenzene (p. 123) by converting it into 

 iodohexahydrobenzene, and reducing the latter with zinc and acetic acid.** 



/CH2 . CH, ,CH„ . CH„ .CH„ . CH, 



2 



CHj \CH0H CH, \CHI CHj ^CHj 



^CH^ . CH„ NcHj . CHj \CH„ . CH„ 



In the earliest attempts to prepare hexahydrobenzene from various 

 benzene and hexahydrobenzene derivatives ^ hydriodic acid was employed 



' The term hydro-aromatic compounds also includes many derivatives of aromatic 

 hydrocarbons containing condensed benzene nuclei. 



" Ber., 1895, 28, 577, 1235; Amer. Chem. J., 1897, 19, 374, 419, 796; 1901, 26, 

 284; Annalen, 1898, 301, 154 ; J.C.S., 1898, 73, 905, 932. 



» Ber., 1897, 30, 2743. ■• Ber., 1897, 30, 2908. 



* Perkin, Ber., 1894, 27, 216. « Baeyer. Annalen, 1894, 278, 110. 



' Berthelot, Bull. Soc. CMvi., 1867-8; Baeyer, Annalen, 1870, 165, 266 ; Wreden, 

 Annalen, 1877, 187, 153; Kistner, J. rim. Chem. Oes., 20 [2], 118. 



