ON THE STUDY OF HYDRO-AROMATIC SUBSTANCES. 181 



derivatives of hexahydrobenzene and its homologues. These substances 

 react readily with magnesium to form organo-metalHc compounds, which 

 with carbon dioxide yield the magnesium salts of the corresponding 

 carboxylic acids. lodohexahydrobenzene is under these conditions 

 transformed into hexahydrobenzoic acid. 



When ethyl dibroniopropanetetracarboxylate ' is condensed with ethyl- 

 disodiopropanetetracarboxylate it gives rise to ethyl hexahydrobenzene- 

 octocarboxylate (i). 



(COOC..H5)., . C . CHj . C . (COOCH,), COOH . CH . CH„ . CH . GOGH 

 I ' ■ I I ■ n 1 - I 



(COOC.H,), . U . CHj . U . (COOC.lIs), COOH . CH . CH, . CH . COOH 



On hydrolysis this ester yields the corresponding octocarboxylic acid, 

 which loses carbon dioxide on heating, with formation of a mixture of 

 <»'««s-hexahydrobenzenetetracarboxyHc acid (n) (hexahydropyromellitic 

 acid), and the double anhydride of the cis modification of the same 

 acid. 



Tra7isjoriiiat{o7i of Ketones. — Cyclic alcohols when dehydrated often 

 form unsaturated hydrocarbons isomeric with those that would be expected 

 from the constitution of the alcohol, thus providing the initial step in the 

 transformation of a ketonic oxygen from one carbon atom to another. "■* 

 For example, 1:3: 3-trimethyl-5-ketohexahydrobenzene (i) (dihydroiso- 

 phoron) on reduction 



CH, CH, CHj CH, CH 



CH CH CH CH O 



/\ //\ /\ /\ /% 



CH., CH, HC CH, HO CH, H,C CH, CC CH 



I I I mi' 11 HI I ■ 'I iv| ■ I V I 



CO CCCHj), H,C C(CH,\, HC C(CH,), HC CCCH,), n^G C(CH,) 



\/ '\/ ■ \/ ' ^/ \/ 



CH, CH, CH, CH CH, 



gives the corresponding alcohol, which on dehydration yields a trimethyl- 

 tetrahydrobenzene identical in every respect with geraniolen, and there- 

 fore possessing formula 11 ; though a hydrocarbon with either formula in 

 or IV would naturally have been expected to result. On treating the 

 nitrosate of this trimethyltetrahydrobenzene with sodium methylate it 

 yields an oxime identical with the oxime of 1 : 3 : 3-trimethyl-6-keto- 

 tetrahydrobenzene (v). The ketone regenerated from this oxime can by 

 the usual reactions be converted into the corresponding saturated ketone 

 1:3: 3-trimethyl-6-ketohexahydrobenzene, thus completing the ti-ans- 

 formation of the ketonic group from its original position 5 to position 6. 



Aromatic from Hydro-aromatic Substances. — Phosphorus pentachloride 

 in excess converts 3 : 5-dichlorodihydrobenzene into metadiohloroben- 

 zene,^ and dichlorodimethyldihydrobenzene into dichloro-ortho-xylene.'* 

 In the former case bromine reacts in the same way as phosphorus 

 pentachloride, but not so in the latter case, where there is obtained a 

 series of chlorobromoxylenes. 



' Gregorj' and Perkin, J.C.S., 190.S, 83, 780. 



- Wallach, Annalen, 1902. 324, 112. 



' Crossley and Haas, J.C.S., 1903, 83, 502. 



* Crossley and Le Sueur, J.C.S., 1902, 81, 153(!. 



