ON THE STUDY OF HYDRO-AROMATIC SUBSTANCES, 105 
The next reducing agent employed was zinc-dust in aqueous alcoholic 
solution, which, as previously shown,! readily replaces halogen by hydrogen 
in saturated hydro-aromatic substances, but in the present instance its 
action is too powerful, as it gives a mixture of the ketones represented 
by formule V. and VI., containing approximately 30 per cent. of the 
latter. However, 3-keto-1 : 1-dimethyl-A‘-tetrahydrobenzene (V.) may be 
CH,—CO CH,—CO 
CMe, te eSCE CMe, » : 
CH, . CHY \CH,. CH, 
(v.) 1) 
obtained quite pure by replacing zinc-dust by zinc-filings, either in the 
cold or on heating, or by using the zinc copper couple. It is a colourless 
liquid, boiling at 88-5° at 32 mm., and its ketonic nature is proved by the 
fact that it gives a semicarbazone and an oxime. When oxidised with 
potassium permanganate in the cold it yields as-dimethylsuccinic acid and 
the lactone of a-hydroxy-/3/3-dimethylglutarie acid : 
H,—CO. CH(CO,H) . 0 
OMe, : > > C eX > 
Nou, . CHY Hi alg) 
Port 
CMe, 
*\cH, . CO,H. 
3-Keto-1 : 1-dimethylhexahydrobenzene (VI.) may be produced from 
chloroketodimethyltetrahydrobenzene by heating it with zinc-dust in 
glacial or dilute acetic acid solution. It is a colourless liquid, boiling 
about 10° lower (75:5° at 25 mm.) than the corresponding unsaturated 
ketone. It forms an oxime and a semicarbazone, and when oxidised with 
_ potassium permanganate gives only /38-dimethyladipic acid (VII.), a fact 
CH,—CO CH, .CO,H 
OMe Sco, > OMe, 
alae: ; *\CH, . CH, . CO,H 
(VIL) 
which proves its constitution beyond doubt. 
Other reducing agents investigated were zinc-dust in strongly alkaline 
solution, also zinc-dust and hydrogen chloride in alcoholic solution. In 
the former case the hydrolytic action of the potassium hydroxide over- 
shadows the reducing action of the zinc, with the result that the only 
product isolated was dimethyldihydroresorcin (VIII.). In the latter case 
a mixture of ketodimethyltetrahydrobenzene and ketodimethylhexahydro- 
benzene was obtained, together with dimethyldihydroresorcin and its ethyl 
ether? (IX.). Here, again, hydrolysis must first take place, giving rise 
CH, co CH,—__co 
CMe : cu OMe Son 
CH, . C(OH)F \cu, . c(OEt)Y 
(VIIL.) (IX.) 
to dimethyldihydroresorcin, which is then esterified by the alcoholic 
hydrogen chloride. 
Dicyclic Compounds.—The compounds of this nature met with are 
all derivatives of a substance formed theoretically by the removal of 
one hydrogen atom from each of two hexahydrobenzene rings, with 
1 J.C.8., 1905, 87, 1497 ; 1906, 89, 43. 
2 Thid., 1899, 75, 775. 
