502 



will not only be much more iiiisatiiivited than berizene, which fact 

 has long been known, it must also he much more supersaturated than 

 cydo-liexane and he converted into henzene under conditions tvhere 

 cyclo-hexane does not yet lose hydroyen thus, for instance at 180^ and 

 in [he presence of a suitable catalyst. For this purpose we have 

 passed cjclo-hexene over nickel at 180° in a current of carbon 

 dioxide and indeed obtained a considerable quantitj' of benzene (with 

 cyclo-liexane) ^). 



The labile cyclo-hexene will begin to split into benzene and hydrogen : 



^6^10 = CgHg -|- 2Hi, , 



but this hydrogen will subsequently form cyclo-hexane with the still 

 undecomposed cyclo-hexane; the whole process thus progresses: 



3 CgHi„ = CgHg -f- 2 CgHjj . 



Hence, according to this equation a mixture of 33.37o of benzene 

 and 66.67ü of cyclo-hexane should have formed; in' reality we found 

 about 407o ol' benzene while 2 a 47ü of cyclo-hexene had remained 

 unchanged; the remainder consisted of cyclo-hexane. 



The fact that too much benzene has been found here may be 

 due to different causes. First of all, the decomposition of cyclo- 

 hexane into benzene and hydrogen starts already at 180° (Zelinsky I.e.); 

 true, we have found no hydrogen in the reaction products but we 

 found CO, which may have been generated by reduction of the CO^. 



This formation of CO points, however, to the fact that, in this 

 case, the CO2 must not be looked upon as an indifferent gas, so 

 that the experiments will have to be repeated in a current of Jiitrogen. 

 Although the vapours evolved were cooled by means of solid carbon 

 dioxide and alcohol there is still a chance that a little has been 

 lost by evaporation which may also be a possible source of an excess 

 of benzene. 



In any case the supersaturation of the system CeH^o in regard to 

 CgH^ -T- 2 11^ has heen proved sufficiently. 



It now speaks for itself that, in the hydrogenation of benzene 

 according to Sabatif,r and Skndkrens, substances like cyclo-hexane 

 — even supposing them to be actual intermediate products — cannot 

 be retained. When they are converted almost completely into benzene 

 and cyclo-hexane in an atmosphere of CO^ nothing is to be expected, 

 in presence of an excess of hydrogen, but cyclo-hexane mixed 



^) For this we have chosen for practical reasons nickel and not palladium 

 particularly because, as a matter of fact, we kept far below 240°. 



At the ordinary temperature Pd. and Pt. were not active enough to promote 

 the transformation. 



