organic chemistry - Converting cyclic compounds to linear compounds (possible ?)

Can one convert from cyclic convert to linear compound? Like

$Cyclohexane$ $+$ $?=Hexane$

Even in High Temp and Pressure?

I know it is very tough since we are going from a stable compound to a relatively more unstable compound.But still...???

And can we also convert $Benzene$ to some $Unsaturated Compounds$ ?

And if possible can anyone please tell the reaction mechanism of it?

Thanks

Answer

Yes, this can be done. Unsaturated cycloalkanes can be ring opened using fairly straightforward methods. For example, heating cyclobutene will produce 1,3-butadiene in an orbital symmetry allowed reaction. But since your example involved cyclohexane, I'm guessing that you are more interested in the ring opening of saturated cycloalkanes, so that's where I'll focus my answer.

Catalysts are needed to ring-open cycloalkanes. The catalyst complexes with a cycolalkane bond and then in a second step, hydrogen is added across this bond. Mechanistically, it is basically the reverse of the hydrogenation reaction (e.g. catalytic hydrogenation of cyclohexene to cyclohexane). Some of these catalysts are very indiscriminate, so the initially formed linear alkane will rebind to the catalyst and undergo subsequent isomerization and fragmentation reactions. More recently catalysts have been developed that can open cycloalkanes to the corresponding linear alkane in fairly high yield and relatively free of other hydrogenolysis products. These reactions are run in solution at temperatures slightly above ambient. Here is a link to a full text article on one such process that uses Lanthanide\Aluminum complexes; Terbium seems to be the preferred lanthanide. Yields are typically in the 65-80% range (cyclohexane, 67%; cyclopentane, 77%; cyclodecane, 77%).