The Acetylene-Allene Rearrangement

The Acetylene-Allene Rearrangement. In Section 4.2.2 we discussed the base-catalyzed acetylene-allene transformation. In a study by Kitagawa et al. a useful 

A unique mechanism was suggested to interpret the difference observed in the isomerization and hydrogenation of 1-butene and ds-2-butene over a stepped Pt(775) surface.360 It was observed that the hydrogenation rates were insensitive to surface structure for both 1-butene and ds-2-butene. The isomerization rates of cis-2-butene to give only trans-2-butene on the stepped Pt(775) surface, however, was double that of 1-butene to yield both cis- and trans-2-butenes. The Horiuti-Polanyi associative mechanism, that is, the involvement of the 2-butyl intermediate (see Section 4.3.2), cannot explain this difference. However, a facile dehydrogenation of ds-2-butene to 2-butyne followed by a rehydrogenation is consistent with the experimental observations  

---