Hydrogenation of binary mixtures of alkynes on rhodium

Abstract

Hydrogenation of mixed 1-hexyne and 1-octyne or the individual alkynes occurs at substantially the same rates and is unselective as both 1 (fast) and 2 moles (slow) of H react. In the mixt. of 1-hexyne and 2-octyne an increase in the rate was obsd. after uptake of part of the required H over 5 Rh/BaSO4 in 96 EtOH at 30 Deg. The rate reached a max. level after about 75 completion of the reaction; 1-hexyne was hydrogenated first, followed by joint reaction of the resulting 1-hexene and 2-octyne. As long as a triple bond was present the catalyst potential gradually moved toward the cathodic values; after consumption of triple bonds the potential remained const. In a mixt. of 1-octyne and 3-heptyne a similar rate max. was obsd., in the case of 3-heptyne mixed with 3-octyne the curve was coincident with the kinetic curves of the individual components and no max. was obsd. [on SciFinder (R)]