The efficiency of W7 Raney nickel
catalysts degassed between 30 and 400�C in the preparation of 2,2'-bipyridyl
has been examined. The highest activities are observed with catalysts which
have been degassed at 200�C, and these catalysts arc up to 20% more efficient
than catalysts previously used and degassed at 100�C. The results obtained are
compared with published data concerning the hydrogen contents of degassed Raney
nickel catalysts (Kokes and Emmett 1959, 1960). This shows that catalysts which
are virtually free of hydrogen are only 25% less efficient than catalysts
degassed at l00�C (containing 65 to 70% of their original hydrogen). Because of
this finding a new mechanism is proposed in which the adsorbed pyridine is
activated by the transfer of an electron from the catalyst. On stereochemical
grounds it is proposed that meso-2,2'-dihydro-2,2'-bipyridyl with axially
disposed hydrogen atoms at the 2,2'-positions and bonded via both nitrogen
atoms to one nickel atom is the energetically most favoured intermediate.