Abstract
Mixing propynoic acid and 4-(l-pyrrolidino)-pyridine in ethanol produces the salt 4-(l-pyrrolidino)-pyridinium propynoate (1) in high yield. An X-ray structure determination of 1 (Space Group P2I , Z=4) shows it to contain two independent cation-anion sets. Each set is interconnected by N-H-0 and C-H-O hydrogen bonds; there are no hydrogen bonds formed between the two sets. Each set contains an infinite array of short acetylene-acetylene contacts (3.57 and 3.74 Å, respectively); despite this characteristic, the material does not polymerize upon exposure to 60Co γ-rays. Heating 1 at 125 °C for 23 hours converts it, in high yield, to a 19:1 mixture of (E and Z)-4-(l-pyrrolidino)-pyridinium-l-acrylate. To the best of our knowledge, this is the first example of the addition of a pyridine moiety to an acetylene in the solid state.