Reactivity of electron donor-acceptor complexes. Part 8.—Exchange reaction of hydrogen between various phthalocyanine EDA complexes and acetylene or molecular hydrogen

Abstract

The exchange reaction of hydrogen between various phthalocyanine EDA complexes and acetylene (or molecular hydrogen) has been studied in the temperature range – 10 to 80°C (or 25 to 120°C). The hydrogen exchange reaction takes place at room temperature between acetylene (or molecular hydrogen) and the EDA complexes of phthalocyanines with sodium according to the following equations, while no reaction takes place in the absence of sodium even at 200°C. C₂D₂(or D₂)+HZ = C₂HD (or HD)+DZ, C₂H₂(or H₂)+DZ = C₂HD (or HD)+HZ, where HZ represents the EDA complexes of phthalocyanines. The reactivity of various phthalocyanine EDA complexes for the exchange reaction is in decreasing order, Fe-, Co-, Cu-, Mg-, and H₂-phthalocyanines.

The position of the exchangeable hydrogen was studied by means of infra-red spectroscopy. The results show that the hydrogen atoms in the centre of the metal-free phthalocyanine molecule (hydrogen in NH bonds) can be exchanged with those in acetylene. It was also suggested that peripheral hydrogen atoms also participate in the exchange reaction.

When the EDA complexes were exposed to an equimolar H₂+D₂ mixture, the exchange reaction to form HD proceeded. The rate of HD formation in these experiments at room temperature was considerably faster, and the activation energy lower than those observed in D₂+HZ exchange reaction. It was accordingly suggested that the H₂+D₂ exchange reaction proceeds via two mechanisms; one involves bonded hydrogen, and the other chemisorbed hydrogen. The activity of various phthalocyanine EDA complexes for the H₂+D₂ exchange via the chemisorbed hydrogen are in decreasing order, Co-, Fe, Mg-, Cu- and H₂-phthalocyanines. The effect of oxygen upon the reactivity of the complexes was also studied.