The reactions of acetylene and propyne at the surface of liquid sodium

Abstract

The reactions of acetylene and propyne at the surface of liquid sodium have been studied at 110, 150, and 200 °C. A fresh metal surface was maintained by magnetic stirring, so arranged that the metal poured continuously over a baffle plate. The course of the reactions was followed from pressure–time curves, and the i.r. spectra of the gas phase. At 110 °C, propyne reacts smoothly according to equation (i) and all hydrogen atoms produced at the 3MeCCH + 2Na → 2NaCCMe + MeCHCH2(i), surface of the metal are employed in the hydrogenation of propyne to propene. A smaller effect (probably polymerisation) also becomes evident at 200 °C. The behaviour of acetylene is markedly different, and the reaction proceeds in two stages. In the first, disodium acetylide (but no hydrogen acetylide) is formed, and the gas phase consists of hydrogen and ethylene in the ratio 1·42 : 1 at 150 °C. No ethane was detected. The second stage involves reaction of hydrogen with sodium metal, and this does not commence until all acetylene is removed from the gas phase. The results are discussed qualitatively in terms of the relative absorption of the gases at the sodium surface, which may have some analogies with their absorption coefficients at transition-metal surfaces.