Hydrolysis of magnesium sesquicarbide Mg2C3

Abstract

Samples of magnesium carbide containing 88.9% Mg2C3 were prepared by choosing suitable conditions (temperature 685 ± 5 °C, magnesium dust particles below 0.05 mm, n-pentane flow rate with reduced pressure 10 l/h, reaction period 1.25 h). In their hydrolysis products, propadiene was found gas chromatographically to be present in quantities about 6% vol. at room temperature; its concentration does not change with time, but it rises with increasing temperature. At temperatures above 200 °C, the hydrocarbons formed start to decompose as a result of their reaction with water vapour; if the temperature exceeds 400 °C, the reaction leads instantaneously to an equilibrium mixture of CH4, C2H4, C3H6, and carbon oxide. During reaction with water at higher temperatures and pressures, reforming reactions proceed to a greater extent. Samples containing more than 60% Mg2C3 cannot be hydrolyzed with liquid water without hazard of thermal decomposition of the hydrocarbons, analogous to the reaction with water vapour at higher temperatures. The actual temperature of the reacting carbide surface can be estimated, up to approximately 300 °C, from the content of propadiene in the hydrolysis products. In accordance with the results of the hydrolysis experiments, the carbide structure is assumed to involve linear C=C=C4- groupings.