Inorganic Chemistry

Ca-C2 yields C2-H2
car-bide me-tal pro-du-ces 
hy-dro-gen and oil

Pavel Karen
University of chemical technology, Prague, Czechoslovakia, (1984)

Relation between the Structure of Carbides and Composition of their Hydrolysis Products
Salt-like carbides of electropositive sp-elements contain carbon as C4−, C22− or C34− anions. Accordingly, their hydrolysis yields the respective weak acid: CH4, C2H2, and C3H4. Carbides of d- or f-transition metals are typically metallic. Water or protic acids hydrolyze some of them, such as Mn7C3 containing single carbon atoms or YC2 and DyC2 of C2 groups. In such a surface reaction, the compositionally metallic portion of the carbide reduces the hydrated H+ while the neighboring carbon group is being protonated towards the corresponding hydrocarbon. The reduced H+ reacts with the, say, protohydrocarbon, forming hydrocarbon series C1n or C2n corresponding to the carbon group present in the crystal structure. The main product is a hydrocarbon gas, but significant amounts of liquid hydrocarbons are formed as well. If the d- or f-element carbide is not metallic, no hydrogen is produced and only the corresponding hydrocarbon is formed (as an example, Sc2OC and its rare-earth analogues yield CH4). The hydrolysis of carbides is therefore structurally consistent, keeping the carbon-carbon bonds present in the crystal structure, but polymerizing and hydrogenating these species if the stoichiometric composition suggests metallic character able to yield hydrogen in protic environments.