Lead carbide

J. F. Durand reported in 1923 the synthesis of lead carbide from calcium carbide CaC₂ by treatment with an aqueous solution of lead(II) acetate Pb(CH₃CO₂)₂, but this result was not reproduced.^[2][3]

A 2007 textbook repeats this claim, describing lead carbide as a green powder with formula PbC₂ that is decomposed by hydrochloric acid HCl to acetylene C₂H₂ and lead(II) chloride PbCl₂.^[4]

A compound analyzed as lead carbide PbC₂ has also been obtained accidentally, as a thin layer (about 10 μm thick) on the inner wall of a graphite crucible that had been used to heat a lead-bismuth eutectic alloy for 100 hours at 1073 K in a helium atmosphere.^{[5]: p.27 [6]}

Several reports of "lead carbide" synthesis appeared in the early 19th century, and were widely cited and copied into textbooks during the next few decades. In 1820, for instance, a certain John claimed to have sublimated a black carbide of lead from finely divided mixture of lead and charcoal,^[7][8] but this claim apparently was never reproduced.^[1]: p.67 Also in 1820, Berzelius claimed that the pyrolysis (decomposition by heat) of iron-lead cyanide resulted in a double iron and lead carbide, FeC₄·2PbC₄.^[9] In 1823 Göbel from Jena obtained, by pyrolysis of lead tartrate in a closed vessel, a black powder that ignited spontaneously in contact with air, and believed it to be a carbide of lead.^[10][11][12] This product still provides a popular school demonstration of pyrophoricity.^[13] Shortly thereafter, Proust obtained a similar product from lead acetate^[7] and Berzelius obtained one from lead cyanide.^{[7]: p.122 [14][15]: p.436}

However, by 1870 those pyrophoric residues came to be regarded as an "intimate mixture" of carbon and lead; and the existence of lead carbide was considered unproven.^[1]: p.67