Purification Methods
It sometimes contains diluents, e.g. xylene, butyl ether or dioxane which can be removed by filtration followed by a vacuum at 65-60o/5mm. Alternatively the acetylide is purged with HCCH at 100-125o to remove diluent. NaC2H adsorbs 2.2x, 2.0x and 1.6x its wt of xylene, butyl ether and dioxane, respectively. Powdered NaC2H is yellow or yellow-gray in colour and is relatively stable. It can be heated to ca 300o in the absence of air. Although no explosion or evolution of gas occurs, it turns brown due to disproportionation. At 170-190o in air it ignites slowly and burns smoothly. At 215-235o in air it “flash-ignites” and burns quickly. It can be dropped into a slight excess of H2O without flashing or burning, but vigorous evolution of HC CH (HIGHLY FLAMMABLE IN AIR) occurs. The sample had been stored in the absence of air for one year without deterioration. Due to the high flammability of HCCH, the salt should be stored dry and should be treated with care. After long storage, NaCCH can be redissolved in liquid NH3 and used for the same purposes as the fresh material. However it may be slightly turbid due to the presence of moisture. [Rutledge J Org Chem 22 649 1957, Greenlee & Henne J Am Chem Soc 77 5013 1955, Campbell & Campbell Inorg Synth II 76, 81 1946, Org Synth 30 15 1950, Beilstein 1 H 238.] It is available commercially under N2 in Sure/Seal bottles as an 18 wt% solution in xylene/mineral oil. See “Aliphatic Compounds”, Chapter 4, for its prepartion.
