Preparation of diiodoacetylene (diiodoethyne; 1,2-diiodoethyne; acetylene, diiodo-)
Diiodoacetylene decomposes explosively! The temperature of decomposition is about 125° C. It also explodes on rubbing in a mortar. 300 ml of a 0.5N solution of potassium hydroxide are placed into a flask fitted with a dropping-funnel, a mechanical or magnetic stirrer and a tube for the introduction of gas. A rapid current of acetylene, previously washed with a solution of basic lead acetate, is passed in, meanwhile stirring and cooling strongly from the dropping funnel a solution of 32 g iodine and 35 g potassium iodide in 25 ml water are dropwise added until the color of the iodine persists in the reaction mixture. This operation lasts 30-40 minutes. The diiodoacetylene precipitate obtained is filtered off, washed with water, dried in a desiccator, and, if necessary, crystallized from ligroin. Yield almost theoretical. Diiodoacetylene forms white crystals melting at 78.5° C which have a strong, disagreeable odor. It has a high volatility and is insoluble in water, but soluble in alcohol, ether, etc. Exposed to light it slowly becomes red with separation of iodine.
Dehn, W. J. Am. Chem. Soc. 34, 1598-1601 (1911)
The war gases chemistry and analysis, by M. Sartory, 52, 1939
By another method acetylene is passed into a solution of 20 g of potassium iodide dissolved in 100 ml of 1N sodium hydroxide with stirring and ice-cooling, whilst simultaneously about 150 ml 1N sodium hypochlorite solution (prepared by passing 12 g of chlorine into ice-cooled 200 ml of 2N sodium hydroxide solution) is dropped in until the initial yellow color no longer appears. The precipitated white diiodoacetylene is collected, washed with water, drained well, and dried in a desiccator over phosphorus pentoxide, diiodoacetylene is obtained 96.5 % yield and m.p. 82° C. It is volatile and must therefore not be dried in a vacuum. The acetylene is developed by dropping water on to 600 g calcium carbide; a pure white product is obtained from the unpurified acetylene derived from calcium carbide, however, if very pure acetylene from a steel bottle yields yellow tetraiodoethylene.
Chem. Ber., 87, 1148 (1954).