Preparation of ethoxyacetylene
Alternative Names: ethoxyethyne; ethoxyacetylene; ethyne, ethoxy-; ethynoxyethane
76.5 g of chloroacetaldehyde diethyl acetal are added during 15 minutes to a manually agitated suspension of sodium amide prepared from 38 g of sodium in 500 ml of liquid ammonia contained in a 1-liter flask. After all the ammonia has been evaporated off in a stream of pure nitrogen, the nitrogen flow is increased and the flask is cooled to —70° C in solid carbon dioxide and methanol. (The increased nitrogen flow avoids the danger of air and water vapour being sucked into the flask by the contraction in volume due to cooling.) A 320 ml of cold (— 20° C) saturated solution of sodium chloride are then added as rapidly as possible (about 5 seconds) with vigorous cooling and agitation. The flask is then fitted with a short reflux condenser connected to a trap cooled to — 30° C and the contents of the flask are slowly heated to 100° C (manual agitation breaks up any foaming quite easily). The condensate is allowed to warm up to 0° C and is then freed from ammonia by the addition of an aqueous slurry of sodium dihydrogen phosphate. The neutral aqueous layer is frozen, and the supernatant liquid is decanted and dried (calcium chloride). Distillation through a short Fenske column with partial reflux gives 21.2 g or 61% of ethoxyacetylene, b.p. 50-52° C, nD=1.3835.
Acetylenic compounds in organic synthesis, by R. R. Alexander, 207, 1955
Eglinton, G., Jones, E. R. H., Shaw, B. L. and Whiting, M. C. J. chem. Soc (1954) 1860