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care was taken to employ reaction conditions which would tend to minimize its formation.A solution of 34.0 g. (0.200 mole) of the diethyl ester of acetylenedicarboxylic acid in 100 ml. of absolute ethanol maintained under high purity nitrogen was treated with a catalytic amount (0.2 g., 0.01 mole) of sodium causing the solution to become a clear, deep red. A second solution of 24.8 g. (0.200 mole) of ^-toluenethiol in 100 ml. of absolute ethanol was then added very slowly, over a period of three hours, with vigorous stirring. After addition was complete, the mixture was brought to reflux for 0.5 hour, and finally was allowed to cool. No crystals formed. The mixture was placed in 500 ml. of water and acidified with a small amount of concentrated HC1 (2-3 ml.). A brown oil was formed which was isolated by extraction with three 100-mi. portions of ether and subsequent evaporation of the combined ether layers under reduced pressure. The oil was purified by distillation (b.p. 166-168°at 2.0 mm.); yield 53.2 g. (90.5%) of a clear yellow oil.

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