Metal acetylide

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A metal acetylide is an alkyne that has had a proton (hydrogen) removed from the terminal end by a metal such as sodium or an organolithium. So, for example, the alkyne CH3C≡CH could be deprotonated to form the acetylide ion CH3C≡C−. Once it has been deprotonated it becomes a strong nucleophile. Some acetylides, eg. silver acetylide, are explosives.

Acetylide ions are very useful in organic chemistry reactions in combining carbon chains, particularly addition and substitution reactions. One type of reaction displayed by acetylides are addition reactions with ketones to form tertiary alcohols. In the reaction in scheme 1 the alkyne proton of ethyl propiolate is deprotonated by n-butyllithium at -78°C to form lithium ethyl propiolate to which cyclopentanone is added forming a lithium alkoxy. Acetic acid is added to remove lithium and liberate the free alcohol [1].


Scheme 1. Reaction of ethyl propiolate with n-butyllithium to form the lithium acetylide.


[edit] References

  1. ↑  Synthesis of alkyl 4-hydroxy-2-alkynoates M. Mark Midland, Alfonso Tramontano, John R. Cable J. Org. Chem.; 1980; 45(1); 28-29. Abstract
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