Internal alkynes are relatively electron rich and are not usually prone to attack by strong (nucleophilic) bases such as hydroxide or alkoxide.

However, this isn't always the case. A very nice overview of the most common reactions of alkynes says:

The sp-hybrid carbon atoms of the triple-bond render alkynes more electrophilic than similarly substituted alkenes. As a result, alkynes sometimes undergo addition reactions initiated by bonding to a nucleophile. This mode of reaction, illustrated below, is generally not displayed by alkenes, unless the double-bond is activated by electronegative substituents, e.g. $\ce{F2C=CF2}$, or by conjugation with an electron withdrawing group.

$\ce{HC≡CH + KOC2H5 —>[in C2H5OH at 150 ºC] H2C=CH-OC2H5}$

I'm interested in more information about this and similar reactions, particular for internal (not acetylenic) alkynes.

Unfortunately, the linked page doesn't provide a reference for this reaction, and searching in Google Scholar for "internal alkyne" "potassium hydroxide" doesn't provide useful results.

Thus my questions are:

  1. Does hydroxide ever react similarly with internal alkynes, at any temperature? If so, under what conditions?
  2. How long does the ethoxide reaction indicated above (at 150 °C) take? Days? Hours? Minutes? Would it be significantly different for an internal alkyne rather than acetylene?
  3. In the case of a hydroxide reaction, would the ultimate product be a ketone (a.k.a. base catalyzed hydration)?
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    $\begingroup$ I can't read German, but this paper is probably relevant. From what I can tell, it is describing the reaction between acetylene, an alcohol/phenol (including ethanol), and KOH at elevated pressures to give a vinyl aryl or vinyl alkyl ether. $\endgroup$ Commented Dec 4, 2016 at 20:22
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    $\begingroup$ There are also multiple patents describing how the reaction can be carried out in industry, for example this one. Page 9 states that the reaction with MeOH (to form vinyl methyl ether) was run with KOMe catalyst at 45 psi, 145 deg C, for 40 hours giving a 96% yield. $\endgroup$ Commented Dec 4, 2016 at 20:39
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    $\begingroup$ And I did another search on Reaxys for vinyl ethers of the form $\ce{R^1HC=C(OR^2)R^3}$ but sadly no syntheses from internal alkynes turned up. I'll leave somebody else more qualified to try to rationalise it. $\endgroup$ Commented Dec 6, 2016 at 2:51

1 Answer 1


According to A Textbook of Organic Chemistry by V. K. Ahluwalia and Madhuri Goyal

1-Butyne may be isomerised to a more stable 2-butyne in presence of alcoholic potassium hydroxide and the reverse of this reaction may occur with sodamide

(see 17.2.1 of Best Synthetic Methods: Acetylenes, Allenes and Cumulenes for reaction conditions in the 2-alkyne to 1-alkyne direction, actually many relevant reactions are in this book)

So in the present of the strong base $\ce{NaNH2}$ the internal alkyne $\ce{H3CC#CCH3}$ rearranges to $\ce{HC#CCH2CH3}$

My thinking is that with just hydroxide the more stable 2-butyne is favored, while if an even-stronger base is used, that fact that the acetylenic-H can deprotonate pulls the equilibrium toward 1-butyne.

Additionally, see 17.2.11 Isomerisation of 1,4 bis(alkoxy)-2-butynes to the corresponding allenes, which is catalyzed by t-BuOK.

Add see table 17.1 "Base catalyzed isomerisations of acetylenic compounds" about 10 different internal acetylene reactions are listed in the table.

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    $\begingroup$ Thanks for this! I'll probably accept & award in the next day or two (unless a better answer materializes). I'm especially impressed w/ table 17.1. It seems like alkynes can readily isomerize to allenes or other slightly more stable isomers under basic conditions. $\endgroup$
    – Curt F.
    Commented Dec 8, 2016 at 17:55

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