Chemistry of acetylenic ethers LII acetylenic tert. Butyl ethers and some other acetylenic ethers with branched alkyl groups: Some remarks concerning the preparation and the pyrolysis of acetylenic ethers

Abstract

Tert. butoxyethyne IV and some 1‐tert.butoxy‐1‐alkynes V have been prepared as outlined in the scheme below. The elimination of HBr from 2‐bromo‐1,2‐unsaturated ethers such as III and VI by means of sodium amide in liquid ammonia gives much better yields of acetylenic ethers than the procedure using KOH. Some examples of this modification of a much used method for the preparation of acetylenic ethers are given. In the case of propynyl ethers CH₃C≡COR an excess of sodamide must be avoided, because this isomerizes the propynyl ethers into propargyl ethers HC≡CCH₂OR.Tert.butoxyalkynes V split off isobutene at 70–80°, forming cyclobutenone ethers X.The thermal stability of 1‐alkoxy‐1‐alkynes decreases in the order C₂H₅O > i.C₃H₇O > t.C₄H₉O.