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Mechanism of reactions of unsaturated ethers and thioethers. IX: Acid-catalyzed alkyl oxygen fission of alkyl ethynyl ethers

✍ Scribed by E. J. Stamhuis; W. Drenth

Publisher
Elsevier Science
Year
2010
Tongue
English
Weight
426 KB
Volume
82
Category
Article
ISSN
0165-0513

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✦ Synopsis

Abstract

As in the formation of esters from alkyl ethynyl ethers with primary alkyl groups by addition of water, isopropyl and tert.‐butyl acetate are produced from isopropoxy‐ and tert.‐butoxyethyne. In addition, the latter ethers show formation of an acidic product and an olefin.

A mechanism is proposed in which the first step is a rate determining proton‐transfer to the triple bond:

The carbonium ion formed initially reacts in two ways. One is by addition of water leading to the production of ester. The other is an alkyl oxygen fission from which keten and an alkyl carbonium ion result. The keten is rapidly converted into acetic acid. The alkyl carbonium ion is stabilized among other things by olefin formation.

Rate constants for HCCOR, as R is varied, obey the Taft equation: log k~R~ = ϱ*σ~R~* + constant. The polar reaction constants, ϱ*, have exceptionally large values of approximately −7.

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