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Mechanism of reactions of unsaturated ethers and thioethers. I: Add catalyzed addition of water to acetylenic thioethers

✍ Scribed by W. Drenth; H. Hogeveen

Publisher
Elsevier Science
Year
2010
Tongue
English
Weight
420 KB
Volume
79
Category
Article
ISSN
0165-0513

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✦ Synopsis

Abstract

The acid catalyzed addition of water to ethylthioethyne has been studied in aqueous solution. The reaction is general acid catalyzed and it is faster in H~2~O than in D~2~O. Substitution of a tertiary butyl group for the ethyl group results in a rate enhancement. The entropies of activation ΔS≠ for the hydration of ethylthioethyne and tertiary butylthioethyne are ‐ 6.1 and ‐ 0.6 cal. mole^−1^, deg.^−1^, respectively. These facts strongly suggest that protonation of the alkylthioethyne is the rate controlling step of the reaction.

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## Abstract Ethoxyethyne slowly adds diazomethane to yield 4‐ethoxypyrazole I, the structure of which has been proved by synthesis from 1,1,2,3,3‐pentaethoxypropane IV and hydrazine. Ethylthioethyne V, on the contrary, is converted by diazomethane into 3‐ethylthiopyrazole VI, the structure of which