Mechanism of reactions of unsaturated ethers and thioethers. XI: Acid‐catalyzed addition of water to 1‐alkynyl thioethers

The effect of structure on the rates of hydration was analyzed with the Taft equation log k = e* u* 4-constant, for the following two series:(a) HCECSR', with R = CaH5, CH(CHs)a, and C(CH3)3, log kR* = -0.13 UR'* -0.15; (b) RCECSCZHF,, with R = CH3, CZH5, CHaCHaCH3, and CH(CH3)a, log kR = -3.16 OR* -2.01. The values of the polar reaction constants are in agreement with the established mechanism of this reaction.The kinetic experiments with HCE CSCaHs and DC= CSCzHs revealed an inverse secondary deuterium isotope effect: kD/kH = 1.03. This value was compared with those calculated either from the alterations of the vibrations during the reaction or from the difference in inductive effect of H and D. Introductiondealt with the mechanism of the acidcatalyzed addition of water to ethynyl thioethers. This study and a continuation 5 of it led to the following conclusions. The presence of general acidcatalysis, the primary kinetic deuterium isotope effect, and acetylenic hydrogen-deuterium exchange, show that the reaction involves a slow proton transfer to the organic species. The entropies of activation, the activity postulate of Grunwufd for reactions in alcohol-water mixtures, the relation of Zucker and Hanzmett and the theory of Bunnett, suggest that the addition of a water molecule is not included in the rate determining step. Therefore, the following mechanism was proposed for this reaction :

show abstract

Mechanism of reactions of unsaturated ethers and thioethers. VIII: Acid‐catalyzed addition of water to 1‐alkynyl ethers

Stamhuis

Drenth

1963

Recl. Trav. Chim. Pays‐Bas

View full text Add to dashboard Cite

Additional evidence for the occurrence of a rate determining proton transfer in the hydration of I-alkynyl ethers is afforded by the value of the solvent deuterium isotope effect, kHao/kDao = 1.7.The addition of water to I-ethoxy-1-propyne was investigated in a series of alcohol-water mixtures. Application of the criterium of Grunwuld indicates that a solvent molecule is not bound covalently in the slow proton transfer step.

show abstract

Mechanism of reactions of unsaturated ethers and thioethers. XI: Acid‐catalyzed addition of water to 1‐alkynyl thioethers

Cited by 18 publications

References 36 publications

Vinyl and Allenyl Cations

Vinyl and Allenyl Cations

Mechanism of reactions of unsaturated ethers and thioethers. VII: Linear free energy relationships and inverse secondary deuterium isotope effect in the addition of water to 1‐alkynyl thioethers

Mechanism of reactions of unsaturated ethers and thioethers. VIII: Acid‐catalyzed addition of water to 1‐alkynyl ethers

Contact Info

Product

Resources

About