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Kinetic and structure–activity studies of the triazolium ion-catalysed benzoin condensation.

Massey, Richard S. and Murray, Jacob and Collett, Christopher J. and Zhu, Jiayun and Smith, Andrew D. and O'Donoghue, AnnMarie C. (2021) 'Kinetic and structure–activity studies of the triazolium ion-catalysed benzoin condensation.', Organic & biomolecular chemistry., 19 (2). pp. 387-393.


Steady-state kinetic and structure–activity studies of a series of six triazolium-ion pre-catalysts 2a–2f were investigated for the benzoin condensation. These data provide quantitative insight into the role of triazolium N-aryl substitution under synthetically relevant catalytic conditions in a polar solvent environment. Kinetic behaviour was significantly different to that previously reported for a related thiazolium-ion pre-catalyst 1, with the observed levelling of initial rate constants to νmax at high aldehyde concentrations for all triazolium catalysts. Values for νmax for 2a–2f increase with electron withdrawing N-aryl substituents, in agreement with reported optimal synthetic outcomes under catalytic conditions, and vary by 75-fold across the series. The levelling of rate constants supports a change in rate-limiting step and evidence supports the assignment of the Breslow-intermediate forming step to the plateau region. Correlation of νmax reaction data yielded a positive Hammett ρ-value (ρ = +1.66) supporting the build up of electron density adjacent to the triazolium N-Ar in the rate-limiting step favoured by electron withdrawing N-aryl substituents. At lower concentrations of aldehyde, both Breslow-intermediate and benzoin formation are partially rate-limiting.

Item Type:Article
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Publisher statement:This article is licensed under a Creative Commons Attribution 3.0 Unported Licence
Date accepted:11 December 2020
Date deposited:06 January 2021
Date of first online publication:14 December 2020
Date first made open access:06 January 2021

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