Mechanism, kinetics and selectivity of a Williamson ether synthesis: elucidation under different reaction conditions,Reaction Chemistry & Engineering

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Mechanism, kinetics and selectivity of a Williamson ether synthesis: elucidation under different reaction conditions
Reaction Chemistry & Engineering ( IF 3.4 ) Pub Date : 2021-1-28 , DOI: 10.1039/d0re00437e
Aikaterini Diamanti _{1,

2,

3,

4,

5} , Zara Ganase _{1,

2,

3,

4,

5} , Eliana Grant _{1,

2,

3,

4,

5} , Alan Armstrong _{5,

6,

7,

8} , Patrick M. Piccione _{9,

10,

11,

12,

13} , Anita M. Rea _{9,

10,

11,

12,

13} , Jeffery Richardson _{5,

14,

15,

16} , Amparo Galindo _{1,

2,

3,

4,

5} , Claire S. Adjiman _{1,

2,

3,

4,

5}

Affiliation

Department of Chemical Engineering
Centre for Process Systems Engineering and Institute for Molecular Science and Engineering
Imperial College London, South Kensington Campus
London SW7 2AZ
UK
Department of Chemistry and Institute for Molecular Science and Engineering
Imperial College London
London W12 0BZ
Process Studies Group
Process Technology AI
Syngenta
Jealott's Hill International Research Center
Bracknell
Discovery Research and Technologies
Eli Lilly and Company
Windlesham

The best route to uncover the mechanism of chemical reactions remains a topic of intense debate. In this work, we deploy a three-faceted approach that combines experimental probing, detailed kinetic modelling and quantum-mechanical calculations for the study of the mechanism and regioselectivity of a Williamson ether synthesis, which is of interest because of its simplicity and its broad scope in laboratory and industrial synthesis. The choice of solvent is found to have a large impact on the experimental regioselectivity, with ratios of O-alkylated to C-alkylated product at 298 K of 97 : 3 in acetonitrile and of 72 : 28 in methanol. Through experiments and kinetic modelling, we identify reaction networks that differ significantly from solvent to solvent, providing insights into the factors (proton-exchange, solvolysis and product degradation) that impact on regioselectivity and the relative rates of O-alkylation and C-alkylation. The kinetic models yield detailed information on reaction rates and energy barriers and on the existence of an additional double alkylation pathway. We carry out quantum mechanical calculations and elucidate the transition states for the two main alkylation pathways. The quantum-mechanical calculations highlight structural differences between the transition states found for the two alkylation pathways and provide information on the effect of the solvent on the stabilisation/destabilisation of various structures and hence on reaction selectivity. The three-faceted approach provides complementary information into the elementary steps of the reaction mechanism.

中文翻译：

Williamson醚合成的机理，动力学和选择性：在不同反应条件下的阐明

揭示化学反应机理的最佳途径仍然是激烈争论的话题。在这项工作中，我们采用了一种三方面的方法，该方法结合了实验探测，详细的动力学模型和量子力学计算，用于研究威廉姆森醚合成的机理和区域选择性，由于它的简单性和广泛的应用范围而引起人们的兴趣。在实验室和工业合成中。发现溶剂的选择对实验区域选择性有很大影响，O-烷基化与C的比率在298 K下的乙烷基化产物在乙腈中为97：3，在甲醇中为72:28。通过实验和动力学建模，我们确定了不同溶剂之间存在显着差异的反应网络，从而深入了解了影响区域选择性以及O烷基化和C相对速率的因素（质子交换，溶剂分解和产物降解）-烷基化。动力学模型产生有关反应速率和能垒以及是否存在其他双烷基化途径的详细信息。我们进行量子力学计算并阐明两个主要烷基化途径的过渡态。量子力学计算突出了在两个烷基化途径中发现的过渡态之间的结构差异，并提供了有关溶剂对各种结构的稳定/去稳定作用以及因此对反应选择性的影响的信息。三方面的方法将补充信息提供给反应机制的基本步骤。

更新日期：2021-02-04

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