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Duality in SN1 and SN2 Mehanisms in Reactions of Benzyl Chlorides with Amines under Solvolytic Conditions

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Bibliographic Details
Title: Duality in SN1 and SN2 Mehanisms in Reactions of Benzyl Chlorides with Amines under Solvolytic Conditions
Authors: Bušljeta, Mia, Matić, Mirela, Denegri, Bernard
Publisher Information: 2025.
Publication Year: 2025
Subject Terms: SN1/SN2 mechanisms, Benzyl chlorides, nucleophile, solvolyses
Description: Reactions of unhindered primary benzylic substrates with various nucleophiles might be expected to proceed through a concerted SN2 displacement mechanism. However, as has been previously reported, these substrates react with some amine nucleophiles in aprotic solvents (nonsolvolytic conditions) simultaneously via both stepwise SN1 and concerted SN2 mechanisms if they are substituted by strong electron-donating substituents and contain very good leaving groups, such as tosylate and bromide. In this study we set out to investigate the mechanism of the nucleophilic displacement reactions of activated benzyl derivatives bearing a moderately good leaving group (i.e., chloride) with piperidine (a strong nucleophile) and pyridine (a weak nucleophile) under solvolytic conditions (that is in a protic solvent). For that purpose, reaction rates at different concentrations of the mentioned nucleophiles were measured in 80 % aqueous ethanol (v/v) at 60 °C using the conductometric method. Reactions of all activated benzyl chlorides with piperidine (a strong nucleophile) in aqueous ethanol followed the rate law in equation (1) with a nucleophile-independent term k1 and a nucleophile-dependent term k2, indicating the duality of nucleophilic substitution mechanism. In addition, the Yukawa-Tsuno treatment of measured rates has confirmed that concurrent SN1 and SN2 pathways occur in the reaction with solvent and piperidine. kobs = k1 + k2[Nucleophile] (1) Kinetic analysis further indicated that the most activated benzyl chlorides (X = 4-OCH3 and 4-SCH3) in the presence of pyridine (a weak nucleophile) reacted only with solvent by the SN1 mechanism. On the other hand, the nucleophilic displacement under solvolytic conditions of the less activated substrates in the presence of pyridine were shown to proceed simultaneously through the both concurrent mechanisms.
Document Type: Conference object
Access URL: https://29hskiki.hkd.hr/book-of-abstracts/
Accession Number: edsair.dris...01492..e4775eea115121d4a6e6b03605e1ae11
Database: OpenAIRE
Description
Abstract:Reactions of unhindered primary benzylic substrates with various nucleophiles might be expected to proceed through a concerted SN2 displacement mechanism. However, as has been previously reported, these substrates react with some amine nucleophiles in aprotic solvents (nonsolvolytic conditions) simultaneously via both stepwise SN1 and concerted SN2 mechanisms if they are substituted by strong electron-donating substituents and contain very good leaving groups, such as tosylate and bromide. In this study we set out to investigate the mechanism of the nucleophilic displacement reactions of activated benzyl derivatives bearing a moderately good leaving group (i.e., chloride) with piperidine (a strong nucleophile) and pyridine (a weak nucleophile) under solvolytic conditions (that is in a protic solvent). For that purpose, reaction rates at different concentrations of the mentioned nucleophiles were measured in 80 % aqueous ethanol (v/v) at 60 °C using the conductometric method. Reactions of all activated benzyl chlorides with piperidine (a strong nucleophile) in aqueous ethanol followed the rate law in equation (1) with a nucleophile-independent term k1 and a nucleophile-dependent term k2, indicating the duality of nucleophilic substitution mechanism. In addition, the Yukawa-Tsuno treatment of measured rates has confirmed that concurrent SN1 and SN2 pathways occur in the reaction with solvent and piperidine. kobs = k1 + k2[Nucleophile] (1) Kinetic analysis further indicated that the most activated benzyl chlorides (X = 4-OCH3 and 4-SCH3) in the presence of pyridine (a weak nucleophile) reacted only with solvent by the SN1 mechanism. On the other hand, the nucleophilic displacement under solvolytic conditions of the less activated substrates in the presence of pyridine were shown to proceed simultaneously through the both concurrent mechanisms.