Li, D. orcid.org/0000-0002-5329-4298 and Williams, N.H. (2016) The solvolysis mechanism of simple secondary tosylates in 50% aqueous TFE. Journal of Physical Organic Chemistry, 29 (12). pp. 709-717. ISSN 1099-1395
Abstract
The solvolysis of simple secondary tosylates in 50% trifluoethanol has been investigated using stereochemical and isotopic labels. 2-butyl, 2-pentyl and 2-octyl tosylates all solvolyse at very similar rates (~1 × 10−5 s−1) at 30 °C. Slow racemisation of S-2-butyl tosylate (~4.6 × 10−7 s−1) was observed during solvolysis, but R-2-octyl tosylate did not show any significant racemisation. Competing rearrangement of 3-pentyl tosylate to 2-pentyl tosylate was observed during solvolysis and is attributed to 1,2-hydride transfer, which occurs at a rate sufficient to account for the difference in the rates of racemisation of 2-butyl and 2-octyl tosylates. The stereochemistry of the alcohol product was studied for the reaction of R-2-octyl tosylate by derivatising the corresponding alcohol to 4-nitrobenzoate and showed high but not complete stereoselectivity (92:8 inversion : retention of configuration). 18O isotope exchange at the leaving group tosylate showed that both 2-butyl (5.4 × 10−7 s−1) and 2-octyl (4.2 × 10−7 s−1) tosylates exchange at similar rates. Partitioning of a common carbenium ion intermediate accounts for all these data only if solvolysis proceeds through pre-organisation of the solvent with 1,2-hydride transfer and isotope exchange competing inefficiently with ion return and solvolysis. Alternatively, a series of parallel concerted reactions (solvolysis, 1,2-hydride transfer and isotope exchange) would also account for these data.
Metadata
Item Type: | Article |
---|---|
Authors/Creators: |
|
Editors: |
|
Copyright, Publisher and Additional Information: | © 2016 John Wiley & Sons, Ltd.. This is an author produced version of a paper subsequently published in Journal of Physical Organic Chemistry. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | 1,2-hydride transfer; carbocation; isotope exchange; solvolysis |
Dates: |
|
Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > Department of Chemistry (Sheffield) |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 15 Aug 2016 13:49 |
Last Modified: | 11 Apr 2017 01:28 |
Published Version: | http://dx.doi.org/10.1002/poc.3559 |
Status: | Published |
Publisher: | Wiley |
Identification Number: | 10.1002/poc.3559 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:101308 |