St Andrews Research Repository

St Andrews University Home
View Item 
  •   St Andrews Research Repository
  • University of St Andrews Research
  • University of St Andrews Research
  • University of St Andrews Research
  • View Item
  •   St Andrews Research Repository
  • University of St Andrews Research
  • University of St Andrews Research
  • University of St Andrews Research
  • View Item
  •   St Andrews Research Repository
  • University of St Andrews Research
  • University of St Andrews Research
  • University of St Andrews Research
  • View Item
  • Login
JavaScript is disabled for your browser. Some features of this site may not work without it.

Proton transfer reactions of N-aryl triazolium salts : unusual ortho-substituent effects

Thumbnail
View/Open
Smith_2014_JPOC_Proton_AM.pdf (965.0Kb)
Date
02/2015
Author
Tucker, David E.
Quinn, Peter
Massey, Richard S.
Collett, Christopher John
Jasiewicz, David J.
Bramley, Christopher R.
Smith, Andrew David
O’Donoghue, AnnMarie C.
Keywords
Deuterium exchange
N-heterocyclic carbene
Organic catalysis
Proton transfer
Triazolium
QD Chemistry
NDAS
Metadata
Show full item record
Altmetrics Handle Statistics
Altmetrics DOI Statistics
Abstract
Previous studies of the C(3)-hydrogen/deuterium exchange reactions of the triazolium ion conjugate acids of triazolyl N-heterocyclic carbenes revealed a change of mechanism under acidic conditions with N1-protonation to a dicationic salt. Interestingly, the data suggested an increase in pKaN1 in the presence of a N-pentafluorophenyl substituent relative to other N-aryl substituents with hydrogens or methyl substituents rather than fluorines at the ortho-positions. To probe the presence of an apparent donor effect of a N-pentafluorophenyl substituent, which differs from the more common electron withdrawing effect of this group, we have studied the analogous deuterium exchange reactions of four triazolium salts with heteroatoms or heteroatom substituents in the 2-position and/or 6-position of the N-aryl ring. These include triazolium salts with N-2,4,6-tribromophenyl 11, N-2,6-dichlorophenyl 12, N-2-pyridyl 13 and N-2-pyrimidinyl 14 substituents. The log kex – pD profiles for 11, 12 and 14 were found to show similar trends at lower pDs as for the previously studied N-pentafluorophenyl triazolium salt, hence supporting the presence an apparent donor effect on pKaN1. Surprisingly, the log kex – pD profile for N-pyridyl salt 13 uniquely showed acid catalysis at lower pDs. We propose herein that this data is best explained by invoking an intramolecular general base role for the N-(2-pyridyl) substituent in conjunction with N1-protonation on the triazolium ring. Finally, the second order rate constants for deuteroxide ion catalysed C(3)-H/D exchange (kDO, M−1 s−1), which could be obtained from data at pDs >1.5, were used to provide estimates of C(3)-carbon acid pKaC3 values for the four triazolium salts 11, 12, 13, 14.
Citation
Tucker , D E , Quinn , P , Massey , R S , Collett , C J , Jasiewicz , D J , Bramley , C R , Smith , A D & O’Donoghue , A C 2015 , ' Proton transfer reactions of N-aryl triazolium salts : unusual ortho -substituent effects ' , Journal of Physical Organic Chemistry , vol. 28 , no. 2 , pp. 108-115 . https://doi.org/10.1002/poc.3399
Publication
Journal of Physical Organic Chemistry
Status
Peer reviewed
DOI
https://doi.org/10.1002/poc.3399
ISSN
0894-3230
Type
Journal article
Rights
Copyright © 2014 John Wiley & Sons, Ltd. This is the accepted version of the following article: Tucker, D. E., Quinn, P., Massey, R. S., Collett, C. J., Jasiewicz, D. J., Bramley, C. R., Smith, A. D., & O’Donoghue, A. C. (2015). Proton Transfer Reactions of N-Aryl Triazolium Salts: Unusual Ortho-Substituent Effects. Journal of Physical Organic Chemistry, which has been published in final form at http://dx.doi.org/10.1002/poc.3399
Description
The authors thank the EPSRC (D. E. T., R. S. and C. J. C.) and Durham University (P. Q., D. J. J. and C. R. B.) for funding of this project.
Collections
  • University of St Andrews Research
URL
http://onlinelibrary.wiley.com/doi/10.1002/poc.3399/suppinfo
URI
http://hdl.handle.net/10023/7893

Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.

Advanced Search

Browse

All of RepositoryCommunities & CollectionsBy Issue DateNamesTitlesSubjectsClassificationTypeFunderThis CollectionBy Issue DateNamesTitlesSubjectsClassificationTypeFunder

My Account

Login

Open Access

To find out how you can benefit from open access to research, see our library web pages and Open Access blog. For open access help contact: openaccess@st-andrews.ac.uk.

Accessibility

Read our Accessibility statement.

How to submit research papers

The full text of research papers can be submitted to the repository via Pure, the University's research information system. For help see our guide: How to deposit in Pure.

Electronic thesis deposit

Help with deposit.

Repository help

For repository help contact: Digital-Repository@st-andrews.ac.uk.

Give Feedback

Cookie policy

This site may use cookies. Please see Terms and Conditions.

Usage statistics

COUNTER-compliant statistics on downloads from the repository are available from the IRUS-UK Service. Contact us for information.

© University of St Andrews Library

University of St Andrews is a charity registered in Scotland, No SC013532.

  • Facebook
  • Twitter