The molecularity of the Newman-Kwart rearrangement

Matthew Burns, Guy C. Lloyd-Jones, Jonathan D. Moseley, Joseph S. Renny

Research output: Contribution to journalArticle (Academic Journal)peer-review

30 Citations (Scopus)

Abstract

It was recently reported that the venerable Newman-Kwart rearrangement (1→2) proceeds via mixed first- and second-order kinetics. Prior to this, the rearrangement had been considered to proceed exclusively via an intramolecular O Ar→S Ar migration. A new bimolecular pathway, possibly involving an 8-membered cyclic transition state, was proposed to account for reaction rates that increased disproportionately with substrate concentration under microwave heating conditions. We report a reanalysis of the kinetics and molecularity of the rearrangement of N,N-dimethyl O-(p-nitrophenyl)thiocarbamate 1a in N,N-dimethylacetamide solvent. Using HPLC, isotopic labeling ( 2H, 18O, 34S), and ESI-ICRMS methods, we show that there is no evidence for a bimolecular pathway en route to 2a, with near-perfect exponential decay in 1a at concentrations ranging from 0.11 to 4.70 M. Instead, it is demonstrated that under the microwave heating conditions, a delayed negative feedback signal to the microwave power balancing loop results in oscillatory reaction overheating. Due to higher tan δ in the solute, the amplitude of this oscillation increases with the concentration of 1a, and this phenomenon best accounts for the kinetic behavior previously misinterpreted as being mixed 'irst- and second-order in nature. © 2010 American Chemical Society.

Original languageEnglish
Pages (from-to)6347-6353
Number of pages7
JournalJournal of Organic Chemistry
Volume75
Issue number19
DOIs
Publication statusPublished - 1 Oct 2010

Structured keywords

  • BCS and TECS CDTs

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