# Newman–Kwart rearrangement
The Newman–Kwart rearrangement (NKR) is a thermal organic reaction that converts an O-aryl thiocarbamate into the corresponding S-aryl thiocarbamate by migration of the aryl group from oxygen to sulfur. Because the S-aryl product can be hydrolyzed to a thiophenol, the rearrangement is the key step in a three-step route that turns readily available phenols into aryl thiols without requiring highly reactive reagents or foul-smelling sulfur chemicals.[1](https://www.research.ed.ac.uk/en/publications/mechanism-and-application-of-the-newman-kwart-o-gt-s-rearrangemen/) • [2](https://pubs.acs.org/orlef7/article/22/1/274/496122)
| Key fact | Detail |
|---|---|
| Transformation | O-aryl N,N-dialkyl thiocarbamate → S-aryl N,N-dialkyl thiocarbamate (Ar–O–C(=S)NR₂ → Ar–S–C(=O)NR₂)[3](https://kmt.vander-lingen.nl/article/313/Newman-Kwart_rearrangement) • [4](https://edoc.ub.uni-muenchen.de/28690/7/Juestel_Patrick.pdf) |
| Purpose | Key step in converting phenols to thiophenols; the S-thiocarbamate is then hydrolyzed with base to the thiol[1](https://www.research.ed.ac.uk/en/publications/mechanism-and-application-of-the-newman-kwart-o-gt-s-rearrangemen/) |
| Discovery | First reports by Edwards and Pianka in 1965; independent development by Newman and Kwart in 1966[1](https://www.research.ed.ac.uk/en/publications/mechanism-and-application-of-the-newman-kwart-o-gt-s-rearrangemen/) • [3](https://kmt.vander-lingen.nl/article/313/Newman-Kwart_rearrangement) |
| Classical conditions | Activation barrier of about 35–43 kcal·mol⁻¹; heating from 150 °C for electron-deficient substrates to over 300 °C for nonactivated arenes[2](https://pubs.acs.org/orlef7/article/22/1/274/496122) |
| Thermal mechanism | Intramolecular, four-membered cyclic transition state with nucleophilic aromatic substitution character; accelerated by electron-withdrawing substituents[5](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/thiocarbamate) • [6](https://pubmed.ncbi.nlm.nih.gov/30672704/) |
| Mild variants | Pd catalysis near 100 °C; photoredox, electrochemical, Ce and Fe single-electron oxidation, and Bi(III) catalysis at room temperature[7](https://www.sciencedirect.com/science/article/pii/S0040403925002394) |
## The three-step phenol-to-thiophenol sequence
The standard sequence begins with the phenol. Treatment of a phenol or its phenoxide with an N,N-dialkylthiocarbamoyl chloride, typically dimethylthiocarbamoyl chloride, gives the O-aryl thiocarbamate. Heating then rearranges this compound to the S-aryl thiocarbamate, and hydrolysis of that product with base releases the thiophenol.[3](https://kmt.vander-lingen.nl/article/313/Newman-Kwart_rearrangement) • [8](https://orgsyn.org/demo.aspx?prep=CV6P0824)
The [Organic Syntheses](https://www.edgepedia.org/organic-syntheses) procedure for 2-naphthalenethiol illustrates the classical practice. [2-Naphthol](https://www.edgepedia.org/2-naphthol) is converted to O-2-naphthyl dimethylthiocarbamate in 68–73% yield; the carbamate is then pyrolyzed neat at 270–275 °C for 45 minutes in a nitrogen-swept flask, and alkaline hydrolysis of the rearranged product furnishes 2-naphthalenethiol in 71–80% yield.[8](https://orgsyn.org/demo.aspx?prep=CV6P0824)
## Mechanism
**Thermal pathway.** The uncatalyzed rearrangement proceeds intramolecularly through a four-membered cyclic transition state, sometimes described as a 1,3-oxathietane, in which the aryl group migrates from oxygen to sulfur.[5](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/thiocarbamate) • [9](https://pubs.acs.org/doi/10.1021/acscatal.6c02238) Quantum-chemical studies place the 298 K free energy of activation above 30 kcal·mol⁻¹ for uncharged substrates and characterize the reaction as having the character of nucleophilic aromatic substitution, which explains why electron-withdrawing substituents on the aromatic ring accelerate it.[6](https://pubmed.ncbi.nlm.nih.gov/30672704/) Kinetic work by [AstraZeneca](https://www.edgepedia.org/astrazeneca) researchers found a strongly negative entropy of activation, consistent with this intramolecular ipso-substitution picture, and reported a competing bimolecular path with an eight-membered transition state at higher substrate concentrations in dichlorobenzene.[3](https://kmt.vander-lingen.nl/article/313/Newman-Kwart_rearrangement)
**Molecularity controversy resolved.** The claimed bimolecular pathway was later reexamined. A 2010 study by Burns, Lloyd-Jones, Moseley, and Renny used HPLC, isotopic labeling with ²H, ¹⁸O, and ³⁴S, and mass spectrometry on N,N-dimethyl O-(p-nitrophenyl)thiocarbamate in N,N-dimethylacetamide, and found near-perfect exponential (first-order) decay at concentrations from 0.11 to 4.70 M, with no evidence for a bimolecular route. The earlier mixed-order kinetics were traced to oscillatory overheating of concentrated samples caused by delayed feedback in the microwave power-balancing loop.[10](https://pubs.acs.org/doi/abs/10.1021/jo1014382)
**Radical-cation pathway.** When the substrate is oxidized by one electron, as under photoredox conditions, the rearrangement follows a different course. The radical-cation mechanism has 298 K activation free energies typically below 20 kcal·mol⁻¹, and it is accelerated by electron-donating substituents, which stabilize the positive hole character transferred to the aryl fragment as the reaction proceeds; this is the opposite substituent trend from the thermal reaction.[6](https://pubmed.ncbi.nlm.nih.gov/30672704/)
## Lowering the temperature: catalytic and redox variants
The high activation barrier of the thermal reaction, requiring roughly 200–300 °C, has been the method's main limitation, causing substrate degradation and side reactions.[2](https://pubs.acs.org/orlef7/article/22/1/274/496122) • [11](https://www.sciencedirect.com/org/science/article/pii/S0022326325002245) Several approaches now operate far below these temperatures.
**Palladium catalysis.** Harvey, Lloyd-Jones, Moseley, and colleagues showed in 2009 that a palladium catalyst substantially reduces the reaction temperature, to around 100 °C, by a mechanism involving oxidative addition of the C–O bond of the O-aryl thiocarbamate through a five-centered Pd–S coordinated transition state.[7](https://www.sciencedirect.com/science/article/pii/S0040403925002394) • [12](https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.200903908)
**Single-electron oxidation.** The photoredox method introduced by Nicewicz and co-workers, reported in the [Journal of the American Chemical Society](https://www.edgepedia.org/journal-of-the-american-chemical-society) in 2015, enables the rearrangement at ambient temperature through organic photoredox catalysis (using light-absorbing catalysts to transfer electrons and drive reactions) and significantly expanded the substrate scope.[7](https://www.sciencedirect.com/science/article/pii/S0040403925002394) • [13](https://pubs.acs.org/toc/jacsat/137/50) This strategy, based on electrophilic thiyl radical intermediates, was extended to protocols using ceric ammonium nitrate in dimethyl sulfoxide, iron(II)/ammonium persulfate in aqueous acetonitrile, and electrochemical methods.[2](https://pubs.acs.org/orlef7/article/22/1/274/496122)
**Electrocatalysis.** Francke and co-workers reported in 2018 that O-aryl thiocarbamates rearrange to S-aryl thiocarbamates under constant-current electrolysis at room temperature, requiring only catalytic amounts of electric charge in an undivided cell; in a microflow reactor, almost quantitative yields were achieved without supporting electrolyte.[14](https://pubs.acs.org/doi/10.1021/acs.orglett.8b03257) Mechanistic work showed the substrate is oxidized to a radical cation at the anode, followed by intramolecular cyclization and selective C–O bond cleavage.[15](https://pubs.rsc.org/en/content/articlehtml/2025/qo/d4qo02437k)
**Bismuth catalysis.** A Bi(OTf)₃-catalyzed variant reported in 2025 in the Journal of Organic Chemistry rearranges heteroaromatic substrates, including aza-arenes and thiophenes, at ambient temperature, addressing the rarity of successful heteroaryl examples under classical conditions.[11](https://www.sciencedirect.com/org/science/article/pii/S0022326325002245)
**Photothermal and bioinspired approaches.** [Microwave heating](https://www.edgepedia.org/microwave-heating) in water and photothermal conversion with carbon black have been used to promote the thermal reaction, and a 2026 report from [Emory University](https://www.edgepedia.org/emory-university) used riboflavin (vitamin B₂) as a cheap photocatalyst for a rapid room-temperature rearrangement under blue and green light, demonstrated on gram scale and compatible with biological buffers.[9](https://pubs.acs.org/doi/10.1021/acscatal.6c02238) • [16](https://pubs.rsc.org/en/content/articlehtml/2016/ra/c6ra20676j)
## Scope and applications
The rearrangement applies to Ar–S species ranging from large-scale industrial processes to complex molecules such as ligands and supramolecular structures, according to the 2008 review by [Guy C. Lloyd-Jones](https://www.edgepedia.org/guy-c-lloyd-jones), Jonathan D. Moseley, and Joseph S. Renny, which covers just over 40 years of literature in 238 references.[1](https://www.research.ed.ac.uk/en/publications/mechanism-and-application-of-the-newman-kwart-o-gt-s-rearrangemen/) Electron-withdrawing substituents aid the thermal reaction by reducing the required temperature or reaction time, while electron-donating substituents slow it; sterically demanding ortho substituents can enhance the rate.[17](https://www.sciencedirect.com/science/article/abs/pii/S004040200600264X) • [18](https://www.electronicsandbooks.com/edt/manual/Magazine/J/Journal%20of%20Organic%20Chemistry%20US/1968%20v.33/06%20%282175-2606%29/2245-2249.pdf) One documented limitation is that the rearrangement does not take place for phenolic compounds bearing an amino group.[19](https://patents.google.com/patent/JP2002512174A/en)
## References
1. [Lloyd-Jones, G. C., Moseley, J. D., Renny, J. S. (2008). Mechanism and application of the Newman-Kwart O -> S rearrangement of O-aryl thiocarbamates. Synthesis (5), 661–689.](https://www.research.ed.ac.uk/en/publications/mechanism-and-application-of-the-newman-kwart-o-gt-s-rearrangemen/)
2. [Iron(II)/Persulfate Mediated Newman–Kwart Rearrangement, Organic Letters (2020)](https://pubs.acs.org/orlef7/article/22/1/274/496122)
3. [Newman-Kwart rearrangement, km.t chemical reaction database](https://kmt.vander-lingen.nl/article/313/Newman-Kwart_rearrangement)
4. [Jüstel, P. Reactivities of Heteroatomic Nucleophiles Towards Carbon Electrophiles, LMU Munich](https://edoc.ub.uni-muenchen.de/28690/7/Juestel_Patrick.pdf)
5. [Thiocarbamate overview, ScienceDirect Topics](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/thiocarbamate)
6. [Chiniforoush, S., Cramer, C. J. (2019). Quantum Chemical Characterization of Factors Affecting the Neutral and Radical-Cation Newman-Kwart Reactions. J. Org. Chem. 84, 2148–2157.](https://pubmed.ncbi.nlm.nih.gov/30672704/)
7. [Recent advances in the Newman–Kwart rearrangement, Tetrahedron Letters 168, 155690 (2025)](https://www.sciencedirect.com/science/article/pii/S0040403925002394)
8. [Newman, M. S., Hetzel, F. W. Thiophenols from Phenols: 2-Naphthalenethiol, Organic Syntheses 1971, 51, 139](https://orgsyn.org/demo.aspx?prep=CV6P0824)
9. [Glenn, C. D., Sharma, M., Biegasiewicz, K. F. (2026). Newman-Kwart Rearrangement Enabled by Flavin Photoredox Catalysis. ACS Catalysis 16, 12957–12964.](https://pubs.acs.org/doi/10.1021/acscatal.6c02238)
10. [Burns, M., Lloyd-Jones, G. C., Moseley, J. D., Renny, J. S. (2010). The Molecularity of the Newman−Kwart Rearrangement. J. Org. Chem. 75, 6347–6353.](https://pubs.acs.org/doi/abs/10.1021/jo1014382)
11. [Bi(III)-Catalyzed Newman–Kwart Rearrangement for Synthesizing S-Heteroaryl Thiocarbamates, J. Org. Chem. 90, 3489–3495 (2025)](https://www.sciencedirect.com/org/science/article/pii/S0022326325002245)
12. [Harvey, J. et al. (2009). The Newman–Kwart Rearrangement of O-Aryl Thiocarbamates: Substantial Reduction in Reaction Temperatures through Palladium Catalysis. Angew. Chem. Int. Ed. 48, 7612–7615.](https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.200903908)
13. [Perkowski, A. J., Cruz, C. L., Nicewicz, D. A. (2015). Ambient-Temperature Newman–Kwart Rearrangement Mediated by Organic Photoredox Catalysis. J. Am. Chem. Soc. 137, 15684–15687.](https://pubs.acs.org/toc/jacsat/137/50)
14. [Broese, T., Roesel, A. F., Prudlik, A., Francke, R. (2018). An Electrocatalytic Newman–Kwart-Type Rearrangement. Org. Lett. 20, 7483–7487.](https://pubs.acs.org/doi/10.1021/acs.orglett.8b03257)
15. [Recent progress in electrochemical rearrangement reactions, Organic Chemistry Frontiers (2025)](https://pubs.rsc.org/en/content/articlehtml/2025/qo/d4qo02437k)
16. [Microwave-mediated Newman–Kwart rearrangement in water, RSC Advances (2016)](https://pubs.rsc.org/en/content/articlehtml/2016/ra/c6ra20676j)
17. [Moseley, J. D. et al. The Newman–Kwart rearrangement re-evaluated by microwave synthesis, Tetrahedron](https://www.sciencedirect.com/science/article/abs/pii/S004040200600264X)
18. [Steric Rate Enhancement in the Newman-Kwart Rearrangement, J. Org. Chem. 33, 2245–2249 (1968)](https://www.electronicsandbooks.com/edt/manual/Magazine/J/Journal%20of%20Organic%20Chemistry%20US/1968%20v.33/06%20%282175-2606%29/2245-2249.pdf)
19. [JP2002512174A, Method for preparing aromatic thiols and derivatives, Google Patents](https://patents.google.com/patent/JP2002512174A/en)
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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Organic reactions, structure and reference › Organic reactions and synthetic methods › Rearrangement reactions › Aromatic and arene rearrangements*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 11, 2026; Oct 15, 2026 · Last review: Oct 15, 2026*
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