Newman-Kwart rearrangement

The Newman-Kwart rearrangement (also known as thiono-thiolo rearrangement ) is a chemical reaction through which thionourethanes aryl-substituted on oxygen can be rearranged into isomeric thiolourethanes at higher temperatures . The thiono -thiolo rearrangement was first described for thion carbonic acid esters in 1930 by the German chemist Alexander Schönberg (1892–1985). It was transferred to thiocarbamates by Newman and Kwart. Since then, the broader term Newman-Kwart rearrangement has been used for this type of rearrangement .

Phenols can be converted into thiophenols with the Newman-Kwart rearrangement within a multi-stage reaction sequence . To do this, the phenol is first converted into thionourethane, then rearranged to thiolourethane and finally split into thiophenol with sodium hydroxide solution .

The rearrangement, initially examined in the gas phase, can also be carried out in solution under microwave irradiation . Electron-withdrawing groups in the para position of the aryl radical accelerate the rearrangement. Mechanistically, the rearrangement apparently takes place via an ipso-substitution with a four-membered transition state , but a bimolecular transition state with an eight-membered ring is also discussed for higher substrate concentrations in solution.

Possible transition states of the Newman-Kwart rearrangement

literature

• Ernst Schaumann (Ed.): Sulfur-mediated rearrangements , Volume 2, Springer Verl. Berlin Heidelberg New York 2003. ISBN 978-3-540-68099-4 ( limited preview in Google book search)

Web links

• Newman-Kwart rearrangement on organic-chemie.ch

Individual evidence

1. ↑ A. Schönberg, L. Vargha: About the (thermal) rearrangement of thione carbonic acid esters into thiol carbonic acid esters. (16. Communication on organic sulfur compounds.) In: Chem. Ber. 1930, 68, 178-180. doi: 10.1002 / cber.19300630125 .
2. ↑ A. Schönberg, L. v. Vargha, W. Paul: About the thermal rearrangement of thion carbonic acid esters in thiol carbonic acid ester. II. On the formation of disulfides from phenols. in: Justus Liebig's Annalen der Chemie 1930, 483, 107-114. doi: 10.1002 / jlac.19304830109 .
3. ↑ MS Newman, HA Karnes: The Conversion of Phenols to Thiophenols via Dialkylthiocarbamates. in: J. Org. Chem. , 1966, 31 (12), 3980-3984. doi: 10.1021 / jo01350a023 .
4. ↑ H. Kwart, ER Evans: The Vapor Phase Rearrangement of Thioncarbonates and Thioncarbamates. in: J. Org. Chem. , 1966, 31 (2), 410-413. doi: 10.1021 / jo01340a015 .
5. ^ JJ Li in: Name reactions: a collection of detailed reaction mechanisms. Springer Verl. Berlin Heidelberg New York 2003. ( limited preview in the Google book search), p. 551.
6. ↑ JP Gilday, P. Lenden, JD Moseley, BG Cox: The Newman-Kwart Rearrangement: A Microwave Kinetic Study. in: J. Org. Chem. , 2008, 73 (8), 3130-3134, doi: 10.1021 / jo702633g .