The Newman–Kwart rearrangement is a type of rearrangement reaction

Rearrangement reaction

A rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another atom in the same molecule...

 in which the aryl group

Aryl

In the context of organic molecules, aryl refers to any functional group or substituent derived from an aromatic ring, be it phenyl, naphthyl, thienyl, indolyl, etc....

 of an O-aryl thiocarbamate

Thiocarbamate

Thiocarbamates are a family of organosulfur compounds. There are two isomeric forms of thiocarbamate esters: O-thiocarbamates, ROCNR2, and S-thiocarbamates, RSCNR2...

, ArOC(=S)NMe₂, migrates from the oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 atom to the sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

 atom, forming an S-aryl thiocarbamate, ArSC(=O)NMe₂. The reaction is named after its discoverers, Melvin Spencer Newman

Melvin Spencer Newman

Melvin Spencer Newman was an American chemist, best known for inventing the Newman projection. He was born in New York City, but shortly after his family moved to New Orleans, Louisiana. When he was 14, they moved back to New York, where he attended Riverdale County School. From 1925 to 1932 he...

 and Harold Kwart.
The Newman–Kwart rearrangement is one the most important ways of synthesising thiophenols. A phenol

Phenol

Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...

 (1) is deprotonated with a base such as DABCO

DABCO

DABCO or 1,4-diazabicyclo[2.2.2]octane is a chemical compound. It is a polyurethane and Baylis-Hillman reaction catalyst, complexing ligand and Lewis base. It is used to regulate the reaction rate in Flexplay time-limited DVDs by adjusting pH. Antioxidants, like DABCO, are used to improve the...

 or NaH

Sodium hydride

Sodium hydride is the chemical compound with the empirical formula NaH. It is primarily used as a strong base in organic synthesis. NaH is representative of the saline hydrides, meaning it is a salt-like hydride, composed of Na+ and H− ions, in contrast to the more molecular hydrides such as...

 and reacted with a thiocarbamoyl chloride (2) to form an O-aryl thiocarbamate (3). Heating 3 to around 250 °C causes it undergo Newman–Kwart rearrangement to an S-aryl thiocarbamate (4). Alkaline hydrolysis or similar cleavage a thiophenol (5).

Mechanism

The Newman–Kwart rearrangement is intramolecular

Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...

; it proceeds via a four-membered cyclic transition state.