The Newman–Kwart rearrangement is a type of

rearrangement reaction In organic chemistry, 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 ...

in which the

aryl group In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used as ...

of an ''O''-aryl thiocarbamate, ArOC(=S)NMe₂, migrates from the

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

atom to the

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

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

Melvin Spencer Newman Melvin Spencer Newman (March 10, 1908 – May 30, 1993) was an American chemist, Ohio State University professor, best known for inventing the Newman projection. Newman was born in New York City in a Jewish family, the youngest of Mae (née P ...

and Harold Kwart. The reaction is a manifestation of the

double bond rule In chemistry, the double bond rule states that elements with a principal quantum number greater than 2 for their valence electrons (period 3 elements and higher) tend not to form multiple bonds (e.g. double bonds and triple bonds). The double bon ...

. :

Mechanism

The Newman–Kwart rearrangement is intramolecular; it proceeds ''via'' a four-membered cyclic transition state. : NKR-mechanism-2D-skeletal

Use for preparation of thiophenols

The Newman–Kwart rearrangement is an important prelude to the synthesis of

thiophenols Thiophenol is an organosulfur compound with the formula C6H5SH, sometimes abbreviated as PhSH. This foul-smelling colorless liquid is the simplest aromatic thiol. The chemical structures of thiophenol and its derivatives are analogous to phenols ...

. A

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...

(1) is deprotonated with a base followed by treatment with a

thiocarbamoyl chloride Dimethylthiocarbamoyl chloride is an organosulfur compound with the formula (CH3)2NC(S)Cl. A yellow solid, it is often encountered as a yellow syrup. It is a key reagent in the synthesis of arylthiols via the Newman-Kwart rearrangement. Synthes ...

(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 In organic chemistry, thiocarbamates (thiourethanes) are a family of organosulfur compounds. As the prefix ''thio-'' suggests, they are sulfur analogues of carbamates. There are two isomeric forms of thiocarbamates: ''O''-thiocarbamates, (ester ...

(4). Alkaline hydrolysis or similar cleavage yields a thiophenol (5). : Phenols-to-thiophenols-via-NKR-2D-skeletal

References

Rearrangement reactions Name reactions {{organic-chemistry-stub

Mechanism

Use for preparation of thiophenols

See also

References