Stevens rearrangement

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Stevens rearrangement

The Stevens rearrangement in organic chemistry

Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
is an organic reaction

Organic reaction

Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions and organic redox reaction....
converting quaternary ammonium salts and sulfonium salts to the corresponding amine

Amine

Amines are organic compounds and functional groups that contain a base nitrogen atom with a lone pair. Amines are derivative s of ammonia, wherein one or more hydrogen atoms are replaced by organic substituents such as alkyl and aryl groups....
s or sulfide

Sulfide

The term sulfide refers to several types of chemical compounds containing sulfur in its lowest oxidation number of −2.Formally, "sulfide" is the dianion, S2−, which exists in strongly alkaline aqueous solutions formed from H2S or alkali metal salts such as Li2S, Na2S, and K2...
s in presence of a strong base

Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
in a 1,2-rearrangement

1,2-rearrangement

A 1,2-rearrangement or 1,2-migration or 1,2-shift or Frank C. Whitmore 1,2-shift is an organic reaction where a substituent moves from one atom to another atom in a chemical compound....
.

The reactants can be obtained by alkylation

Alkylation

Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene ....
of the corresponding amines and sulfides.

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Encyclopedia

The Stevens rearrangement in organic chemistry

Organic chemistry

Organic reaction

Amine

Sulfide

Base (chemistry)

1,2-rearrangement

The reactants can be obtained by alkylation

Alkylation

Substituent

In organic chemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon. The suffix -yl is used when naming organic compounds that contain a substituent....
R next the amine methylene

Methylene

Methylene is the chemical species, R2C:, named after methane, in which two of the carbon atom's valence electrons form no bonds. The word is applicable to:...
group is an electron-withdrawing group.

The original 1928 publication by T.S. Stevens concerned the reaction of 1-phenyl-1- (N, N-dimethyl) ethanone with benzyl bromide

Benzyl bromide

Benzyl bromide, or a-bromotoluene, is an organic compound consisting of a benzene ring substituted with a bromomethyl group. It can be prepared by the bromination of toluene at room temperature in air, using manganese dioxide as a heterogeneous catalyst....
to the ammonium salt followed by the rearrangement reaction with sodium hydroxide

Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
in water to the rearranged amine.

A 1932 publication described the corresponding sulfur reaction.

Reaction mechanism

Key in the reaction mechanism

Reaction mechanism

In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs .Although only the net chemical change is directly observation for most chemical reactions, experiments can often be designed that suggest the possible sequence of steps in a reaction mechanism....
for the Stevens rearrangement (explained for the nitrogen reaction) is the formation of an ylide

Ylide

An ylid or ylide is a electric charge molecule with a positive and a negative charge on adjacent atoms. They appear in organic chemistry as reagents or reactive intermediates....
after deprotonation

Deprotonation

Deprotonation is a chemistry term that refers to the removal of a proton from a molecule, forming the conjugate base. The relative ability for a molecule to give up a proton is measured by a pKa value....
of the ammonium salt by a strong base. Deprotonation is aided by electron-withdrawing properties of substituent R. Several reaction modes exist for the actual rearrangement reaction.

A concerted reaction

Concerted reaction

In chemistry, a concerted reaction is a chemical reaction in which all bond breaking and bond making occurs in a single step. Reactive intermediates or other unstable high energy intermediates are not involved....
requires an antarafacial reaction mode but since the migrating group displays retention of configuration this mechanism is unlikely.

In an alternative reaction mechanism the N-C bond of the leaving group is homolytically

Homolysis

In chemistry, homolysis or homolytic fission is chemical bond dissociation of a neutral molecule generating two free radicals. That is, two electrons that are involved in the bond are distributed one by one to the two species....
cleaved to form a di-radical pair (3a). In order to explain the observed retention of configuration, the presence of a solvent cage is invoked. Another possibility is the formation of a cation-anion pair (3b), also in a solvent cage.

Scope

Competing reactions are the Sommelet reaction

Sommelet reaction

The Sommelet reaction is an organic reaction in which a benzyl halocarbon is converted to an aldehyde by action of hexamine and water .A conceptually related reaction is the Duff reaction ....
and the Hofmann elimination

Hofmann elimination

Hofmann elimination is a process where an amine is reacted to create a tertiary amine and an alkene by treatment with excess methyl iodide followed by treatment with silver oxide, water, and heat ....
.

In one application a double-Stevens rearrangement expands a cyclophane

Cyclophane

A cyclophane is a hydrocarbon consisting of an aromatic unit and an aliphatic Chain that forms a bridge between two non-adjacent positions of the aromatic ring....
ring . The ylide is prepared in situ

In situ

In situ is a Latin phrase meaning in the place. It is used in many different contexts....
by reaction of the diazo

Diazo

Diazo refers to a type of organic compound that has two linked nitrogen compounds. The general formula is R2C=N2. The simplest example of a diazo compound is diazomethane....
compound ethyl diazomalonate with a sulfide

Sulfide

Reflux

Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations....
ing xylene

Xylene

The term xylene or xylol refers to a mixture of three aromatic hydrocarbon isomers which is used as a solvent in the printing, rubber, and leather industries....
.