Fries rearrangement

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Fries rearrangement

The Fries rearrangement, named for the German chemist Karl Theophil Fries

Karl Theophil Fries

Karl Theophil Fries was a Germany chemist....
, is a 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 ....
of a phenyl ester

Ester

Hydroxy

'Hydroxy' can refer to:* In chemical nomenclature, the prefix "hydroxy-" shows the presence of a hydroxyl functional group * An abbreviation for the medication hydroxyzine, which is commonly sold under the brand names Atarax, Ucerax, Serecid, and Vistaril....
aryl

Aryl

In the context of organic molecules, aryl refers to any functional group or substituent derived from a simple aromatic ring, may it be phenyl, thiophene, indole, etc ....
ketone

Ketone

In organic chemistry, a ketone is a type of organic compound which contains a carbonyl group bonded to two other carbon atoms in the form:Neither of the substituents R1 and R2 may be equal to hydrogen ....
by catalysis

Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
of lewis acid

Lewis acid

A Lewis acid is a chemical compound, A, that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB.Gilbert N....
s.

ite many efforts a definitive 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 Fries rearrangement is not available. Evidence for inter- and 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....
mechanisms have been obtained by so-called cross-experiments with mixed reactants. Reaction progress is not dependent on solvent

Solvent

A solvent is a liquid or gas that dissolves a solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water....
or substrate.

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Encyclopedia

The Fries rearrangement, named for the German chemist Karl Theophil Fries

Karl Theophil Fries

Karl Theophil Fries was a Germany chemist....
, is a 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 ....
of a phenyl ester

Ester

Hydroxy

Aryl

In the context of organic molecules, aryl refers to any functional group or substituent derived from a simple aromatic ring, may it be phenyl, thiophene, indole, etc ....
ketone

Ketone

Catalysis

Catalysis is the process in which the reaction rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst....
of lewis acid

Lewis acid

A Lewis acid is a chemical compound, A, that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB.Gilbert N....
s.

Mechanism

Despite many efforts a definitive reaction mechanism

Reaction mechanism

Intramolecular

Solvent

A solvent is a liquid or gas that dissolves a solid, liquid, or gaseous solute, resulting in a solution.The most common solvent in everyday life is water....
or substrate. A widely accepted mechanism involves a carbocation

Carbocation

A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer Electron shell#Valence shell instead of the eight valence electrons that ensures maximum stability ....
intermediate. In the first reaction step a lewis acid

Lewis acid

A Lewis acid is a chemical compound, A, that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB.Gilbert N....
for instance aluminium chloride

Aluminium chloride

Aluminium chloride is a chemical compound of aluminium and chlorine. The solid has a low melting and boiling point, and is Covalent bond. It sublimation at 178 ?Celsius....
co-ordinates to the carbonyl

Carbonyl

In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double bond to an oxygen atom : C=O.The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex ; in this situation, carbon is triple-bonded to oxygen : C=O....
oxygen atom of the acyl

Acyl

An acyl group is a functional group derived by the removal of one or more hydroxyl groups from an oxoacid.. In organic chemistry, the acyl group is usually derived from a carboxylic acid of the form RCarbon Oxygen hydroxyl....
group. This oxygen atom is more electron

Electron

The electron is a subatomic particle that carries a negative electric charge. It has elementary particle and is believed to be a point particle....
rich than the phenol

Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
ic oxygen atom and is the preferred lewis base. This interaction polarizes

Polarization

Polarization is a property of waves that describes the orientation of their oscillations. For transverse waves such as many electromagnetic waves, it describes the orientation of the oscillations in the plane perpendicular to the wave's direction of travel....
the bond

Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or between atoms and other covalent bonds....
between the acyl residue and the phenolic oxygen atom and the aluminium chloride group rearranges to the phenolic oxygen atom. This generates a free acylium carbocation

Carbocation

A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer Electron shell#Valence shell instead of the eight valence electrons that ensures maximum stability ....
which reacts in a classical electrophilic aromatic substitution

Electrophilic aromatic substitution

Electrophilic aromatic substitution or EAS is an organic reaction in which an atom, usually hydrogen, appended to an aromatic ring is replaced by an electrophile....
with the aromat. The abstracted proton is released as hydrochloric acid

Hydrochloric acid

Hydrochloric acid is the solution of hydrogen chloride in water. It is a highly corrosive, strong acid mineral acid and has major industrial uses....
where the chlorine is derived from aluminium chloride. The orientation of the substitution reaction is temperature dependent. A low reaction temperature favors para substitution

Arene substitution patterns

Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon....
and with high temperatures the ortho

Arene substitution patterns

Scope

Phenol

Phenol, also known as carbolic acid, is a toxic, white crystalline solid with a sweet tarry odor, commonly referred to as a "hospital smell"....
s react to ester

Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
s but do not react to hydroxyarylketones with acylhalogen compounds under Friedel-Crafts acylation reaction conditions and therefore this reaction is of industrial importance for the synthesis of hydroxyarylketones which are important intermediates for several pharmaceutics such as paracetamol

Paracetamol

Paracetamol or acetaminophen is a widely used over-the-counter drug analgesic and antipyretic . It is commonly used for the relief of fever, headaches, and other minor aches and pains, and is a major ingredient in numerous common cold and Influenza remedies....
and salbutamol

Salbutamol

Salbutamol or albuterol is a short-acting beta2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease....
. As an alternative to aluminium chloride

Aluminium chloride

Aluminium chloride is a chemical compound of aluminium and chlorine. The solid has a low melting and boiling point, and is Covalent bond. It sublimation at 178 ?Celsius....
, other Lewis acid

Lewis acid

A Lewis acid is a chemical compound, A, that can accept a pair of electrons from a Lewis base, B, that acts as an electron-pair donor, forming an adduct, AB.Gilbert N....
s such as boron trifluoride

Boron trifluoride

Boron trifluoride is the chemical compound with the chemical formula BF3. This pungent colourless toxic gas forms white fumes in moist air....
and bismuth

Bismuth

Bismuth is a chemical element that has the symbol Bi and atomic number 83. This heavy, brittle, white crystalline trivalent poor metal has a pink tinge and chemically resembles arsenic and antimony....
triflate

Triflate

Triflate, more formally known as trifluoromethanesulfonate, is a functional group with the formula CF3SO3-. The triflate group is often represented by -OTf, as opposed to -Tf....
or strong protic acids such as hydrogen fluoride

Hydrogen fluoride

Hydrogen fluoride is a chemical compound with the chemical formula HF. It is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers ....
and methanesulfonic acid

Methanesulfonic acid

Methanesulfonic acid is a colorless liquid with the chemical formula CH3SO3H. It is the simplest of the alkylsulfonic acids....
can also be used. In order to avoid the use of these corrosive and environmentally unfriendly catalysts altogether research into alternative heterogeneous

Heterogeneous

Heterogeneous is an adjective used to describe an object or system consisting of multiple items having a large number of structural variations. It is the opposite of homogeneous, which means that an object or system consists of multiple identical items....
catalysts is actively pursued.

Limits

In all instances only ester

Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
s can be used with stable acyl components that can withstand the harsh conditions of the Fries rearrangement. If the aromatic or the acyl component is heavily substituted then the chemical yield will drop due to steric constraints. Deactivating meta-directing groups on the benzene group will also have an adverse effect as can be expected for a Friedel-Crafts acylation.

Photo-Fries rearrangement

In addition to the ordinary thermal phenyl ester reaction a so-called photochemical

Photochemistry

Photochemistry, a sub-discipline of chemistry, is the study of the interactions between atoms, small molecules, and light . The pillars of photochemistry are UV/VIS spectroscopy, photochemical reactions in organic chemistry and photosynthesis in biochemistry....
Photo-Fries rearrangement exists that involves a radical

Radical (chemistry)

In chemistry, radicals are atoms, molecules or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly chemical reaction, so radicals are likely to take part in chemical reactions....
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....
. This reaction is also possible with deactivating substituent

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....
s on the aromatic group. Because the yields are low this procedure is confined to the laboratory.

Anionic Fries rearrangment

In addition to Lewis acid and photo-catalysed Fries rearrangements, there also exists an anionic Fries rearrangement. In this reaction, the aryl ester undergoes ortho-metallation with a strong base, which then rearranges in a nucleophillic attack mechanism.

Fries rearrangement

Mechanism

Scope

Limits

Photo-Fries rearrangement

Anionic Fries rearrangment

See also