The Fries rearrangement, named for the German chemist Karl Theophil Fries, is a rearrangement reaction of a phenyl ester to a hydroxy aryl ketone by catalysis of lewis acids. Karl Theophil Fries ( March 13, 1875 - September 6, 1962) was a German Chemist. 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 In Organic chemistry, the phenyl group or phenyl ring (often abbreviated as -Ph) is the Functional group with the formula - Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least In the context of organic molecules aryl refers to any Functional group or Substituent derived from a Simple aromatic ring, may it be Phenyl A ketone (pronounced as key tone) is either the Functional group characterized by a Carbonyl group (O=C linked to two other Carbon atoms or Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst [1][2][3]
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Mechanism
Despite many efforts a definitive reaction mechanism for the Fries rearrangement is not available. Chemistry, a reaction mechanism is the step by step Sequence of Elementary reactions by which overall Chemical change occurs. Evidence for inter- and intramolecular mechanisms have been obtained by so-called cross-experiments with mixed reactants. Intramolecular in Chemistry describes a process or characteristic limited within the structure of a single Molecule; a property or phenomenon limited to the extent Reaction progress is not dependent on solvent or substrate. A solvent is a liquid or gas that dissolves a solid liquid or gaseous Solute, resulting in a Solution. A widely accepted mechanism involves a carbocation intermediate. A carbocation (ˌkɑrboʊˈkætaɪɒn is an Ion with a positively-charged Carbon Atom.
In the first reaction step a lewis acid for instance aluminium chloride AlCl3 co-ordinates to the carbonyl oxygen atom of the acyl group. Aluminium chloride (AlCl3 is a compound of Aluminium and Chlorine. In Organic chemistry, a carbonyl group is a Functional group composed of a Carbon Atom double-bonded to an Oxygen acyl group ( IUPAC name alkanoyl) is a Functional group derived by the removal of one or more Hydroxyl group from an Oxoacid. This oxygen atom is more electron rich than the phenolic oxygen atom and is the preferred lewis base. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Phenol, is a toxic colourless Crystalline Solid with a sweet tarry odor commonly referred to as a "hospital smell" This interaction polarizes the bond between the acyl residue and the phenolic oxygen atom and the aluminium chloride group rearranges to the phenolic oxygen atom. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations This generates a free acylium carbocation which reacts in a classical electrophilic aromatic substitution with the aromat. acyl group ( IUPAC name alkanoyl) is a Functional group derived by the removal of one or more Hydroxyl group from an Oxoacid. A carbocation (ˌkɑrboʊˈkætaɪɒn is an Ion with a positively-charged Carbon Atom. Electrophilic aromatic substitution or EAS is an Organic reaction in which an atom usually Hydrogen, appended to an aromatic system is replaced The abstracted proton is released as hydrochloric acid where the chlorine is derived from aluminium chloride. Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water The orientation of the substitution reaction is temperature dependent. A low reaction temperature favors para substitution and with high temperatures the ortho product prevails. Arene substitution patterns are part of Organic chemistry IUPAC nomenclature and pinpoint the position of Substituents other than Hydrogen in Arene substitution patterns are part of Organic chemistry IUPAC nomenclature and pinpoint the position of Substituents other than Hydrogen in
Scope
Phenols react to esters 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 and salbutamol. Phenol, is a toxic colourless Crystalline Solid with a sweet tarry odor commonly referred to as a "hospital smell" Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least The Friedel-Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877. Paracetamol ( INN) (ˌpærəˈsiːtəmɒl -ˈsɛtə- or acetaminophen ( USAN) is a widely-used Analgesic and Antipyretic Medication Salbutamol ( INN) or albuterol ( USAN) is a short-acting β2-adrenergic receptor agonist used for the relief of Bronchospasm As an alternative to aluminium chloride, other Lewis acids such as boron trifluoride and bismuth triflate or strong protic acids such as hydrogen fluoride and methanesulfonic acid can also be used. Aluminium chloride (AlCl3 is a compound of Aluminium and Chlorine. Boron trifluoride is the Chemical compound with the formula BF3 Bismuth (ˈbɪzməθ is a Chemical element that has the symbol Bi and Atomic number 83 Triflate, more formally known as trifluoromethanesulfonate, is a Functional group with the formula CF3SO3- Structure HF forms orthorhombic crystals consisting of zig-zag chains of HF molecules Methanesulfonic acid is a colorless liquid with the chemical formula CH4O3S In order to avoid the use of these corrosive and environmentally unfriendly catalysts altogether research into alternative heterogeneous catalysts is actively pursued. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst Heterogeneous is an adjective used to describe an object or system consisting of multiple items having a large number of structural variations
Limits
In all instances only esters can be used with stable acyl components that can withstand the harsh conditions of the Fries rearrangement. Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least If the aromatic or the acyl component is heavily substituted then the chemical yield will drop due to steric constraints. In Chemistry, yield, also referred to as chemical yield and reaction yield, is the amount of product obtained in a Chemical reaction See also Intramolecular forces ' Steric effects arise from the fact that each Atom within a Molecule occupies a certain Deactivating meta-directing groups on the benzene group will also have an adverse effect as can be expected for a Friedel-Crafts acylation. The Friedel-Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877.
Photo-Fries rearrangement
In addition to the ordinary thermal phenyl ester reaction a so-called photochemical Photo-Fries rearrangement exists[4] that involves a radical reaction mechanism. Photochemistry, a sub-discipline of Chemistry, is the study of the interactions between Atoms, small Molecules, and light (or Electromagnetic radiation In Chemistry, radicals (often referred to as free radicals) are atoms molecules or ions with Unpaired electrons on an otherwise Open shell Chemistry, a reaction mechanism is the step by step Sequence of Elementary reactions by which overall Chemical change occurs. This reaction is also possible with deactivating substituents on the aromatic group. 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 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.
References
- ^ Fries, K. ; Finck, G. Karl Theophil Fries ( March 13, 1875 - September 6, 1962) was a German Chemist. (1908). "Über Homologe des Cumaranons und ihre Abkömmlinge". Chemische Berichte 41 (3): 4271–4284. See also Anales de Química Bulletin des Sociétés Chimiques Belges Bulletin de la Société Chimique de France doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ Fries, K. ; Pfaffendorf, W. (1910). "Über ein Kondensationsprodukt des Cumaranons und seine Umwandlung in Oxindirubin". Chemische Berichte 43 (1): 212–219. See also Anales de Química Bulletin des Sociétés Chimiques Belges Bulletin de la Société Chimique de France doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ March, J. Advanced Organic Chemistry, 3rd Ed. ; John Wiley & Sons: Chichester, 1985; S. 499ff.
- ^ Bellus, D. Advances in Photochemistry; John Wiley & Sons: Chichester, 1971; Vol. 8, 109–159.
See also
- The Fischer-Hepp rearrangement and the Hofmann-Martius rearrangement, conceptually related reactions
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