Imine
Overview
 
"Ketimine" redirects here. It should not be confused with "Ketamine
Ketamine
Ketamine is a drug used in human and veterinary medicine. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar. Pharmacologically, ketamine is classified as an NMDA receptor antagonist...

"


An imine (icon or ˈ) is a functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 or chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 containing a carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 double bond
Double bond
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...

, with the nitrogen attached to a hydrogen atom (H) or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base
Schiff base
A Schiff base, named after Hugo Schiff, is a compound with a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group, not hydrogen....

. The carbon has two additional single bonds.
It is related to ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s and aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

s by replacement of the oxygen with an NR group.
Encyclopedia
"Ketimine" redirects here. It should not be confused with "Ketamine
Ketamine
Ketamine is a drug used in human and veterinary medicine. Its hydrochloride salt is sold as Ketanest, Ketaset, and Ketalar. Pharmacologically, ketamine is classified as an NMDA receptor antagonist...

"


An imine (icon or ˈ) is a functional group
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 or chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 containing a carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

 double bond
Double bond
A double bond in chemistry is a chemical bond between two chemical elements involving four bonding electrons instead of the usual two. The most common double bond, that between two carbon atoms, can be found in alkenes. Many types of double bonds between two different elements exist, for example in...

, with the nitrogen attached to a hydrogen atom (H) or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base
Schiff base
A Schiff base, named after Hugo Schiff, is a compound with a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group, not hydrogen....

. The carbon has two additional single bonds.

Nomenclature and classification

It is related to ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s and aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....

s by replacement of the oxygen with an NR group. When R = H, the compound is a primary imine, when R is hydrocarbyl, the compound is a secondary imine. Imines exhibit diverse reactivity and are commonly encountered throughout chemistry. When R3 is OH, the imine is called an oxime
Oxime
An oxime is a chemical compound belonging to the imines, with the general formula R1R2C=NOH, where R1 is an organic side chain and R2 may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted oximes form a closely related family of compounds...

, and when R3 is NH2 the imine is called a hydrazone
Hydrazone
Hydrazones are a class of organic compounds with the structure R1R2C=NNH2. They are related to ketones and aldehydes by the replacement of the oxygen with the NNH2 functional group...

.

Aldimines and ketimines

A primary imine in which C is attached to both a hydrocarbyl and a H is called a primary aldimine; a secondary imine with such groups is called a secondary aldimine
Aldimine
In organic chemistry, an aldimine is an imine that is an analog of an aldehyde.As such, aldimines have the general formula R–CH=N–R. Aldimines are similar to ketimines, which are analogs of ketones.An important subset of aldimines are the Schiff bases,...

.

A primary imine in which C is attached to two hydrocarbyls is called a primary ketimine; a secondary imine with such groups is called a secondary ketimine.

Synthesis of imines

Imines are typically prepared by the condensation of primary amines and aldehydes and less commonly ketones. In terms of mechanism, such reactions proceed via the nucleophilic addition
Nucleophilic addition
In organic chemistry, a nucleophilic addition reaction is an addition reaction where in a chemical compound a π bond is removed by the creation of two new covalent bonds by the addition of a nucleophile....

 giving a hemiaminal
Hemiaminal
A hemiaminal is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: -C-. R can be hydrogen or an alkyl group...

 -C(OH)(NHR)- intermediate, followed by an elimination
Elimination reaction
An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism...

 of water to yield the imine. (see alkylimino-de-oxo-bisubstitution
Alkylimino-de-oxo-bisubstitution
Alkylimino-de-oxo-bisubstitution in organic chemistry is the organic reaction of carbonyl compounds with amines to imines . The reaction name is based on the IUPAC Nomenclature for Transformations...

 for a detailed mechanism) The equilibrium in this reaction usually favors of the carbonyl
Carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....

 compound and amine, so that azeotropic distillation
Azeotropic distillation
In chemistry, azeotropic distillation is any of a range of techniques used to break an azeotrope in distillation. In chemical engineering, azeotropic distillation usually refers to the specific technique of adding another component to generate a new, lower-boiling azeotrope that is heterogeneous...

 or use of a dehydrating agent such as molecular sieve
Molecular sieve
A molecular sieve is a material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids.Molecules small enough to pass through the pores are adsorbed while larger molecules are not. It is different from a common filter in that it operates on a...

s is required to push the reaction in favor of imine formation.
Several other methods exist for the synthesis of imines.
  • Condensation of carbon acids with nitroso
    Nitroso
    Nitroso refers to a functional group in organic chemistry which has the general formula RNO. Nitroso compounds are a class of organic compounds containing the nitroso functional group, R−N=O....

     compounds.
  • The rearrangement of trityl N-haloamines in the Stieglitz rearrangement
    Stieglitz rearrangement
    The Stieglitz rearrangement is a rearrangement reaction of a trityl hydroxylamine Ar3CNHOH to a triaryl imine . The reaction is related to the Beckmann rearrangement as both reaction involve a carbon to nitrogen shift....

    .
  • Dehydration of hemiaminal
    Hemiaminal
    A hemiaminal is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: -C-. R can be hydrogen or an alkyl group...

    s.
  • By reaction of alkene
    Alkene
    In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...

    s with hydrazoic acid
    Hydrazoic acid
    Hydrazoic acid, also known as hydrogen azide or azoimide, is a colorless, volatile, and extremely explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen, having chemical formula HN3. It was first isolated in 1890 by Theodor Curtius...

     in the Schmidt reaction
    Schmidt reaction
    The Schmidt reaction is an organic reaction involving alkyl migration over the carbon-nitrogen chemical bond in an azide with expulsion of nitrogen...

    .
  • By reaction of a nitrile, hydrochloric acid and an arene in the Hoesch reaction.
  • Multicomponent synthesis of 3-thiazolines in the Asinger reaction
    Asinger reaction
    The Asinger-reaction was invented in 1956 by Friedrich Asinger . The Asinger-reaction is a multicomponent reaction and is classified as A-4CR :...

    .

Imine reactions

The most important reactions of imines are their hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 to the corresponding amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

 and carbonyl
Carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....

 compound. Otherwise this functional group participates in many other reactions, many of which are analogous to the reactions of aldehydes and ketones.
  • An imine reacts with an amine
    Amine
    Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

     to an aminal
    Aminal
    An aminal or aminoacetal is a functional group or type of chemical compound that has two amine groups attached to the same carbon atom: -C-. Again R can be hydrogen or an alkyl group....

    , see for example the synthesis of cucurbituril
    Cucurbituril
    Cucurbiturils are methylene-linked macrocyclic molecules made of glycoluril [=C4H2N4O2=] monomers. The oxygen atoms are located along the edges of the band and are tilted inwards, forming a partly enclosed cavity...

    .
  • An imine reacts with diene
    Diene
    In organic chemistry a diene or diolefin is a hydrocarbon that contains two carbon double bonds.Conjugated dienes are functional groups, with a general formula of CnH2n-2. Dienes and alkynes are functional isomers...

    s in the Aza Diels-Alder reaction
    Aza Diels-Alder reaction
    The Aza Diels-Alder reaction converts imines and dienes to tetrahydropyridines. This organic reaction is a modification of the Diels-Alder reaction. The nitrogen atom can be part of the diene or the dienophile....

     to a tetrahydropyridine.
  • An imine can be oxidized with meta-chloroperoxybenzoic acid
    Meta-Chloroperoxybenzoic acid
    meta-Chloroperoxybenzoic acid is a peroxycarboxylic acid used widely as an oxidant in organic synthesis. mCPBA is often preferred to other peroxy acids because of its relative ease of handling...

     (mCPBA) to give an oxaziridine
    Oxaziridine
    An oxaziridine is an organic molecule that features a three-membered heterocycle containing oxygen, nitrogen, and carbon.-History:Oxaziridine derivatives were first synthesized in the mid 1950s by Emmons and subsequently by Krimm and Horner and Jürgens...

  • An aromatic imine reacts with an enol ether
    Enol ether
    An enol ether is an alkene with an alkoxy substituent. The general structure is R_1R_2C=CR_3-O-R_4 with R an alkyl or an aryl group. Enol ethers and enamines are so-called activated alkenes or electron rich alkenes because the oxygen atom donates electrons to the double bond by forming a resonance...

     to a quinoline
    Quinoline
    Quinoline is a heterocyclic aromatic organic compound. It has the formula C9H7N and is a colourless hygroscopic liquid with a strong odour. Aged samples, if exposed to light, become yellow and later brown...

     in the Povarov reaction
    Povarov reaction
    The Povarov reaction is an organic reaction described as a formal cycloaddition between an aromatic imine and an alkene. The imine in this organic reaction is a condensation reaction product from an aniline type compound and a benzaldehyde type compound . The alkene must be electron rich which...

    .
  • A tosyl
    Tosyl
    A tosyl group is CH3C6H4SO2. This group is usually derived from the compound 4-toluenesulfonyl chloride, CH3C6H4SO2Cl, which forms esters and amides of toluenesulfonic or tosylic acid...

    imine reacts with an α,β-unsaturated carbonyl compound to an allyl
    Allyl
    An allyl group is a substituent with the structural formula H2C=CH-CH2R, where R is the connection to the rest of the molecule. It is made up of a methylene , attached to a vinyl group . The name is derived from the Latin word for garlic, Allium sativum. Theodor Wertheim isolated an allyl...

    ic amine
    Amine
    Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

     in the Aza-Baylis–Hillman reaction.
  • Imines are intermediates in the alkylation of amines with formic acid in the Eschweiler-Clarke reaction
    Eschweiler-Clarke reaction
    The Eschweiler–Clarke reaction is a chemical reaction whereby a primary amine is methylated using excess formic acid and formaldehyde. Reductive amination reactions such as this one will not produce quaternary ammonium salts, but instead will stop at the tertiary amine stage...

    .
  • A rearrangement in carbohydrate chemistry involving an imine is the Amadori rearrangement
    Amadori rearrangement
    The amadori rearrangement is an organic reaction describing the acid or base catalyzed isomerization or rearrangement reaction of the N-glycoside of an aldose or the glycosylamine to the corresponding 1-amino-1-deoxy-ketose...

    .
  • A methylene transfer reaction of an imine by an unstabilised sulphonium ylide
    Ylide
    An ylide or ylid is a neutral dipolar molecule containing a formally negatively charged atom directly attached to a hetero atom with a formal positive charge , and in which both atoms have full octets of electrons. Ylides are thus 1,2-dipolar compounds...

     can give an aziridine
    Aziridine
    Aziridines are organic compounds containing the aziridine functional group, a three-membered heterocycle with one amine group and two methylene groups...

     system.
  • An imine is an intermediate in reductive amination
    Reductive amination
    Reductive amination is a form of amination that involves the conversion of a carbonyl group to an amine via an intermediate imine...

    .

Acid-base reactions

Somewhat like the parent amines, imines are mildly basic and reversibly protonate to give iminium salts. Iminium derivatives are particularly susceptible to reduction to the amines using transfer hydrogenation
Transfer hydrogenation
Transfer hydrogenation is the addition of hydrogen to a molecule from a source other than gaseous H2. It is applied in industry and in organic synthesis, in part because of the inconvenience and expense of using gaseous H2...

 or by the stoichiometric action of sodium cyanoborohydride
Sodium cyanoborohydride
Sodium cyanoborohydride is the inorganic compound with the formula NaBH3. This colourless salt is widely used in organic synthesis for the reduction of imines.-Preparation and use:...

. Since imines derived from unsymmetrical ketones are prochiral
Prochiral
In stereochemistry, prochiral molecules are those that can be converted from achiral to chiral in a single step.If two identical substituents are attached to a sp3-hybridized atom, the descriptors pro-R and pro-S are used to distinguish between the two...

, their reduction is a useful method for the synthesis of chiral amines.

As ligands

Imines are common ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

s in coordination chemistry. The condensation of salicylaldehyde
Salicylaldehyde
Salicylaldehyde is the chemical compound with the formula C6H4CHO-2-OH. Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oily liquid has a bitter almond odor at higher concentration and a characteristic buckwheat...

 and acetylacetone
Acetylacetone
Acetylacetone is an organic compound that famously exists in two tautomeric forms that rapidly interconvert. The less stable tautomer is a diketone formally named pentane-2,4-dione. The more common tautomer is the enol form. The pair of tautomers rapidly interconvert and are treated as a single...

 give families of imine-containing chelating agents such as salen
Salen ligand
Salen is the abbreviation for a popular chelating ligand used in coordination chemistry and homogeneous catalysis. The name salen is a contraction for salicylaldehyde and ethylenediamine. The ligand is a bright yellow micaceous solid that is soluble in polar organic solvents.-Nomenclature:The...

.

Imine reductions

An imine can be reduced to an amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...

 via hydrogenation
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...

 for example in a synthesis of m-tolylbenzylamine:


Other reducing agents are lithium aluminium hydride
Lithium aluminium hydride
Lithium aluminium hydride, commonly abbreviated to LAH or known as LithAl, is an inorganic compound with the chemical formula LiAlH4. It was discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters,...

 and sodium borohydride
Sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are...

.

The first asymmetric imine reduction was reported in 1973 by Kagan
Henri B. Kagan
Henri B. Kagan is currently an Emeritus Professor at the Université Paris-Sud in France. He is widely recognized as a pioneer in the field of asymmetric catalysis...

 using Ph(Me)C=NBn and PhSiH2 in a hydrosilylation
Hydrosilylation
Hydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds. Ordinarily the reaction is conducted catalytically and usually the substrates are unsaturated organic compounds. Alkenes and alkynes give alkyl and vinyl silanes; aldehydes and...

 with chiral ligand DIOP
Diop
Diop is a surname, and may refer to:* Aïda Diop* Birago Diop* Boubacar Boris Diop* Cheikh Anta Diop* DeSagana Diop* Djibril Diop Mambéty Senegalese film director, brother of Wasis Diop* Mamadou Diop* Mustapha Papa Diop...

 and rhodium
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed...

 catalyst (RhCl(CH2CH2)2)2. Many systems have since been investigated.

Biological role

Imines are common in nature. Vitamin B6
Vitamin B6
Vitamin B6 is a water-soluble vitamin and is part of the vitamin B complex group. Several forms of the vitamin are known, but pyridoxal phosphate is the active form and is a cofactor in many reactions of amino acid metabolism, including transamination, deamination, and decarboxylation...

 promotes the deamination of amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s via the formation of imines, for example.

See also

  • Schiff base
    Schiff base
    A Schiff base, named after Hugo Schiff, is a compound with a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group, not hydrogen....

  • Carboximidate
    Carboximidate
    Carboximidates are organic compounds which can be thought of as esters formed between a carboximidic acid and an alcohol...

  • Oxime
    Oxime
    An oxime is a chemical compound belonging to the imines, with the general formula R1R2C=NOH, where R1 is an organic side chain and R2 may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted oximes form a closely related family of compounds...

  • Other functional groups with a CN double bond: oximes, hydrazone
    Hydrazone
    Hydrazones are a class of organic compounds with the structure R1R2C=NNH2. They are related to ketones and aldehydes by the replacement of the oxygen with the NNH2 functional group...

    s
  • Other functional groups with a CN triple bond: nitrile
    Nitrile
    A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, one example being super glue .Inorganic compounds containing the -C≡N group are not called...

    s, isonitriles
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