In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...
, an imide is a
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the r ...
consisting of two
acyl groups bound to
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
. The compounds are structurally related to
acid anhydrides, although imides are more resistant to hydrolysis. In terms of commercial applications, imides are best known as components of high-strength polymers, called
polyimides.
Inorganic imides are also known as solid state or gaseous compounds, and the imido group (=NH) can also act as a
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...
.
Nomenclature
Most imides are cyclic compounds derived from
dicarboxylic acid
In organic chemistry, a dicarboxylic acid is an organic compound containing two carboxyl groups (). The general molecular formula for dicarboxylic acids can be written as , where R can be aliphatic or aromatic. In general, dicarboxylic acids sho ...
s, and their names reflect the parent acid. Examples are succinimide, derived from succinic acid, and phthalimide, derived from phthalic acid. For imides derived from
amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s (as opposed to ammonia), the ''N''-substituent is indicated by a prefix. For example, N-ethylsuccinimide is derived from succinic acid and
ethylamine
Ethylamine, also known as ethanamine, is an organic compound with the formula CH3CH2NH2. This colourless gas has a strong ammonia-like odor. It condenses just below room temperature to a liquid miscible with virtually all solvents. It is a nucl ...
. Isoimides are isomeric with normal imides and have the formula RC(O)OC(NR′)R″. They are often intermediates that convert to the more symmetrical imides. Organic compounds called
carbodiimides have the formula RN=C=NR. They are unrelated to imides.
Imides from dicarboxylic acids
The
PubChem links gives access to more information on the compounds, including other names, ids, toxicity and safety.
:
Properties
Being highly polar, imides exhibit good solubility in polar media. The N–H center for imides derived from ammonia is acidic and can participate in
hydrogen bond
In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...
ing. Unlike the structurally related acid anhydrides, they resist hydrolysis and some can even be
recrystallized from boiling water.
Occurrence and applications
Many high strength or electrically conductive polymers contain imide subunits, i.e., the
polyimide
Polyimide (sometimes abbreviated PI) is a polymer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, e. ...
s. One example is
Kapton
Structure of poly-oxydiphenylene-pyromellitimide
Kapton insulating pads for mounting electronic parts on a heat sink
Kapton is a polyimide film used in flexible printed circuits ( flexible electronics) and space blankets, which are used on spa ...
where the repeat unit consists of two imide groups derived from aromatic tetracarboxylic acids. Another example of polyimides is the polyglutarimide typically made from polymethylmethacrylate (PMMA) and ammonia or a primary amine by aminolysis and cyclization of the PMMA at high temperature and pressure, typically in an extruder. This technique is called reactive extrusion. A commercial polyglutarimide product based on the methylamine derivative of PMMA, called Kamax, was produced by the Rohm and Haas company. The toughness of these materials reflects the rigidity of the imide functional group.
Interest in the bioactivity of imide-containing compounds was sparked by the early discovery of the high bioactivity of the
Cycloheximide
Cycloheximide is a naturally occurring fungicide produced by the bacterium '' Streptomyces griseus''. Cycloheximide exerts its effects by interfering with the translocation step in protein synthesis (movement of two tRNA molecules and mRNA in rel ...
as an inhibitor of protein biosynthesis in certain organisms.
Thalidomide, famous for its adverse effects, is one result of this research. A number of
fungicide
Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality ...
s and herbicides contain the imide functionality. Examples include
Captan
Captan is a general use pesticide (GUP) that belongs to the phthalimide class of fungicides. It is a white solid, although commercial samples appear yellow or brownish.
Applications
Although it can be applied on its own, Captan is often added ...
, which is considered carcinogenic under some conditions, and
Procymidone.
In the 21st century new interest arose in thalidomide's immunomodulatory effects, leading to the class of immunomodulators known as
immunomodulatory imide drugs (IMiDs).
Preparation
Most common imides are prepared by heating dicarboxylic acids or their anhydrides and
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
or primary
amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent ...
s. The result is a
condensation reaction:
: (RCO)
2O + R′NH
2 → (RCO)
2NR′ + H
2O
These reactions proceed via the intermediacy of
amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...
s. The intramolecular reaction of a carboxylic acid with an amide is far faster than the intermolecular reaction, which is rarely observed.
They may also be produced via the oxidation of
amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it i ...
s, particularly when starting from
lactam
A lactam is a cyclic amide, formally derived from an amino alkanoic acid. The term is a portmanteau of the words '' lactone'' + ''amide''.
Nomenclature
Greek prefixes in alphabetical order indicate ring size:
* α-Lactam (3-atom rings)
* β-Lac ...
s.
: R(CO)NHCH
2R' + 2
→ R(CO)N(CO)R' + H
2O
Certain imides can also be prepared in the isoimide-to-imide
Mumm rearrangement.
Reactions
For imides derived from ammonia, the N–H center is weakly acidic. Thus, alkali metal salts of imides can be prepared by conventional bases such as potassium hydroxide. The conjugate base of phthalimide is
potassium phthalimide
Potassium phthalimide is a chemical compound of formula C8H4KNO2. It is the potassium salt of phthalimide, and usually presents as fluffy, very pale yellow crystals. It can be prepared by adding a hot solution of phthalimide in ethanol to a soluti ...
. These anion can be alkylated to give ''N''-alkylimides, which in turn can be degraded to release the primary amine. Strong nucleophiles, such as potassium hydroxide or
hydrazine
Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
are used in the release step.
Treatment of imides with halogens and base gives the ''N''-halo derivatives. Examples that are useful in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
are
''N''-chlorosuccinimide and ''N''-
bromosuccinimide, which respectively serve as sources of "Cl
+" and "Br
+" in
organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
.
Imides in coordination chemistry
In
coordination chemistry
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Man ...
transition metal imido complexes feature the NR
2- ligand. They are similar to oxo ligands in some respects. In some the M-N-C angle is 180º but often the angle is decidedly bent. The parent imide (NH
2-) is an intermediate in
nitrogen fixation
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
by synthetic catalysts.
[Nugent, W. A.; Mayer, J. M., "Metal-Ligand Multiple Bonds," J. Wiley: New York, 1988.]
References
External links
IUPAC: imides
{{Authority control
Functional groups