Amidines are organic compounds with the functional group RC(NR)NR₂, where the R groups can be the same or different. They are the imine derivatives of amides (RC(O)NR₂). The simplest amidine is formamidine, HC(=NH)NH₂. Examples of amidines include: *

DBU The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a Power, root-power, and field quantities, power or root-power quantity on a logarithmic scale. Two signals whose ...

* diminazene *

benzamidine Benzamidine is the organic compound with the formula C6H5C(NH)NH2. It is the simplest aryl amidine. The compound is a white solid that is slightly soluble in water. It is usually handled as the hydrochloride salt, a white, water-soluble solid. ...

Pentamidine Pentamidine is an antimicrobial medication used to treat African trypanosomiasis, leishmaniasis, ''Balamuthia'' infections, babesiosis, and to prevent and treat pneumocystis pneumonia (PCP) in people with poor immune function. In African trypano ...

* Paranyline

Preparation

A common route to primary amidines is the

Pinner reaction The Pinner reaction refers to the acid catalysed reaction of a nitrile with an alcohol to form an imino ester salt (alkyl imidate salt); this is sometimes referred to as a Pinner salt. The reaction is named after Adolf Pinner, who first described ...

. Reaction of the nitrile with alcohol in the presence of acid gives an iminoether. Treatment of the resulting compound with ammonia then completes the conversion to the amidine. Instead of using a Bronsted acid, Lewis acids such as

aluminium trichloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...

promote the direct

amination Amination is the process by which an amine group is introduced into an organic molecule. This type of reaction is important because organonitrogen compounds are pervasive. Reactions ;Aminase enzymes Enzymes that catalyse this reaction are termed a ...

nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix ''cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including met ...

s. They are also generated by amination of an imidoyl chloride. They are also prepared by the addition of organolithium reagents to

diimine Diimines are organic compounds containing two imine (RCH=NR') groups. Common derivatives are 1,2-diketones and 1,3-diimines. These compounds are used as ligands and as precursors to heterocycles. Diimines are prepared by condensation reactions ...

s, followed by protonation or alkylation. Dimethylformamide acetal reacts with primary amines to give amidines: :Me₂NC(H)(OMe)₂ + RNH₂ → Me₂NC=NHR + 2 MeOH

Properties and applications

Amidines are much more basic than amides and are among the strongest uncharged/unionized bases. Protonation occurs at the sp² hybridized nitrogen. This occurs because the positive charge can be delocalized onto both nitrogen atoms. The resulting

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

ic species is known as an amidinium ion and possesses identical C-N bond lengths. Amidineresonance

Several drug or drug candidates feature amidine substituents. Examples include the antiprotozoal Imidocarb, the insecticide amitraz , the anthelmintic tribendimidine, and

xylamidine Xylamidine is a drug which acts as an Antagonist (pharmacology), antagonist at the 5-HT2A receptor, 5HT2A Receptor (biochemistry), receptor, and to a lesser extent at the 5HT1A receptor. It does not cross the blood–brain barrier, which makes it ...

, an

antagonist An antagonist is a character in a story who is presented as the chief foe of the protagonist. Etymology The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, riv ...

at the 5HT2A receptor. Formamidinium (see below) may be reacted with a metal halide to form the light-absorbing semiconducting material in perovskite solar cells. Formamidinium (FA) cations or halides may partially or fully replace

methylammonium halide Methylammonium halides are organic halides with a formula of , where X is Cl for methylammonium chloride, Br for methylammonium bromide, or I for methylammonium iodide. Generally they are white or light colored powders. Applications These salts ...

s in forming perovskite absorber layers in photovoltaic devices.

Nomenclature

Formally, amidines are a class of oxoacids. The oxoacid from which an amidine is derived must be of the form R_''n''E(=O)OH, where R is a

substituent A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...

. The −OH group is replaced by an −NH₂ group and the =O group is replaced by = N R, giving amidines the general structure R_''n''E(=NR)NR₂. When the parent oxoacid is a

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

, the resulting amidine is a carboxamidine or carboximidamide ( IUPAC name). Carboxamidines are frequently referred to simply as amidines, as they are the most commonly encountered type of amidine in organic chemistry.

Derivatives

Formamidinium cations

A notable subclass of amidinium ions are the formamidinium

s; which can be represented by the chemical formula . Deprotonation of these gives

stable carbene A persistent carbene (also known as stable carbene) is a type of carbene demonstrating particular stability. The best-known examples and by far largest subgroup are the ''N''-heterocyclic carbenes (NHC) (sometimes called Arduengo carbenes), for ex ...

s which can be represented by the chemical formula .

Amidinate salts

An amidinate salt has the general structure M⁺ NRCNRsup>− and can be accessed by reaction of a carbodiimide with an organometallic compound such as methyl lithium. They are used widely as ligands in organometallic complexes.

References

{{Reflist Functional groups