Amidine#Acid-base chemistry

A common route to primary amidines is the Pinner reaction. 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.{{cite journal|doi=10.15227/orgsyn.008.0001|title=Acetamidine Hydrochloride|journal=Organic Syntheses|year=1928|volume=8|pages=1|author=A. W. Dox}} Instead of using a Bronsted acid, Lewis acids such as aluminium trichloride promote the direct amination of nitriles,{{cite journal|doi=10.15227/orgsyn.036.0064|title=N-Phenylbenzamidine|journal=Organic Syntheses|year=1956|volume=36|pages=64}} or, in certain exceptional cases, of amides.{{cite journal|journal=Organic Chemistry Highlights|date=1 Dec 2008|first=Douglass F.|last=Taber|title=The Takayama synthesis of (-)-cernuine|url=https://www.organic-chemistry.org/Highlights/2008/01December.shtm}} Dimethylformamide acetal reacts with primary amines to give amidines:{{cite journal|doi=10.15227/orgsyn.067.0052|title=(S)-N,N-Dimethyl-N'-(1-tert-Butoxy-3-Methyl-2-Butyl)formamidine|journal=Organic Syntheses|year=1989|volume=67|pages=52|author1=Daniel A. Dickman |author2=Michael Boes |author3=Albert I. Meyers}}

:Me₂NC(H)(OMe)₂ + RNH₂ → Me₂NC=NHR + 2 MeOH

Catalysis is likewise not required for direct amination of an imidoyl chloride.{{cite journal|doi=10.15227/orgsyn.031.0048|title=N,N-Diphenylbenzamidine|journal=Organic Syntheses|year=1951|volume=31|pages=48|author=Arthur C. Hontz, E. C. Wagner}}

Amidines are also prepared by the addition of organolithium reagents to diimines, followed by protonation or alkylation.

Amidines are much more basic than amides and are among the strongest uncharged/unionized bases.Roche VF. Improving Pharmacy Students’ Understanding and Long-term Retention of Acid-Base Chemistry. American Journal of Pharmaceutical Education. 2007;71(6):122.{{cite book |title=Organic chemistry |last1=Clayden |last2=Greeves |last3=Warren |year=2001 |publisher=Oxford university press |isbn=978-0-19-850346-0 |page=[https://archive.org/details/organicchemistry00clay_0/page/202 202] |url-access=registration |url=https://archive.org/details/organicchemistry00clay_0/page/202}}

Protonation occurs at the sp²-hybridized nitrogen. This occurs because the positive charge can be delocalized onto both nitrogen atoms. The resulting cationic species is known as an amidinium ion{{cite book|title=Functional synthetic receptors|editor-first=Thomas|editor-last=Schrader|editor2-first=Andrew D.|editor2-last=Hamilton|publisher=Wiley-VCH|year=2005|ISBN=3-527-30655-2|pages=132}} and possesses identical C-N bond lengths.

File:Amidineresonance.png

Several drug or drug candidates feature amidine substituents. Examples include the antiprotozoal imidocarb, the insecticide amitraz, xylamidine, an antagonist at the 5HT2A receptor,{{cite book|doi=10.1016/S0079-6468(08)70378-3|title=5 Amidines and Guanidines in Medicinal Chemistry|series=Progress in Medicinal Chemistry|year=1993|last1=Greenhill|first1=John V.|last2=Lue|first2=Ping|volume=30|pages=203–326|pmid=7905649|isbn=9780444899897}} and the anthelmintics amidantel and tribendimidine.

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 halides in forming perovskite absorber layers in photovoltaic devices.

Formally, amidines are a class of oxoacids. The oxoacid from which an amidine is derived must be of the form R_nE(=O)OH, where R is a substituent. The −OH group is replaced by an −NH₂ group and the =O group is replaced by =NR, giving amidines the general structure R_nE(=NR)NR₂.{{GoldBookRef|title=amidines|file=A00267}}{{GoldBookRef|title=carboxamidines|file=C00851}}{{GoldBookRef|title=sulfinamidines|file=S06107}} When the parent oxoacid is a carboxylic acid, 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.

Image:Formamidinium cation.png

A notable subclass of amidinium ions are the formamidinium cations; which can be represented by the chemical formula {{chem|[R|2|N−CH{{=}}NR|2|]|+}}. Deprotonation of these gives stable carbenes which can be represented by the chemical formula {{chem|R|2|N−C:−NR|2}}.{{cite journal|last1=Alder|first1=Roger W.|last2=Blake|first2=Michael E.|last3=Bufali|first3=Simone|last4=Butts|first4=Craig P.|last5=Orpen|first5=A. Guy|last6=Schütz|first6=Jan|last7=Williams|first7=Stuart J.|title=Preparation of tetraalkylformamidinium salts and related species as precursors to stable carbenes|journal=Journal of the Chemical Society, Perkin Transactions 1|date=2001|issue=14|pages=1586–1593|doi=10.1039/B104110J}}{{cite journal|doi=10.15227/orgsyn.046.0039|author1=Edward C. Taylor |author2=Wendell A. Ehrhart |author3=M. Kawanisi

|title=Formamidine Acetate|journal=Organic Syntheses|year=1966|volume=46|pages=39}}

File:CpZrMe2(iPr2amidate)AFIHEC.png

An amidinate salt has the general structure M⁺[RNRCNR]⁻ and can be accessed by reaction of a carbodiimide with an organometallic compound such as methyl lithium.{{cite book|last1=Ulrich|first1=Henri|title=Chemistry and technology of carbodiimides|date=2007|publisher=John Wiley & Sons|location=Chichester, England|isbn=9780470065105}} They are used widely as ligands in organometallic complexes.

• Guanidines — a similar group of compounds where the central carbon atom is bonded to three nitrogen atoms.
• Imidazolines contain a cyclic amidine.

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Category:Functional groups

Category:Superbases