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Concept
Hémiaminal
Résumé
In organic chemistry, a hemiaminal (also carbinolamine) is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: . R can be hydrogen or an alkyl group. Hemiaminals are intermediates in imine formation from an amine and a carbonyl by alkylimino-de-oxo-bisubstitution. Hemiaminals can be viewed as a blend of aminals and geminal diol. They are a special case of amino alcohols.
The adducts formed by the addition of ammonia to aldehydes have long been studied. Compounds containing both a primary amino group and a hydroxyl group bonded to the same carbon atom are rarely stable, as they tend to dehydrate to form imines which polymerise to hexamethylenetetramine. A rare stable example is the adduct of ammonia and hexafluoroacetone, .
The C-substituted derivatives are obtained by reaction of aldehydes and ammonia:
3 RCHO + 3 NH3 -> (RCHNH)3 + 3 H2O
N-substituted derivatives are somewhat stable. They are invoked but rarely observed as intermediates in the Mannich reaction. These N,N',N''-trisubstituted hexahydro-1,3,5-triazines arise from the condensation of the amine and formaldehyde as illustrated by the route to 1,3,5-trimethyl-1,3,5-triazacyclohexane:
3 CH2O + 3 H2NMe -> (CH2NMe)3 + 3 H2O
Although adducts generated from primary amines or ammonia are usually unstable, the hemiaminals have been trapped in a cavity.
One of the simplest reactions entails condensation of formaldehyde and dimethylamine. This reaction produces first the carbinolamine (a hemiaminal) and bis(dimethylamino)methane ():
Me2NH + CH2O -> Me2NCH2OH
Me2NH + Me2NCH2OH -> Me2NCH2NMe2 + H2O
The reaction of formaldehyde with carbazole, which is weakly basic, proceed similarly:
Again, this carbinol converts readily to the methylene-linked bis(carbazole).
Hemiaminal ethers have the following structure: R′′′-C(NR'2)(OR")-R′′′′. The glycosylamines are examples of cyclic hemiaminal ethers.
Methanolamine.svg|[[methanolamine]], an intermediate in the reaction of ammonia with formaldehyde
OC(NHCH2OH)2.
Source officielle
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