Carboximidates (or more general imidates) are organic compounds, which can be thought of as formed between an imidic acid () and an alcohol, with the general formula .
They are also known as imino ethers, since they resemble () with an oxygen atom connected to the carbon atom of the C=N double bond.
Synthesis
Imidates may be generated by a number of synthetic routes,
but are in general formed by the
Pinner reaction. This proceeds via the acid catalyzed attack of nitriles by alcohols.
Imidates produced in this manner are formed as their hydrochloride salts, which are sometimes referred to as Pinner salts. Carboximidates are also formed as intermediates in the Mumm rearrangement and the Overman rearrangement.
Imidate/amidate anions
An
amidate/imidate anion is formed upon
deprotonation of an
amide or
imidic acid. Since amides and imidic acids are
tautomers, they form the same anion upon deprotonation. The two names are thus synonyms describing the same anion, although arguably, imidate refers to the resonance contributor on the left, while amidate refers to the resonance contributor on the right. However, they are distinguished when they act as ligands for transition metals, with
O-bound species referred to as imidates and
N-bound species referred to as amidates. They can be considered aza-substituted analogues of
with the formula R-N=C(O
−)R.
Reactions
Carboximidates are good
electrophiles and undergo a range of addition reactions; with
aliphatic imidates generally reacting faster than
aromatic imidates.
[ They can be hydrolysis to give esters and by an analogous process react with amines (including ammonia) to form . Aliphatic imidates react with an excess of alcohol under acid catalysis to form RC(OR)3, aromatic imidates can also be converted but far less readily.
]
Chapman rearrangement
The Chapman rearrangement is the thermal conversion of aryl N-arylbenzimidates to the corresponding amides, via intramolecular migration of an aryl group from oxygen to nitrogen.
As a protecting group
Carboximidates can act as protecting group for alcohols.
See also
