Benzophenone imine


Benzophenone imine is an organic compound with the formula of 2C=NH. Benzophenone imine is widely used as a reagent for the protection of primary amines, and the starting materials to synthesize aniline.

Synthesis

Benzophenone imine is available via the addition of MeOH to the complex of a nitrile and a Grignard reagent or the reaction between benzophenone and ammonia.

Synthesis by Grignard-nitrile complexes

The first report about the preparation of ketimines involved Grignard-nitrile complexes followed by careful hydrolysis, which is known as Moureu-Mignonac ketimine synthesis. Then Pickard and Tolbert improved the preparation by using methanol in the addition of Grignard-nitrile complexes.

Synthesis by benzophenone and ammonia

In 1988, A. G. Guimanini discovered a new route to synthesize benzophenone imine by a reaction using benzophenone and ammonia. A chemical pure-grade ammonia gas is added to a benzophenone solution, forming Ph2C=NH2+. After sodium hydroxide pellets are added to the solution, the Ph2C=NH2+ is neutralized, generating the expected benzophenone imine.

Applications

Protecting group for primary amines

Primary amines can be protected benzophenone imine, and the protected amines are stable in flash chromatography.

Amination of aryl halides

is a very important kind of reaction for coupling aromatic halide and amine to form carbon-nitrogen bonds with the help of palladium-involved catalysts. In order to obtain anilines, ammonia is required in this reaction. However, ammonia can bind to palladium tightly, which makes the normal Buchwald-Hartwig reaction unavailable. In 1997, Buchwald et. al found that benzophenone imine can be used as an ammonia-equivalent and solve the above limitations.