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Benzophenone imine

Benzophenone imine is an organic compound with the formula of (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NH. A pale yellow liquid, benzophenone imine is used as a reagent in organic synthesis.

Synthesis

Benzophenone imine can be prepared by the thermal decomposition of benzophenone oxime:

2(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NOH → (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NH + (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=O

Benzophenone imine can also be synthesized by addition of phenylmagnesium bromide to benzonitrile followed by careful hydrolysis (lest the imine be hydrolyzed):

C<sub>6</sub>H<sub>5</sub>CN + C<sub>6</sub>H<sub>5</sub>MgBr → (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NMgBr
(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NMgBr + H<sub>2</sub>O → (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NH + MgBr(OH)

This method is known as Moureu-Mignonac ketimine synthesis. Yet another route to benzophenone imine involves reaction of benzophenone and ammonia.

Reactions

Benzophenone imine undergoes deprotonation with alkyl lithium reagents.

(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NH + CH<sub>3</sub>Li → (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NLi + CH<sub>4</sub>
(C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NLi + CH<sub>3</sub>I → (C<sub>6</sub>H<sub>5</sub>)<sub>2</sub>C=NCH<sub>3</sub> + LiI

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

Buchwald-Hartwig amination involves coupling aromatic halide and amine to form carbon-nitrogen bonds with the help of palladium-based catalysts. Benzophenone imine can be used as an ammonia-equivalent in such reactions.

References