Lesson31 - Substitution of the Carbonyl Oxygen of Ketones...

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C O N H C O N H H O H R R C N R H H C O C N R C O C N H H O H R R H R H α H α C C N R R α Substitution of the Carbonyl Oxygen of Ketones and Aldehydes by Nitrogen: Imines and Enamines addition When primary amines are combined with ketone and aldehyde groups, the carbonyl C=O is replaced by the C=N ( imine ) group. The mechanistic sequence is addition followed by elimination of water (the second N–H proton is necessary for imine formation). When secondary amines are combined with aldehydes and ketones, there is no second proton on nitrogen to permit imine formation. In this case, elimination of water is achieved via proton transfer from a H–C α bond (assuming that the aldehyde or ketone substrate has at least one α -hydrogen). The functional group that results is called an enamine . addition imine enamine 1˚ amine 2˚ amine elimination and [pt] from N elimination and [pt] from C α
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Examples of Imine and Enamine Formation primary amine O + N H 2 H N + H O H (cat.) N + H H O α N H H H H α H O H + H (cat.) secondary amine enamine imine
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Mechanism of Imine Formation O + N H 2 H N + H 2 O O N H H H N H H O H H H O N H H H N H H 2 O [pt] [pt] [pt] [Ad N ] [E β ] http://www.chemtube3d.com/
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N + H H O H N H α H 2 O N H H H H H H O H N O H H H N O H H H H 2 O + H N H α Mechanism of Enamine Formation http://www.chemtube3d.com/ [pt] [Ad N ] [E β ] [pt] [pt] (or [D E ])
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Other Amino Reagents that Produce Derivatives of Aldehydes and Ketones H 2 N OH hydroxylamine Reagent H 2 N R Derivative Name Structure oxime N OH H 2 N NHR hydrazine hydrazone N NHR H 2 N H N semicarbazide C O NH 2 semicarbazone N NH C O NH 2
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Hydride Reduction of Imines Produces Amines: Reductive Amination CH 3 O NH 3 NaBH(OAc) 3 pH 6 CH 3 H NH 2 CH 3 NH 2 excess C=O NaCNBH 3 pH 6 CH 3 N CH 3 CH 3 Imines and iminium ions are reduced by hydride sources to make amines. The process is known as reductive amination . The hydride reducing reagents in the above equations are carefully chosen so as to remain stable
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Lesson31 - Substitution of the Carbonyl Oxygen of Ketones...

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