20 17 The Hofmann Rearrangement The Hofmann Rearrangement

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20. 17 The Hofmann Rearrangement

20. 17 The Hofmann Rearrangement

The Hofmann Rearrangement Treatment of amides with bromine in basic solution gives an amine

The Hofmann Rearrangement Treatment of amides with bromine in basic solution gives an amine with loss of the carbonyl carbon. O RCNH 2 Br 2 HO– RNH 2 + CO 32–

Examples O (CH 3)3 CCH 2 CNH 2 Br 2, Na. OH (CH 3)3

Examples O (CH 3)3 CCH 2 CNH 2 Br 2, Na. OH (CH 3)3 CCH 2 NH 2 H 2 O O CNH 2 (94%) Br 2, KOH NH 2 H 2 O Br Br (87%)

Mechanism of the Hofmann Rearrangement O RCNH 2 O RCNHBr RNCO RNH 2 The

Mechanism of the Hofmann Rearrangement O RCNH 2 O RCNHBr RNCO RNH 2 The Hofmann rearrangement involves 6 steps in 3 stages. 1. formation of an N-bromo amide (2 steps) 2. conversion of the N-bromo amide to an isocyanate (2 steps) 3. hydrolysis of the isocyanate (2 steps)

Stereochemistry H C 6 H 5 CH 2 O C H 3 C C

Stereochemistry H C 6 H 5 CH 2 O C H 3 C C 6 H 5 CH 2 CNH 2 Br 2, Na. OH, H 2 O H C H 3 C NH 2 alkyl group migrates with retention of configuration

Isocyanates are intermediates When the reaction is carried out in methanol instead of water,

Isocyanates are intermediates When the reaction is carried out in methanol instead of water, the product shown is isolated. O CH 3(CH 2)14 CNH 2 O Br 2 Na. OCH 3 OH CH 3(CH 2)14 NHCOCH 3

Isocyanates are intermediates When the reaction is carried out in methanol instead of water,

Isocyanates are intermediates When the reaction is carried out in methanol instead of water, the product shown is isolated. O O CH 3(CH 2)14 CNH 2 via: Br 2 Na. OCH 3 OH CH 3(CH 2)14 NHCOCH 3 C O

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