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24 Jan 2012 14:04:22 IST

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what is hoffmann bromamide reaction ?

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what is hoffmann bromamide reaction ?

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RISHABH BAJPAI

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25 Jan 2012 12:48:02 IST

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RCONH2 + Br2 + KOH ---> RNH2 + KBr + H2O.......this is thus a method to convert an amide to a primary amine having one carbon less...if u want the mechanism then i can write that also..

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25 Jan 2012 15:34:27 IST

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i want..............

RISHABH BAJPAI

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25 Jan 2012 18:10:38 IST

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1) R-CO-NH-H +OH-(from KOH abstracts acidic H) ------> RCONH-

2) RCONH- +Br2 (this anion causes heterolysis of Br2) -----> RCONHBr (known as BROMAMIDE) + Br-

3) RCONHBR +OH-(from base abstracts another proton) ------> RCONBr-

4)RCONBr- (by back attack of lone pair over nitrogen Bromide is eliminated) ----> RCON (acyl nitrene)

5) RCON undergoes synchronous migration to give R-N=C=O (isocyanate)

6) RNCO undergoes hydrolysis in KOH (Already presnt) -----> RNH2 + K2CO3

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25 Jan 2012 21:47:39 IST

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why doesnt H+ from medium shifts to the nitrene, synchronous migration of R shud taks place... . But hydrogen is one of the fastes nd highr donatin group then R-....... Also wts the reson fr heterolysis...... Of Br. And explain the acidity of hydrogen in amtide tooo........ One more thing i am gettin CO2.... Plz provide me appropriate reson fr carbonate......

RISHABH BAJPAI

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26 Jan 2012 11:15:44 IST

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there is no free H+ in the medium...the medium has KOH (base)....there is no hydride formed(H-) so alkyl gorup migrates R-CON changes to R-N=C=O...Charges species are capable of causing heterolysis so the anion RCONH- (RCONH minus) causes heterolysis...the acidity of amide here can be explained by the fact that the Nitrogen-Hydrogen bond is polar and the anion formed is stablised by the strong electron withdrawing nature of C=O group...yes indeed you will get CO2 which combines with already present KOH (Acid base rxn.) to give K2CO3...

RISHABH BAJPAI

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4 Feb 2012 11:30:40 IST

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hope the doubt is cleared...

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