Amides Hofmann rearrangements, bromine

Benzyltrimethylammonium tribromide has been used for the A -bromination of amides in good yield [54]. Under basic conditions, Hofmann rearrangement to amines is also possible (see Section 9.3). 

Electrolysis of amides in MeOH containing the bromide ion efficiently led to products of the Hofmann rearrangement (for example, 119 to 120 Scheme 43) [131]. This reaction, named the electrochemically induced (E-I) Hofmann rearrangement, is achieved without any bromine and base under mild and neutral reaction conditions. 

Treatment of amides with bromine in alkaline medium promotes the Hofmann rearrangement, which may or may not involve a free nitrene intermediate." The oxidation of primary amides with lead tetraacetate and the resulting Lossen rearrangement also produces isocyanates, with the possible intervention of an acylni-... 

In 1882 Hofmann discovered that when amides are treated with bromine in basic solution, they are converted to amines with one carbon less than the starting amide.180 He also isolated the N-bromo amine (114) and the isocyanate (115) as intermediates on the reaction path. The mechanism in Equation 6.56 accounts for the products and the intermediates. This reaction (or the analogous rearrangement of the N-chloro amine) is now known as the Hofmann rearrangement or, because of its synthetic usefulness in eliminating a carbon atom, the Hofmann degradation. 

Overall, then, the Curtius rearrangement converts an acid chloride to an amine with loss of a car- tk>n atom—very useful. Also useful is the related Hofmann rearrangement, which turns an amide ito an amine with loss of a carbon atom. This time we start with a primary amide and make a trene by treatment with base and bromine. Notice how close this nitrene-forming reaction is to the tarbene-forming reactions we talked about on p. 1072. The nitrene rearranges just as in the Curtius reaction, giving an isocyanate that can be hydrolysed to the amine. 

The Hofmann rearrangement can also be used to convert a carboxylic acid derivative to an isocyanate. A carboxamide is treated with Br2 and aqueous base to give an isocyanate, which is usually hydrolyzed under the reaction conditions to give an amine with one fewer C atom than the starting material. The reaction proceeds by deprotonation of the amide and /V-bromination, then a second deprotonation and rearrangement. The amide N is more reactive than the amide O in the bromination step because N is deprotonated under the reaction conditions. 

In the Hofmann rearrangement, when an unsubstituted amide is treated with sodium hydroxide and bromine, the corresponding amine with one fewer carbon atom is produced. The first intermediate is the jV-bromo amide, which then undergoes the three steps of the rearrangement reaction simultaneously. Suggest the pathway for this reaction, and how the final product is achieved. 

Hofmann rearrangement The reaction of an amide with bromine and sodium methoxide in methanol to give the corresponding amine, with the loss of the carbonyl carbon atom as carbon dioxide. Also called the Hofmann degradation. 

On treatment with bromine in basic solution, amides of the type RCNH2 undergo an interesting reaction that leads to amines. This reaction was discovered by the nineteenth century German chemist August W. Hofmann and is called the Hofmann rearrangement. 

Only amides of the type RCNH2 undergo the Hofmann rearrangement. The amide nitrogen must have two protons attached to it, of which one is replaced by bromine to give the A-bromo amide, whereas abstraction of the second by base is neces-... 

The Hofmann rearrangement (Section 20.17) Amides are converted to amines by reaction with bromine in basic media. An A/-bromo amide is an intermediate it rearranges to an isocyanate. Hydroiysis of the isocyanate yieids an amine. 

Hofmann rearrangement (Section 20.17) Reaction in which an amide reacts with bromine in basic solution to give a primary amine having one less carbon atom than the amide. 

Amide degradation. In a liquid triphasic system made up of NaOCl, NaBr, a phase-tranfer agent, Na3P04, benzene, and water, primary amides are degraded to nitriles of one fewer carbon atom. After Hofmann rearrangement the amine products undergo bromination and eventually elimination. 

In the presence of a strong base, primary amides react with chlorine or bromine to form shortened amines with loss of the carbonyl carbon atom. This reaction, called the Hofmann rearrangement, is used to synthesize primary alkyl and aryl amines. 

Hofmann rearrangement of amides (Hofmann degradation) Treatment of a primary amide with sodium hydroxide and bromine or chlorine gives a primary amine, (p. 919)... 

Hofmann rearrangement of amides Conversion of a primary amide to an amine (with one less carbon) by treatment with a basic bromine solution. The C=0 group is lost as CO2. (pp. 919, 1023)... 

Hofmann Rearrangement Amides with no substituent on the nitrogen react with solutions of bromine or chlorine in sodium hydroxide to yield amines through loss of their carbonyl carbon by a reaction known as the Hofmann rearrangement or Hofmann degradation-. 

---